bissoejosh Posted November 9, 2017 Share Posted November 9, 2017 (edited) Bit of an odd one this... Our drawings show the first floor i-stud walls being built on a P5 deck which rests on posi joists. All pretty standard and drawn by the timber frame designers and approved by the frame engineer. Our BCO has apparently never seen a timber frame done this way & is worried about the P5 being strong enough for the wall loading. He wants to see BBA certification or similar that this is OK and won't be crushed. Failing this he he would like the deck to stop short of the walls and be an infill deck which would be tedious. The thing is no one has certification (that I can find) which shows the necessary detail. I've spoken to Norbord & Egger who both recognize it as a standard detail and see no issue. I've also spoken to TRADA who have the same opinion. Any idea how to sway the BCO without upsetting him? In all other elements of the build he has been fantastic and is super approachable - we just have a sticking point with this. My fallback is to ask the engineer to make it a frame requirement but I'd rather not play top trumps with BCO for the reasons mentioned. Edited November 9, 2017 by bissoejosh typo Link to comment Share on other sites More sharing options...
ProDave Posted November 9, 2017 Share Posted November 9, 2017 I have to ask why the TF company wants to do this. Normally the upper floor's walls are built off a sole plate laid onto the joists. This is how ours is done. The floor deck then plays no part in holding the walls up. How about a strip of 6" by 1" as a sole plate / packer that fills the gap the TF company is expecting to be made up with the P5? I would be worried in the event of a leaking pipe for instance that the P5 could swell or disintegrate. Link to comment Share on other sites More sharing options...
bissoejosh Posted November 9, 2017 Author Share Posted November 9, 2017 26 minutes ago, ProDave said: I have to ask why the TF company wants to do this. Normally the upper floor's walls are built off a sole plate laid onto the joists. This is how ours is done. The floor deck then plays no part in holding the walls up. How about a strip of 6" by 1" as a sole plate / packer that fills the gap the TF company is expecting to be made up with the P5? I would be worried in the event of a leaking pipe for instance that the P5 could swell or disintegrate. That's really interesting, I had thought it was just the way it was done having spoken to our frame designers and the suppliers/TRADA. The proposal would still use a 45mm sole plate. I hadn't considered the leak issue either which sounds sensible. So just to clarify the sequencing for yours was sole plate, wall, then deck after? Link to comment Share on other sites More sharing options...
ProDave Posted November 9, 2017 Share Posted November 9, 2017 Basically the downstairs wall panels went up first. Then all the floor joists. Then the sole plate and first floor wall panels. The floor deck gets laid some time later when it has a roof on and is water tight. This is how every timber frame that I have seen has been built. Link to comment Share on other sites More sharing options...
Russell griffiths Posted November 9, 2017 Share Posted November 9, 2017 I have seen the flooring continued under the second story many times it seams to be a detail added for extra bracing within the frame. So they are using the floor sheets as a sort of lateral brace and a spreader tie. Link to comment Share on other sites More sharing options...
CC45 Posted November 9, 2017 Share Posted November 9, 2017 Our floor boards continue under the upstairs timber walls. I thought it was the norm. Link to comment Share on other sites More sharing options...
dpmiller Posted November 10, 2017 Share Posted November 10, 2017 All depends on whether the floor is constructed on-site or instead as factory-built cassettes I think. With cassettes the airtightness is lapped round the outside of the floor module before being craned in? Link to comment Share on other sites More sharing options...
Bitpipe Posted November 10, 2017 Share Posted November 10, 2017 MBC definitely lay deck first and then wall panels on top with the airtightness detail mentioned above lapped from inside of GF panel, outside over the joists, back inside and onto the inner face of the FF panel. Link to comment Share on other sites More sharing options...
bissoejosh Posted November 10, 2017 Author Share Posted November 10, 2017 15 hours ago, Russell griffiths said: I have seen the flooring continued under the second story many times it seams to be a detail added for extra bracing within the frame. So they are using the floor sheets as a sort of lateral brace and a spreader tie. Our frame co have mentioned that engineers have insisted on it in the past for this exact reason, as did TRADA. 10 minutes ago, Bitpipe said: MBC definitely lay deck first and then wall panels on top with the airtightness detail mentioned above lapped from inside of GF panel, outside over the joists, back inside and onto the inner face of the FF panel. Exactly what I intended to do. I also like the fact that I would have a nice working deck to build from. It doesn't sound like anyone else was questioned about the compressive strength of the deck board. I think we're going to fall back to the engineer for this and get some point load calcs confirming the board is fit for purpose. Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 10, 2017 Share Posted November 10, 2017 2 hours ago, dpmiller said: All depends on whether the floor is constructed on-site or instead as factory-built cassettes I think. With cassettes the airtightness is lapped round the outside of the floor module before being craned in? Airtightness is only on the outside cassettes so different reasons for that approach vs internal room dividers. 18 hours ago, ProDave said: Basically the downstairs wall panels went up first. Then all the floor joists. Then the sole plate and first floor wall panels. The floor deck gets laid some time later when it has a roof on and is water tight. This is how every timber frame that I have seen has been built. In contrast, I have NEVER seen one built that way. Always joists, then deck for a walking platform and additional lateral restraint, then upper walls done ( regardless if they're built on site or cassettes ). @bissoejosh I can only assume this is for instances where the underlying joists are running parallel to the walls in question, as if perpendicular then they'd be traversing the joists anyway. It goes without saying that it should be 22mm deck if there are any 'floating' walls. The norm, in exceptional circumstances, is to provision an additional joist directly where the stud wall is to lay, thus taking the load. An alternative, if the stud wall is dead centre of the void in between two joists, so is 'floating', is to fit full size noggins, ( or "dwangs" if your from a different persuasion ), at 600mm centres to provide a brace. Your BCO should accept that in a heartbeat, but you don't say if the joists are to be 600 or 400mm centres? All I can tell you is if your designer has them at 600mm then pay extra and beef up to 400's as the difference in the feel of the floor is massively noticeable, even with additional strong-backs it's obvious that there's deflection. Link to comment Share on other sites More sharing options...
bissoejosh Posted November 10, 2017 Author Share Posted November 10, 2017 1 hour ago, Nickfromwales said: Airtightness is only on the outside cassettes so different reasons for that approach vs internal room dividers. In contrast, I have NEVER seen one built that way. Always joists, then deck for a walking platform and additional lateral restraint, then upper walls done ( regardless if they're built on site or cassettes ). @bissoejosh I can only assume this is for instances where the underlying joists are running parallel to the walls in question, as if perpendicular then they'd be traversing the joists anyway. It goes without saying that it should be 22mm deck if there are any 'floating' walls. The norm, in exceptional circumstances, is to provision an additional joist directly where the stud wall is to lay, thus taking the load. An alternative, if the stud wall is dead centre of the void in between two joists, so is 'floating', is to fit full size noggins, ( or "dwangs" if your from a different persuasion ), at 600mm centres to provide a brace. Your BCO should accept that in a heartbeat, but you don't say if the joists are to be 600 or 400mm centres? All I can tell you is if your designer has them at 600mm then pay extra and beef up to 400's as the difference in the feel of the floor is massively noticeable, even with additional strong-backs it's obvious that there's deflection. The joists are all at 400mm, with a 22mm deck specified so pretty belt and braces. No mention from the BCO about wall/joist direction just about the P5 being crushed in general from the loading. The frame guys have gone to the engineer now to get him to calc and sign it all off. Hopefully this will prove satisfactory as evidence for BC and we can move on. Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 10, 2017 Share Posted November 10, 2017 35 minutes ago, bissoejosh said: The joists are all at 400mm, with a 22mm deck specified so pretty belt and braces. No mention from the BCO about wall/joist direction just about the P5 being crushed in general from the loading. The frame guys have gone to the engineer now to get him to calc and sign it all off. Hopefully this will prove satisfactory as evidence for BC and we can move on. The words "storm" and "teacup" may be in the report Link to comment Share on other sites More sharing options...
PeterW Posted November 10, 2017 Share Posted November 10, 2017 56 minutes ago, bissoejosh said: The joists are all at 400mm, with a 22mm deck specified so pretty belt and braces. No mention from the BCO about wall/joist direction just about the P5 being crushed in general from the loading. The frame guys have gone to the engineer now to get him to calc and sign it all off. Hopefully this will prove satisfactory as evidence for BC and we can move on. Not the same guy that @curlewhouse is having the issues with is it ...??!! Link to comment Share on other sites More sharing options...
bissoejosh Posted November 10, 2017 Author Share Posted November 10, 2017 1 hour ago, PeterW said: Not the same guy that @curlewhouse is having the issues with is it ...??!! Ha, no I think not. He has honestly been great throughout & genuinely hasn't seen it done 'that way' before hence the questions. Link to comment Share on other sites More sharing options...
jamiehamy Posted November 10, 2017 Share Posted November 10, 2017 We've done what you have upstairs but they are non load bearing partition walls. But I have the Trada book and recall that's the design for both cases. My BCO says he is happy to be challenged if there is proof - as per above, might come a case of sending emails /design standard and saying sonething like 'as per previous discussion, please see attached. Let me know if any further questions' and leave it at that rather than seek in his explicit approval? Link to comment Share on other sites More sharing options...
ProDave Posted November 10, 2017 Share Posted November 10, 2017 This must be a regional variation thing then. My only concern is how long will the P5 be exposed to the weather? Another poster on here had his sag and swell due to exposure to rain. I have only known one stick build where the first floor deck went down early and they used a truly waterproof chipboard because it was going to be exposed for a while. for working on, we had a temporary OSB deck as soon as the joists were down. Link to comment Share on other sites More sharing options...
PeterW Posted November 10, 2017 Share Posted November 10, 2017 I had the proper Egger Protect P5 down for 4 months open to the elements and it didn’t budge - had a few puddles at some points too ..! That stuff is designed to stand 90 days exposed, with 35% rain and I think in total we only had 12-14 days of rain in the end. Link to comment Share on other sites More sharing options...
bissoejosh Posted December 14, 2017 Author Share Posted December 14, 2017 To round this up... Engineer did worst case point load calc with data taken direct from Norbord. Huge margin of safety in the end. BCO happy and thanked me for providing the extra detail. Happy days. 1 Link to comment Share on other sites More sharing options...
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