Tue, 19 Dec 2023 04:58:48 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235380#Comment_235380 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235380#Comment_235380 Sun, 24 Jan 2016 15:53:42 +0000 shandyd05
new on site although read quite a few threads in stalking mode I'll debut by opening up a possible can of worms here (based on prev threads) though I haven't found anything analogous to my situation in the threads so far (apologies for the length a few things to explain) ...
insulating a beam & block floor!
My house is a late 1960s bungalow built on a hill with B&B floor but the voids are huge - in fact roughly 25% under the house is garage, another 25% a store room/workshop and the height to the bottom of floor here is well over 2m; the height at back of house is less dropping to as little as maybe 1.35m in 1 corner. The bottom of the B&B floor is around 390mm above ground level at the back ( over 2m at front) beams sit on the internal brick leaf on a dpc and solid concrete cavity fill below dpc, insulated cavity above. The ground under the cavities is either concrete (50%) or dry earth.

The floor itself is currently un-insulated and no dpm, total depth to top of (newest) tile surface around 200mm. I know the general recommendations seem to be insulate above but 50mm (or greater) celotex plus boarding on top then a finish is going to play havoc with my door openings which are currently 1960mm; ceiling height at 2410mm is less of a concern but there are also 2 fairly new (and expensive) external doors to consider.

My initial thoughts were some kind of solid insulation bonded to the bottom of the B&B floor given the access is so good but I'm picking up warning signs about ventilation under the beams to avoid moisture build-up and the fact that thermal bridging may be an issue!

So in a nutshell any bright ideas? Does my floor still count as a ground floor given the size of the voids?
I'm due to start a new kitchen installation in a few weeks so want to sort the approach by then.

Thanks for reading!]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235392#Comment_235392 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235392#Comment_235392 Sun, 24 Jan 2016 18:33:53 +0000 Jeff B http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235394#Comment_235394 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235394#Comment_235394 Sun, 24 Jan 2016 19:22:21 +0000 Nick Parsons http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235397#Comment_235397 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235397#Comment_235397 Sun, 24 Jan 2016 19:52:45 +0000 Ed Davies
Or hang a wooden frame (sort of sideways Larsen truss) and stuff with mineral wool with peg board or something to hold it in place?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235418#Comment_235418 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235418#Comment_235418 Mon, 25 Jan 2016 11:24:50 +0000 ringi
Whatever you do below the floor there will be a cold bridge at the edges where it sits on the wall. Hence the normal advice to put the insulation above.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235424#Comment_235424 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235424#Comment_235424 Mon, 25 Jan 2016 12:20:54 +0000 Jeff B Posted By: Nick ParsonsFar less of an issue than if it were a timber floor. If you can get it 'tight' enough it's good. I cannot see where thermal bridging will be a significant issue. A former client is doing something similar.

That's what I was thinking. I would stick some sheets of Celotex or similar to the undersides of the B&B floor and secure with 50 x 25 treated battens, screwed through using frame fixings (ok, yes, some thermal bridges here). Seal edges well. Then fix plasterboard to the battens if required for aesthetics e.g. in garage, workshop]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235442#Comment_235442 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235442#Comment_235442 Mon, 25 Jan 2016 16:20:27 +0000 Peter_in_Hungary I'M no expert on condensation but as Nick said above - less of a problem that with a timber floor.
I just went to
http://www.vesma.com/tutorial/uvalue01/uvalue01.htm
to check out U values and the application also has a condensation analysis. Selected 'floor' as the building element, entered concrete from the Layer pull down menu, 200mm thickness and the default temp. values showed a condensation risk. Entered 5mm EPS as the (next) outside layer and the condensation risk went away. So from that I would presume any amount of insulation would mitigate the condensation risk. (you can use this application to see what you need for your target 'U' value (or see what 'U' value you get for the size of your wallet!)]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235445#Comment_235445 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235445#Comment_235445 Mon, 25 Jan 2016 16:48:10 +0000 ringi
All the ones I have seen have the bottom of the beams lower then the bottom of the blocks.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235448#Comment_235448 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235448#Comment_235448 Mon, 25 Jan 2016 17:05:59 +0000 djh Posted By: ringiIs the underside of the B&B floor level?

All the ones I have seen have the bottom of the beams lower then the bottom of the blocks.
I think that's probably true except for the ones that are already insulated as built, using weirdly shaped EPS 'blocks'.

I expect the spaces could be filled with loft roll or something to cut down any convection currents, or otherwise could be used to circulate heated air under the floor ...]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235471#Comment_235471 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235471#Comment_235471 Mon, 25 Jan 2016 20:06:57 +0000 Jeff B Posted By: ringiIs the underside of the B&B floor level?

All the ones I have seen have the bottom of the beams lower then the bottom of the blocks.

Would that matter as long as the insulation is well sealed at the edges/joins?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235473#Comment_235473 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235473#Comment_235473 Mon, 25 Jan 2016 21:13:10 +0000 djh Posted By: Jeff BWould that matter as long as the insulation is well sealed at the edges/joins?
Airspaces inside insulation lead to the phenomenon known as thermal bypass, where air movement, even just circulation within the space, causes extra heatloss.

I think that this situation is not likely to lead to a large thermal bypass, but adding some extra insulation to fill the gaps and so help to reduce air movement as I suggested is best practice.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235475#Comment_235475 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235475#Comment_235475 Mon, 25 Jan 2016 22:03:33 +0000 ringi Posted By: Jeff BWould that matter as long as the insulation is well sealed at the edges/joins?

Yes because the insulation will not be 100% sealed at the edges or between boards however hard someone tries. There will also be gaps in the floor.

Hence I would be inclined to get a quote for spray on insulation.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235556#Comment_235556 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235556#Comment_235556 Wed, 27 Jan 2016 09:22:40 +0000 Jeff B
Ringi - I admit that whenever I think of additional insulation works I immediately switch into DIY mode and therefore spray-on insulation would not enter my thinking! Whilst I'm sure it would be efficient wouldn't that look a bit out of place on the ceiling of a garage and workshop? Would it need to be plaster-boarded over after?

I suppose it is impossible to prove 100% but I have always been able to well seal joins/edges in rigid insulation using acrylic mastic and self-adhesive aluminium tape. The OP's floor is tiled so presumably there is a concrete screed over the B&B system - would there be any serious gaps in that?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235575#Comment_235575 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235575#Comment_235575 Wed, 27 Jan 2016 11:16:16 +0000 ringi http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235760#Comment_235760 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235760#Comment_235760 Sat, 30 Jan 2016 14:19:58 +0000 gyrogear Posted By: shandyd05My house is a late 1960s bungalow built on a hill with B&B floor but the voids are huge - in fact roughly 25% under the house is garage, another 25% a store room/workshop and the height to the bottom of floor here is well over 2m; the height at back of house is less dropping to as little as maybe 1.35m in 1 corner. The bottom of the B&B floor is around 390mm above ground level at the back ( over 2m at front) beams sit on the internal brick leaf on a dpc and solid concrete cavity fill below dpc, insulated cavity above. The ground under the cavities is either concrete (50%) or dry earth.

You could consider insulating the vertical walls under the slab, using rigid foam.
("conditioned crawlspace" approach)
(The area involved might work out much less than the underside of the slab).

gg]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235768#Comment_235768 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235768#Comment_235768 Sat, 30 Jan 2016 19:32:50 +0000 shandyd05 To clarify a little, the underside of the B&b floor is flat so I was planning to stick celotex (or equivalent) on directly, though will have to move a cable or two first. I will likely apply plasterboard as the celotex is a fire risk in a garage/workshop space apparently. I'll give thought to battens or direct fixing there. Thanks esp to Peter_in_Hungry for the really useful link - I've been searching for ages for something like this! Ill also look into the spray option so thanks Ringi.
Consensus seems to be that condensation won't be a problem and no-one has mentioned the dreaded beam ends getting moist problem which I've seen on other B&B posts though they were mainly small voids and floor bottom sub ground level. I've considered putting a moisture sensor right up against the beam ends so I can monitor what happens afterwards.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235813#Comment_235813 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13995&Focus=235813#Comment_235813 Mon, 01 Feb 2016 14:49:04 +0000 Jeff B
Jeff B]]>