Bird's mouth - badly cut

Joe Shmoe · 31 Oct 2018

I've cut some rafters for my new build, and I've messed up the angle of the bird's mouth on several of them somehow.

Instead of sitting flush on the wall plate, it's 5mm high on one side of the cut , so only the deepest part of the birds mouth makes contact the wall plate, instead of the entire cut sitting flush on it(hope this makes sense).

Anyway, I don't want to have to buy new timber if possible as its 6" treated c24, so costly mistake....

Can I fill the gap with something (do I even need to?) or are they a lost cause now and replace the bad ones.

topchippyles · 31 Oct 2018

Can yo take a photo,How deep is the birdsmouth cut as you may be able to go a little bit deeper and re cut them,Golden rule is max a third but you could go 10mm more on a 6 inch rafter.

MikeG. · 31 Oct 2018

Your new build what? If this is a house and you've got a building inspector you have to work to a different standard than if this is a garden shed.

Joe Shmoe · 1 Nov 2018

Hi Mike. Just a garden workshop for my guitars etc, so no building inspector.

Under normal circumstances I wouldn't be too concerned but it's a 4.2m wide span, and will be carrying the weight of marley tiles and also 1 sheet of 18mm OSB and 2 layers of 15mm plasterboard (for sound isolation).

I *was* intending of raising the accompanying joists up 200mm (which is less than a 1/3 of the height of the rafter, but unsure at this stage. Just concerned about the weight. I've installed all the rafters but still deciding about the joists and the required size.

MikeG. · 1 Nov 2018

Are they nailed or screwed in place? If they are screwed, then you can unscrew one at a time and run a saw through the joint a couple of times before rescrewing and moving on to the next one. If it is only a few, but the gap is large, you could unfasten them (again, leaving in situ), slip a scrap of ply in the gap, and again run a saw through the joint a few times until the rafter is back in line. As I've been told many a time, it's a roof, not a piece of furniture. If it moves 3 or 4mm, so what. There is absolutely no chance that the roof isn't strong enough to take the load simply because of the quality of the joins.