Green Building Forum - All Discussions

New Green Building Forum & Website

BWork — Mon, 01 Sep 2025 15:58:30 +0100

Crowd funding

Greenbuilding.co.uk, owned by the AECB, promotes excellence in design and construction. This website, including the very popular Green Building Forum, was set up by Keith Hall, who co-founded the AECB back in 1989. Keith kindly donated the site to the AECB on his retirement in 2025.

The Greenbuilding site is for everyone from industry professionals including architects, builders, developers to green enthusiasts and homeowners looking for information and a place to discuss all aspects of sustainable building.

With the money that we hope to raise from this Crowdfunder we will be able to update the original website and forum, currently working using older technology that does not allow for necessary changes to the platform. With your support of a much-needed funding boost we will be able to invest in new technology that will bring the site into the 2020s. This will make it easier for visitors to navigate around the site and read the valuable information and resources we share, for those on their sustainable building journey. Users will also be able to sign up quicker and get involved in the conversations.

https://www.crowdfunder.co.uk/p/qr/dyR52gZn?utm_campaign=sharemodal&utm_medium=referral&utm_source=shortlink

Welcome to Guests

GBP-Keith — Tue, 15 May 2007 18:00:44 +0100

Subscribing to and participating on this forum is no longer available to new users from December 2023. However it is a great resource to browse. Existing subscribers can continue to participate as normal.

Silicone or grout

Rex — Thu, 12 Nov 2026 19:28:55 +0000

What ho one and all,

Obviously, I'm looking for jobs!!!! The tile grout (white) on the bathroom walls, around the bath and shower, is no longer nice and white.

I can rake out the grubby parts but wondering about replacing with white silicone. I would not rake out the full depth so the silicone would only be a few mm thick, sitting on the underlying grout. It would not be flush with the tile surface but slightly concave. The obvious issue could be mold appearing on the feather edges sooner rather than later.

Is this a 'good' idea or would I be making things too difficult for the future?

Thanks and toodle pip

Fading (or not?)

Rex — Fri, 06 Nov 2026 13:56:25 +0000

What ho one and all,

Recently removed the kickboards from below the kitchen units and surprised to find this 'fading' (although since there is virtually zero light / IR, fading is not really the right description.)

I have noticed it in some of the cupboards but not this badly.

It is a rather expensive vinyl floor covering; everything visible to daylight (all walking areas), looks to be still the same light grey as originally bought.

Not that it really matters but why would the vinyl where there is no light, fade / change colour in this manner?

Thanks and toodle pip

Rex

Masonry stoves

earth bau — Tue, 10 Nov 2026 12:35:45 +0000

**Masonry stoves – why are they so uncommon in the UK?**

I've been interested in masonry stoves (also known as masonry heaters or thermal mass stoves) for many years and have built them in the past.

They're relatively common in parts of continental Europe, but seem to have very little presence in the UK, despite their potential advantages over conventional wood-burning stoves.

For those unfamiliar with them, they burn a load of wood relatively quickly at high temperatures, storing the heat in a large masonry structure which then releases it gradually over many hours.

I've recently been looking into the possibility of designing and building them again, potentially commercially, and I'm curious about how much interest there might be in the UK. I'm not looking to advertise my services here, but would genuinely appreciate people's thoughts.

Has anyone here installed one, lived with one, or considered having one built?

For those who have considered them, what were the main obstacles? Cost, space requirements, difficulty finding a builder, or something else?

And more generally, do people think there's a place for masonry stoves in UK homes, particularly given the increasing emphasis on insulation, airtightness and low heating demand?

Sunamp with heat pump

ChrisGT — Fri, 06 Nov 2026 12:47:01 +0000

Got a small bathroom with a space of 650x650mm for a cylinder working with a heat pump. Would a surnamp thermal store be better than a cylinder in this space. Probably need a buffer or volumiser as only 3 rads also. Ive seen there some discussion about this few years ago.

MVHR cold loft insulation shed/igloo

oliviaaa99 — Tue, 10 Nov 2026 15:26:25 +0000

Hello! I was wondering if anyone was able to share photos if you have built a frame/insulation shed/igloo for your MVHR unit, especially if the unit is suspended from the frame?

We are retrofit installing in a cold loft bungalow (not ideal but no other options sadly). It’s a Zehnder ComfoAir 180 Luxe with preheater and enthalpy exchanger.

The plan is to build a frame (still working on the design - any suggestions would be amazing especially for an alternative to the counterbalance beams) from CLS to suspend the unit and both manifolds (no gable walls to hang the unit from). Then wrap OSB then PIR board, not sure yet whether it needs to be airtight or not?

The ducting will then travel down inside the ‘igloo’, and exit below loft boarding/within the loft insulation layer across joists (each duct will also be individually insulated from the ‘igloo’ exit point too).

I’ve seen this recommended a few times but I cannot find any guides/visual examples, and the exact details are throwing me a little bit!

- Even though it’s an insulated box, will it still be cold inside or will the heat from the mvhr unit be enough to keep it comfortable (ours has a preheater if that makes any difference?)

- Not sure how to PIR insulate underneath without impacting the frame, it cannot be a continuous layer as the frame is going to have to be secured to the joists and counterbalanced so it doesn’t fall with the weight of the unit. I believe the PIR has to be on the outside rather than the inside of the box, though it would be much easier to get a continuous fit.

- I’ve read mixed things on airtighting. We have put an airtight membrane down on the loft floor, up and over the joists but below the insulation level. Not sure if we need to include the ‘igloo’ in this airtight layer (remove membrane where the ‘igloo’ sits, then up and over), or if that would just compromise the layer? Or do we airtight the ‘igloo’ as it’s own separate entity? I’ve also read that the unit needs airflow and ventilation, not sure if that’s needed from outside the ‘igloo’ or if it’s more about making sure the unit has breathing room and the frame isn’t flush against it?

- For the door of the ‘igloo’, again how best to make sure we can access the unit without compromising the insulating properties?

If anyone has done anything similar, advice would be much appreciated! Thank you!

Solar Options

Victorianeco — Sat, 05 Sep 2026 20:55:02 +0100

Up to date solar recommendations?

Any grants available?
Preferred kit setup and size?
Export tariffs available?

I have little knowledge on the subject and we're a few weeks away from scaffold going up for the re-roof currently looking at cladco corrugated profiles and greencoat roofing systems but may be swayed by standard slate or tiles, but 100% confirmed either way.

But would like to start getting a few solar quotes together but looking at specs. to ensure I'll be comparing apples with apples in the quotes.

We have a cross gable roof with one elevation facing true south and the other roof section is half east and half west.

Let me know your thoughts on what the ideal setup is these days

The Retrofit EWI Window box

Victorianeco — Thu, 01 Oct 2026 20:15:09 +0100

Hi everyone,

I’m finalising the detailing for replacing my windows as part of an External Wall Insulation (EWI) retrofit on an existing masonry cavity wall property, and I’d love to tap into the real-world experience of those who have executed this on site.

I’ve decided to move the new window frames forward out of the cold masonry opening and set them entirely within the new EWI layer using a cantilevered sub-frame box. My plan is to fix the windows into this box, seal for airtightness, and then lap the 150mm EPS EWI over the window frame perimeter by ~30mm.

Before I lock in the exact window unit dimensions and place the order (there is an 8-week lead time I want to get ticking!), I want to sense-check my proposed execution and get your thoughts on a few specific questions.

1. Box Material & Dimensions
Material: I am planning to rip 18mm OSB3 into strips to form the box. Is OSB3 suitable here for strength and airtightness, or is exterior-grade WBP Plywood heavily preferred in real-world moisture conditions?

Depth: Assuming a window frame depth of ~80mm front-to-back, should I make the OSB box the full 200mm depth (spanning the EWI + window overlap zone flush to the outer render line) to give a solid substrate for reveal insulation, or stop the box just behind the window frame face?

2. Construction & Fixing Methodology
Workbench vs. In-Situ: Is it better to pre-build a rigid 4-sided OSB box on a workbench and offer it up to the opening as one piece, or can I install the boards piece-by-piece directly into the reveal (starting with the bottom sill board, then jambs, then header) and screw the corners together in situ?

Fixings to Masonry: Should I use concrete frame screws (e.g., 7.5mm Spax/Thunderbolts) driven at a 45° angle through the OSB straight into the masonry reveals, or am I better off using heavy-duty steel angle brackets (L-brackets) on the exterior face of the brick?

Which Leaf to Anchor To?: Should the cantilevered box fixings anchor strictly to the outer masonry leaf, keeping the cavity and inner leaf completely untouched/thermally broken?

Frame-to-Masonry Bedding: Should I apply a continuous bead of high-tack structural PU adhesive foam (e.g., Illbruck PU010) between the back of the OSB boards and the brickwork before driving frame fixings home?

Picture Frame / Batten Alternative: Some have suggested using 3x2 (75x50mm) timber battens screwed flat to the outer brick face to form a "picture frame" that the window sits against. Does an 18mm cantilevered OSB box beat this on thermal performance and ease of taping, or are battens easier on site?

3. Window Sizing & Expansion Gaps
Perimeter Gap: When ordering windows, how much tolerance should I deduct from the internal box dimensions? Should I leave a 10mm gap all around (20mm total on width/height) packed with shims/packers and backfilled with flexible low-expansion window foam (e.g., Illbruck FM330)?

4. Weatherproofing During Phased Work
Exposed Box Protection: If the OSB boxes and windows go in several weeks before the EWI system is applied, how should I protect the OSB box from driving rain?

Can I coat the OSB box with a liquid DPM / brush-applied airtight membrane (e.g., Blowerproof / Soliterm), or will liquid membranes stop the wood from breathing and trap moisture inside the reveal?

5. Specification & EWI Depth Sanity Check
EWI Thickness: I am aiming for roughly 150mm Grey EPS (Graphite) EWI, which seems to be the sweet spot for cost vs. performance (aiming for near-Passivhaus wall U-values around 0.14–0.15 W/m²K on top of cavity bead fill). Is 150mm standard practice here, or does jumping to 200mm deliver diminishing returns relative to the extra reveal depth and cill costs?

Window Spec vs. Detail: Is it worth spending big on top-tier German/Nordic triple glazing, or does a mid-range triple-glazed unit deliver 95% of the performance once set correctly inside a well-detailed EWI box envelope?

Any practical advice, site photos, or "things I wish I knew before doing this" would be hugely appreciated so I can get these opening dimensions finalized and get the windows ordered!

Thanks in advance!

Sub floor ventilation

Artiglio — Thu, 03 Sep 2026 13:33:20 +0100

Good day all.

Over last 5 years , i’ve been renovating and improving a listed property, (old barn with attached cottage), in the cottage section, there are 3 parts , original cottage and a 1930’s extension, added coal store (now included in cottage) again 1o30’s.
This has a mix of solid and suspended floors. Lots of alterations over its history. When floors were lifted, lots of rubbish and debris beneath, all cleared out. Evidence of previous damp / rot. But once cleared this all dried out over a year or so. There were only air bricks in the main extension, 6 more were added and ducted under solid floors where needed. A mix of insulation methods as it was all reinstated. All’s well and good most of year. But in hot humid periods ( i’m half mile from coast) i get a musty smell, that’s seemingly coming from under the floor.

My thoughts are it’s moist air condensing under the floor sufficiently to allow a bit of mould/damp. The void space is mostly about a metre deep, cool and has a lean mix blinding ( this was there already). Whilst i’d tried to make sure that there was good airflow patently it’s not been enough.

I’m considering adding some forced ventilation using a constantly running fan to draw air out via an airbrick that’s ducted to what i believe is the problem area. The air being drawn in via the other airbricks.

Is this a sensible way forward or am I risking just drawing more moisture into the area and adding to the problem? Is constant low volume flow any better or worse that going for periodic high flow (downside of background noise) either way the fans will be on a voltage controller so that extraction rate can be varied.

I expect there’ll ne the suggestion of adding a humidity sensor to the problem area to control the fan. That is’nt going to be practical now that this section of the house is now finished. I’d rather add the fan and see if it makes a difference then consider if the amount of work to add a sensor is worth any likely improvement ( especially if a low volume fan works).
Fan i’m considering has a max air flow of 180 m3 /hr.
Lastly whilst my intention is to extract, would it be better to force air into the suspected area instead?

Many thanks.

AECB Carbonlite new build certification costs

richardelliot — Sat, 24 Oct 2026 14:09:07 +0100

Has anyone had their self build certified under the AECB Carbonlite scheme and is able.to share how much their certifier charged?

We've just received planning permission for our second self build and received a planning condition that we must obtain BREEAM UK New Construction: Residential certification. The BREEAM scheme is designed for multiple units and is very expensive to do for one off builds. The local authority have been refusing applications to remove the condition from other self builders based on it being unreasonable. My current thought is to apply to the local authority to amend the condition to the, more suitable for self builders, AECB Carbonlite.

I can ask some certifiers for quotes but I thought I'd ask on the forum as well.

Noisy MVHR

alant — Sat, 31 Oct 2026 20:18:35 +0000

Hi,
Before you all despair with thoughts of "not again", i wonder if anyone has any ideas.
We have started using our new Zehnder MVHR in our passive house and we have been surprised how noisy it is. he other issue is the levels of CO2 which i thought would be lower.
We paid for a design service and commissioning but we fitted it ourselves. Many days were spent carefully ensuring all bends were swept, runs kept short, ducts not touching potential problems areas and carefully following all the guidance.
The supply plenum and valves in the bedroom and lounge are the worst culprits although we can hear them all. The people commissioning have had 2 goes at it and it is disappointingly noisy. We are having to set it to turn down low before bedtime then increase later at night to allow us to go asleep. The problem then is the CO2 builds up over 1000.
Anybody had any similar issues.

extending brick vents through extension HOWTO ?

cc64 — Fri, 16 Oct 2026 12:33:48 +0100

Hello All,

We're enclosing a previously open-sided porch to create an unconditioned entrance lobby. A vent serving the void below the beam-and-block floor, and positioned below the original front door, will vent into the new porch enclosure. Building control will not be impressed if we don't extend from the brick vent aperture and duct out to the side wall and through a new brink vent.

Naively I thought this would be straightforward enough. But am not finding suitably dimensioned ducting. It seems "there's not much call for that".

Has anyone else successfully grappled with this conundrum, and if so how? Having trawled through "countless" websites ( DOMUS, Manrose, Airvent, Mapthorpe, Wolseley, AirflowDevelopments, Timloc) I'm asking for a reality check; can this vent be re-established with a horizonal extension, a horizontal 90 flat corner, and another horizontal extension out to the new sidewall brink vent? Or is my architect havin a larf?

Thanks

timber frame extension wall build up

mitchino — Sat, 31 Oct 2026 20:52:11 +0000

I was visiting my sister today who is having an extension built, timber frame inner leaf with 140mm deep studs, filled with Kingspan, 10mm OSB, 50mm cavity then rendered blockwork. I was surprised to note that on the inside, the approved plans just have a vapour barrier and 12.5mm plasterboard. I thought regs would require 25mm insulated plasterboard to combat cold bridging, especially as in some areas there are 4 studs nailed together to support timber lintels over windows etc. The roof is the same, poorly fitted Kingspan between the joists, vapour barrier and 12.5mm plasterboard.

Apparently building control have been onsite and are happy. Is this normal practice?

EPS below ground in plinth

ChrisGT — Sat, 24 Oct 2026 11:46:15 +0100

Hi, I have used 150mm EPS graphite 70 below ground in a plinth that will have EWI above. Its fixed with adhesive and a 4 part Baumit plinth render system and will have a french drain and gravel above. The BCO is saying I should have used XPS. Ive got a vague email FROM Baumit saying its likely to be ok that dosent seem to entirely satisfy them. I really dont want to have to remove it! I used EPS belwo ground on my present house. Any advice welcome.

Biscuit Mix - First floor UFH

Victorianeco — Sun, 18 Oct 2026 12:59:36 +0100

?Hi all,
?I’m currently planning the underfloor heating (UFH) installation for a bathroom / en-suite on a suspended timber floor as part of a whole-house central heating upgrade.

?In our previous home, we fitted UFH between joists using Celotex insulation boards with a sand/cement "biscuit mix" laid on top around the pipes, covered with OSB, and then tiled directly over. It worked well in terms of heat, but I’d like to see how best practices have evolved before starting this project.

?I’d appreciate the forum's advice on a few key points:

?Biscuit Mix vs. Modern Alternatives: Is a sand/cement biscuit mix still recommended for suspended timber floors, or should I be looking at aluminum spreader plates or routed foiled boards?

?Subfloor Substrate: Would you recommend OSB3 or exterior-grade Plywood as the structural floor before tiling? Should an uncoupling membrane or cement backer board (e.g., HardieBacker) be added on top to prevent cracked tile joints?

?Pipe Routing Layout: Do you run UFH pipework under baths, shower trays, vanity units, or fitted cupboards? The goal is max thermal mass, but I want to avoid issues with trap evaporation or overheating fixtures.

?Controls Strategy: The rest of the house will be running as an open zone governed by weather compensation. Should the bathroom UFH be part of this open loop, or is it better to isolate it with its own thermostat, manifold actuator, and floor probe to achieve the higher target temperature (21°C–22°C)?

?Thanks in advance for your insights and recommendations!

Kitchern Tap

Rex — Sun, 18 Oct 2026 16:08:19 +0100

What ho one and all,

Have a kitchen tap that no longer rotates. Figured it was an easy fix to dismantle and clean the calcium build-up, but not so....

Had hoped not to remove it, but could not separate from and thought it may dismantle from below.

I have achieved nothing... I'm assuming that the top part (red arrow) unscrews from the base (green arrow) but it will not move. Probably 'welded' with calcium. Have soaked with vinegar, given a shot of silicone lube spry and although the neck now turns, it is still too tight.

How do the two parts separate? Or more usefully, how are they held together?

Thanks and toodle pip

Domestic Water Schematics

Victorianeco — Sat, 17 Oct 2026 13:25:49 +0100

We are currently in the middle of installing a 210-litre hot water cylinder fed from our unvented/heat pump setup. Since all ceilings are currently down, access for roughing-in the plumbing will be straightforward.

I am planning to use plastic pipework (I have previous experience with Hep2O) or MLCP (Multi-Layer Composite Pipe). Before finalizing the install, I would appreciate some advice or schematic recommendations regarding:

Pipe Sizing & Bore Differences: What pipe sizes should I run for main feeds versus branches? I’m aware of the internal diameter (bore) reduction with standard plastic/pipe inserts and MLCP fittings compared to copper.

Maximum Pipe Runs: Are there recommended maximum run lengths to prevent noticeable pressure drop or long dead-legs (wait times for hot water)?

Manifold Layout Strategy: Is it better to run one central manifold supplying all outlets individually (home-run system), or use local secondary manifolds/sub-branches (e.g., one trunk to a manifold upstairs, another downstairs)?

Schematics / Layout Examples: Does anyone have a basic pipework schematic or layout diagram they could share for a 2-bathroom plus kitchen domestic setup?

Any advice, diagrams, or lessons learned would be hugely appreciated!
Thanks in advance!

Salt Free Water Softener - is this bunk?

Simon Still — Fri, 10 Nov 2017 15:15:25 +0000

https://www.uk-water-filters.co.uk/treatments/saltless_water_softeners.html

I'm looking for a 'undersink' unit (https://www.uk-water-filters.co.uk/Your_Scale_Centurion_Undersink_Cartridge.html) but more detail on the page above. Trying to work out if it actually works or not. I can't find anyone else in the Uk selling them which makes me suspicious

"Our Scale Centurion is a proven and fully tested technology.
It works by extracting harmful dissolved limescale from your water via a patented process.
The Scale Centurion beads mimic the natural tendency of dissolved limescale to crystallise by forming microscopic hard crystals on the media surface. But it accelerates the process before the scale can stick to pipe and other surfaces further downstream.
Once the microscopic crystals grow large enough, they are freed from the surface by the water pressure / flow.
When the Scale Centurion treated water dries on surfaces, these crystals form a fine residue that is easily wiped off without any need for scouring cleansers. Often you won't see any residue at all.
Please note our salt fee softeners do NOT use Polyphosphates. These remove only 81% of Scale, release chemicals into the water and require regular replacement.
The unique media in our softeners create a ceramic template which allows the calcium ions to form into non-scaling crystals (guaranteed). "

Isofast Brackets

borpin — Tue, 22 Sep 2026 09:29:39 +0100

Has anyone else seen these? Seem to be a US firm, but to my mind a great system for warm roofs and EWI.
No fixing through the insulation.

https://www.insofast.com/products/insofast-batt-brackets

FttP and VoiP

Rex — Sat, 10 Oct 2026 12:36:57 +0100

What ho one and all,

After three months of faffing around, Openreach orders created then cancelled, three cancelled engineer visits and one visit who only managed to find problems (small branch hanging across the pole, no survey to ensure there is no gas/elec/water in the apex where the current phone line enters) yesterday, finally, an OR engineer with common sense managed to fit the fibre, ans as she described the job to a colleague, it was 'p*ss easy!'

The original copper has been removed and apparently, EE will assign a temp phone number before moving my existing number to the new service. One phone is plugged into the router and give a 'no number on this service' message, which is fine. Have plugged the supplied Home Phone Adaptor into the 13a but it is not syncing with the router; perhaps that is because there is no connection yet. Time will tell.

However, although there is no copper connection to the outside world, all the BT wiring and Master Socket is of course,still in place. Is there a way to connect extension phones to the router using the existing wiring rather than relying on a wi-fi signal? In other words, can the extension phones be plugged into the BT wiring as normal and the Master Socket connected directly to the router with the RJ11 socket?

Thanks and toodle pip

Is Hinkley C dead?

SteamyTea — Mon, 07 Mar 2016 18:10:53 +0000

What do people think?

Garden Slab - Future Planning

Doubting_Thomas — Tue, 25 Aug 2026 16:01:56 +0100

I have an area behind the house, 2.5m x 6.5m, where I plan to put various outdoor storage: bike shed, composter, raised beds, possibly IBC rainwater tank (inspired by another thread). Eventually it could even become the floor of an outdoor 'garden room' of some kind.

It feels sensible to pour a level hard standing here as a base for all of the above. My current thought is a concrete raft slab of 100-150mm thickness would be more than enough support, but I'm open to suggestions on this.

Three sides are enclosed by ~2m high concrete retaining walls supporting neighbour's gardens, so formwork along the remaining edge should be straightforward.

My questions are:

- Should I insulate and/or damp proof below it, anticipating the potential ultimate use as an outdoor room? Or are these generally raised up on pedestals anyway?

- Will I need reinforcement and or movement/expansion joints in this footprint?

- Anything missing? Ducting for electrics perhaps?

I realise this could spiral into a full-on house slab if I'm not careful, and I'm keen to keep things simple and affordable. More likely than not it will remain a concrete extension of the patio for many years - I just don't want to miss an opportunity for some future-proofing.

NB - I can't dig down much deeper for the risk of upsetting the retaining walls, so underground nuclear bunkers aren't going to happen!

AECB conference

tony — Sat, 26 Sep 2026 08:40:17 +0100

Great conference again, great speakers and thoughts great lifetime award (shame about the soundtrack)

I loved Barnabas when he suggested that we should be willing to compromise comfort! Brave suggestion
And for floating the idea that we should be recording energy rather than (or as well as carbon) - fully agree.

Evan, I am loved your stories and the serious points about facilitating the uptake of heat pumps, return next year pls

GivEnergy equipment

marsaday — Thu, 16 Jul 2026 12:22:41 +0100

My 4 yo inverter has possibly died. It is not covered by any warranty as GE went bust earlier this year.

I have spoken to the installer and they are looking into my options. They can supply a new inverter I think.

I am pretty poor on understanding the electrics, so if anyone can help me out that will be appreciated.

I think my inverter has failed because I signed up to Axle energy to sell some of my surplus energy. They took control of the inverter on 7th July and I know for a fact the inverter was down from 11th July and has been ever since. I should have checked everything was ok aster the first control event by Axle energy, but I didn't.

Is it likely Axle energy have caused by inverter to die or is it coincidence ?

Dry lining

tony — Sat, 19 Sep 2026 07:10:43 +0100

I looked at a new house yesterday that had been dry lined and where we measured the U-value of the walls as built, it was about half of the intentions of the design. On investigation it hadn’t been Dot and Dabbed or battened in a sense of either wood or metal battens, but rather they had used strips of plasterboard effectively as battens presumably dubbed out to plumb and flat using a laser and then applied the plasterboard onto those. They must have use either drywall adhesive or foam to stick it all together. There is no evidence of metal fixings on the thermal images. The house is brick cavity block construction with aerated concrete blocks on the inner skin and the cavity has been nicely filled with platinum expanded polystyrene beads.

I can’t see why the U-value is so bad, but I think that outdoor air must be getting in between the blockwork and the plasterboard.

Any ideas or help, please?

Timber frame internal extenal junctions

WC_B — Tue, 22 Sep 2026 16:33:22 +0100

Hi there

We are designing a small timber framed extension with internal exposed timber frame and warm roof above.
Rafters above main structure to extend outside to form a canopy.

I have been going in circles about how to detail the moment where the timber rafter goes from inside to outside.
Roofing suppliers are insistant on a VCL at the internal side of the insualion.
Which ideally would form a continues lap from the roof to the curtain walling head.
But getting this lap is very awkward with rafters going in 2 different directions.
We want to leave the external rafters exposed from below.

Has anyone detailed something similar and could advise how they have done or would do it?

Window and doors in EWI

englishjohn — Sun, 13 Sep 2026 10:20:33 +0100

I am now well underway with my house renovation after a prolonged break due to illness, following on from my previous discussion.

We have settled on 200mm EPS EWI and are now looking at the windows. The wife is concerned that the sunken-window look won’t look very nice. The windows would originally have sat on the blockwork, approximately 200mm inboard of the finished face of the EWI.

I need to move them outwards, ideally in the easiest and cheapest way possible, as I’m having to make some sacrifices due to the costs spiralling.

Compacfoam is expensive, and cutting and setting out individual blocks would also be quite time-consuming for the builder. He has suggested simply using 100mm treated timber, similar to a fence post, and fixing it back into the blockwork, perhaps with some steel brackets along the bottom and possibly the sides.

I would also like to be able to remove the windows from the inside if anything goes wrong in the future, without having to destroy or significantly disturb the EWI.

Can anyone give me any guidance on whether the timber approach would be suitable, or suggest a better/cheaper way of achieving this? Windows approx 3G 1600mmx1700mm, doors 3000mmx2100mm and 2100mmx2100mm.

Secondly, I’ve also been quoted approximately £16/m² for graphite EPS beads to fill the existing cavity. Does that sound about right?

Exterior window blinds

englishjohn — Thu, 24 Sep 2026 14:54:20 +0100

Commonplace all over Europe. Speaking with my German cousin over the summer, he found it odd that I was struggling to find anything. Well, I found a few, but they were really expensive, especially compared to the electric roller door installed at my father’s house.

So, after another hot year, I thought it would be good to add them into the build, until I noticed the prices. That aside, thermal bridging appears to be an issue, along with possible ongoing maintenance access.

External shading, though, sounds like a win-win. Does anyone have any recommendations or experience with them?

Synchronous Condenser

Artiglio — Wed, 23 Sep 2026 13:01:26 +0100

Good day

In my local paper there’s been an article in respect of a synchronous condenser being planned for connection to the grid.
I’ve tried reading up on what is, but i’m no electrical engineer.
However am i right in thinking that it’s effectively a standalone flywheel connected to the grid to provide inertia ( iirc this was the term used in the thread about the spanish blackout last year), and that there may be a need for more of these across the country as time passes?

https://theisleofthanetnews.com/2026/09/21/plan-for-synchronous-condenser-to-be-installed-on-farm-site-in-ramsgate/

Postcrete

Rex — Sat, 19 Sep 2026 11:41:07 +0100

What ho one and all,

I know that Postcrete does what it says on the box and have used it as such.

Currently, in the process of 'leveling' some 450 x 450 paving slabs for the base for two IBC tanks. The soil is well compacted (around 15 years of walking and wheel barrows) but inevitably, not quite level and slightly slopes.

I'm wondering if I get the slabs level and shutter around them, can Postcrete be an easy way to make a solid base for the pavers?

Just found Slablayer; presumably does a better job for this purpose than Postcrete? Or is a regular sand/cement mix still the preferred method?

Thanks and toodle pip

log cabin style renovation

elodius — Fri, 18 Sep 2026 22:13:31 +0100

I'm considering buying a place that has a few problems, and I'm trying to figure out how difficult/expensive they'd be to remedy, and if it's worth it or not.

It's an old fishing lodge and is totally made of timber, other than one brick built boiler room set into the foundations that level out the slope it's on. It was built in the 70s.

A large proportion has had further thin timber cladding added at a later date so it's hard to assess the condition of the timbers behind that, but some of the original timbers can be seen and are rotting in a couple of places (I also saw some wasps come out from under one part). It does look like there may be some insulation behind it, rather than being 'single skin', but what I can see looks like it's encased in plastic, which I would have though would sweat against wood. I'm not sure if this is original or not

I don't know much about this kind of construction, but from the looks of it, it's essentially logs cut so that they stack up and interlock, and it's presumably quite hard to swap out one at the bottom, and potentially quite specialist work?

Ultimately, I'd like to fit a heat pump so presumably (unless timber is a much better insulator than I realise?) I'd need to remove all the existing cladding, replace any bad timbers in the main structure, then have a layer of modern, high performance insulation and cladding added. Presumably something composite is best for the cladding, and I'd want it to be highly fire retardant.

The roof would need similarly insulating - this looks to be some kind of bitumen like substance - it's the original roof and looks to be solid enough, but of course is 50 years old and won't last forever.

There's also an old oil tank in the boiler room - it's too big to fit through the door so would need cutting up to get it out, but oil reside will make it flammable, so is it practically possible to do this at all? It doesn't cause a problem per se, but wastes a lot of potential storage space

I've attached a few picture showing the construction, and the sort of rot I'm seeing, and also a rough floor plan with approximate dimensions.

Does anyone have a feel for the difficulty of doing this, and what sort of ballpark costs are likely to be involved? Should I just walk away?

edit - this picture doesn't seem to show up very well, but the whole place is about 19 metres wide by 6 metres deep, single storey

Integrated Solar Roof

Triassic — Mon, 08 Jul 2013 18:34:58 +0100

We're planning our next self build and the chief designer (wife) hates retrofit solar PV panels ("they look like they have been plonked on the roof without any thought about the asthetics"), we're also in a National park and the South elevation of our roof faces the road and the village beyond.

So I am looking at integrated PV systems and having searched online I'm left wondering, which systems are best? Anyone here got the latest view on the subject?

Wall Build-up for timber frame structure validation

Oj0001 — Tue, 25 Aug 2026 14:38:05 +0100

Hey,

I’m currently in the progress of building a single story extension on the rear of my house, located in the midlands.

For the extension I drew up and got approved plans for a timber frame structure. The wall build up from inside to outside is currently:

15mm plasterboard
145mm studs with 100 PIR. (Resulting service space to inside, all joints tapped for Vapor sealing)
11mm OSB
Vapour barrier
70mm EPS with direct render.

However, since then I have read more into interstitial condensation, and under winter conditions there is a risk at the outside face of the PIR could suffer, this is behind the OSB and could lead to issues. Also the OSB becomes sandwiched between two layers, although EPS should have some permeability.

So far I’ve looked at :

-Increasing the PIR to 140mm and adding an internal service void does not seem to resolve it.

-Switch to 140mm Rockwool between studs. (Decreased performance notably, but increase breathability). Still need to add internal service void as internal vapour layer needed.

-Switch to internal PIR layer, add external ventilated cavity and render board. Also considered external PIR to reduce thickness, then cavity and render board.

Really just looking for a sanity check, is there a fundamental issue with the project as designed, is there a way to add improvements, or does anyone have experience with similar?

There’s a lot of discussion on similar build ups on here, but nothing quite the same.
Any and all help is appreciated!

Clay roof tiles with a Nordic feel

Victorianeco — Tue, 08 Sep 2026 23:16:48 +0100

Can anyone recommend brands that fit the bill?

We don't want concrete as they fade over time, we have realised we won't get away with a re-roof in our area with standing seam or corrugated due to planning and keeping the street similar.

So we need to pick slates or tiles but we're thinking larger format tiles will achieve the look we are aiming for.

Any pointers on this?

Embodied carbon, EWI, CWI, ASHP, Exposure zone 4

fostertom — Thu, 11 Jun 2026 11:42:34 +0100

A multi-faceted issue:

1. The new thinking, which removes high-standard External Wall Insulation (EWI) from its pedestal as the default/ideal for retrofit, on grounds that the embodied carbon (i.e. the CO2 and CO2-equivalent released to atmosphere) created in 'quarrying', manufacturing, transporting and installing EWI, is likely to exceed, sooner and for longer duration, the in-use carbon it saves over the building's subsequent lifetime.
Couple that with the rapidly declining carbon content of mains electricity, which means that electricity consumed over the building's in-use lifetime, already and increasingly carries little penalty in global heating.
Then, compared to super-insulation hence consuming minimal energy-in-use, the alternative of omitting the super-insulation hence consuming plenty of 'harmless' electric (via heat pump) energy-in-use, can actually be a lot better for planetary climate, both in this emergency-short-term, and over the building's lifetime.

2. Retrofitting the 30% of UK building stock which is still-uninsulated cavity wall, with or without EWI the cavities should be filled (CWI), as it's near-impossible to prevent outside air blowing around in the cavity. Even fitting EWI can't be relied on to seal the multiple cracks, entry points and open-to-loft top of typical cavities - outside air is still liable to bypass the EWI, separated from the interior only by the inner skin. External render can't be relied on either. Even Partial-fill CWI is poor at preventing outside air blowing around in the cavity; it really needs to be full-fill CWI.

3. CWI is cheap to install, with small embodied carbon. So, considering both 1. and 2. above, the new default looks like installing full-fill CWI, without EWI, along with electric (via heat pump) energy-in-use. In which the CWI is an indispensable part, hardly works without.

4. But what about cavity-wall buildings in high-exposure areas? There, CWI is pretty much banned by Building Regs, certainly with traditional 50 wide cavities (as opposed to more recent 100-ish cavities) and certainly in exposure Zone 4 areas (i.e. most of the west/southwest of UK). External render doesn't help.
https://assets.publishing.service.gov.uk/media/606c366ad3bf7f400e10af54/wic-final-report.pdf also gives little hope that a coat of gunk would make the wall more suitable for CWI.
Does anyone know different?

5. Without CWI, a house has nearly zero insulation, if outside air is blowing about only separated from the interior by the inner skin - even if accepting plenty of 'harmless' electric (via heat pump) use. Especially if extending an unfilled cavity-wall house; the existing cavity wall becomes an internal wall, but super-cooled because its cavity is continuous with the still-external parts of the cavity wall adjacent.

6. Similar applies if you've EWI'd your half of a semi-detached house; your unfilled cavity, inside the EWI, will be super-cooled because continuous with next-door's unfilled cavity.

So WTF to do about all this? Any solutions, bright ideas?

PH barn?

fostertom — Mon, 07 Sep 2026 18:55:40 +0100

Part Q barn conversion, steel frame portal, 115m2 2-bed, almost cubic, severe restraint on vertical/headroom, every milimetre counts.

Hence only 25 PIR over the extg reinf conc slab with 32 timber floating flooring, but downstanding 'coffer dam' of 250 EPS (continuous with wall insul) in slit trench 1200 deep, french drain at bottom, gives floor 0.25U, the BldgRegs Table 4.2 'improved' figure, as the whole is a Material Change of Use, not newbuild. The block of subsoil beneath, inside its 'coffer dam', will somewhat adopt an intermediate temp which will be partly-ground-coupled to the interior via the weak insulation.

Blockwork ground floor and stairwell partitions built off the slab on insulating strip stuff (so penetrating the weak floor insul hardly matters) add more interior massiveness. As ever-strengthening heatwaves become the norm, overheating at least as important as winter loss, internal massiveness has new importance.

Roof and walls can have extremely good insulation, airtightness and continuity, copiously through-ventilated (vertical bris-soleil?) to keep cladding cooler, as well as shielding from winter clear-sky cold. Windows thoroughly shaded by brise soleil etc.

Question is - is PH, no heating system, within reach? Though not the classic PH approach, would PHPP be impressed by insulation elsewhere compensating for the floor, internal massiveness and ground coupling particularly as affecting overheating, walls and roof shading?

If not, it's a centralised plan, so AAHP with very short ducts, incl AC (why not, as well as the passive overheating measures?) which might do the DHW, and/otherwise night-store, and wet solar - is that still a thing? MVHR of course.

How to make a complicated penetration airtight?

djh — Sat, 05 Sep 2026 12:18:31 +0100

I'm looking for advice and reassurance! We're planning to fit an air-air heat pump to replace the direct electric duct heater we presently use to heat our house, and to provide cooling in summer. It's a conventional split unit with internal units and an external condenser unit. To connect the internal and external units we will need to make 60mm holes for the refrigerant, condensation and power in a conduit.

I'm planning to make the holes in areas where there is warmcel insulation instead of straw bales, so as I remember the construction from inside to outside is:
- lime plaster (30mm or so)
- 15mm Savolit board
- Intello Plus membrane (connected to lime plaster over straw bales with mesh
product)
- muslin to contain Warmcel
- 450mm of blown-in Warmcel
- 25mm Savolit board
- lime render (40mm or so)

My thoughts are to drill from the inside, starting with a pilot hole. Are there likely to be any issues to watch out for?

My other worry is airtightness. The main airtightness barier is the internal lime plaster but there are places (such as these areas) where the airtightness barrier is the Intello PLus membrane and it is connected to the plaster with Pro Clima Contega PV tape. We used Dafa pipe and cable collars or Siga Rissan tape to seal penetrations. Lots of short lengths of Rissan around the MVHR ducts and around the incoming water pipe for example.

I'm not sure how best to seal a 60mm pipe containing several other pipes and a cable though, and in theory it should be sealed to the Intello Plus although sealing to the plaster seems a lot easier. Any thoughts on the best approach?

https://proclima.com/products/connections/window-sealing/contega-pv
https://www.siga.swiss/gb_en/products/rissan

CAT6 male plug

Rex — Tue, 08 Sep 2026 11:30:01 +0100

What ho one and all,

Having managed to fish the CAT6 cable fro the loft (second floor?) to the g/f office space, I need a 3m length to connect form the wall socket to the router (when Openreach finally manage to install the fibre; at the moment, this year, next year sometime, never!!)

The cable is a factory made, 50m with male at each end. I wonder about cutting a 3m length off, and fitting a male plug to each cut end, then I will have the necessary extension. But.... how do I know which wiring standard the factory fitted plugs? Either T568A or T568B? Is there a way to determine? Or is it just a case of wire one way and if it does not work, try the other?

Although I hardly need an RJ45 network tester, by chance, my favorite Lidl has them on sale today so bought one for the mega sum of £4.99.

roofing slates

rsk1 — Sun, 08 Jan 2017 19:32:57 +0000

Can anyone give a comparison of the eco credentials of real versus artificial roofing slates? And while we're at it, any other kind of comparison such as longevity and cost

Passive house V rodents

Beau — Sun, 18 Nov 2012 07:52:17 +0000

At the moment I am fighting a battle with rodents chewing there way into our house. Now our place is not super insulated or airtight so the effects this damage being caused it not going to have a massive effect but I was thinking if you are working on PH what extra precautions should be taken to prevent rodent damage to the air tight layers?

Window Detailing CWI v CWI with EWI

Victorianeco — Sun, 30 Aug 2026 09:27:39 +0100

1960's uninsulated property

Still undecided if I'm going to adopt the fabric first approach (focussing on CWI beads and then EWI with windows in the insulation layer)

or

More later research focussing on reducing embodied energy at source and just use CWI beads and then silicone render over existing.

Just wondering if anyone could share the optimal window fitting detail for each approach and how I could mitigate thermal bridging particularly if I adopt the latter approach?

Property is currently ~20mm render on external reveals and PB and skim internally on the reveals but solid render/skim on the internal walls.

Windows will likely be alu-clad 3G from Allan Brothers, property will be having ASHP and solar.

I know I've harped on about which approach to take but this decision of CWI v CWI with EWI is holding up the project and causing conflict with her indoors.

Property in question linked below for context:
https://drive.google.com/file/d/12ZZsoLmjjSMoA4AW8HBQ_oQzmi9waWuE/view?usp=drivesdk

Water saving: grey water top-up

Doubting_Thomas — Fri, 28 Aug 2026 17:11:51 +0100

Hello again.

Since it's on everyone's minds right now, we've been discussing how we can use less water at home. One idea is using cold bath water to top up our WC cistern.

Ours is a concealed cistern (Geberit Duofix) so the proper access is via a removable faceplate. The idea with this would be to introduce a separate hole and hose arrangement on one side, with some sort of inlet valve to allow topping up the water level using a watering can or jug filled from the bath.

Any suggestions for what we could use at the filling end? All I can think of is some sort of wall-mounted tundish like the below.

Also, is this mad? Anything we should be wary of, other than probably needing to de-scale/clean the cistern more frequently?

IBC rainwater storage

Rex — Fri, 07 Aug 2026 15:32:33 +0100

What ho one and all,

Have a 6000 liter rainwater collection tank in the garden (mainly for toilet flushing but also garden use) and it has of course, been empty for the past two months.

Wish I had installed an even larger tank but 15 years ago, who could predict this extended drought.

So at the behest of SWMBO, I am investigating most likely, one (or perhaps two) IBC and how to fill. Obviously, the best location is somewhere that I can divert rainwater but the design of the house is such that the only place would be against a side wall and these are somewhat ugly things.

Since the loft tank (for flushing) is filled by a submersible timer pump, I could access the pipe and T off to an IBC situated in a less obnoxious location. But is it possible to install a ball valve in an IBC so that when fill, it does not overflow?

I have not researched this idea but thoughts would be welcome.

CAT6 install

Rex — Wed, 26 Aug 2026 13:32:37 +0100

What ho one and all,
Thought I had a separate CAT6 thread but only topics relating to my attempts, namely toilet seat and plasterboard.

Knowing that y'all are sitting on the edge of your seats, after a lot of procrastination and alternative plans, plus attempting limited demolition (Right said Fred, gotta take the wall down!), persistence has paid off and yesterday, I found the fish rod end and have finally have the CAT6 cable form the loft (second floor), horizontally through the Posi-joist / Warmcell floor/ceiling and into the wardrobe. From there , it will be a simple vertical drop to where I will install the CAT6 socket.

Don't recall any job where I have been so persistent in my efforts.

I won't make good until the fibre to the house is installed and I know the CAT6 is working; then a simple decoration job.

I did not remove the toilet but did remove the small cabinet beside the toilet which allowed me to bore another 100mm hole into the 22mm OSB to get a better angle.

Appreciate all the advice and suggestions.

Broadband and VoIP

Rex — Sat, 04 Jul 2026 14:48:15 +0100

What ho one and all,

Frequently happening as I get older, I am getting my knickers in a twist as technology leaves me behind.
At the moment, broadband and landline is with PlusNet via fibre to the pole. We are not paying for the landline, but it does receive incoming and we would pay per minute for outgoing calls.

My contract is ending but PlusNet are no longer offer a landline, just Full Fibre b/b. However, their associate company EE, will offer full fibre to the house and I assume, VoIP to keep the phone and phone number.

I am told that an engineer will have to assess how to get the fibre to, and then, into the house. At the moment, it is overhead to the front roof apex, then phone cable to the various RJ45 sockets which was part of the building process. The ''customer help' was not exactly helpful with my questions, but ......

Fibre has to come to the router which if it was in the loft, can I then use the existing wiring to the computers on the g/f?

The 'unhelpful' assistant was suggesting the fibre will have to be routed down the wall then drilled through the wall to where the office is located. The house is timber frame with Warmcel insulation. There is the breather paper on the frame (but that is inside the cavity) and internally, there is scrim under the Fermacel. Drilling through either of these materials is like drilling into a ball of wool; it just rips everything to shreds.

How does a fibre cable come into a very well sealed house if it has to be drilled through the frame and insulation? Once inside the house, can I use the existing wiring to use additional computers in different rooms?

Thanks and toodle pip

Making good a cracked footpath

thebeacon — Thu, 20 Aug 2026 11:33:40 +0100

Hello,

I’m seeking some advice on making good the pathway at the front of my house. Its currently a 50-100mm slab of concrete which has some cracks and a drain in. The water currently runs towards and pools in front of the door.

I would like to repair the footpath and add a slight ramping in front of the door to direct the water to run away from the house. The entire path is about 2.6 x 1.3m. I imagine some areas would need 40mm while others less than 10mm.

I’d rather not break out the entire slab and add a resin based concrete product on top. Does anyone have any experience or advice with doing this? I have been looking at Cretex® EP Mortar (https://polycote.com/contact/) as a possible option to use.

Thanks,
Tom

MVHR, heatwaves, chiller?

john.connett — Thu, 02 Jul 2026 12:54:37 +0100

My house in Cambridge had a low energy renovation around 15 years ago with triple glazing, increased thermal insulation, solar thermal system, thermal store and MVHR. The MVHR unit is a Vent-Axia Sentinel Kinentic BH.

For most of the time since it was installed it has worked very well and I rarely needed to open any of the windows. However, during the recent Amber Heat Alert the house overheated badly. Possibly the high humidity made it worse than in earlier years or my age and, maybe medication, made me less resilient.

My suspicion is that during an extended heatwave with tropical nights the MVHR is unable to maintain comfortable indoor temperatures. With or without a summer bypass, if the air temperature is over 35º C outside then the MVHR will import that air. Even if the air temperature drops lower overnight it can't catch up and the house continues to retain the heat, made worse by the high quality of thermal insulation.

Some form of air cooling may be required! My back garden is nowhere near big enough for a ground-coupled heat exchanger so active cooling may be an option.

I have seen an example where a reversible heat pump was connected to a water/air duct heat exchanger (eg. Zehnder ComfoPost). However, my house has a gas boiler.

Has anyone else experienced similar problems or can suggest possible solutions?

Water prices

Rex — Sun, 16 Aug 2026 17:16:07 +0100

What ho one and all,

The headline on the front of today's Telegraph is what can only be described as 'surge pricing' for water during droughts. The aim is to encourage us to use less water.

This really anger me as we have a 6k liter rainwater collection tank and apart fro the fact that I'm not paying for incoming and by default, sewerage charges for using that water, I am unlikely to get any consideration for the fact that I am using less treated water than most houses.

With all the building regs we have in place, surely it makes sense that every new build, whether single houses or estates, must have a large rainwater collection to be used for toilet flushing. After all, every new build has to have a large soak-away, so why not collect that water before it goes to the soak-away?

It is absolute madness to flush expensively treated, potable water down the lavatory.

Now I'm off my soapbox!!

Solar Panel Fire

Rex — Thu, 28 May 2026 20:27:00 +0100

What ho one and all,

Just seen this on the Mail on Line web site.

https://www.dailymail.com/news/article-15854881/solar-panels-explode-home-explodes-flames-family-inside-escape.html

Will we ever hear why this happened? Bet the estate developers will have a nightmare with all the other owners wanting reassurance their solar panels will not catch fire. There is a 100 Taylor Wimpey built estate near me and they all have solar panels.