jamiehamy Posted January 9, 2018 Share Posted January 9, 2018 I'll dig out pics when back home but our floor joists are Posi Joists. For our upstairs sitting room I wanted 300mm centres but the designer insisted 600mm would be fine. In practise I wish I'd stuck to my guns as the floor doesn't feel as solid as I wanted it. Don't get me wrong, it's acceptable, especially as it's carpeted but there is some small movement detectable. However our joists are hung from the top chord only - the lower is not attached - and we have acceptable, albeit not perfect, performance. I do recall the designer telling my most issues with bounce are due to installation...! I think I've said this before that when I coach bolted the string back in twice to each joist, and it made quite a difference. Anyway, in terms of solution, how far are you prepared to go @readiescards? If you are able to strip the ceiling you probably have a few options from fiddling with joist hangars, to doing some form of webbing onto the joists to stiffen to possible adding additional joists. 1 Link to comment Share on other sites More sharing options...
readiescards Posted January 9, 2018 Author Share Posted January 9, 2018 45 minutes ago, jamiehamy said: Anyway, in terms of solution, how far are you prepared to go @readiescards? If you are able to strip the ceiling you probably have a few options from fiddling with joist hangars, to doing some form of webbing onto the joists to stiffen to possible adding additional joists. My aim off starting this post was to truly identify what the cause is and and therefore who was at fault so the issue can be 'discussed' (don't want to say more than that for the moment) Thanks all Link to comment Share on other sites More sharing options...
PeterW Posted January 9, 2018 Share Posted January 9, 2018 Floor bounce is a product of a number of components, not least the floor surface and how it’s attached to the joists. We have 600 centres on our posijoists and what is interesting is in the ensuite where there is glued and bonded boards only across the centre section with approx 600mm either side with no boards, the floor is subject to more vibration and movement than the other floors where the floor is to the walls. Secondly, we have built in the joists rather than use hangers and I’m pretty sure that contributes to allowing the flex of the bottom chord. Before we close the ceiling up from below I may well glue and screw some stiffening plates to the joists to see if we can add a little strength to the floor. 1 Link to comment Share on other sites More sharing options...
curlewhouse Posted January 10, 2018 Share Posted January 10, 2018 Not sure centre distances or use of hangers are necessarily the culprits - ours are at 600 centres, on hangers, and the floor is really rock solid, not an iota of movement. In fact on reading this I've just been testing it by jumping up and down in the centre of the widest span and not a jot of movement or noise (apart from me landing ) could we detect. Our floor is nailed and glued 22mm thick Eggar Protect board on top. Minor thought - do all the holes in the hangers have nails in? My BCO picked up that there were no nails in the lower holes in the hangers and made me do them. I protested at first saying that clearly they are superfluous since the joists aren't about to jump out of the hangers, being nailed also in the upper holes, but his point (probably correctly) was that movement has been encountered when the lower nails have been omitted, resulting in squeaks, (and subsequent complaints) so they like to see every hole in them nailed. 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 10, 2018 Share Posted January 10, 2018 1 hour ago, curlewhouse said: Not sure centre distances or use of hangers are necessarily the culprits - ours are at 600 centres, on hangers, and the floor is really rock solid, not an iota of movement. In fact on reading this I've just been testing it by jumping up and down in the centre of the widest span and not a jot of movement or noise (apart from me landing ) could we detect. Our floor is nailed and glued 22mm thick Eggar Protect board on top. Minor thought - do all the holes in the hangers have nails in? My BCO picked up that there were no nails in the lower holes in the hangers and made me do them. I protested at first saying that clearly they are superfluous since the joists aren't about to jump out of the hangers, being nailed also in the upper holes, but his point (probably correctly) was that movement has been encountered when the lower nails have been omitted, resulting in squeaks, (and subsequent complaints) so they like to see every hole in them nailed. It's the type of hangar and the way they are used that's key. Follow the standard detail in the Posijoist technical paper and hangars work fine; fail to follow it and they may not. There's also a relationship between the depth of the Posijoist (in this case 254mm) and the spacing. Use deeper joists and you can space them wider for the same floor stiffness. Finally, adding proper strongbacks across the joists at the appropriate spacing stiffens things up a lot too, by tying each joist to it's neighbour and helping to distribute applied loads over a greater area. 1 Link to comment Share on other sites More sharing options...
readiescards Posted January 14, 2018 Author Share Posted January 14, 2018 (edited) My partner's bathroom is part of the floor I'm at issue with. She just informed me the door gap looks odd. The door does not natural open or shut so I'm taking it as being a true vertical. And assuming the door bottom is 90degree to the vertical then this looks like confirmation the floor joists are not installed correct. Other reasons ? Edited January 14, 2018 by readiescards Clarification Link to comment Share on other sites More sharing options...
dpmiller Posted January 14, 2018 Share Posted January 14, 2018 which side is the wall, and which is the centre of the span? Link to comment Share on other sites More sharing options...
jamiehamy Posted January 14, 2018 Share Posted January 14, 2018 I would confirm the 'plumbness' of the door before you go any further. Vertical and horizontal. If nothing else it's better than assuming - either use a laser line or a checked long bead - I say checked before I sadly found out after 3 frames and a lot of headscratching that one of my short beads was not true - which explained why I had a lot of problems (I ended up buying a small cross line laser early that was to be for the tiling, made it ten times easier if anyone else is doing this)! And check the level of the floor across the threshold too. Also check the hinges have been morticed uniformly - just in case. Best have a firm confirmation of all the above before going on any further (I suspect they will all be fine tho). If it is the floor, if you have the laser you could try work out just how much out of plumb it is - if you want to know. 2 Link to comment Share on other sites More sharing options...
readiescards Posted January 14, 2018 Author Share Posted January 14, 2018 1 hour ago, dpmiller said: which side is the wall, and which is the centre of the span? The centre of the joist span is very approx under the door hinge. With the wall being about half a metre to left of this photo. (It's not that simple because of chimney breast etc) Link to comment Share on other sites More sharing options...
Simplysimon Posted January 15, 2018 Share Posted January 15, 2018 so we're looking at not only joists but trimming around a chimney which is a whole different ball game? bottom of door looks to be square to stile but clearance under door definitely not eq. were the hinges cranked and sunk into the standard as well as the door? clearance looks a bit tight on that side. Link to comment Share on other sites More sharing options...
readiescards Posted January 16, 2018 Author Share Posted January 16, 2018 Yes, nearest the camera is joists that make up the floor that bounces most annoyingly - you can just see the chimney. I'm going to try measuring the flatness of the floor using a rotating laser level as a reference - though with carpet and underlay down it is going to be tricky to note less than a mm but now that I can see the difference just across the bathroom door gap I think there will be something I can measure Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 16, 2018 Share Posted January 16, 2018 Why are some of the steel webs missing on some of the posijoists? From the photo, it looks like some joists only have metal webs on one side, not both. 1 Link to comment Share on other sites More sharing options...
ProDave Posted January 16, 2018 Share Posted January 16, 2018 ^^ I was going to ask that. It also looks like the one sided joists are spanning the same gap as the rest of the normal ones. I know I am no expert, but I have never seen posi joists with the metal webs only fitted to one side. Is the floor bounce the ones in the corner that are one sided? or the ones in line with the chimney? Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 16, 2018 Share Posted January 16, 2018 +1. Very strange indeed . I've never seen such a compromise, and I fail to see the thought behind not having the extra webs. They're not exactly gold plated so why ever would you ( they ) omit them ? Link to comment Share on other sites More sharing options...
Alexphd1 Posted January 16, 2018 Share Posted January 16, 2018 This thread is very interesting, we are installing the posi joist tomorrow. Quick question what length is the span? Link to comment Share on other sites More sharing options...
CC45 Posted January 16, 2018 Share Posted January 16, 2018 We've got 5m span with 254 posi joists at 600mm. Should have done them at 400mm. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 17, 2018 Share Posted January 17, 2018 10 hours ago, readiescards said: Yes, nearest the camera is joists that make up the floor that bounces most annoyingly - you can just see the chimney. And nearest the camera are also the joists with the apparently missing steel webs - could be a clue there. Link to comment Share on other sites More sharing options...
Barney12 Posted January 17, 2018 Share Posted January 17, 2018 11 hours ago, JSHarris said: Why are some of the steel webs missing on some of the posijoists? From the photo, it looks like some joists only have metal webs on one side, not both. My MBC installed posi joist floor had some webs “missing” on one side. I assumed it was simply the design calcs that specified them. Fortunately we don’t have the bounce issues that the OP has. Link to comment Share on other sites More sharing options...
jamiehamy Posted January 17, 2018 Share Posted January 17, 2018 I'd be interested to know how the strong back was afixed to each joist, not clear in pic. Link to comment Share on other sites More sharing options...
Barney12 Posted January 17, 2018 Share Posted January 17, 2018 3 hours ago, jamiehamy said: I'd be interested to know how the strong back was afixed to each joist, not clear in pic. I'm in no way an expert but can tell you that my strong backs are fixed using a multitude of gas nailed ring shanks to every joist. We actually had a slight squeak in the master bedroom floor when first installed. I pointed it out to Brendan (MBC) and he found that the guys had missed nailing a section of joists to the strong back down the centre of the room. A few minutes of Paslode action later and the squeak was gone. Link to comment Share on other sites More sharing options...
ProDave Posted January 17, 2018 Share Posted January 17, 2018 6 hours ago, jamiehamy said: I'd be interested to know how the strong back was afixed to each joist, not clear in pic. I suspect in that picture they are not yet fixed. You have to slot them in at that stage as it will be impossible later, but mine were not actually fixed to the joists until some time later. Is it possible that someone forgot to attach them? Link to comment Share on other sites More sharing options...
readiescards Posted January 17, 2018 Author Share Posted January 17, 2018 http://www.mitek.co.uk/Products/Posi-Joist/Posi-Joist-Handbook/ States: Posi-Joists™ can be designed to include single sided Posi-Strut™ webbing where appropriate to provide considerable material savings. So single sided seems ok. Link to comment Share on other sites More sharing options...
readiescards Posted January 17, 2018 Author Share Posted January 17, 2018 5 hours ago, ProDave said: Is it possible that someone forgot to attach them? Disappointingly I can not find any photos to answer this Link to comment Share on other sites More sharing options...
readiescards Posted January 17, 2018 Author Share Posted January 17, 2018 22 hours ago, Alexphd1 said: This thread is very interesting, we are installing the posi joist tomorrow. Quick question what length is the span? From the floor plan just under 4.5m Link to comment Share on other sites More sharing options...
readiescards Posted January 17, 2018 Author Share Posted January 17, 2018 23 hours ago, ProDave said: Is the floor bounce the ones in the corner that are one sided? or the ones in line with the chimney? The centre of the room (which is also inline with the chimney) is the worse place - but the whole room moves and rattles as one walks across it to be honest Link to comment Share on other sites More sharing options...
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