Green Building Forum - Best Spec for EWI retrofit Thu, 11 Jun 2026 20:31:41 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102376#Comment_102376 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102376#Comment_102376 Mon, 14 Feb 2011 00:15:30 +0000 pmagowan
I think I saw somewhere a sheet which was designed for loads. The top of the EWI could be a structural type of insulation.

? a run of Phenolic at the top of the EWI and bottom of ERI!

Thanks
Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102479#Comment_102479 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102479#Comment_102479 Mon, 14 Feb 2011 21:37:41 +0000 Viking House http://www.viking-house.ie/downloads/BS%20EN%2013163%20-%202001.pdf]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102481#Comment_102481 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102481#Comment_102481 Mon, 14 Feb 2011 21:49:04 +0000 pmagowan
Thanks again, I will try and get my head around it, I promise.
Paddy

PS do you know where you can buy all this stuff?]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102483#Comment_102483 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102483#Comment_102483 Mon, 14 Feb 2011 22:01:33 +0000 fostertom http://www.kingspanpanels.com/Resource_Centre/Technical-Information/Structural-Performance/Basic-Snow-Loads.aspx - try holding that up! - it far exceeds the dead weight of the materials.

EPS and the accessory items obtainable from specialist suppliers the likes of Chris Hirst http://thinjoint.com/, who also provides a bit of training and supervision in the package, so the warranties will apply.]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102484#Comment_102484 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102484#Comment_102484 Mon, 14 Feb 2011 22:50:27 +0000 pmagowan
Does it sound that big a bodge?
The verge is tricky also
Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102499#Comment_102499 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102499#Comment_102499 Tue, 15 Feb 2011 08:41:05 +0000 davidfreeborough
David]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102505#Comment_102505 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102505#Comment_102505 Tue, 15 Feb 2011 09:31:22 +0000 pmagowan
Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102522#Comment_102522 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102522#Comment_102522 Tue, 15 Feb 2011 11:33:24 +0000 davidfreeborough
http://www.aecb.net/conference2007.php

He's not using EWI, but I'm sure you can re-use many of the same ideas.

David]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102531#Comment_102531 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=102531#Comment_102531 Tue, 15 Feb 2011 11:52:18 +0000 pmagowan
Thanks

Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103300#Comment_103300 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103300#Comment_103300 Wed, 23 Feb 2011 08:01:13 +0000 jamesingram Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103344#Comment_103344 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103344#Comment_103344 Wed, 23 Feb 2011 19:37:43 +0000 jamesingram Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103345#Comment_103345 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103345#Comment_103345 Wed, 23 Feb 2011 19:48:32 +0000 jamesingram Nogging between hit nd miss stub rafters to fix to main rafters , could you use 50/50 to reduce thermal bridging in 2 layer ERI or would a full 100/50 be better
how about nogging from below and fixing stub rafter through OSB into this

Is the benefit worth the effort in reduced thermal bridging or would fixing stub rafters directly over main rafter be a structually sounder jobs

cheers Jim]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103346#Comment_103346 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103346#Comment_103346 Wed, 23 Feb 2011 20:09:27 +0000 fostertom
The inboard 'nogs' can be a continuous runner nailed across the ends of the stubs.

I'd drop the top of the blockwork so the main rafters just birdmouth slightly onto the wall plate and the tween-rafter insulation unites almost without interruption with the EWI - another major semi-bridge eliminated.

The outboard nogs then need to be substantial, same ht as the stubs, bearing firmly on the main rafters' ends and cantilevering both ways to provide all the support for the stubs where they hang in 'mid air'!]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103348#Comment_103348 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103348#Comment_103348 Wed, 23 Feb 2011 20:18:12 +0000 jamesingram Cant drop the blockwork , as 152/152 steel below plate for windows/doors at 2050mm from FFL
Pitch restricted due to other end needing to finish under first floor windows.
"and cantilevering both ways to provide all the support for the stubs where they hang in 'mid air'! "
bit confused by this bit ? what the "both ways" bit ?
how about stub length , could I get away with less than 750mm inboard for 500m over hang?
thanks]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103354#Comment_103354 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103354#Comment_103354 Wed, 23 Feb 2011 22:11:53 +0000 jamesingram This nog on rafter end is fulcrum point , and the outer stubs extension is exposed to uplift and downwards force,
hence the need to strengthen
so could inboard section of stubs be same length as outboard 500mm?

Unfortunately due ot pitch/rafter foot cut in my situation wont this act as a bridge thro. the plate and up , some what defeating the object of the hit and miss idea.]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103378#Comment_103378 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103378#Comment_103378 Thu, 24 Feb 2011 08:42:16 +0000 pmagowan Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103380#Comment_103380 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103380#Comment_103380 Thu, 24 Feb 2011 08:50:29 +0000 davidfreeborough Posted By: pmagowanI still wonder if a decent baton running over the top of all the insulation wouldn't be strong enough to support the eave especially if both stuck on and screwed through the EWI. This would completely avoid thermal bridging.I think this would be better thermally, but it would block the water drainage path unless you made the counter battens thicker still.

David]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103388#Comment_103388 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103388#Comment_103388 Thu, 24 Feb 2011 09:24:16 +0000 fostertom Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103392#Comment_103392 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103392#Comment_103392 Thu, 24 Feb 2011 09:43:11 +0000 pmagowan
Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103393#Comment_103393 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103393#Comment_103393 Thu, 24 Feb 2011 09:56:36 +0000 davidfreeborough
As the membrane is under the counter battens, the gutter needs to be close to the toe of the first tile & the gutter needs to be fixed to the counter batten ends. If the counter battens taper to 100-125mm thick on the overhang then the membrane needs to come up through this thickness to drain into the gutter while maintaining a downwards slope. This can be done, but then there's nothing to fix the gutter to. Some solutions get around this by not draining the roofing membrane into the gutter. Instead it just drains over a flashing on top of the EWI.

It is best practice to ventilate the undertile void. If the roofing membrane drains over the EWI then you need to fit a ventilator to each of the rafter openings. A continuous ventilator is a lot easier.

These issues & the need to ventilate above a woodfibre sarking board led me to the "cantilevered eaves board" solution. Here a plywood eaves board is used to tie together the rafters, eaves batten & false rafter feet. This could be easily adapated for a EWI/warm roof junction & avoids all the thermal bridges.

David]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103406#Comment_103406 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103406#Comment_103406 Thu, 24 Feb 2011 11:56:43 +0000 pmagowan
thanks
Paddy]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103477#Comment_103477 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103477#Comment_103477 Thu, 24 Feb 2011 22:33:28 +0000 jamesingram ones an improved version of my warm roof sketch more along the lines of what Toms suggesting i think .
the others a cold roof option, I've attach it below

Posted By: fostertomIf custom made windows/doors, they needn't be nom 2000 high - drop the heads by 100, squeeze the pitch a bit flatter, push it a bit higher under the 1stFl cills. Must be all-window, no EWI'd wall, to need 152x152 steel! What a high-conductive bridge - how about a slim column to reduce span, subst a 100x150 timber lintol laid flat, needing no additional wall plate.


Yes , 2400 doors and 1800 window , 1100 inbetween , hadn't really thought about the "high-conductive bridge" i presumed the EWI above heads would be my get out of jail free card.
I considered 2 140/140 box lintels but went for a steel to tie it all together.
I should have considered the wood option , though possibly wrongly I presumed wood lintels tricky to get accepted by BC . Not really up on that area. would be interested in more info.
Tile finishes just under 1st flr cills so no room for change there.
I cut and pitched it today so will look to insulate/felt and batton tomorrow and post some pics]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103484#Comment_103484 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=103484#Comment_103484 Fri, 25 Feb 2011 08:51:58 +0000 davidfreeborough
What are the tile battens fixed to above the end of the secondary rafters? Are there 50x50mm counter battens fixed to the primary rafters?

The only weakness I see is windtightness. The sarking membrane will need to drape over the secondary rafters &/or counter battens making it difficult to seal this to the top of the EWI.

David]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105600#Comment_105600 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105600#Comment_105600 Sat, 19 Mar 2011 15:17:46 +0000 jamesingram here's some pixs of what i did in the end , a bit of a mix of several methods
there are also 2 x 2/2 noggs below the OSB spaced equally down the stub rafter , towards the plate and a wooden wedge under each stub rafter where it hits the plate ( this is a point of insulation bridge)

So 150mm rafters with full fill rockwall in between / 110mm ( 60+50 staggered joins ) PUR above rafters / counter battons fixed with 200mm timber lock structural screws at recomended spacing to main rafters ( much easier to use than helixfix spiral fixing etc. ) / breather felt / battons /tiles

Was unable to follow previous warm roof drawing i attached due to plate height/pitch restrictions etc. but by perhaps looking into using wooden beam ( rather than steel) to reduce plate height and raising main rafter so a it hit the plate as shown in the designers diagram , would have been a better solution
Lining up counter battons with rafter under the ERI was simple and only missed once or twice out of 200+ fixings, it's a good idea to mark up the PUR so as you dont need to think about it.]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105601#Comment_105601 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105601#Comment_105601 Sat, 19 Mar 2011 15:38:33 +0000 jamesingram skim / Plasterboard / 25mm service cavity / 2 layers of cheap polythene vapour barrier / 150mm rafter etc.
VB brought down and meshed over and wet plastered at wall junctions for long term airtightness]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105629#Comment_105629 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105629#Comment_105629 Sat, 19 Mar 2011 23:22:34 +0000 tony Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105635#Comment_105635 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105635#Comment_105635 Sun, 20 Mar 2011 08:20:32 +0000 jamesingram Intending to EWI (100-200mm) the wall at first floor at some point, so this will bring the wall out along the pitch and increase the sil to tile distance for flashing , also the sil extensions will help . For now i'll just bodge it with flashband.
cheers Jim]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105661#Comment_105661 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105661#Comment_105661 Sun, 20 Mar 2011 10:16:21 +0000 fostertom Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105670#Comment_105670 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=105670#Comment_105670 Sun, 20 Mar 2011 11:50:31 +0000 jamesingram i often tidy/round up my tools twice a day , especially when doing plumbing stuff, otherwise you cant move without treading on something.]]> Best Spec for EWI retrofit https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=120909#Comment_120909 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6967&Focus=120909#Comment_120909 Thu, 27 Oct 2011 11:17:50 +0100 gooday
Again I have put together a sketch up file based on all the ideas above. if anyone wants a copy let me know.

Any comments/suggestions welcome, I havent shown the fascia/soffit on the diagram as it covers up the details, but I would fix the fascia to the false rafters.

I have a couple of questions:

1.Does the OSB need to be 18mm thick or would say 9mm do?

2. 'Bubble glue' has been suggested in the past for joining the osb, any trade names for this?

3. If using EPS/Fibre glass for insulation do we need a vapour barrier in board of the insulation?

4. Does the EPS sheets need joining with anything or is just pushing them togehter good enough?

Thanks]]>