Barny Posted April 16 Share Posted April 16 Hi. Has anyone done a passivhaus (aiming for) timberframe using block and beam foundations but not using Tetris? Our foundation design currently uses Tetris to keep the thermal bridging down but it is coming out 50% more than a raft (which we can’t have due to site conditions) and 100% more than traditional block and beam with 200mm of PIR. Just wondering if anyone else has achieved near passivhaus using block and beam and can share foundation designs? thanks Link to comment Share on other sites More sharing options...
Thorfun Posted April 16 Share Posted April 16 can't you just use normal block and beam and put loads of insulation on top? 🤷♂️ 1 Link to comment Share on other sites More sharing options...
Thorfun Posted April 16 Share Posted April 16 ps. have a read of this thread as the OP was also told couldn't have an insulated raft due to ground conditions but their SE made it possible. Link to comment Share on other sites More sharing options...
Barny Posted April 16 Author Share Posted April 16 17 minutes ago, Thorfun said: can't you just use normal block and beam and put loads of insulation on top? 🤷♂️ I think there will be thermal bridging issues between the block and frame. Has anyone got a design that works around this? Link to comment Share on other sites More sharing options...
Iceverge Posted April 20 Share Posted April 20 @ProDave did a suspended I joist floor with a screed on top. Search his recent posts. Added to his external woodfiber layer it should have excellent thermal bridging characteristics. Or like @Thorfun says just shove lots of insulation on top of block and beam. Perimeter thermal bridges are pretty straightforward to deal with for timber frame anyway. What's your planned wall build up. Link to comment Share on other sites More sharing options...
IanR Posted April 20 Share Posted April 20 On 16/04/2024 at 11:26, Barny said: (which we can’t have due to site conditions) Have you looked at all options of raft? Ie. Rafts with piling support. Link to comment Share on other sites More sharing options...
Roundtuit Posted April 20 Share Posted April 20 On 16/04/2024 at 11:48, Barny said: I think there will be thermal bridging issues between the block and frame. Has anyone got a design that works around this? Marmox blocks. I looked at them for ours, but in the end decided the benefit was neglible as we had continuous 40mm pir layer around the inside of the frame. Link to comment Share on other sites More sharing options...
JohnMo Posted April 20 Share Posted April 20 This is a construction detail for block and beam from the Durisol build manual it may be some you could use or modify. 2 hours ago, Roundtuit said: Marmox blocks. I looked at them for ours, but in the end decided the benefit was neglible as we had continuous 40mm pir layer around the inside of the frame. I also looked at Marmox, and once I had been through the calculations, couldn't see the benefits. I constructed as per the below, but with the additional 70mm upstand not shown on the screed perimeter. My slab isn't block and beam, but similar in many respects, but ground bearing, see image above for an idea - 160mm reinforced slab on numerous stub walls, cast in place. Then insulation, then a further cast concrete floor. Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 4 Share Posted June 4 On 16/04/2024 at 11:26, Barny said: Hi. Has anyone done a passivhaus (aiming for) timberframe using block and beam foundations but not using Tetris? Our foundation design currently uses Tetris to keep the thermal bridging down but it is coming out 50% more than a raft (which we can’t have due to site conditions) and 100% more than traditional block and beam with 200mm of PIR. Just wondering if anyone else has achieved near passivhaus using block and beam and can share foundation designs? thanks Keen to know the answer to this too - there must be a way to mitigate thermal bridging using a standard block and beam? I saw on another thread on here, which I'll try and dig out, that someone used some insulation in the outer cavity but wasn't sure how keen building control would be on that idea. Link to comment Share on other sites More sharing options...
JohnMo Posted June 4 Share Posted June 4 37 minutes ago, Mark Greenfield said: Keen to know the answer to this too - there must be a way to mitigate thermal bridging using a standard block and beam? See my post above, block and beam drawing thermal bridge free - by durisol (carbonplan drawing) giving all the details. Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 4 Share Posted June 4 3 hours ago, JohnMo said: See my post above, block and beam drawing thermal bridge free - by durisol (carbonplan drawing) giving all the details. It doesn't work for timber frame construction though, I don't think? Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 4 Share Posted June 4 On 16/04/2024 at 11:29, Thorfun said: can't you just use normal block and beam and put loads of insulation on top? 🤷♂️ Problem seems to be the junctions; where frame meets blocks etc. Link to comment Share on other sites More sharing options...
JohnMo Posted June 4 Share Posted June 4 52 minutes ago, Mark Greenfield said: It doesn't work for timber frame construction though, I don't think? Could quite easily work. The Durisol block takes all the structural loads on the inside of the block. A timber frame with a structural wall inside and Larson strut on outside to carry insulation. So this type of construction above for the block and beam as detailed above and timber frame as below. Link to comment Share on other sites More sharing options...
Conor Posted June 4 Share Posted June 4 There are various options, structural insulation, lightweight blocks, insulation upstands etc. Should be something your architect / PH designer can specify and update drawings accordingly. Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 5 Share Posted June 5 16 hours ago, JohnMo said: Could quite easily work. The Durisol block takes all the structural loads on the inside of the block. A timber frame with a structural wall inside and Larson strut on outside to carry insulation. So this type of construction above for the block and beam as detailed above and timber frame as below. I don't think this build-up would meet the approval of warranty companies would it? The problem is I would have to find a company that manufactures this type of timber frame that is accredited, and of all the shows I have been to I've never seen this arrangement, so that strikes me as tricky! Out of interest, the load bearing frame element of the image would also be the service cavity in this scenario I guess - which seems great! Also, where would the racking board go as it's not shown on the drawing? Link to comment Share on other sites More sharing options...
JohnMo Posted June 5 Share Posted June 5 30 minutes ago, Mark Greenfield said: don't think this build-up would meet the approval of warranty companies would it? Not sure why it wouldn't, pretty standard arrangement. Do a stick build? Have a read up on Larson strut! 31 minutes ago, Mark Greenfield said: where would the racking board go as it's not shown on the drawing Behind the load bearing frame and the airtight membrane would be stuck to it. Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 5 Share Posted June 5 1 hour ago, JohnMo said: Not sure why it wouldn't, pretty standard arrangement. Do a stick build? Have a read up on Larson strut! Behind the load bearing frame and the airtight membrane would be stuck to it. Stick build is a nightmare for structural warranties, and even if I could get past that lenders really don't like it either. I've done a few for extensions over the years, but warranty not required. It's not a standard arrangement at all - but if you can point me to a manufacturer and installer that works with it and can give me the accreditation standards I need for a warranty and mortgage I guess I could look into it! Link to comment Share on other sites More sharing options...
JohnMo Posted June 5 Share Posted June 5 4 hours ago, Mark Greenfield said: It's not a standard arrangement at all - but if you can point me to a manufacturer and installer It is here is one supplier and installer, plenty of people on here seem to have used them. 4 hours ago, Mark Greenfield said: can give me the accreditation standards I need for a warranty and mortgage I guess I could look into it! There are are others also, but I will leave you to investigate. You wanted to know how to use block and beam with passivhaus, have provided your starter for ten. Foundation details and wall system. Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 5 Share Posted June 5 1 hour ago, JohnMo said: It is here is one supplier and installer, plenty of people on here seem to have used them. There are are others also, but I will leave you to investigate. You wanted to know how to use block and beam with passivhaus, have provided your starter for ten. Foundation details and wall system. Yes - I'm familiar with twin-frame (and MBC - I'll be asking them to price for me), but I don't really want a twin-frame as it's expensive. Link to comment Share on other sites More sharing options...
JohnMo Posted June 5 Share Posted June 5 15 minutes ago, Mark Greenfield said: familiar with twin-frame FYI a twin frame, is a Larson truss. A structural element and non structural to hold the additional insulation. Link to comment Share on other sites More sharing options...
Mark Greenfield Posted June 6 Share Posted June 6 15 hours ago, JohnMo said: FYI a twin frame, is a Larson truss. A structural element and non structural to hold the additional insulation. Kind of; typically a Larsen truss is a complete truss (joist) fixed to the structural element, which is a bit wasteful and isn't quite as effective in terms of thermal bridging as a twin frame, but agree that in principle they're similar. Link to comment Share on other sites More sharing options...
Nic Posted June 6 Share Posted June 6 My apologies for what is likely to be a silly question . but if you are looking at a block and beam ground floor and aiming for passive , with passive timber frame . Can you still have a flush patio to finished floor ( so the level outside is the same for wheelchairs etc ? ) if so can some show me a drawing of how this might work please 🙏 Link to comment Share on other sites More sharing options...
Mr Punter Posted June 6 Share Posted June 6 4 minutes ago, Nic said: My apologies for what is likely to be a silly question . but if you are looking at a block and beam ground floor and aiming for passive , with passive timber frame . Can you still have a flush patio to finished floor ( so the level outside is the same for wheelchairs etc ? ) if so can some show me a drawing of how this might work please 🙏 I don't see how you can have any timber frame where the flush patio doors are, as the frame needs to be 150mm above ground. All you need under the doors is something rot proof with good insulation that is strong enough to support them. 1 Link to comment Share on other sites More sharing options...
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