Posted By: lineweightComing back to this... further investigations brought me to "structural cavity closers" and products from Cavalok who seem to be part of Eurocell.

This has been mentioned in a previous thread, I see:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9392

It's hard to find any very useful information on the Eurocell site. I had a bit of a confusing conversation with one of their technical people, where I tried to explain that I wanted to understand whether they can offer something that will span a cavity under the sill and take the weight of a door/window installed above it. His answer seemed to be that this would never be an issue because the frame itself can simply span the cavity, but that's not what the window installers I've talked to have said. They always want a continuous solid base across the depth of the frame.

Anyway - they pointed me to here:

https://www.subframes.co.uk/cavity-closers/structural-door-packs/

And I'm making some enquiries with them. But I think that this system is not actually designed to be load bearing across the bottom horizontal member - it's more that you can fix directly into the jamb closers and they will transfer the load into the outer and inner leaves.

By the way regarding the above - the answer was very much that no, the bottom member is not supposed to be load bearing.

Posted By: lineweightthe compacfoam could then sit directly onto the masonry wall, like the timbers

If the masonry is wide enough to accomodate both, that sounds like an ideal solution.

So this is a prescient discussion.... our large sliding patio doors went in today.

We went with Maxlight, a London company who we were very happy with, but their standard detail was to install onto a concrete upstand, which I point blank refused - and so my journey into insulated upstands commenced!

Internally, the floor is a flush finished 75mm polished concrete screed on top of 50mm K103 which is on top of the original slab. Isolating the polished concrete was a key criteria for me to preserve the thermal mass in the house, and so a huge thermal bridge in the rear of the house was just a flat out no.

I originally spec'd Marmox Thermoblocks, which both our SE and Marmox were happy with, however Maxlight's engineers were concerned about the bending moments not being restrained by the concrete pillars inside them, as each door panel was 230Kgs.

The SE and myself went through a number of options none very satisfactory, until we came across Armadillo's Armatherm. https://www.armatherm.co.uk/products/500-structural-thermal-break-material/

This is a structural insulation that comes pre-cut to size that is literally just bolted into the slab underneath. I actually thought I'd been sent the wrong product as it's so light and looks like a few lengths of 2x4 timber!

Super simple to drill through, fixed at 400 c/c with countersunk M8 bolts and then silicone sealed, standard DPC on top. Despite this non-standard detail the install team cracked on. They were concerned that as it was so soft that their fixings wouldn't hold, but found their M8 fixings of the track into the Armatherm were perfectly robust.

The team said actually was easier to install onto than a normal concrete upstand because it was dead flat & smooth, so easier to fix & seal.

Only downside - it's damn expensive stuff, but for the performance and ease of install it delivered what we wanted - YMMV.

Attached some pics from today and the original drawings I produced with Thermoblocks replaced with Armatherm

Cheers,

N

Track

Thanks, useful to see drawing and photos. Did you consider putting a bit of perimeter insulation between the back of the aluminium track and the screed slab?

How to do thresholds properly, without creating cold bridges, continues to be something that largely just gets ignored, I think.

Currently I'm looking at a Velfac door - not even a sliding one, just a regular hinged door so no load really goes onto the threshold. I asked the supplier how they normally deal with the threshold detail when fitted into a cavity wall and they sent me this not very helpful drawing.