- Joined
- 10 Oct 2008
- Messages
- 43
- Reaction score
- 0
- Country
Hi,
I have a bungalow that uses trusses that have a 6m span which are spaced apart by 0.6m for a total length of about 12m (about 20 trusses).
Each truss uses 4 webs/posts in a 'w' formation. Forgive me if this is not the correct terminology. The trusses are made from 72mm x 36mm timber. The roof pitch is 5.6/12 (i.e. it rises 1.4m for a 3m run) so the loft area is very tight especially after the loft insulation has been added.
I have done some research and found that new builds make an allowance of 25kg/square meter and for a person that is about 90kg to move around the loft space. Correct me if I am wrong here. My bungalow is now about 25 years old.
Currently the ceiling plasterboard has been removed and prior to starting the work described below the ceiling had some sag in it but unfortunately, I did not measure it. I did, however, remove a water tank some years ago that caused the plasterboards below it to sag which could be easily seen. In fact when the tank was removed the plasterboard cracked where the water tank was placed.
What I have done so far is as follows:
For each of the centre sections of the joists I have added one 88mm high timber on top of another 88mm high timber, raising joist height to about 250mm. On top of this I have laid centrally, 0.6m wide OSB (18mm thick) for the length (i.e. over 20 built up joists). In addition there are two 2.4m lengths where two OSB boards have been added side-by-side to provide two 1.2m x 2.4m storage platforms.
The joists generally sag throughout by about 10 or 11mm at the midpoint of the span in the worst case. Typically it is about 5 or 6mm. I guess the sag can only get worse when the plasterboard is refitted. I am pretty certain that my boarding has added to this.
In retrospect I should have cross battened the joists instead of building up the joists as I did which would have distributed the load better. I calculate that the weight of doing the cross battening would be about the same as it is now if I use three runs along the full 12m length of the bungalow, so presumably the weight would be about the same which makes me wonder why there is such sagging.
Perhaps I need to re-enforce the existing trusses somehow, either by adding drops from the apex or running additional joists from wall plate to wall plate and joining in the middle. I am thinking of removing the boarding work and rethinking the problem.
Any help would be appreciated.
Regards
FarmerJo
I have a bungalow that uses trusses that have a 6m span which are spaced apart by 0.6m for a total length of about 12m (about 20 trusses).
Each truss uses 4 webs/posts in a 'w' formation. Forgive me if this is not the correct terminology. The trusses are made from 72mm x 36mm timber. The roof pitch is 5.6/12 (i.e. it rises 1.4m for a 3m run) so the loft area is very tight especially after the loft insulation has been added.
I have done some research and found that new builds make an allowance of 25kg/square meter and for a person that is about 90kg to move around the loft space. Correct me if I am wrong here. My bungalow is now about 25 years old.
Currently the ceiling plasterboard has been removed and prior to starting the work described below the ceiling had some sag in it but unfortunately, I did not measure it. I did, however, remove a water tank some years ago that caused the plasterboards below it to sag which could be easily seen. In fact when the tank was removed the plasterboard cracked where the water tank was placed.
What I have done so far is as follows:
For each of the centre sections of the joists I have added one 88mm high timber on top of another 88mm high timber, raising joist height to about 250mm. On top of this I have laid centrally, 0.6m wide OSB (18mm thick) for the length (i.e. over 20 built up joists). In addition there are two 2.4m lengths where two OSB boards have been added side-by-side to provide two 1.2m x 2.4m storage platforms.
The joists generally sag throughout by about 10 or 11mm at the midpoint of the span in the worst case. Typically it is about 5 or 6mm. I guess the sag can only get worse when the plasterboard is refitted. I am pretty certain that my boarding has added to this.
In retrospect I should have cross battened the joists instead of building up the joists as I did which would have distributed the load better. I calculate that the weight of doing the cross battening would be about the same as it is now if I use three runs along the full 12m length of the bungalow, so presumably the weight would be about the same which makes me wonder why there is such sagging.
Perhaps I need to re-enforce the existing trusses somehow, either by adding drops from the apex or running additional joists from wall plate to wall plate and joining in the middle. I am thinking of removing the boarding work and rethinking the problem.
Any help would be appreciated.
Regards
FarmerJo
