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Hi all,
I am looking for advice on how to fix new 8x2 joists to existing 4x2 rafters. This is a loft conversion and the structural engineer has told me to use 2 x 10mm bolts to fix the new joists to the existing rafters. The existing 4x2 rafter spans have been calculated as ok by the SE. There will also be a new Ashlar wall fitted all the way round the outside (1m high)
On his drawing he has said the new joists need to be 400mm centres and where double or triple joists are needed they need to be bolted together with m8 bolts at 600mm centres. There is to be 21 x single joists, 1 x double and 2 x triples (triples are where the end ashlar walls sit and support post at each end for new ridge beam)
The new 8x2's will be packed off the inside wall plates and 2 x internal supporting wall plates using 18mm ply so they don't touch the existing plasterboard.
The new joists will go in between the existing 4 x 2 joists it has to be done like this for 2 reasons one is there is only a 4" gap above the outside wall plates and tiles and the other reason is to obtain as must standing height as possible.
I am going to get these new joists delivered in 7.2m lengths and get a scaffold put up along the side of the property so we can remove a few rows of tiles and slide them in in whole lengths rather than join them (only 350mm gap between existing joists and some of the new ones are triple joists)
It is not possible to simply bolt them to the existing rafters using 2 x 10mm bolts as of the SE's spec due to the existing joists being in the way i.e there is an existing 4x2 currently nailed to one side of the rafter of which is overlapped/joined in the centre of the span then nailed to the other side of the rafter of the opposite end of the span..
I told the SE about this predicament last week and asked if we can add more timber to form packers off the existing rafters with longer bolts but he said he would prefer we didn't due to possible shearing force on the bolts...even if we were to use packers the triples would need 300mm bolts! (150mm for the 3 8x2's - 2" packer - existing rafter)
I have a carpenter friend helping me but rather than go by what he says and possibly get it wrong of which might result in the building inspector telling us to redo it id like any advice you can on this please...
Any ideas appreciated (this wont be an uncommon problem to people doing roof conversions within 50 or so year old bungalows...)
I am looking for advice on how to fix new 8x2 joists to existing 4x2 rafters. This is a loft conversion and the structural engineer has told me to use 2 x 10mm bolts to fix the new joists to the existing rafters. The existing 4x2 rafter spans have been calculated as ok by the SE. There will also be a new Ashlar wall fitted all the way round the outside (1m high)
On his drawing he has said the new joists need to be 400mm centres and where double or triple joists are needed they need to be bolted together with m8 bolts at 600mm centres. There is to be 21 x single joists, 1 x double and 2 x triples (triples are where the end ashlar walls sit and support post at each end for new ridge beam)
The new 8x2's will be packed off the inside wall plates and 2 x internal supporting wall plates using 18mm ply so they don't touch the existing plasterboard.
The new joists will go in between the existing 4 x 2 joists it has to be done like this for 2 reasons one is there is only a 4" gap above the outside wall plates and tiles and the other reason is to obtain as must standing height as possible.
I am going to get these new joists delivered in 7.2m lengths and get a scaffold put up along the side of the property so we can remove a few rows of tiles and slide them in in whole lengths rather than join them (only 350mm gap between existing joists and some of the new ones are triple joists)
It is not possible to simply bolt them to the existing rafters using 2 x 10mm bolts as of the SE's spec due to the existing joists being in the way i.e there is an existing 4x2 currently nailed to one side of the rafter of which is overlapped/joined in the centre of the span then nailed to the other side of the rafter of the opposite end of the span..
I told the SE about this predicament last week and asked if we can add more timber to form packers off the existing rafters with longer bolts but he said he would prefer we didn't due to possible shearing force on the bolts...even if we were to use packers the triples would need 300mm bolts! (150mm for the 3 8x2's - 2" packer - existing rafter)
I have a carpenter friend helping me but rather than go by what he says and possibly get it wrong of which might result in the building inspector telling us to redo it id like any advice you can on this please...
Any ideas appreciated (this wont be an uncommon problem to people doing roof conversions within 50 or so year old bungalows...)
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