redtop Posted December 8, 2019 Share Posted December 8, 2019 SE proposed 253mm (or similar) posi joists for all floors (ground floor is raised off ground on posts). Roof is flat, green roof. frame builder (chippy, stick build) reckons solid timber joists would be better, more solid, less bounce for ground floor and will take a higher load for roof. Going up a size in posi joists to get higher roof loading (3xx mm, to get to the 90KG per m sq) pushes price up a lot. We are near Sea in cornwall so mild but wet and windy we will be running MVHR and do have quite a few steels at ground, and first floors but again builder reckons he can orientate joists soo we wont need to cut big holes for the pipes what do you reckon guys??? Link to comment Share on other sites More sharing options...
nod Posted December 9, 2019 Share Posted December 9, 2019 It’s many years since I’ve seen solid joists used on site Always posi or I joists There’s little difference between posi and solid though I would use solid on the ground floor and posi in the first floor Link to comment Share on other sites More sharing options...
ProDave Posted December 9, 2019 Share Posted December 9, 2019 We used JJI I joists on the ground floor and posi joists on the first floor. I can'r remember why the SE recommended different like that, other then the obvious, hardly any pipes in the ground floor, but plenty in the first floor which is where posi joists really shine. Both have done the job well. In fact I would say the split is good. The JJI's downstairs have a natural ledge to lay strips of OSB to form a hard shelf to support whatever insulation you choose. Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 9, 2019 Share Posted December 9, 2019 7 hours ago, ProDave said: We used JJI I joists on the ground floor and posi joists on the first floor. I can'r remember why the SE recommended different like that, other then the obvious, hardly any pipes in the ground floor, but plenty in the first floor which is where posi joists really shine. Maybe to remove metal from a cold ventilated space? Even though they’re not in ‘direct contact’ maybe it was a wise precaution. Link to comment Share on other sites More sharing options...
Big Jimbo Posted December 9, 2019 Share Posted December 9, 2019 I am a huge fan of either the metal web, or jji joists. Less bounce.... Is he taking the p1$$. Will be far better than solid timber without question. The timber you can buy these days is shite. Link to comment Share on other sites More sharing options...
joe90 Posted December 9, 2019 Share Posted December 9, 2019 22 minutes ago, Big Jimbo said: I am a huge fan of either the metal web, or jji joists. Less bounce.... Is he taking the p1$$. Will be far better than solid timber without question. The timber you can buy these days is shite. +1, solid timber also is not very accurate always a little bow somewhere, on my build jji were specked and used but I asked fir said joists (calculated at 600mm centres) to be installed at 400mm to make even more solid. I was able to cut holes in the webs for electrics and MVHR without a problem (they come with a cutting guide). Link to comment Share on other sites More sharing options...
redtop Posted December 9, 2019 Author Share Posted December 9, 2019 he owns a sawmill so I think was going to cut the joists himself from douglass fir trunks. Seeing him tomorrow to discuss. Apparently the extra cost for taking the post joists in the roof to the 3xx mm size costs an extra £5k! Link to comment Share on other sites More sharing options...
PeterW Posted December 9, 2019 Share Posted December 9, 2019 Sounds a bit odd ... you either need a lot of joists, or they have been priced wrong. Is he certifying the joists then as they will need to be stamped either C16 or C24 for strength / span purposes. Link to comment Share on other sites More sharing options...
redtop Posted December 9, 2019 Author Share Posted December 9, 2019 no he wouldn't be able to stamp them; I will find out more tomorrow Link to comment Share on other sites More sharing options...
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