Green Building Forum - Cavity ties to avoid thermal bridging

Cavity ties to avoid thermal bridging

delprado — Tue, 14 Nov 2017 11:52:46 +0000

If you have to use them, in a renovation, is there any options out there that minimise bridging?

Ancon Teplo range

https://www.ancon.co.uk/products/wall-ties-restraint-fixings/cavity-wall-ties/ties-for-brick-to-block-construction

Cavity ties to avoid thermal bridging

tony — Tue, 14 Nov 2017 14:39:23 +0000

They are good, I used them, someone was selling left over ones on here recently

Cavity ties to avoid thermal bridging

delprado — Tue, 14 Nov 2017 14:44:51 +0000

I am suprised you used them Tony - arent they a significant compromise still? They are still a thermal bridge after all

Cavity ties to avoid thermal bridging

tony — Tue, 14 Nov 2017 15:42:11 +0000

Bassalt fibre, verylike fibreglass with lumps, as good as it gets, something has to tie the masonry s kind together and I wouldnâ€™t use metal ties, tried for nylon but not made long enough for my 300mm cavity.

Cavity ties to avoid thermal bridging

djh — Tue, 14 Nov 2017 16:29:43 +0000

Posted By: delpradoI am suprised you used them Tony - arent they a significant compromise still? They are still a thermal bridge after all

As Tony says you have to tie the wythes together somehow. There are cavity-walled passivhaus and they use those ties; it's all a compromise but you just have to do better eleswhere - make the cavity wider or whatever.

Of course simplest is not to use cavity-walled construction, but people in this country are obsessed with it.

Cavity ties to avoid thermal bridging

delprado — Tue, 14 Nov 2017 16:35:19 +0000

Denby Dale used these ties (and so my concerns have evaporated). There is an interesting research paper which talks about Denby and in it was this fact which I thought was interesting

in Austria or Germany (and the former almost has exclusively timber while the latter uses solid masonry, in each case externally insulated). And also interesting that cavity is still common in Benelux and Denmark.

Cavity ties to avoid thermal bridging

Donkey — Tue, 14 Nov 2017 17:32:57 +0000

Posted By: tonyThey are good, I used them, someone was selling left over ones on here recently

It was Woodgnome who was selling them.
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12994

Cavity ties to avoid thermal bridging

delprado — Wed, 15 Nov 2017 05:47:33 +0000

Thanks. I need 200mm long and only 35. They come in boxes of 55 so ordered from TP yesterday

Cavity ties to avoid thermal bridging

TimSmall — Wed, 15 Nov 2017 13:29:28 +0000

This stuff is supposed to do away with the need for cavity wall ties (one of its uses is as a remedial wall tie alternative).

http://walltite.basf.co.uk/applications/wall-applications/masonry-cavity-wall-insulation

... giant brick SIP ! The video on that page is interesting to watch. It'd be good to keep an eye on the installers too.

I think the same system can be used to fill residual cavities too, which might be a good thing to do for PIR-filled new build walls to stop thermal bypass.

Cavity ties to avoid thermal bridging

Mike1 — Wed, 15 Nov 2017 14:26:51 +0000

Posted By: TimSmallThis stuff is supposed to do away with the need for cavity wall ties (one of its uses is as a remedial wall tie alternative).

It's an interesting product (other are available, such as Isothane Technitherm), however omitting wall ties would mean that until the insulation was installed the cavity wall would not be structurally sound - which could endanger the building (or maybe just the external leaf if the internal leaf has sufficient support from cross-walls) if the wind picked up during construction, for example.

Cavity ties to avoid thermal bridging

TimSmall — Wed, 15 Nov 2017 19:07:40 +0000

It is permissable to put in lower strength structural support during construction, on the grounds that designing for a once in 200 year wind storm during a 1 month construction window is not justified, but I agree that this needs to be considered. I wonder if temporary ties (shuttering style) would be viable?

Cavity ties to avoid thermal bridging

Peter_in_Hungary — Wed, 15 Nov 2017 19:36:33 +0000

For new build would it be acceptable to install the product, say, half a floor at a time? At least then you could confirm a good fill and it would aid the structural soundness of the build.

For retro fit a quick calculation would seem to show that a cavity wall would get down to about 0.35 U value or better depending on the cavity width. IMO a fairly decent figure for a retro-fit without going too much over the top. Of course it depends upon the costs........

Cavity ties to avoid thermal bridging

djh — Wed, 15 Nov 2017 21:31:45 +0000

Posted By: Peter_in_HungaryFor new build would it be acceptable to install the product, say, half a floor at a time? At least then you could confirm a good fill and it would aid the structural soundness of the build.

I expect the BBA covers that. I can't be bothered to check

For retro fit a quick calculation would seem to show that a cavity wall would get down to about 0.35 U value or better depending on the cavity width. IMO a fairly decent figure for a retro-fit without going too much over the top. Of course it depends upon the costs........

The BBA certs include U-values for various cavity widths.

Cavity ties to avoid thermal bridging

Mike1 — Thu, 16 Nov 2017 13:23:11 +0000

Posted By: TimSmallIt is permissable to put in lower strength structural support during construction, on the grounds that designing for a once in 200 year wind storm during a 1 month construction window is not justified, but I agree that this needs to be considered.

Maybe, but don't underestimate the power of the wind, or the lateral weakness of unreinforced brick walls.

The wind was only gusting at 'up to 69mph' when the Oxgangs Primary School wall collapsed in January 2016 - that's strong but not rare (https://www.metoffice.gov.uk/public/weather/climate-extremes/#?tab=climateExtremes), and that wall was tied together, albeit not adequately.

Cavity ties to avoid thermal bridging

TimSmall — Thu, 16 Nov 2017 16:38:15 +0000

Posted By: Mike1don't underestimate the power of the wind, or the lateral weakness of unreinforced brick walls

Info on recommendations for wind force calculations for temporary works are given on page 11:

https://www.twforum.org.uk/media/47604/tw14.030__en_pt1_issued_july14.pdf

Cavity ties to avoid thermal bridging

fostertom — Thu, 16 Nov 2017 18:28:19 +0000

With wind loads, which are generally hugely underestimared, I thing of a yacht sail - how much pressure does that area experience, which when resoved at quite a low-mechanical-advantage angle, can force the hull through water and waves at tens of mph?

Cavity ties to avoid thermal bridging

delprado — Thu, 16 Nov 2017 20:04:44 +0000

As a secondary question, why would anyone (Tony) build a cavity build house from scratch?

Cavity ties to avoid thermal bridging

tony — Fri, 17 Nov 2017 15:05:41 +0000

Only idiots!

I sometimes think of my walls as solid 100mm recycled aggregate block walls with external insulation, 300mm r32 batts and a brick skin for the cladding.

My inner skin is air tight unlike most cavity walls, wet plaster hermetically sealed round all openings and a tony tray to keep wind out from under the floors.

Letâ€™s talk about blob and dob now that is idiotic

Cavity ties to avoid thermal bridging

delprado — Fri, 17 Nov 2017 15:51:33 +0000

If I was building from scratch I think I'd still use masonry, even thugh passiv haus advocates seem to suggest timber frame is easier, but I'd use some crazy thick blockwork, like that 300mm stuff, then external insulation rendered.

Although my real dream is actually some sort of old looking house, maybe stone with a thatched roof, but passiv...

Cavity ties to avoid thermal bridging

tony — Fri, 17 Nov 2017 16:08:54 +0000

nice.

Cavity ties to avoid thermal bridging

marsaday — Fri, 17 Nov 2017 18:37:19 +0000

If building from scratch how do you not use cavity ? For me i would like the external face to be brick or stone. I would want an oak frame ideally.

Cavity ties to avoid thermal bridging

Mike1 — Fri, 17 Nov 2017 20:04:48 +0000

Posted By: marsadayIf building from scratch how do you not use cavity ? For me i would like the external face to be brick or stone.

Using brick slips / stone slips / stone cladding.

Cavity ties to avoid thermal bridging

gravelld — Fri, 17 Nov 2017 20:15:00 +0000

Walltite can be used as a replacement for cavity ties? Wow.

Cavity ties to avoid thermal bridging

Pord — Fri, 17 Nov 2017 22:03:14 +0000

Strawbale - cheap material, thermally efficient and no cavity required.

Cavity ties to avoid thermal bridging

mikael — Tue, 21 Nov 2017 23:01:31 +0000

Posted By: Peter_in_HungaryFor new build would it be acceptable to install the product, say, half a floor at a time? At least then you could confirm a good fill and it would aid the structural soundness of the build.

For retro fit a quick calculation would seem to show that a cavity wall would get down to about 0.35 U value or better depending on the cavity width. IMO a fairly decent figure for a retro-fit without going too much over the top. Of course it depends upon the costs........

Posted By: TimSmallThis stuff is supposed to do away with the need for cavity wall ties (one of its uses is as a remedial wall tie alternative).

http://walltite.basf.co.uk/applications/wall-applications/masonry-cavity-wall-insulation" rel="nofollow" >http://walltite.basf.co.uk/applications/wall-applications/masonry-cavity-wall-insulation

... giant brick SIP ! The video on that page is interesting to watch. It'd be good to keep an eye on the installers too.

I think the same system can be used to fill residual cavities too, which might be a good thing to do for PIR-filled new build walls to stop thermal bypass.

I have been lurking here for a while and recently subscribed to these forums. This post has prompted me to share some information about this idea. I am currently in the process of building a house that I hope will achieve passivhaus levels of performance, but is built from masonry. The house is being built in the Cotswolds so the outer leaf is natural stone and the inner leaf is blockwork. The blockwork will carry prestressed hollowcore slab floors on every level.

When I was researching the different methods for insulating the building I settled upon BASF walltite, which was supposed to insulate all cavities. However I did not trust that the foam could reliably provide a replacement for wall ties, so I used Telplo ties. The way we have put the foam in is to build a lift of wall up to a max of about 2m then clean the cavitiy full and fill it with PU foam. However after I started, I found that the PU foam shrinks when it cools and can cause significant damage to the masonry. BASF walltite seems a bit worse than other foams, which I also tried. The only solution to prevent all damage was to line the inside face of the outer leaf with polythene sheet to stop the foam bonding to it. This has allowed it to shrink back a little without causing any damage. However this does mean that wall ties are mandatory as the foam is providing no alternative to the ties. My installer has said he has seen many examples of retrofit foam causing cracking in the same way, but it was only when he saw it happen in an open cavity where everything was visible when it became clear what causes the problem.

Cavity ties to avoid thermal bridging

tony — Tue, 21 Nov 2017 23:24:39 +0000

but presumably leaves a gap for potential draughts. are there any lateral cracks?

Cavity ties to avoid thermal bridging

mikael — Tue, 21 Nov 2017 23:35:56 +0000

Posted By: tonybut presumably leaves a gap for potential draughts. are there any lateral cracks?

The gap left is about 10mm between the foam and the inside face of the outer leaf. As long as the entire cavity is filled properly, then the gap left would not result in any draughts, as the inner leaf is still fully covered and sealed. The cracks that occurred were predominantly in external corners, where the foam pulled in, but the force on one side is always slightly higher than the other and one side ends up having to move.

Cavity ties to avoid thermal bridging

DarylP — Wed, 22 Nov 2017 06:53:18 +0000

interesting... ... any photos of the polyethene sheet in situ, before and after foam pour?
Good luck

Cavity ties to avoid thermal bridging

mikael — Wed, 22 Nov 2017 10:40:34 +0000

Sure, here are three pictures. One showing the sheeting around a cavity tray. I have selected a cavity tray that only crosses half the 300mm cavity (Cavity trays only have to cross half the cavity) so we can get foam behind it and around it. The sheet around the cavity tray will prevent the foam from forming any bond to it, but we have carefully poured it to prevent the tray being deformed by much. When fully covered and cured the cavity tray will stick up inside the foam so an moisture which can travel down on the inside face of the outer leaf will be caught.

The early advice I had from the foam manufacturers was to not cover the foam once it was poured and any discoloration due to UV exposure was not a problem. However I did find a few instances of new layers not bonding as well as they should to older layers, so now I always cover the foam with cheap 300mm wide black polythene DPC from toolstation to keep it pristine for the next lift. The moral of the story is not to listen to the foam manufacturers. Their foam shrinks much more than they say, and UV exposure is not as minor as claim either.

When I started reading up on how materials are protected from UV, I found that one of the best and cheapest materials to protect from UV is carbon black. It was then I realised that black plastic would be ideal, as carbon black is used as the pigment in black plastics.

Cavity ties to avoid thermal bridging

mikael — Wed, 22 Nov 2017 10:44:47 +0000

Second picture