Two birdsmouth or One for lean to roof

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Nosey, whats the point in fitting a ridge board like that in photo 1.

Why the steel in photo 2. And why were you using eml in that blockwork?
Both are vaulted roofs using slightly differing ridge beams. One example is a steel beam with a wall plate fixed to the top the other is a pair of 8" x 2"'s bolted together but doing the same thing. The EML was an architect's' overzealous overkill addition as well as galv' strapping across the rafter tops.

Photo 3 is of those under sized steels again isn't it:eek:
Yes! (groan).
 
A lean to roof needs both ends of the rafter to be seated to prevent a vaulted roof from spreading.
Its just a sign of the times that these things don't matter anymore.
 
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A lean to roof needs both ends of the rafter to be seated to prevent a vaulted roof from spreading.
Eh? how can the roof spread if the rafter is against a wall and the bottom seat cut is fixed to a rigid wall plate?
A lean to roof behaves exactly like a (twin) vaulted roof because it has a brick wall preventing one end from allowing the rafter to rotate. The bottom seat and wall plate does the rest.

Woody for some bizarre reason has forgotten the existence and relevance of the top plumb cut and what it does on a standard roof. He's now going around properties in the UK warning those with a standard roof that their abutting rafter top plumb cuts require a seat.:rolleyes:
 
Nosall
A lean to roof behaves exactly like a (twin) vaulted roof because it has a brick wall preventing one end from allowing the rafter to rotate. The bottom seat and wall plate does the rest.

A lean to roof doesn't behave the same as a normal roof with plumb cuts because it has ceiling ties to resist them coming apart.
A lean roof doesn't have these so will want to slide with gravity.
Having seat cuts top and bottom will go along way to making sure that force is eliminated. ( its good building practice )
 
A lean roof doesn't have these so will want to slide with gravity.
Not if the wall plate is fixed and the wall is rigid. Besides that, there is also a pole plate below the rafter. There is no need for a top seat cut on a lean-to roof.
 
I guess I just like to construct strong roofs then.
Lol.

Are you suggesting that the pole plate bolts are more likely to fail and the roof push downward due to the absence of a top seat cut? I'm more inclined to believe a top seat cut actually weakens the rafter end rather than adds any strength to the roof.
 
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I don't like the idea of the fixings playing a large part of holding the roof up when its not necessary, also they are likely to fall on you head while you are constructing the roof.
Venting the roof will also be another problem without the seat cut.
 

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