Ridge beam to rafters connection

SamDIYnot · 26 Aug 2015

Hi, new to here and currrently doing my biggest diy job to date. It is a single storey extension with a 25 degree pitched roof to have a vaulted ceiling. Currently just finished walls.

Our drawings show the top of the rafters resting against the ridge beam as normal. But in my head the pitch makes the angle small at the top and feel cutting a birds mouth and having the rafters sit on top of the beam. Is this a goog idea or bad?

freddiemercurystwin · 26 Aug 2015

Show us the drawing.

freddiemercurystwin · 26 Aug 2015

And re-post in Building.

< mod note: >
No.
I've moved to roofing.

r1flyguy · 1 Sep 2015

Can you use a greater depth rafter to prevent weakening at the cut out

^woody^ · 1 Sep 2015

One's a ridge board, the other is a ridge beam, and they have different functions.

A ridge beam is structural and needs to be calculated.

r1flyguy · 1 Sep 2015

I'd agree we need drawings!

I assumed that the single story extension would be a face plate fixing to the existing property wall with the rafters connected by hangers or similar and the only cuts would be to the new wall of the extension on top of the wall plate.
Thus not sure why the OP has a ridge beam issue if the fixing and calcs are correct.

Has the OP calculated the pitch? Simple bit of trig will give you the answer you need

noseall · 1 Sep 2015

r1flyguy said:
Can you use a greater depth rafter to prevent weakening at the cut out

How does that work?
Everything to do with a cut rafter roof is set out with the TOP of the rafter in mind. Replacing the rafters with deeper ones means that you will end up taking even more material out.

It would make more sense to lower the ridge beam/wall plate/purlin etc.

^woody^ · 1 Sep 2015

It seems that it is a mono pitch roof and the OP has a pole/pitching plate and not a ridge beam or board.

So yes, notch the rafters and fix them on top of the plate.

r1flyguy · 2 Sep 2015

noseall said:
r1flyguy said:

Can you use a greater depth rafter to prevent weakening at the cut out

Click to expand...

How does that work?
Everything to do with a cut rafter roof is set out with the TOP of the rafter in mind. Replacing the rafters with deeper ones means that you will end up taking even more material out.

It would make more sense to lower the ridge beam/wall plate/purlin etc.

Not wishing to detract from the initial post & the fact I'm a relative newbie & NOT a professional trades person in these matters...
My extension had an issue with the trusses having to be made to the same pitch as the existing house but due to local regs, there was a step back from the front elevation.
To overcome this, taller rafters were used to compensate for the birds mouth cutouts to the wall plate location otherwise there would not have been much wood left and be a weak point.

If you want exact details I can provide them if you wish but this may not be what you were trying to get at which I appreciate too.

r1flyguy · 2 Sep 2015

As you can see from this photo, the trusses are quite deep

freddiemercurystwin · 2 Sep 2015

This thread ain't going anywhere unless the OP bothers to reply.

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Ridge beam to rafters connection

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