Mr Blobby Posted September 7, 2023 Share Posted September 7, 2023 (edited) The masonry walls on our cavity build will be above ceiling height. To accomodate a cold roof (warm loft) our architect has suggested raising the rafters about a block height (250 ish) above the ceiling joists. Its a cut roof hanging off two steel purlins at 35 degree pitch. Were not really limited by ridge height. As far as I can see, the proposed design has two benefits. Firstly it increases loft space head height. Secondly, and perhaps more importantly, this looks a lot easier to acheive good airtightness. With this design the airtight membrane will not be penetrated by each ceiling joist. Instead the ceiling joists are suspended from hangers attached to a wall plate below the rafters so either a parge coat or airtight paint is applied behind the joist-wall plate, or run a membrane behind the joist-wall-plate into the loft. Does this design look ok? Am I missing something here? Has anyone else done this? Edited September 7, 2023 by Mr Blobby Link to comment Share on other sites More sharing options...
markc Posted September 7, 2023 Share Posted September 7, 2023 If you are not limited by ridge and internal height then that looks like a good option, 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 7, 2023 Share Posted September 7, 2023 Looks good to me 👍 Link to comment Share on other sites More sharing options...
George Posted September 15, 2023 Share Posted September 15, 2023 (edited) You need to get this checked by an engineer. Ceiling joists tie the rafters together and prevent roof spread. There are ways round this (the purlins may be sufficient) but potentially as sketched this is not a suitable arrangement. .... ruddy architects. Edited September 15, 2023 by George 3 Link to comment Share on other sites More sharing options...
Temp Posted September 17, 2023 Share Posted September 17, 2023 On 15/09/2023 at 22:06, George said: You need to get this checked by an engineer. Ceiling joists tie the rafters together and prevent roof spread. There are ways round this (the purlins may be sufficient) but potentially as sketched this is not a suitable arrangement. .... ruddy architects. +1 We needed a structural ridge beam. Quite a lot of steel. Link to comment Share on other sites More sharing options...
Mr Blobby Posted September 19, 2023 Author Share Posted September 19, 2023 (edited) On 15/09/2023 at 22:06, George said: You need to get this checked by an engineer. Ceiling joists tie the rafters together and prevent roof spread. There are ways round this (the purlins may be sufficient) but potentially as sketched this is not a suitable arrangement. On 17/09/2023 at 04:24, Temp said: We needed a structural ridge beam. Quite a lot of steel. Indeed. Our SE has looked at this and we have a ridge beam going in. As well as the two purlins. I think we probably needed a ridge beam all along anyway because we have a section of vaulted ceiling. 🤔 Anyway, moving on, our ridge beam will be supported in two places near the centre of the roof as well as at the gables. Its a long roof. Our builder has suggested steel columns in the loft to support the ridge beam instead of building two walls of blocks up into the loft to the ridge. We do have existing horizontal steel beams at ceiling height to support either steel columns or a wall. The cynic inside me suspects our builder has suggested the steel columns because it is easier to schedule roofers and go forward quickly. I can't see a downside of a steel column but then I generally have no clue about such things. Is there anything wrong in using steels to support the ridge beam? Is a block wall in the loft (with an opening to walk through of course) a better solution? Structural Engineer is happy with either option. Edited September 19, 2023 by Mr Blobby crap speeeling 1 Link to comment Share on other sites More sharing options...
George Posted September 19, 2023 Share Posted September 19, 2023 Yeah either will work OK. 1 Link to comment Share on other sites More sharing options...
Temp Posted September 19, 2023 Share Posted September 19, 2023 Either will normally work but do run it past your SE. 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 19, 2023 Share Posted September 19, 2023 24 minutes ago, Mr Blobby said: Our builder has suggested steel columns in the loft to support the ridge beam instead of building two walls of blocks up into the loft to the ridge. I did exactly this, dead easy and quicker and less fuss than building with blocks. 1 Link to comment Share on other sites More sharing options...
Mr Blobby Posted September 19, 2023 Author Share Posted September 19, 2023 46 minutes ago, joe90 said: I did exactly this, dead easy and quicker and less fuss than building with blocks. Steels it is then 👍 I will tell builder to crack on when I meet him on site in half hour. Link to comment Share on other sites More sharing options...
Mr Blobby Posted September 19, 2023 Author Share Posted September 19, 2023 (edited) Off on a slight tangent here, but if running an airtight membrane under the roof-joists-wall-plate into the loft, then how are the holes driled through the wall plate to fix it to the wall made airtight? Squirt some airtight sealant like orcon-f into the hole? Or some other sealant? And what membrane is suitable? Something like intello? Edited September 19, 2023 by Mr Blobby Link to comment Share on other sites More sharing options...
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