willbish Posted December 18, 2018 Share Posted December 18, 2018 Is there a standard method of fixing/hanging JJI joists to solid timber rafters? Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 18, 2018 Share Posted December 18, 2018 Anything in here? Link to comment Share on other sites More sharing options...
MikeSharp01 Posted December 18, 2018 Share Posted December 18, 2018 (edited) Not sure if there is a standard detail for this but if there is it will require you to block the end of the joist and take the main load underneath the bottom flange. Edited December 18, 2018 by MikeSharp01 2 Link to comment Share on other sites More sharing options...
Russell griffiths Posted December 18, 2018 Share Posted December 18, 2018 (edited) That sketch is missing a bit of info, I’m thinking that the junction of the two timbers is sitting on top of a wall plate fixed down to your wall, so as has been said the jji joist will need end blocking to stiffen it up and take the load, I would then treat it as a solid timber, so your rafter will need a birdsmouth over the wallplate and then you can use heavy gauge construction screws to secure them both together or coach bolt through the web stiffeners and through the solid rafter, we used to use a funny washer with spikes on it to stop rotating forces you will also have a nailable hold down plate on the side of the i joist. Has this not been covered by the roof designer ? my roof design has all the truss clips and joist hangers marked on it. Who are you getting your ijoists off, I’m just getting quotes and there a bit pricey compared to solid timber. Edited December 18, 2018 by Russell griffiths Link to comment Share on other sites More sharing options...
scottishjohn Posted December 18, 2018 Share Posted December 18, 2018 12 minutes ago, Russell griffiths said: That sketch is missing a bit of info, I’m thinking that the junction of the two timbers is sitting on top of a wall plate fixed down to your wall, so as has been said the jji joist will need end blocking to stiffen it up and take the load, I would then treat it as a solid timber, so your rafter will need a birdsmouth over the wallplate and then you can use heavy gauge construction screws to secure them both together or coach bolt through the web stiffeners and through the solid rafter, we used to use a funny washer with pokes on it to stop rotating forces you will also have a nailable hold down plate on the side of the i joist. Has this not been covered by the roof designer ? my roof design has all the truss clips and joist hangers marked on it. Who are you getting your ijoists off, I’m just getting quotes and there a bit pricey compared to solid timber. whats the attraction of them if they are more expensive? Link to comment Share on other sites More sharing options...
Russell griffiths Posted December 18, 2018 Share Posted December 18, 2018 Just now, scottishjohn said: whats the attraction of them if they are more expensive? For me it’s the fact they are straight and true in the longer lengths, they also stay straight once fixed i have been looking at 225x48 in 4.8 m lengths and although they look very nice the thought of twisting and getting ceiling cracks is something I want to avoid Link to comment Share on other sites More sharing options...
scottishjohn Posted December 18, 2018 Share Posted December 18, 2018 (edited) 1 minute ago, Russell griffiths said: For me it’s the fact they are straight and true in the longer lengths, they also stay straight once fixed i have been looking at 225x48 in 4.8 m lengths and although they look very nice the thought of twisting and getting ceiling cracks is something I want to avoid you mean you do not have to fit "dwangs" as they call them up here ,or noggins as they say in england Edited December 18, 2018 by scottishjohn Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 18, 2018 Share Posted December 18, 2018 4 minutes ago, scottishjohn said: you mean you do not have to fit "dwangs" as they call them up here ,or noggins as they say in england That’s racist We call them noggins too boyo. Link to comment Share on other sites More sharing options...
scottishjohn Posted December 18, 2018 Share Posted December 18, 2018 1 minute ago, Nickfromwales said: That’s racist We call them noggins too boyo. and thats sexist --i could be LGBT LOL Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 18, 2018 Share Posted December 18, 2018 That’s a mouthful in more than one way ? Link to comment Share on other sites More sharing options...
scottishjohn Posted December 18, 2018 Share Posted December 18, 2018 17 minutes ago, scottishjohn said: you mean you do not have to fit "dwangs" as they call them up here ,or noggins as they say in england 19 minutes ago, Russell griffiths said: For me it’s the fact they are straight and true in the longer lengths, they also stay straight once fixed i have been looking at 225x48 in 4.8 m lengths and although they look very nice the thought of twisting and getting ceiling cracks is something I want to avoid I would have thought if you are not too stingy with the noggins and board the floor at same time then there is little chance of them getting out of shape Link to comment Share on other sites More sharing options...
willbish Posted December 18, 2018 Author Share Posted December 18, 2018 1 hour ago, Nickfromwales said: Anything in here? Nada, will bung them an email tomorrow. 1 hour ago, MikeSharp01 said: Not sure if there is a standard detail for this but if there is it will require you to block the end of the joist and take the main load underneath the bottom flange. Yep that's what I'm imagining. I would also think the top flange would need supporting to prevent any rotation 1 hour ago, Russell griffiths said: I’m thinking that the junction of the two timbers is sitting on top of a wall plate fixed down to your wall The wall plate is lower. The rafter sits on the wall plate in a traditional way. 1 hour ago, Russell griffiths said: Has this not been covered by the roof designer ? The SE has said select joists from a standard span table. They are not part of the roof structure just ceiling joists. But the span is 6750 so solid timber isnt really an option. Most joists will have a stud wall or two to bear on but as these aren't structural I don't want to rely on them (might change layout one day). Also its only an attic with low loading. It doesn't need to be future proofed for a loft conversion; ridge height is too low, oh and the bats have priority! Just exploring options really and thought Id see if JJI was a possibility Link to comment Share on other sites More sharing options...
PeterW Posted December 18, 2018 Share Posted December 18, 2018 That’s a lovely shape and could be triangulated simply by a truss manufacturer to make it into a single span truss. You would only then need wall plate detail. Link to comment Share on other sites More sharing options...
willbish Posted December 18, 2018 Author Share Posted December 18, 2018 6 minutes ago, PeterW said: That’s a lovely shape and could be triangulated simply by a truss manufacturer to make it into a single span truss. You would only then need wall plate detail. Very true but Mr Ecologist has specified 'open loft space' cant be crowding the bat roost with trusses. Even an attic truss wouldn't satisfy. Lord have mercy! Link to comment Share on other sites More sharing options...
Russell griffiths Posted December 19, 2018 Share Posted December 19, 2018 I did a roof like that years ago, but with solid timber so I think I would treat the I joists like solid timber install blocking to both sides of the i joist then install those funny washers with the spikes on between the solid timber and i joist and bolt together cant remember what the washers are called, but they are meant to stop rotating between the timber. I cannot see the difference between an antic truss and what you have drawn up. Link to comment Share on other sites More sharing options...
Ed Davies Posted December 19, 2018 Share Posted December 19, 2018 1 hour ago, Russell griffiths said: those funny washers with the spikes on Prosaically, they're just called timber connectors: https://shop4fasteners.co.uk/fasteners/washers/timber-connectors.html Link to comment Share on other sites More sharing options...
Russell griffiths Posted December 19, 2018 Share Posted December 19, 2018 53 minutes ago, Ed Davies said: Prosaically, they're just called timber connectors: https://shop4fasteners.co.uk/fasteners/washers/timber-connectors.html That’s the ones. Link to comment Share on other sites More sharing options...
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