Lapping Joists into beams

[penrymmj]

I am currently planning an extension to my house. I have to support some of the floor joists with a beam but, for continuity of the ceiling, I would like to lap the joists into the beam. Is there a limit as to the width of beam I need to cut the joists into?

The longest joist span is 4.5m.

Also, do I need two layers of plasterboard over the ceiling for fire protection, or will one surfice.

Thanks in advance

Pen

 

[Guy7469]

Hi

Not sure about the joists.
But the plasterboard can be two layers of normal board or one layer of pink fire protected board, which I think is 15mm.
I assume you are doing this because it is a garage below a habitable room, thus slowing fire spread from a vehicle etc.
If not you should only need one layer of normal board.

Cheers
Guy

 

[^woody^]

If the beam is enclosed within the floor void, then it need no additional protection.

The joists can slot into the web of a standard beam (ie Universal Beam, or UB). But you should fit noggins or strutting at this end to prevent them twisting in the web.

But it is technically not the best way, as the load from the floor should be on top of the beam not in the web, and if that long joist shrinks, then the bearing could be less than 50mm

 

[noseall]

and if that long joist shrinks, then the bearing could be less than 50mm

wood shrinkage along the grain is minimal.


even in ancient timber