Casti Posted February 27, 2021 Share Posted February 27, 2021 Hello! I've done quite a lot of searching and even more reading and have ended up with even more questions. The background is, I am undergoing an extension in my house and am undertaking the majority of the internal building works save for plastering. Within the upstairs front bedroom (this falls under the existing property and nothing to do with the extension) whilst removing the existing plaster from the walls and the lath and plastered ceilings, it is clear the ceiling joists are undersized (appear to be 75x38 deep timbers at very rough 400mm centres with a single ceiling binder of same section size at mid span, there are some 2x1 looking timbers which are nailed in to every other joist back up to the roof rafters - will add photo later for clarity). It is clear they are undersized (3m span) due to the give away sag in the middle of the joists, and by the by they are well and truly warped and won't be good to receive plasterboard. I've decided the route I'd like to take is to sister the joists with some additional 3x2s (approx. 70x44 kiln dried timbers). I intend to install noggins at midspan and at perimeters to stiffen the ceiling and possibly compensate the removal of the existing ceiling binder with two at third points. The reasons I've elected to go down this route are I don't want to replace the joists with deeper more suitable joists as this would add significantly more time to the project (and possibly cost) The rest of the existing rooms (smaller spans) have same size joists so the floor in the loft would be at different levels and at the moment the loft has not got any boarding so all the joists are visible from above, but in the future I would like to board them with t&g loft chipboard for ease of access and possibly very light storage (<0.1kN/m2) In terms of joining the timbers together I think the route I want to take is to bolt them together with some M12 bolts at 1200 centres. I'm intending on drilling a 12mm hole and hammering the bolt in tight (so there's less chance of slip in the joint), using a double sided toothed timber connector between the joists, M12 washer below nut and bolt and large square washer plate against the timber faces. If anyone could comment on the above and give any suggestions for my proposals it would be much appreciated. Please let mevk now if any more information is required. I'll do a sketch of my proposal and attach with some photos of the existing ceiling/roof construction later. Thanks! Link to comment Share on other sites More sharing options...
nod Posted February 27, 2021 Share Posted February 27, 2021 It’s normal to simply counter baton using 75x25 dawn timbers These will even out the joists and allow you to pack any bad shapes Link to comment Share on other sites More sharing options...
Casti Posted February 28, 2021 Author Share Posted February 28, 2021 I suppose this might work in terms of dealing with not fixing plasterboard to warped joists provided the counter battens remain flat. If I did proceed with sistering the joists, would bolting with M12 bolts at 1200mm centres be suitable (noting the above re washer plates & double toothed connectors). Link to comment Share on other sites More sharing options...
markc Posted March 1, 2021 Share Posted March 1, 2021 8 hours ago, Casti said: I suppose this might work in terms of dealing with not fixing plasterboard to warped joists provided the counter battens remain flat. If I did proceed with sistering the joists, would bolting with M12 bolts at 1200mm centres be suitable (noting the above re washer plates & double toothed connectors). M12 through 3x2`s is massive overkill, plus 1200mm centers is too far to be of any real benefit. Clamp the timbers together and then screw or Annular ring nails in a zig-zag pattern at around 150-200mm spacing. (this is how trusses and joists are doubled or trebled) Link to comment Share on other sites More sharing options...
Casti Posted March 1, 2021 Author Share Posted March 1, 2021 8 hours ago, markc said: M12 through 3x2`s is massive overkill, plus 1200mm centers is too far to be of any real benefit. Clamp the timbers together and then screw or Annular ring nails in a zig-zag pattern at around 150-200mm spacing. (this is how trusses and joists are doubled or trebled) Don't have a nail gun, and impact driver needs replacing. Have a drill however. Do you think M10's at 600c/c is a good compromise? Link to comment Share on other sites More sharing options...
dpmiller Posted March 2, 2021 Share Posted March 2, 2021 surely you'll need an impact driver for the rest of the build? 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 2, 2021 Share Posted March 2, 2021 54 minutes ago, dpmiller said: surely you'll need an impact driver for the rest of the build? Why’s that??? Link to comment Share on other sites More sharing options...
dpmiller Posted March 2, 2021 Share Posted March 2, 2021 putting screws in... 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 2, 2021 Share Posted March 2, 2021 28 minutes ago, dpmiller said: putting screws in... I’ve put in many thousands of screws and I don’t have one, in fact I sold it as the noise it made was horrible. Link to comment Share on other sites More sharing options...
TonyT Posted March 2, 2021 Share Posted March 2, 2021 Agree, horrible noisy things coped for years with normal drill/driver Link to comment Share on other sites More sharing options...
Mr Punter Posted March 2, 2021 Share Posted March 2, 2021 I would go with Screwfix cheapo coach screws like these https://www.screwfix.com/p/turbocoach-coach-screws-yellow-zinc-plated-8-x-70mm-50-pack/38295 I don't mind an impact driver if I am the person using it and I have a similar attitude to multi tool. Both are very annoying when used by others! Link to comment Share on other sites More sharing options...
ianfish Posted March 6, 2021 Share Posted March 6, 2021 On 02/03/2021 at 09:28, Mr Punter said: I would go with Screwfix cheapo coach screws like these https://www.screwfix.com/p/turbocoach-coach-screws-yellow-zinc-plated-8-x-70mm-50-pack/38295 I don't mind an impact driver if I am the person using it and I have a similar attitude to multi tool. Both are very annoying when used by others! but dam useful Link to comment Share on other sites More sharing options...
tonyshouse Posted March 6, 2021 Share Posted March 6, 2021 I would prop the ceiling frame back to level and flat, you will need to remove the 2x1 hangers to do this, I would sister the binder with 6x2, then use some simple metalwork to fixe each ceiling joist to it easiest is Banda strapping /builders and with holes in it replace the hangers with say 4x2 nailed to ceiling joist, binder, presumed purlin and roof rafter only half as many needed Link to comment Share on other sites More sharing options...
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