Housing - New Build: external EPS on timber frame

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- CommentAuthordjh
- CommentTimeSep 24th 2014
Are there approved details showing the use of EPS sheets external to a timber frame, plus some insulation between the studs? Specifically something usable in England (Trada or a BBA etc etc) and that shows the position and materials for racking, airtightness, wind & rain tightness and vapour tightness if required.

I'm sure there must be an easy answer to this, and it may well have been answered on GBF before now, but google hasn't yet thrown up an answer for me...

I have found some details for proprietary insulation boards, but not yet anything for generic EPS. There will be battens and timber cladding on the outside and probably a service zone on the inside but they're not too important.
- CommentAuthorjamesingram
- CommentTimeSep 24th 2014
check out Vikinghouse's site
- CommentAuthorfostertom
- CommentTimeSep 24th 2014
Lots on here about just this - but you're specifically after Approved Details? VH and I recommend slight differences! - naturally, I know which I prefer, from work with chippies.
- CommentAuthordjh
- CommentTimeSep 24th 2014 edited
Posted By: fostertomLots on here about just this - but you're specifically after Approved Details? VH and I recommend slight differences! - naturally, I know which I prefer, from work with chippies.

Not specifically Approved Details but the more quotable at a BCO if necessary the better!

I have a link to the VH site, which has some marginal value, and I don't remember anything on here that is more quotable?
- CommentAuthorfostertom
- CommentTimeSep 25th 2014
VH's and my writings on here, our near-agreement on favoured method, def don't quote anything authoritative like that.
- CommentAuthorDarylP
- CommentTimeSep 25th 2014
djh,

Pinewood use PIR, might that be of any use: http://www.pinewood-structures.co.uk/content/1/62/quantum--high-performance-insulated-panel.html

Good luck
- CommentAuthorfostertom
- CommentTimeSep 25th 2014 edited
See http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=12582&page=1#Item_12 - my posts of today 25 Sept 2014 - would perhaps have been better posted here.
- CommentAuthordjh
- CommentTimeSep 25th 2014
Posted By: DarylPPinewood use PIR, might that be of any use: http://www.pinewood-structures.co.uk/content/1/62/quantum--high-performance-insulated-panel.html

But the Quantum panel doesn't appear to have any insulation outboard of the studs?
- CommentAuthordjh
- CommentTimeSep 25th 2014
Posted By: fostertommy posts of today 25 Sept 2014 - would perhaps have been better posted here

Thanks for the link Tom, but I don't think your posts help my search. It does seem bizarre if there are no standard published details at all for an externally insulated timber frame!?
- CommentAuthorTimber
- CommentTimeSep 25th 2014
The TRADA timber frame construction book does talk about external insulation, but it is more passing comment than indepth discussion.

From memory it says something like it is fine, subject to a favorable condensation risk and 3rd party cert on certain types of insulation.

Are you fitting a breather membrane over the insulation? There really should be a breather membrane on the outside of the insulation to prevent cavity moisture getting between board joints/through the face and getting trapped in and around the timber structure. A breather membrane between the insulation and the frame behind is less effective as if water is trapped against the membrane by the insulation, it can soak through the breather membrane over time.

It also helps when detailing flashings and cavity trays etc.
- CommentAuthorPaulJ
- CommentTimeSep 26th 2014
Celotex have a BBA cert for their pir boards http://www.bbacerts.co.uk/CertificateFiles/46/4667PS1i3.pdf covering between stud plus sheathing.
- CommentAuthordjh
- CommentTimeSep 26th 2014 edited
Posted By: TimberThe TRADA timber frame construction book does talk about external insulation, but it is more passing comment than indepth discussion.

From memory it says something like it is fine, subject to a favorable condensation risk and 3rd party cert on certain types of insulation.

I had found 4.4.2.3 Warm wall construction but as you say it is more a passing comment. About the only thing it says for definite is 'structural stud voids remain uninsulated', which is unfortunate for our hope of having some insulation between the studs and some outside.

Are you fitting a breather membrane over the insulation? There really should be a breather membrane on the outside of the insulation to prevent cavity moisture getting between board joints/through the face and getting trapped in and around the timber structure. A breather membrane between the insulation and the frame behind is less effective as if water is trapped against the membrane by the insulation, it can soak through the breather membrane over time.

It also helps when detailing flashings and cavity trays etc.

I'd like to think we are, but that's exactly the sort of detail we're looking for a detail to show. I think my architect is a little wary that 'warm roof' details are easily available whilst the apparently similar 'warm wall' details are as common as rocking horse droppings.

I have some Intello left over from the roof, and some Fronta WA left over from parts of the walls, and some grey EPS left over from the foundations, and I'm hoping to upcycle them into a flat-roofed sun room since most of the wall area is glazed. A warm wall construction will join nicely with its passive slab foundation. (edit: I should say that it's unheated and outside the thermal envelope).

Yes, we are planning to put the Intello on the inside and the Fronta on the outside, behind timber cladding on battens.
- CommentAuthordjh
- CommentTimeSep 26th 2014 edited
Posted By: PaulJCelotex have a BBA cert for their pir boards http://www.bbacerts.co.uk/CertificateFiles/46/4667PS1i3.pdf covering between stud plus sheathing.

Thanks for that. That's pretty close.
- CommentAuthorTimber
- CommentTimeSep 26th 2014
Posted By: djh
Posted By: TimberThe TRADA timber frame construction book does talk about external insulation, but it is more passing comment than indepth discussion.

From memory it says something like it is fine, subject to a favorable condensation risk and 3rd party cert on certain types of insulation.

I had found 4.4.2.3 Warm wall construction but as you say it is more a passing comment. About the only thing it says for definite is 'structural stud voids remain uninsulated', which is unfortunate for our hope of having some insulation between the studs and some outside.

Is that the latest version, as the 5th edition does show a wall construction with insulation between and outside of the frame!?
- CommentAuthordjh
- CommentTimeSep 26th 2014
Posted By: TimberIs that the latest version, as the 5th edition does show a wall construction with insulation between and outside of the frame!?

Yes, that's 5th edition. What page is the drawing, or any other information?
- CommentAuthorVictorianeco
- CommentTimeJul 17th 2017
Any further info. regarding this detail?
- CommentAuthordjh
- CommentTimeJul 17th 2017
I never heard back from Timber, or anybody else for that matter. We did build it. From the inside - plasterboard with skim, battens, polythene vapour barrier, studs infilled with rockwool, 18 mm OSB, 100 mm grey EPS, Fronta Wa breather membrane, battens, cedar cladding. The building inspector was happy but then this was probably the most normal part of our build, despite my never finding anything that said it was OK.
- CommentAuthorborpin
- CommentTimeJul 18th 2017
IT is a big gap in the regulations. I wanted to build this way but the BC got rather anti as I could not find approved buildups at the time. He wanted a ventilation gap between the frame and the insulation! Personally I think this is the most sensible build-up and should be the standard way of doing things.

Keep the frame on the warm side and it will simply dry out, just do not fit a vapour barrier inside; make the frame itself air tight. I'd spray Icynene in the frame as well.
- CommentAuthorTimSmall
- CommentTimeJul 19th 2017
OSB as airtight layer here sounds good. In a similar situation, my building inspector accepted a wufi analysis showing max timber water content (approved document says that whatever BS-EN standard that wufi complies with is an acceptable alternative means of meeting the regs).

Could also use PIR instead of EPS outside (slightly better insulation and fire performance), or phenolic (excellent fire performance).

My particular build-up was from the inside - plasterboard with skim, studs infilled with PIR (not foil faced), 18 mm OSB (T+G "Smartply" edges glued), 100 mm PIR (not foil faced), Fakro breather membrane, battens, render carrier board, Weber render.

Could also use celullose or wood fibre instead of rock wool internally. I used PIR everywhere since I had loads of it (and limited space) which I got cheap as waste from a SIPs factory (they also made roofing sheets and these were from bond failure or other QC fail boards). Foil PIR is probably OK on the outside, but not so much on the inside.

You may need to use some rockwool on the outside in a fire break strip at every floor level from first floor ceiling level and above and/or intumescent closers in the ventilation gap.
- CommentAuthorfostertom
- CommentTimeJul 19th 2017
Agreeing mainly with borpin and TimSmall, Dave why did you think the inboard VCL necessary?
- CommentAuthordjh
- CommentTimeJul 19th 2017
I don't remember, Tom. Maybe because it is conventional and I didn't see much difference either way.

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