Fri, 17 Apr 2026 11:48:44 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18341 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18341 Mon, 01 Sep 2025 15:58:30 +0100 BWork
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]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=289 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=289 Tue, 15 May 2007 18:00:44 +0100 GBP-Keith https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18361 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18361 Tue, 07 Oct 2025 12:20:39 +0100 Nick Parsons
I'm just raising this in a new thread since I am not sure where it goes from here. I have a 'soft spot' for GBF, and was 'in' long enough ago not to have paid anything, but if we assume (I don't *know*) that the number of active users ('supporters') is relatively small I am not at all sure how the £6500 will be raised. I'd be sad to see it go, but maybe that has to be??

Just some random ramblings, but any other thoughts would be useful to users and, I am sure to AECB as new 'Guardians of GBF'.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18421 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18421 Sat, 11 Apr 2026 11:40:30 +0100 minisaurus
Has anyone experience of them? The positives are many, but what are the negatives? price I guess]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423 Wed, 15 Apr 2026 10:35:53 +0100 andyman99
Whilst starting to help my son renovate his bathroom we came across a rather unpleasant problem. The tiles on an external wall pretty much fell off and everything behind is very wet.
Construction: this “front” wall appears to be a simple timber frame structure. From outside to in: PVC cladding - roofing felt (what I would call old style felt not a breathable membrane) - timber frame filled with fibreglass type insulation - plasterboard. The water ingress does appear to have come from the inside. The timber structure is very wet, the insulation a sodden mess and the roofing felt disintegrates as you touch it. We have an insurance assessment this Friday but I would like to understand a way forward if possible before then. I think the main structural walls are brick, left and right whilst front and back appear to be this timber frame structure. 2 rooms across the front, bathroom and bedroom. No obvious signs of a problem in the bedroom front wall. I’m wondering how fixing this would best be approached? Any ideas welcomed]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18414 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18414 Thu, 12 Mar 2026 08:19:49 +0000 fostertom https://www.greenregister.org.uk/civicrm/?civiwp=CiviCRM&q=civicrm%2Fmailing%2Fview&reset=1&id=5840&cid=40824&cs=f4a98d878cf7eb7a71342f57279ea33e_1773283838_720

"... research into stone structures to help move their use back into everyday construction.

Standing three storeys tall, the Stone Demonstrator shows stone’s potential as a contemporary, low-carbon, structural material.

Natural stone offers a route to cut carbon emissions sharply. Compared with a conventional reinforced concrete frame, the Stone Demonstrator drops embodied carbon by roughly 70%, and by around 90% when set against steel.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18419 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18419 Fri, 10 Apr 2026 07:20:37 +0100 Victorianeco
Any suggestions on materials that give a good corporate image but also boast good green credentials.

They must all be standardised and suitable for standing desks

TIA]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18422 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18422 Sun, 12 Apr 2026 16:34:50 +0100 tony
Document here - https://docs.google.com/document/d/e/2PACX-1vQ2s-HB1cud4gZISwGuQvP8oIifaCVcF94ySusEaaPanqcCf4md3UPJDOKeD02Gg9MitbCVb4vXe5SW/pub]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18418 Tue, 31 Mar 2026 18:59:32 +0100 Peter_in_Hungary
The question is - Is a VCL above the plasterboard (i.e. on the warm side of the insulation) required?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18420 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18420 Fri, 10 Apr 2026 15:32:59 +0100 tony
I’m gonna make some suggestions

1) the client
2) the designer
3) a building physicist - they could be a consultant
4) an engineer
5) an energy assessor
6) a QS ?


? Crack on then ……]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17796 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17796 Sun, 26 Mar 2023 23:01:59 +0100 zak99
We need to replace our broken concrete driveway and also provide a separate hardstanding for parking/working on a vehicle etc

Other than the usual concrete, block paving, slabs, gravel are there any other lowish impact surfaces I may not be aware of please?

Permaculture garden designer suggested gravel and sleepers for the drive or gravel with random planting in the gravel but she is hard to nail down on the details. Like will a wheelie bin or wheel barrow pull through the gravel or how do I do low nutrient random planting with type 1 sub base or will the sleepers be slippery in winter. My wife would like to break up the gravel expanse with some sparse slabs but designer feels gravel will always end up on top of slabs.

For the hard standing beside the garage I may possibly be able to reuse some old slabs but wondered if there are other lowish impact materials for a new surface?

Whats your experience please?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17406 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17406 Sat, 05 Mar 2022 20:47:49 +0000 chrisinbrighton
The walls are all 700mm thick stone and one of these walls is covered in slate with a 50mm gap. I was thinking this would be a good place to add insulation.Is there a particular type which would be best and does a vertical slate wall need a breathable membrane?
Thanks.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18417 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18417 Fri, 27 Mar 2026 09:22:41 +0000 tony
In sustainability terms, it seems crazy to build hugely deeper foundations which use an awful lot more concrete and produce additional problems and costs of disposing of the spoil when it may well not have been necessary. I think this approach would be better for the environment too. :-)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18415 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18415 Mon, 16 Mar 2026 11:29:31 +0000 ChrisinYorkshire
Hopefully this makes sense – if its hard to follow let me know and I’ll look at posting a diagram.

I would like any thoughts about my planned action for insulating a wall where my house transitions from being underground to above ground.

Context
The house is built against a valley side. It is mostly of traditional thick sandstone construction, although 30-40 years ago or so some areas were rebuilt with cavity walls.

To one side of the house two floors are effectively underground – the top floor pokes above ground approximately at floor level. The wall against the earth has been fitted with a cavity drainage system, metal studs, with PIR insulation and careful attention to airtightness/VCL.

My current area of concern – the transition point of said wall, as it pokes out from the ground. This involves 3 large wooden beams that are bedded into the wall (upon which sit the top floor floor-joists). I am switching to breathable insulation for the top floor room (a kitchen).


Further context and observations

It has been a very wet winter, the kitchen is unheated and has no mechanical ventilation. Where one of the beams enters the wall I am getting a 23% moisture reading ( this is the top face of the beam)

Floorboards have been cut away (approx. 70-80mm) from the wall during summer last year. They are reading 20% moisture at the edge closest to the wall, this is in the coldest corner of the room.

A floor joist running along side the wall, but separated with DPM and a gap, is reading 21% moisture.

Therefore I think there is a general humidity/condensation issue, though the beams bedded into the wall might also be wicking some moisture from the wall.
The coldest corner of the room, is a bit damp, also from condensation I believe. Note this corner is going to be behind kitchen cabinets.



Current course of action:
- I have dubbed out and parged the wall with NHL 3.5 and sand mix.
- Planning to meet the PIR insulation with wood fibre board which will then continue up the wall.
- I have considered but don’t want to use an eps/xps plinth layer at the transition from PIR to wood fibre boards, because I don’t want to trap condensation/moisture around the large beams that enter the wall.
- There is a leaky gutter externally that will be repaired/replaced.
- Kitchen will have mechanical ventilation and heating installed.

Any concerns over ‘wet process’ vs ‘dry process’ wood fibre boards? Wet process appear to be more capillary active than dry process boards. Frustratingly it's hard to find suppliers of wet process boards in tongue and groove.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18416 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18416 Tue, 24 Mar 2026 11:40:09 +0000 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18379 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18379 Thu, 04 Dec 2025 16:25:55 +0000 revor https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18413 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18413 Mon, 09 Mar 2026 20:04:02 +0000 Gareth J
I didn't ask him, but what's the advantage over a non breathable setup? Something like DPM, concrete slab, PIR/EPS, top layer/s. His place is all above ground and is a well built house.

I can see that there are likely lower carbon and non plastic based advantages but from a performance perspective, does the floor need to breath? Is it mitigating potential moisture issues? This might have been covered loads or be completely obvious and I've missed it so apologies in advance!

The suspensoended floor in my own solid wall cottage needs attention at some point in the future so am keeping half an eye on options. It's complicated by being half dug into the ground around it though.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18412 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18412 Sat, 07 Mar 2026 08:36:18 +0000 tony
During the 2021/2022 season at DraughtBusters we started to encounter a lot of problems with trickle ventilators. These have been even more of a problem prevalent in 2026.

Some of the problems are : -

Draughty when closed
Insect protection gone or decayed
Wouldn’t or couldn’t close
Householder didn’t know how to open or close them

Draughty when closed.
We found that in a lot of cases draughts were emanating from the trickle vents even when closed. These vents were surprisingly insubstantial and it was rather a shame to find that they were letting in draughts. It would be possible to seal them to the frames to prevent some of the draughts but this would be tricky. If the windows can be used on a ventilate position, i.e. fixed in a secure vent position using the second position on the window handle then we recommend sealing up the trickle ventilators.

Insect protection gone or decayed.
We have identified whole estates where trickle ventilators have lost their insect protection, these are often with ‘over the head’ type ventilator arrangements. The insect grilles become brittle and fall out or are knocked out with window cleaner’s brushes.

Won’t close - this is different from draughty when closed as those do close but a draught enters between the frame and the vent. Some ventilators have plastic clips that hold the vent in place and these can break and the vent flaps about remaining open all the time, others just don’t close and allow draughts all the time even when closed.

Householder can’t open them, we didn’t like this one! There are a lot of different types of trickle ventilators many and varied ways of opening them some push left or right some up and or down, others click open, while others need a sharp but gentle press. It is nor really surprising that some people can’t open them.

Trickle ventilators are the bane of a DraughtBusters life, they are intended to let draughts in, in a controlled way. They are proving themselves to be unfit for purpose. We see ventilation as an active thing, to be controlled by occupants as and when required and a general government directive of ‘one size fits all’ is resulting in draughty homes. We have said before that draughts do too much by way of ventilation when it is windy and not enough when it is calm. Trickle ventilators should now be outlawed in favour of saving energy. Controlled ventilation is what we need.

The adage, ‘build tight ventilate right’ is a very good one, unfortunately trickle vents although the intention was for them to help have turned out to be unhelpful, they cause draughts as highlighted above, do not ventilate right and it will take a lot of work to rectify the situation. Sadly this is a repeat of the same mistake made in the fifties with compulsory through the wall vents in all bedrooms in new homes, DraughtBusters expend a lot of effort blocking those ones up even two generations after they were installed.

The next generation of DraughtBusters will need to spend even more time sorting out leaking trickle ventilators in windows.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18411 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18411 Thu, 05 Mar 2026 16:48:47 +0000 oliviaaa99
Quite a lot of our electrics are in the loft& attached to the current boards. These will be removed for insulating, so we aim to attach the cables to the floor joist sides instead.

Should the order of layers go:
1) membrane > insulation up to joist level > layer of ducting with insulation around it above joists > loft boards

2) insulation up to joist level > membrane across joists > layer of ducting with insulation around it > loft boards

3) ducting with insulation around within and above joists where necessary > membrane above joists and ducting ( > potentially a layer of insulation above joists and ducting so the membrane is on the warm side?) > loft boards

4) something else? We’re open to any alternative ways as we’re not sure which is correct!

We are also not sure if we need an intelligent membrane, VCL or just airtight? For reference, the joist depth is appx 8cm and the roof is ventilated at the eaves. The floor was sealed with VCL over the subfloor but under a plywood base, and the house has been replastered/painted (still some new cracks though!).


Thank you!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12591 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12591 Fri, 26 Sep 2014 09:05:00 +0100 Triassic
I realise Panelvent is more permeable than OSB and this is to aid moisture movement, but I'm left wondering what part the external breather membrane plays and is it necessary?

Why have a high permeability board covered with a low permeability fabric?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18408 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18408 Sun, 22 Feb 2026 19:05:31 +0000 Victorianeco
Considering roofing options to replace 70 year old concrete tiles.

Solar makes perfect sense at this point and so does a standing seam roof.

This could be a good all in one system?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18380 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18380 Fri, 05 Dec 2025 17:11:27 +0000 tony
The big news is that my dream is about to come true

I would be keen to from any others who have heat flux data for walls of any type please]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18063 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18063 Thu, 11 Jan 2024 10:48:07 +0000 GreenApprentice
Been busy renovating our 1960s bungalow and making the floor and walls airtight as we do it. We’ve now completed nearly half the house in terms of living area and need to consider sorting the roof space so we can get some insulation up there. As we’re aware that the airtight tight membrane is to go on the warm side, we have been waiting to be in a position to install that before insulating, but this will require better weather as we’ll need to be doing some of the work from the outside by removing roof tiles (shallow roof space).

As we will be installing MVHR when we’ve finished all the building work, we’ve decided to install recycled-plastic insulation as the first layer (110mm) as we’ll need to be messing about with it to install vents.

The question is, can we put the airtight barrier over this layer of insulation, across the ceiling joists and then pile on other insulation, probably a deep layer of fibreglass or rockwool, the MVHR ducts will be within this layer - we’re going to create a ‘warm area’ around the loft hatch where the MVHR equipment will be housed.

It’s not the end of the world if we have to move the insulation out of the way to install the membrane if this is a complete no-no, but wanted to get a view if this would be ok as it will save time and it will be easier to install over the joists than around them.

Many thanks in advance for any advice]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18409 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18409 Fri, 27 Feb 2026 12:10:37 +0000 SteveZ
I have not active for a few years due to ill health. My mystery illness was diagnosed in 2022 as myeloma - definitely not nice. Although in partial remission thanks to the NHS, my DIY abilities and energies have been much reduced and I am beginning to clear out my garage.

I have an Evolution 255mm sIngle sliding mitre saw with its own Evolution stand and an extra roller stand. The items ar still on sale at Screwfix and with their latest discounts, come to £265. All the kit is in very good condition having been lightly used building a temporary shed store and bit of post and rail fencing.

The Evolution blade is the Rage multi-material one and happily cuts plastic, timber, plastic and steel. Surprised me too! I also have a suitable diamond cutting wheel - good for tiles or stone, in the garage somewhere which will be include if I can find it.

Offers around £130 would secure the set, or possibly break into individual items at half price. I am in North Cornwall, near Launceston.

Thanks for reading this - Next step is eBay]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14266 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14266 Sat, 14 May 2016 19:09:13 +0100 jwd
Cheers]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18410 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18410 Sun, 01 Mar 2026 10:27:23 +0000 Rex
We own a maisonette that is rented out. An old Potterton Kingfisher cast iron boiler, bullet proof, always passes the annual test but by today's standards, very inefficient, provides the DHW and heating.

The gas guy always recommends replacing with an electric boiler. My wife sees the Fischer Future Heating (https://fischerfutureheat.com/product/electric-boiler/) ads in the weekend papers and is keen for me to investigate (advertising pays!)

I don't know one end of a replacement electric boiler for the other; the Trustpilot reviews are all great, but they are mostly based upon installation in the past few months, not long term usage. Are these boilers any good? Apart from boosting the EPC rating and a small saving on the annual test, are they worth the installation expense?

Thanks and toodle pip]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18391 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18391 Tue, 06 Jan 2026 12:45:55 +0000 fostertom Thickness - 15, 12, or will 10 ply be adequate?
Material - WBP ply? - any concerns about poss long-term intersitial condensation, positioned as they are well outboard in the insulation/sandwich? Is fibre-cement or other mineral board used instead? I guess interstitial condensation is no more likely than on/in the the window frame itself, but with less drying potential?
Assuming air-sealing to the wall, and to the window frame, are do-able, what about air-sealing the four corner-edges of the box?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14817 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14817 Sun, 08 Jan 2017 19:32:57 +0000 rsk1 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16745 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16745 Mon, 05 Oct 2020 23:22:40 +0100 graham_cbruk
I have a conundrum... we're installing a Geocell/limecrete floor with underfloor heating. I'm planning on laying engineered wood flooring but have found conflicting advice with regard to the best approach to installing it.

Some experts say you should lay the wood on treated battens with an air gap, whilst others say it's fine to float the wood on a breathable underlay. The downside of the batten approach is that the air will diminish the transfer of heat from the UFH, whilst the (possible) downside of the floating approach is that the floorboards will be damaged, over time, by moisture coming up through the breathable limecrete floor. However as the Geocell, is non-capillary, it's also possible that this will manage the moisture effectively below the UFH and leave the limecrete dry.

Has anyone else had to deal with this conundrum - and if so what solution did you settle on? I'm particularly interested in the experiences of people that have had engineered wood floors down over limecrete for some years and so have real world experience of the outcomes over a decent period of time!

Thanks in advance for any thoughts.

Graham]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18407 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18407 Sat, 21 Feb 2026 21:37:47 +0000 Victorianeco
While I can appreciate it's quicker and lighter we feel we would possibly like vertical cladding.

I guess that would mean we'd need vertical battens followed by horizontal followed by the cladding...

What are the pros and cons of each? And are there any simpler methods of fixing vertical boards while ensuring drainage?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18406 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18406 Tue, 17 Feb 2026 17:03:54 +0000 Rex
My slab is reinforced poured concrete sitting an industrial corrugated galvanized metal base with an air gap below.

When I park the car following a wet drive, inevitably, water drips onto the concrete and there is frequently a puddle in the morning. It is probably not of concern to me, but it does cross my mind that reinforced concrete with water sitting on top can in time, cause the rebar to rust with the obvious consequences.

Is this something I should be concerned about? Alternatively is there anything I can apply / paint on the surface to reduce the absorption of water?

the mats at the front are to 'contain' water from the front arches, but the large damp patch is from water that I guess is dripping for the various under-body panels.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18398 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18398 Fri, 23 Jan 2026 07:59:39 +0000 Rex
Kinda trivial as it does not concern me but just out of interest!

Have a new neighbour in a 1930's house and they are having the place re-wired. Obviously, it mean removing all the wiring that is covered with plaster.

Which gets me thinking, how would a future owner of my t/f house with Warmcel insulation, do the rewiring?
Not easy as they would have to cut slots out of Fermacel. I also have the ceiling fully insulated with Warmcel.

How is it done?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18401 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18401 Sun, 01 Feb 2026 15:30:07 +0000 TonyinOxford
Newbie here. First post. It is a big one, so I very much appreciate any advice given in advance. Thank you.

I live in Oxford and I have commissioned an architect to transform our 3 bed 1929 semi into a 4 bed EnerPhit home. Overall the house will end up at around 160m2. The architects have done many retrofits to EnerPhit standard.
The house is in a flood plain, with an immediate drop at the back of the house of 1.5m down to land that regularly floods. Side access is narrow. For this reason I would prefer not to have an external ASHP unit.

We have been back and forth on how to ventilate and heat the house, and supply hot water.
We have had multiple quotes but all seem alarmingly expensive.
Total Home Environment want £37K to design, supply at Pichler PKOM4 all in one unit, install and commision. VAT free but no BUS grant.
Williams Energy Design want £14 to design, supply a Zehnder ComfoAir Q600, install and commision. VAT payable but no heating / cooling or hotwater. To add the Comfoclime unit is an additional £6K plus VAT (but my understanding is that if an ASHP is attached then it can be zero rated). But still no hot water or cylinder, and would also need to additional heating through electric towel radiators and/or IR panels. The architect says Rod Williams is particularly good at the design so that there is no unnecessary boxing of ductwork.
Energy My Way want £26K for MVHR and separate external ASHP, hot water cylinder with a small amount of UFH and towel radiators. No VAT, and this has already taken into account BUS grant.
Heat Space and Light were cheaper but do not install and could not give me the name of a reliable installer in the Oxford area.
All of the above will also be subject to main contractor builder's 10% overhead and profit charge.

The first question is about approach. How would you knowledgeable guys go about heating and ventilating the place?

Secondly, it is feeling very, very expensive compared to the indicative prices I see online, but maybe I am missing something.
I am a competent DIYer, but I feel this might be too big a job, and as it is instrumental to meeting Enerphit and having a comfortable home it is not something I want to get wrong.

Am I being over-changed? Is there an architect's premium? Does anyone have any advice, or details of a reliable Passivhaus MVHR that covers Oxfordshire.

So many thanks in advance.

Tony]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18402 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18402 Thu, 05 Feb 2026 17:59:25 +0000 davidj
Just a query about insulation. We are trying to retrofit a 1976 bungalow. Cavity wall with loft. We are going to insulate the cavity and externally and clad in timber. We are intending to remove part of the loft./ceiling to create an open plan kitchen/living room. We are raising the ceiling over the kitchen just to give some visual interest to the room. The roof above the kitchen is an east facing pitch roof with a bitumen felt beneath Burlington slates. We will install some roof lights, taking the ceiling up to the rafters.

The bungalow roof has had three large purlins installed, each 350 mm deep, 5600mm long. These were installed because of a failed trussed purlin before we moved into the house. The new purlins are vertically installed and variably at approximately 900-1000 mm apart measured along the rafter slope. The purlins consist of two pieces of timber glued and bolted together and appeared to be doing their job satisfactory, although I don't know why they needed so many given the small spans between the rafters.

We are hoping to put as much insulation in as possible. We are intending to insulate under the rafters to allow ventilation to the full depth of rafters, which are 100 mm deep. We were then going to insulate between the purlins. Sorry, can't seem to attach a drawing.

The question I have is what type of insulation to use. One of the cheapest and possibly easiest is to use PIR. After angle cutting the PIR to ensure the sheets would fit accurately between the vertical purlins I would add Gapotape to ensure a snug fit, though would probably needing some support at the lower end where the angle wilth the purlin is obtuse. We were intending to install 260 mm of PIR in whole 2.4m boards, staggering the joints between layers. We would then tape the edges to the purlins and between each board to form a continuous VCL and achieve air tightness.

However, we have been spooked by the potential condensation issues and whether we should go for a more breathable/vapour permeable solution. Given this is above a kitchen generating lots of moisture, we are wondering which way to go. We are intending in any case to install a ventilation system, hopefully an MVHR, to manage the moisture levels in the house. The purlins are not fixed via brackets to the gable so at least no embedded timber to worry about and the cavity and exterior would be insulated.

The other options is to use flexible wood fibre or Thermafleece batts. These cost quite a bit more as we needs 280-300 mm, and don't achieve quite the same level of thermal performance (albeit I am not convinced about the claimed performance of PIR). But they are at least vapour permeable and more sustainable products. Mineral wool batts are another option but it is actually quite expensive at the moment and because of the spacing between the purlins (900-1000mm), it would involve lots of cutting, bearing in mind this material is horrible for lungs and skin.

The other problem with batts is that they are quite tricky to install as I would probably have to install lots of regularly spaced "I" beams or Larsen trusses to achieve a friction fit. Annoyingly, the rafters are variably spaced at around 400 mm (the some are 450mm!) so it is not simply a case of hanging these directly from them. I would have to screw the larsen truss ends into the purlins first then fit the plywood inbetween for the friction fit. I would need approximately 30 of these and then cut every 1200mm batt, so pretty tedious to do.

If I put the batts in horizontally I could put a horizontal "I" /larsen truss beam in between the purlins, though I would probably have to hang these vertically so that the width between is consistent for the depth of insulation. So a bit of a phaff. Also, the width of bats is inconvenient so would have to be cut down.

To add to the difficulty, batts would require a membrane above to minimise wind washing from the ventilation above and also an air tightness membrane below the insulation. This all adds to the trickiness of the installation and the cost.

Thermafleece would probably be the way to go rather than wood fibre as the sharp angles with the purlins may be easier to fill with the softer wool. Hemp is another option

The risk with PIR is obviously condensation on the purlins. Moreover with the purlins being composed of two pieces of wood glued and clamped, there is a risk of condensation if there are any gaps inbetween (so would need to seal these). But at least there would be plenty of ventilation above the insulation, with the ventilation in the rafters linking to the loft space which is cross ventilated at either end of the gables.

The big sheets of PIR would also minimise the joints through which moisture could enter the roof space and also avoid cold bridging (though appreciate moisture has a way of finding its way in however well this is installed).

I guess there is also the option of loose fill...

I would really appreciate some advice on which way I should go on this. Many thanks.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18394 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18394 Tue, 13 Jan 2026 13:51:59 +0000 D Cooke
Plasterboard and skim
125 x 50mm stud at 400 centres (vented air gap)
15mm OSB3 taped joints (functioning as a VCL amongst other jobs). Could apply another VCL over this OSB if needed/use smartply if we have to!
120mm PIR
50mm Counter batten (vented air gap)
Breather membrane
Wood cladding

The aim here is to avoid the inevitable breaks and gaps that occur when an internally applied VCL is installed around a structural oak frame. I also like the idea of a VCL that retards but doesn't 'trap'. The design idea also allows for an unbroken insulation layer that fully wraps the structure without thermal breaks (other than counter batten screws)
Ubakus tells me the condensation risk is zero. Does anyone have any thoughts? I can apply a stand alone VCL over the OSB if needed.

Thanks for any thoughts!
:bigsmile:]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18396 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18396 Mon, 19 Jan 2026 21:07:50 +0000 morsing
I installed a Vent-Axia Kinetic quite a few years ago, but this month I have suddenly had a new problem pop up.

We suddenly noticed a damp patch on the ceiling which turned out to be condensation on the outside of the condensation drain pipe. I originally fitted pipe insulation on the first two meters of pipe, can't easily go any further, and water is dripping out from the end of that.

It's very odd. I wasn't quite sure if removing or extending the pipe insulation would help, but I am more puzzled about why this is suddenly happening.

What should I look for? It's like the condensation water is suddenly colder than normal? Oddly it first happened when there was over-night frost but it is still happening now it is warmer.

Thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18404 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18404 Wed, 11 Feb 2026 15:41:09 +0000 Mikeee5
Has anyone experienced white marks on external brick cladding and damp problems on the internal walls following the installation of external insulation? I have attached a pic of one of the walls being affected. This is the side elevation of of a 3 sided semidetached property, the front elevation wall is being affected on the adjoining property.

Regards

Mikey]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18405 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18405 Sat, 14 Feb 2026 16:01:38 +0000 Victorianeco I’m looking for some guidance and shared experience as we move into the early stages of a rear extension project.
We’re proposing a single-storey rear extension, approximately 10m wide x 4m deep (c.40m²). There is a possibility it could become two storeys, but at this stage my wife and I are still undecided. Our intention is to start making progress this year, and from April we’d like to begin with the groundworks so we can at least get something tangible underway.
We are strongly considering a timber frame build, ideally on an insulated slab with underfloor heating within the main slab. At present we’re undecided on the roof design:
Pitched roof (possibly with eaves), or
Flat roof incorporating 1–2 roof lanterns
The rear elevation is likely to have two or possibly three sets of French doors, although we may also consider sliding doors.
We fully expect to engage a structural engineer for calculations, but before getting too far down that road I’m keen to understand best practice from those who have done something similar—particularly from a low-energy / green building perspective.
Some of the specific areas I’d appreciate advice on:
Insulated slab vs traditional strip foundations
Given the footprint (~40m²), would an insulated slab typically be preferable, or are strip foundations still a sensible option in this scenario?
Slab depth, insulation type and thickness
Any guidance on typical build-ups, edge detailing, and thermal performance targets would be very helpful.
Timber frame wall build-ups
From reading previous posts on this forum, a timber frame with OSB sheathing for racking strength and an EWI system externally seems to be a robust and efficient approach. I’d be keen to hear views on this and any lessons learned.
Roof build-ups
Whether flat or pitched, are there recommended best-practice details for insulation, airtightness, and moisture control?
Building in masonry is still an option, but one reason we’re leaning towards timber frame is that my 16-year-old son is currently doing a carpentry apprenticeship, and this feels like a great opportunity for him to be involved and develop his skills.
If anyone can point me towards online resources, technical details, drawings, or case studies covering slab, wall, and roof best practice—or share their own experience with a similar project—I’d be extremely grateful.
For roofing finishes, if we go pitched I’d likely consider Eternit / fibre-cement slates, possibly aluminium-clad profile sheets, or other lightweight profiled systems.
Thanks in advance for any advice or pointers—really appreciate the collective knowledge on this forum.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18403 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18403 Mon, 09 Feb 2026 13:32:54 +0000 Nick Parsons https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18270 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18270 Sat, 01 Mar 2025 16:21:48 +0000 Artiglio
I’m looking for a half way decent humidistat 6” extractor fan, the room it’ll be in suffers from damp ( one wall is half height below ground level, and house has had all sorts of changes in its history that have’nt helped), the fan is intended to hopefully improve the internal conditions a bit until such time as the causes can be dealt with.
Also internal condensation can be a problem. Lots of fans available, however does anyone have experience of either one they’ve been happy with or ones to avoid. Noise levels will be important.

Many thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18400 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18400 Thu, 29 Jan 2026 10:14:05 +0000 DanS
I'm currently detailing my self-build home - Main wall fabric: Plasterboard+skim (breathable paint), timber frame studs + FrameTherm40, 9mm OSB, breather membrane, 50mm PIR, 50mm cavity, masonry skin. All standard (ish!** no VCL!).

My issue is the 50mm cavity I believe offers a ventilated space to deal with water ingress through the masonry. BR AD-B says this cavity must be sealed by fire rated cavity barriers, top, sides, openings, compartment floors etc. So what's the best practice here?

Intumescent cavity barriers obviously maintain the open cavity and solve this issue, but there are plenty of other compression mineral wool style barriers/socks that are approved for this use in timber frames with masonry skin. How is this acceptable? Plus dividing/sealing the cavities must be of some benefit thermally!? My gut tells me that a vapour-open sock would be the best of both worlds, but none of the manufacturers datasheets express this as a feature. And they appear to be wrapped in polythene...
I don't really understand why the need for a 50mm cavity, if it is then going to be sealed shut for fire spread. A 25mm (or even 10mm! - as is now commonplace with T&G PIR cavity insulation) would suffice if circulation is not deemed necessary?

Thanks in advance :)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18399 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18399 Sat, 24 Jan 2026 16:41:33 +0000 gravelld
Tescon Vana works up to 90C, but that would be no good for the flue, certainly.

What have people used?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18395 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18395 Sat, 17 Jan 2026 11:30:06 +0000 Rex
Easy peasy! But he and his wife do live in what can only be described as a complete and utter chaotic mess (think those house clean TV shows!) and there was not way I was going to empty the under sink cupboard with the very limited space they have. They can do that.

He called his friendly plumber and later reported to me that is was a fat-ball in the trap. But he also told me that the plumber told him that there is now a kinda fat-ball vacuum that plumbers use to clear kitchen traps without having to access the trap

Purely out of interest, what is this tool? Surely it cannot be as efficient as dismantling the trap and giving it a through clean?

But what do I know?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18393 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18393 Fri, 09 Jan 2026 14:09:23 +0000 alant We are going to install an engineered wood floor on top of 22mm OSB subfloor in the living area (first floor) of our house and we need to reduce the impact / noise transmission to the bedrooms underneath. We fitted 100m of Hemp batts between the I joists but this has been pretty useless at reducing much sound.
Does anyone have any recommendations of what to install as an underlay of up to 10mm thickness to reduce impact noise. Ideally we don't want to use material that has lots of VOC's or off gasses. We have tried several specialist retailers and it seems that they are very good at quoting dB reduction for complete systems of floor make ups not for providing reliable figures for just underlay. Some say Cork is good but its relatively light so i can't see how that helps much.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15876 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15876 Tue, 25 Sep 2018 19:55:13 +0100 andyman99
Render - 150 EPS - 215 Block - Plaster (poss plaster board on battens).

Will this be OK or do I need add a vapour control layer?

Many thanks again

Andy]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18392 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18392 Thu, 08 Jan 2026 15:52:17 +0000 Jeff B 2025
It seems all our efforts to improve the insulation in the place combined with solar PV and solar thermal panels have paid off in that we are now in band B (previously D).

I have a question regarding the estimated annual figures for the space heating and hot water requirement:

The annual heating figure in the new EPC is 9168 kWh and for hot water 2195 kWh – total 11,363.
1 litre of kerosene yields 10.35 kWh of potential energy. As my boiler is obviously not 100% efficient and is actually 90%, then I assume in my case that 1 litre of kerosene potentially would produce 0.9 x 10.35 = 9.31 kWh of “useful” heat. So 11363 kWh of useful heat would require the burning of 11363/9.31 = 1220 litres of kerosene.
This is odd because we use on average 1500 litres of kerosene p.a. combined with the fact that our solar thermal system provides us with hot water for most of the summer months and the boiler is off for weeks at a time. 1500 litres is equivalent to 13965 kWh (boiler efficiency 90%), some 2602 more than the EPC prediction.

My question is why is there such a large difference between the calculated and the actual oil consumption? Is the boiler less than 90% efficient? I’d be surprised, as it is only 4 years old and regularly serviced. Or is there some other factor that I am overlooking?

I’m just concerned because a prospective buyer (if a bit geekish like me) might question this inconsistency!

Thanks for any feedback.
Jeff]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18387 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18387 Thu, 25 Dec 2025 09:52:44 +0000 minisaurus
I can’t see any downsides to doing this?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18386 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18386 Sun, 21 Dec 2025 22:08:00 +0000 reed https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18390 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18390 Sat, 03 Jan 2026 00:37:17 +0000 ChrisinYorkshire
What do you recommend for insulating an RSJ when:

- the wall is mostly solid stone build, and being insulated internally with wood fibre board, lime plasters, breathable system, however;
- there is a retrofit cavity section that spans approximately 4m width of the wall, which involves a row of windows and an external door.
- the inner leaf of this part of the wall has the RSJ above it, with a cavity tray extending to the outer leaf.

I'm concerned that if I fill the RSJ with wood fibre batts between the flanges and front this with rigid wood fibre insulation, that vapour might reach and condense on the beam and saturate/overload the insulation more often than it can dry out, particularly in the winter months - is this a valid concern? Equally I'm concerned that if I fill the RSJ and cover with non-breathable insulation, XPS/PIR or similar, that moisture will creep in and be trapped against it. Since the RSJ is already in situ, I cannot fit a perfect DPM around it.


Other factors:

The RSJ has had considerable rust with flaky rust sheets that I've mostly removed and were presumably caused by approx. 30 years of kitchen humidity with no extraction. I am planning on scraping off any remaining flaky rust and treating RSJ with Jenolite rust convertor.

I can quite easily reach into the cavity and insulate the cavity side of the RSJ.

I also need to consider fire boarding, particularly with this being above the main entrance/exit to the house.

Any guidance most greatly received! :-)

Chris]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18371 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18371 Tue, 18 Nov 2025 17:34:03 +0000 djh
PS They've also included subsidies for 'heat batteries', but since heat batteries are now more expensive than electrical batteries for the same capacity, it seems like another poorly thought-out scheme!]]>