Fixing Centers for Sister Joists.

[Useroftheforce]

I am sure there is a BS table for this operation I need to find - but I can't find it...

I have a 3.7m span floor at 320mm centers, spanned with 50 X 175 timber. It's already over engineered.

I just need to level the thing out since it's crowned as the walls dropped over the years and the middle crowned round a supporting post.

I wonder what size sisters I should use?? The thought I have is that the new joists will sit about 1/12" above the old and need to overlap enough to join sensibly... So I thought 47 X 150 mm ?

Next part is I am going to use M12 bolts and toothed timber connectors. What sort of fixing pattern is appropriate? All in the center - or staggered? What centers?

Thanks.

 

[Useroftheforce]

For anyone else searching this post - if your not adding sisters for structural strength reasons (as I am not doing) - then the thing you need are "Timber Drive Screws" I used 4" screws at 600mm centres. Any old timber with a reasonable overlap is sufficient. I used 150 X 47.

As advised by a structural engineer I am using for consultation on this project.