Hi,

I want to reinforce an existing timber beam by sistering it to another piece of timber. Having searched the forum, and elsewhere online, i still have a few questions.

First, I can only access the existing beam from one side. So:

1. Is it OK to reinforce the existing beam from just one side?

2. Assuming i reinforce using timber, can it be fixed with coach screws, with timber connectors between the two beams?

3. If so, how far should the screws penetrate into the existing joist?

4. I seem to recall that the screws shouldn't be in the middle of the beam, but closer to one edge. The top or the bottom edge?

More generally:

5. How important is it to have the sistered timber also bear on the wall? Opinion on this seems to differ. It might be possible to do, but will be much more work that having the new timber simply stop flush with the wall.....

For background, based on timber-span loads, this is probably not strictly necessary, but i am keen on a "belt-and-braces" approach. Specifically, the current joist measures 65mm x 95mm and spans a distance of almost 4 metres. Crucially, along its length the joist is supported by four vertical beams, each measuring roughly 100mm square and resting on the solid floor below. Bearing onto the main joist are the first-floor floor-bearing joists, 450 mm apart.

I want to remove one of the vertical timbers that provide intermediate support, creating an unsupported span of 1650mm.

Apologies for writing so much - feedback very welcome!!!

Crawf

Don't forget to glue the sister to the original joist. Nails are better than screws if you have room to use a nail gun - if you do use screws, make sure they are rated for shear. Coach screws are probably OK. Even if the sister doesn't bear on a support, it will still stiffen the joist.

Your original joist sounds way too small - see http://www.johnbridge.com/vbulletin/deflecto.pl and put in some figures.

Paul in Montreal.

Don't think screws would pull the two together with timber connectors in between. Would need a 12mm bolt to pull them up. If you only have access from one side the reinforcement glued onto the side sound good but I would use screws to pull it in and trust in the glue for the shear strength. Hard to get nails to pull faces tight together IMO especially when working horizontally.

I don't think in this instance nails are the best choice. If the underside is plaster boarded you'll loosen it with any hammering. Nail guns are kinder in this respect but you'll need a framing nailer.
As Beau said you won't be able to get a tight surface fit between the two surfaces if there is even an inkling of skew or twist in the timber, hence, I suspect, PIMs suggestion of PU?? adhesive. Ideally I'd go for hex head coach bolts but because access is limited it's ruled out.

My architect asked me to get my SEs sign-off on every place where we were fixing structural timber together. I don't know whether that was a requirement or just an abundance of caution.