Tue, 19 Dec 2023 08:38:03 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298524#Comment_298524 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298524#Comment_298524 Tue, 01 Nov 2022 10:53:18 +0000 lineweight
However ... this seems to conflict with most standard details for the installation of restraint straps - for example those shown here:

https://nhbc-standards.co.uk/7-roofs/7-2-pitched-roofs/7-2-8-restraint/

which assume that the inner leaf rises to be level with the *top* of the rafters.

And I think that's to do with making sure the downward-turned arm of the restraint strap gets a good enough hold on the blockwork.

Is there a commonly accepted way of dealing with this conflict? for example using restraint straps with a longer downward arm?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298526#Comment_298526 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298526#Comment_298526 Tue, 01 Nov 2022 11:34:54 +0000 djh Posted By: lineweightHowever ... this seems to conflict with most standard details for the installation of restraint straps - for example those shown here:

https://nhbc-standards.co.uk/7-roofs/7-2-pitched-roofs/7-2-8-restraint/Sorry but when I go to that link, I see a lot of stuff about lateral restraints but nothing about vertical ones? And the illustrations seem to show restraints under the rafters?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298527#Comment_298527 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298527#Comment_298527 Tue, 01 Nov 2022 12:07:11 +0000 lineweight Posted By: djhSorry but when I go to that link, I see a lot of stuff about lateral restraints but nothing about vertical ones? And the illustrations seem to show restraints under the rafters?

Yes, it is lateral restraints that I'm talking about.

The illustrations show the restraints fixed to the underside of rafters, but the inner leaf built up to the level of the tops of the rafters (not immediately obvious, but is made clear if you look at the 3d one in 3d, or look at the position of the "omitted for clarity" bit of blockwork relative to the strap).]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298528#Comment_298528 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298528#Comment_298528 Tue, 01 Nov 2022 12:08:32 +0000 lineweight http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298530#Comment_298530 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298530#Comment_298530 Tue, 01 Nov 2022 12:59:19 +0000 djh http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298532#Comment_298532 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298532#Comment_298532 Tue, 01 Nov 2022 13:15:49 +0000 lineweight
That makes me wonder if it's really necessary or just a habit of building conventions that didn't worry about insulation continuity. For example, building the inner leaf up to that level is probably handy as support for tiling battens and so on.

Given that there are plenty of standard details about which show the masonry stopped lower, I was hoping someone might know of a "standard" and non controversial way of doing the restraint straps ... it had not occurred to me as a problem until just now, with a structural querying details showing inner leaf stopped lower down.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298537#Comment_298537 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298537#Comment_298537 Tue, 01 Nov 2022 20:36:41 +0000 tony http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298539#Comment_298539 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298539#Comment_298539 Wed, 02 Nov 2022 10:05:47 +0000 lineweight Posted By: tonyI am increasingly worried about the thermal bridging of gable wall inner skins from inside the insulation barrier to outside it.

Does this mean you've not really found a solution to the problem I've described?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298550#Comment_298550 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298550#Comment_298550 Wed, 02 Nov 2022 18:24:22 +0000 tony
On my new house no one said anything, single skin gable well tied to roof structure, no problems and no thermal bridging]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298552#Comment_298552 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298552#Comment_298552 Wed, 02 Nov 2022 18:47:57 +0000 lineweight Posted By: tonyI have, yes, stop the inside skin at ceiling level or take it down to that level.



How then to put the restraint straps in - just wrap them over top of blockwork and not worry about building them in?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298559#Comment_298559 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298559#Comment_298559 Wed, 02 Nov 2022 20:10:06 +0000 tony http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298579#Comment_298579 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298579#Comment_298579 Thu, 03 Nov 2022 09:52:05 +0000 lineweight
Additionally, what I'm looking at is an existing building, where the roof is getting refurbished. When you say windposts, I'm not sure if you mean the type that sit inside the cavity? Not really an option when the gable wall is already there and not newbuild.

With anything newbuild I think the problem can be avoided by having insulation between+above rafters rather than between+below because then the relative position of rafter and inner leaf can be as per conventional arrangement, and the above-rafter insulation layer can continue across both.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298728#Comment_298728 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298728#Comment_298728 Thu, 10 Nov 2022 17:17:31 +0000 wookey
I do agree with Tony that the inner leaf bridging is quite significant with EWI (and generally ignored as it's hard to fix).

I think builders make the inner leaf the same height as the outer because it's just easier to cut it off there (and yes it helps support the tile battens). I'm not at all convinced that an extra ~120mm of block on top makes much difference to how well the restraint works.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298775#Comment_298775 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298775#Comment_298775 Sun, 13 Nov 2022 00:28:45 +0000 lineweight http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298777#Comment_298777 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=298777#Comment_298777 Sun, 13 Nov 2022 08:13:52 +0000 tony
I like an exact 47mm gap between the first rafter and the blockwork. Then off cuts of 4x2 can be used as blocking pieces at the requisite centres to stop the gable falling in, no straps needed . Then on the outside if there is a barge board I like a backing rafter as it is very useful to nail battens to, if this either touches the outside skin or sits 47mm out then again blocking pieces can be used trapping the top of the whole gable.

So long as there are wall ties in the gable then it is now trapped and can’t fall over even without straps!

I never much liked noggins to fix straps to, preferring to nail on a chunk of wood and fix the strap to that or to any lateral braces, purlins etc. Sometimes we used to butt that against the blockwork and hook a strap over the block trapping it between the end of the wood and the bent bit of the strap, no need to fix to the block only fix the strap to the bearer. We think such a strap can be considerably shorter as the wood is connecting it to the rafters.

The same thing can be done at ceiling level - I like fail safe.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=300511#Comment_300511 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=300511#Comment_300511 Tue, 28 Feb 2023 16:46:37 +0000 lineweight
Agree that the solution described by Tony, just above, works.

But not where there is no barge board or rafter to the outside of the outer leaf. This might be a bedded verge type detail, or the modern "dry verge" version of the same where there's a plastic or aluminium profile clipped over the edges of the slates/tiles. In either case, the outer leaf masonry runs up to the level of the tiling battens.

In the example illustrated below ... this is a pitched roof, all insulation over rafters, then counterbatten & batten to support slates. It needs to meet a cavity gable wall, with a bedded type verge.

Here, the roof buildup has a ply deck on top of the rafters anyway, which can continue over the inner blockwork. If the ply deck is secured to the inner leaf then it can't move inwards or outwards ... but how best to secure? I've not yet found a "standard solution for this arrangement.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=300512#Comment_300512 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=300512#Comment_300512 Tue, 28 Feb 2023 16:46:54 +0000 lineweight http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=300516#Comment_300516 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17627&Focus=300516#Comment_300516 Tue, 28 Feb 2023 20:17:04 +0000 tony
Then doubled the number of wall ties so the outside skin was well joined to the inner shin that now was solid.]]>