Tue, 09 Jun 2026 10:48:13 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150111#Comment_150111 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150111#Comment_150111 Sun, 01 Jul 2012 13:18:45 +0100 Shevek
1. It's a shame with you can't start the sill flashing halfway up the Geneo window frames; this means you can't overlap the insulation at the sill.
3. Existing internal plaster - should we remove the whole lot and start again or just strip it at the junctions if we can and make good?
3. Perimeter insulation and plywood - do you think we need to take the plywood around the whole perimeter? How should we attach the XPS? Does polyurethane expanding foam react with XPS?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150119#Comment_150119 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150119#Comment_150119 Sun, 01 Jul 2012 14:15:34 +0100 tony
your numbers 1. you could lift the bottom of the window frame further away from the structure to allow more insulation, remove a course of bricks or smaller window, 2. make good, 3. I cant see why you need ply atall unless you push the window out into the EWI

Important -- you MUST have a drip at the render above the window, I make the render slope upwards towards the window,

Looks like a good detail, shame everyone hasn't got it on their houses we would all be a lot better off them.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150128#Comment_150128 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150128#Comment_150128 Sun, 01 Jul 2012 16:04:17 +0100 Shevek
The idea behind the plywood is to spread the load of the window so it doesn't damage and compress the XPS. And for something firm to seal against. Do you think XPS will be man enough by itself? And sufficient to seal against?

Good question on the packers. I didn't really think about it putting them in. Just in the habit of showing them on details, for levelling the window I guess. Clearly not needed for levelling as we can make sure the XPS is level. What about the seal to the bottom edge of the window frame, do I need to keep a gap for that or just sit the window down over the seal?

What's the best way to fix the window into place, screws?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150132#Comment_150132 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150132#Comment_150132 Sun, 01 Jul 2012 16:37:43 +0100 tony
I cant see the window squashing the insulation, how wide are the windows? I did support my wide 2400 ones centrally with a bracket up the outside of the brick wall onto the outside few mm of the front of the frame.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150133#Comment_150133 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150133#Comment_150133 Sun, 01 Jul 2012 16:47:58 +0100 Shevek
Why would you push the window out? This would reduce the amount of insulation cover in front of the jambs and head.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150134#Comment_150134 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150134#Comment_150134 Sun, 01 Jul 2012 17:46:58 +0100 fostertom
Prime principle is to move the frame outboard away from the (now internal) masonry. As it is, you have a v short heat-flow path from outside frame face, thro the frame chambers, reveal insulation, to masonry. V lossy. Move the frame right outboard, into the EWI zone, away from the masonry - that's one of the reasons for using EWI at least 150, pref 200 thick, to fully accomodate frame depth plus a bit of reveal depth.

Depth of insul cover in front of the frame - depth only say 1.3 x the width of cover will be effective. So, if 25mm width of cover, no point in making reveals more than 40 deep (except for visual and weather-shedding reasons). You could increase your width of cover considerably - entirely 'lose' the fixed frames, esp as open-in - no open-out hinges etc to clear.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150138#Comment_150138 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150138#Comment_150138 Sun, 01 Jul 2012 18:54:28 +0100 Shevek
I thought Timber had modelled it in Therm on this thread but it looks like he didn't get round to it:
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=8550

Will hopefully model this myself if I can get Windows running on my machine again.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150161#Comment_150161 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150161#Comment_150161 Sun, 01 Jul 2012 21:17:46 +0100 Timber
Have you got your head around how to actually do the modelling in therm? You need to model a 1m long section of blank wall first and get the U-Value. Then model the detail (excluding the window and frame (see BR496)) and then do a quick sum with the two sets of numbers.

I can post up the calculation, although it is in BR496 anyway.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150162#Comment_150162 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150162#Comment_150162 Sun, 01 Jul 2012 21:22:11 +0100 TimSmall
I was wondering how robust your airtight detailing would be, especially with the degree of movement which you might get in a softwood board? Normally best to have a sealant bead attached on two opposite sides only (not pushed into a corner, or attached on three sides). Butyl (DPM-jointing) tape, or something more proprietary instead/as-well?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150164#Comment_150164 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150164#Comment_150164 Sun, 01 Jul 2012 21:30:17 +0100 Shevek
With the window pushed out 30 mm, wouldn't the screw fixings now be too close to the edge of brick?

Another one, would this comply with NHBC requirements? Don't they require two barriers against water ingress or something? Whereas I've only got one seal where the render meets the window frame to the jambs and head, and just the sill flashing to the sill.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150165#Comment_150165 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150165#Comment_150165 Sun, 01 Jul 2012 21:46:47 +0100 Shevek I'm guessing once you know what you're doing Therm is pretty quick, but at the moment I'm still trying to get the detail into a tidy usable form. Haven't got round to any calcs yet. Didn't realise you model a length of the wall first, thanks for that tip.

@TimSmall
Not sure what you mean by "Normally best to have a sealant bead attached on two opposite sides only (not pushed into a corner, or attached on three sides)." Is there any guidance/diagrams/photos anyone can point me to? We're trying to reach Passivhaus standards so airtightness detailing is going to be crucial.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150166#Comment_150166 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150166#Comment_150166 Sun, 01 Jul 2012 21:49:29 +0100 tony
17. you can angle the fixings a bit towards the middle of the wall.

it is looking like a great detail now though]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150169#Comment_150169 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150169#Comment_150169 Sun, 01 Jul 2012 22:19:45 +0100 Shevek
If all the load is being taken by the screws to the jambs I guess there's no reason not to make the perimeter insulation PIR as well?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150170#Comment_150170 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150170#Comment_150170 Sun, 01 Jul 2012 22:50:40 +0100 fostertom Posted By: TimberI can post up the calculation, although it is in BR496 anyway.I'd love to see that - I couldn't understand that bit on the course, not concentrating in fact, struggling with a useless borrowed laptop (got my own (useless) laptop now!).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150177#Comment_150177 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150177#Comment_150177 Mon, 02 Jul 2012 07:45:12 +0100 TimSmall
"Not sure what you mean by "Normally best to have a sealant bead attached on two opposite sides only (not pushed into a corner, or attached on three sides)." Is there any guidance/diagrams/photos anyone can point me to?"

Try this (45 year old!) article:

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-96.html]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150192#Comment_150192 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150192#Comment_150192 Mon, 02 Jul 2012 08:57:28 +0100 davidfreeborough Posted By: ShevekWith the window pushed out 30 mm, wouldn't the screw fixings now be too close to the edge of brick?Window fixing straps are available in lengths of up to around 200mm. They are screw fixed to the perimeter of the frame before inserting the window in the opening.

I wouldn't rely on silicone sealant for airtightness. I would seal the perimeter of the frame to the interior face of the insulation with something like illbruck ME500 Duo Flexible Window Membrane:

http://www.tremco-illbruck.co.uk/products/01920_index.html

And then seal the insulation to the inner face of the masonry with something like illbruck ME404 Butyl Fleece Tape:

http://www.tremco-illbruck.co.uk/products/03254_index.html

This can be incorporated into the plaster to maintain the continuity of the air barrier.

David]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150204#Comment_150204 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150204#Comment_150204 Mon, 02 Jul 2012 09:56:26 +0100 Timber
Ψ = L2D - ΣU1D * Wi

where
L2D is the linear thermal coupling coefficient obtained from a 2-dimensional calculation of the component separating the two environments being considered; U1D is the thermal transmittance of the 1-dimensional component, separating the two environments being considered; Wi is the width within the 2-dimensional geometrical model over which the value of U1D applies.

In simple terms, calulcate the U-Value of the plane wall in therm and multiply it by the length of the wall (in the model (so normally 1m)) in meters (anwser X). Then model the junction and multiply the U-Value by the length in meters (Answer y) (relevant lengths to be taken in accordance with BR497). Then, subtract X from Y and you have an answer.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150282#Comment_150282 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150282#Comment_150282 Mon, 02 Jul 2012 21:47:11 +0100 Shevek
@David thanks for the tape pointer.

I read through the ME500 literature but couldn't decide whether the W or the E is more appropriate:
http://www.tremco-illbruck.co.uk/celumdb/documents/ME500-E_DS_GB_22553.pdf
http://www.tremco-illbruck.co.uk/celumdb/documents/ME500-W_DS_GB_22554.pdf

I assume then that XPS will be the best insulation for the perimeter because it will be nice and firm to consolidate the tap against with a roller... I'm in two minds whether to use XPS or the same as the external wall insulation (which will probably be PIR or Phenolic).

Updated detail attached using the W product.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150330#Comment_150330 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150330#Comment_150330 Tue, 03 Jul 2012 10:04:48 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150338#Comment_150338 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150338#Comment_150338 Tue, 03 Jul 2012 10:44:38 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150344#Comment_150344 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150344#Comment_150344 Tue, 03 Jul 2012 11:28:40 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150356#Comment_150356 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150356#Comment_150356 Tue, 03 Jul 2012 12:29:18 +0100 Shevek https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150449#Comment_150449 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150449#Comment_150449 Wed, 04 Jul 2012 09:36:06 +0100 davidfreeborough Posted By: ShevekI read through the ME500 literature but couldn't decide whether the W or the E is more appropriate... I'm in two minds whether to use XPS or the same as the external wall insulation (which will probably be PIR or Phenolic).The E membrane is intended to be fixed to the internal face of the frame & has the two adhesive strips on the same side of the tape. The W membrane is intended to be fixed to the perimeter face of the frame & so has the adhesive strips on opposite sides of the tape.

Which you choose depends upon the frame. If you're using a PVC frame with a series of ribs/channels to the perimeter then probably better to seal to the internal face with the E membrane. If you're using a timber frame with a smooth face to the perimeter then probably better to seal to the perimeter face with the W membrane.

Foil face PIR/PUR insulation gives you a ready made air barrier to seal to & may allow you to use narrower/cheaper tape.

David]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150491#Comment_150491 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150491#Comment_150491 Wed, 04 Jul 2012 16:52:05 +0100 Timber
I modelled the Jamb very quickly using some standard material specs, as I am not sure 100% what materials you are using and got a PSI value of 0.013 W/mK which is very good.

Here is the Heat Flux output. Shows minimal patches of elevated heat flux around the window frame, but they are tiny.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150492#Comment_150492 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150492#Comment_150492 Wed, 04 Jul 2012 16:52:55 +0100 Timber
Not really too much to improve on I don't think. 0.013 is great, but might be a little better if the window were pushed out just a smidge. I will leave those for you to do!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150494#Comment_150494 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150494#Comment_150494 Wed, 04 Jul 2012 16:55:25 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150498#Comment_150498 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150498#Comment_150498 Wed, 04 Jul 2012 17:13:42 +0100 Timber ]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150499#Comment_150499 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150499#Comment_150499 Wed, 04 Jul 2012 17:32:26 +0100 Shevek https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150509#Comment_150509 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150509#Comment_150509 Wed, 04 Jul 2012 18:21:08 +0100 Timber https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150550#Comment_150550 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9270&Focus=150550#Comment_150550 Thu, 05 Jul 2012 09:15:16 +0100 Timber
We now have a calculated psi value of 0.004 W/mK for the jamb detail. That is excellent. So with EWI on masonry, it seems that pushing the window out improves the calculated PSI values.

Caviat again, I just used some normal material properties etc, so you might come up with a slightly different result when you do the sums for yourself using your own materials. I just used standard values for EPS, brick, plaster and render.]]>