JohnMo Posted August 30 Share Posted August 30 16 hours ago, Dunc said: Assume you've got a single 300mm block R = 0.3/0.18 = 1.67 m2K/W. The U value (1/R) is 0.6 W/m2K. 38 minutes ago, Dunc said: General question for you & others: I'm not sure on the value of 2x300mm aircrete blocks? Two blocks high becomes 440mm .44/0.18 = 2.44, 1/2.44 so a U value of 0.4. So U value downwards, but really with the buildup by the time you have got to the second block it's depth is being comprised by plenty of sideways cold areas. So as said maybe one block would be enough. 1 Link to comment Share on other sites More sharing options...
Dunc Posted August 30 Share Posted August 30 @SBMS the architectural drawing appears different to your initial coloured plan: the insulation seems to be UNDER the slab on the architectural drawing? Link to comment Share on other sites More sharing options...
Dave Jones Posted August 30 Share Posted August 30 to eliminate the thermal bridge you really want a marmox block at screed/DPC level all the way round 1 high, no advantage going more than 1 block. where you have openings take them to the outside skin so your door frames sit on them. It's once of the largest thermal bridge junctions in the entire build, not worth bodging. concrete blocks are rubbish for insulation. Link to comment Share on other sites More sharing options...
SBMS Posted August 30 Author Share Posted August 30 1 hour ago, Dunc said: @SBMS the architectural drawing appears different to your initial coloured plan: the insulation seems to be UNDER the slab on the architectural drawing? Thanks, yes it's not been updated yet following SE's drawings. DPC is in wrong place too! Link to comment Share on other sites More sharing options...
SBMS Posted August 30 Author Share Posted August 30 1 hour ago, Dave Jones said: to eliminate the thermal bridge you really want a marmox block at screed/DPC level all the way round 1 high, no advantage going more than 1 block. where you have openings take them to the outside skin so your door frames sit on them. It's once of the largest thermal bridge junctions in the entire build, not worth bodging. concrete blocks are rubbish for insulation. Have you quantified the difference in heat loss from the increased thermal bridging? I calculated that a perimeter row of 215mm thermoblock would be circa £2k additional cost. I wonder what the energy saving would be, but I'm not sure payback justifies it? No hard data for that though, just a gut feeling... Link to comment Share on other sites More sharing options...
Dave Jones Posted August 30 Share Posted August 30 15 minutes ago, SBMS said: Have you quantified the difference in heat loss from the increased thermal bridging? I calculated that a perimeter row of 215mm thermoblock would be circa £2k additional cost. I wonder what the energy saving would be, but I'm not sure payback justifies it? No hard data for that though, just a gut feeling... wait till you start pricing up thermally broken lintels! What's your SAP specify as that is what your having to comply with. Dont forget if your on new regs, every thermal bridge junction has to be photographed for the EPC, no photo - no EPC. Link to comment Share on other sites More sharing options...
Dunc Posted August 30 Share Posted August 30 @Dave Jones that diagram appears to be for a single skin (e.g. 140mm timberframe) where the only horizontal insulation is 25mm PIR + the marmox block. In the case under discussion the build appears to be 2 skin blockwork with cavity insulation. If the cavity is insulated, the thermal bridge of interest is downwards to the foundation blockwork. @JohnMo's maths shows 440mm deep aircrete blocks will do just as well (if not better) than the marmox block. Link to comment Share on other sites More sharing options...
Dave Jones Posted August 30 Share Posted August 30 (edited) 4 minutes ago, Dunc said: @Dave Jones that diagram appears to be for a single skin (e.g. 140mm timberframe) where the only horizontal insulation is 25mm PIR + the marmox block. In the case under discussion the build appears to be 2 skin blockwork with cavity insulation. If the cavity is insulated, the thermal bridge of interest is downwards to the foundation blockwork. @JohnMo's maths shows 440mm deep aircrete blocks will do just as well (if not better) than the marmox block. its for an outside door albeit they havent stepped it out. inner skin is basically the same. aircretes are nowhere near U value of a marmox. your calculating losses through not up as well remeber. otherwise there would be zero market for marmox. Edited August 30 by Dave Jones Link to comment Share on other sites More sharing options...
Oz07 Posted August 30 Share Posted August 30 How durable are these thermoblocks. That outside render detail looks a right pita. Admittedly you wouldn't have to do this if using them on the inside skin of cavity wall but doesn't fill you with confidence. Is the thermal bridge on the bottom of a door cill that much worse than up the jambs that it justifies a row of these below frames? What about windows?! Link to comment Share on other sites More sharing options...
JohnMo Posted August 31 Share Posted August 31 9 hours ago, Oz07 said: Is the thermal bridge on the bottom of a door cill that much worse than up the jambs that it justifies a row of these below frames? What about windows?! Think you are missing the point and what thermal bridge is being discussed, this for a thermal bridge that exists between the house internal wall and the ground. But to answer your question above - yes, because that area of the wall is in direct contact with the ground so will suffer downwards heat loss unless mitigated. None of your other examples are relevant. Link to comment Share on other sites More sharing options...
SBMS Posted August 31 Author Share Posted August 31 19 hours ago, Dave Jones said: its for an outside door albeit they havent stepped it out. inner skin is basically the same. aircretes are nowhere near U value of a marmox. your calculating losses through not up as well remeber. otherwise there would be zero market for marmox. @Dave Jones when you say calculating heat loss ‘through’ - isn’t both sides of your marmox insulated? CWI one side and the floor PIR the other? Or is this not how it works Link to comment Share on other sites More sharing options...
Oz07 Posted August 31 Share Posted August 31 38 minutes ago, JohnMo said: Think you are missing the point and what thermal bridge is being discussed, this for a thermal bridge that exists between the house internal wall and the ground. But to answer your question above - yes, because that area of the wall is in direct contact with the ground so will suffer downwards heat loss unless mitigated. None of your other examples are relevant. Unless you are breaking the bridge with a continuous course of these on the outside then surely you still have a similar bridge towards the bottom of the door jambs and bottom edges of the cills. Is the cold bridge towards the bottom of the building significantly worse than the masonry at 1m above ground?! Link to comment Share on other sites More sharing options...
Dave Jones Posted August 31 Share Posted August 31 10 hours ago, Oz07 said: How durable are these thermoblocks. That outside render detail looks a right pita. Admittedly you wouldn't have to do this if using them on the inside skin of cavity wall but doesn't fill you with confidence. Is the thermal bridge on the bottom of a door cill that much worse than up the jambs that it justifies a row of these below frames? What about windows?! they are structural. will be below ground on outside door with level threshold windows are different as they are built into the cavity. Link to comment Share on other sites More sharing options...
Dave Jones Posted August 31 Share Posted August 31 47 minutes ago, Oz07 said: Unless you are breaking the bridge with a continuous course of these on the outside then surely you still have a similar bridge towards the bottom of the door jambs and bottom edges of the cills. Is the cold bridge towards the bottom of the building significantly worse than the masonry at 1m above ground?! Inside skin becomes the outside skin for doors maybe you are not understanding this Link to comment Share on other sites More sharing options...
Oz07 Posted August 31 Share Posted August 31 37 minutes ago, Dave Jones said: Inside skin becomes the outside skin for doors maybe you are not understanding this I suppose the thermo brick creates a bigger buffer between the slab and outside masonry instead of just an insulation upstand. Sorry i was just thinking of the effect on the door frame. Are these ok to be exposed below ground then or do they still require rendering? Link to comment Share on other sites More sharing options...
JohnMo Posted August 31 Share Posted August 31 2 hours ago, Oz07 said: Sorry i was just thinking of the effect on the door frame The example from the OP is a twin skin block and brick with insulated cavity. The external skin is isolated from the building by cavity insulation first, any openings in the cavity are blocked off with cavity closers. Windows and doors straddle the insulation, so as not to compromise or generate a new thermal bridge. Example Link to comment Share on other sites More sharing options...
SBMS Posted September 1 Author Share Posted September 1 23 hours ago, JohnMo said: The example from the OP is a twin skin block and brick with insulated cavity. The external skin is isolated from the building by cavity insulation first, any openings in the cavity are blocked off with cavity closers. Windows and doors straddle the insulation, so as not to compromise or generate a new thermal bridge. Example @JohnMo this detail would be okay for non ground floor.. but on ground floor there won’t be cavity insulation under the door.. with a 200mm cavity and potentially a 160mm door track, what’s supporting the track over the cavity? Would you recommend a structural cavity closer? Or take the floor insulation and screed to the outer brick skin (dropping the inner block a course or so)? Is PIR and screed enough to carry the weight of the doors? Link to comment Share on other sites More sharing options...
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