Flat roof - Can I cut roof timber to fit wall plate?

[BobTheBear]

Tomorrow I'm fitting lintels into my existing house outer and inner walls, ready to knock through into the extension I'm building.

My drawings recomend flat roof joists of 175mm x 63mm in size, but 63mm isnt a standard size not are 63mm joist hangers made (not jiffys). Therefore I'm going with 175mm x 75mm joists, which are actually cheaper as well.

Where the 219mm in hieght lintel is going, I'm going to use some 225mm joist hangers for the 175mm timbers, so that the bottom of the timber is just below the linter and the ceiling with hide the linter totally. These joist hangers will sit on the top of the lintel.

The rest of the extension roof timbers will need to sit on a timber wall plate fitted to the all of the house, but I cant get 175mm joist hangers for 75mm timbers.

So I was thinking can I cut the wall plate and roof timbers half through so the roof timber sits on the wall plate without using a joist hanger? Wont this decrease the strength of the roof joist though?

Your thoughts appreciated, thanks

 

[r896neo]

No you can not notch the joists as you are effectively reducing the timber size to whatever your notch is. If you cut a 75mm notch you may as well have used 100mm timbers.

175mmx75mm hangers are available you just need to look harder/ find a better merchant.

 

[BobTheBear]

OK thanks, I dd think that but thought I'd check

 

[chickenlips]

OK thanks, I dd think that but thought I'd check

Wait Im confused, if the roof timbers are sitting on a wallplate why do you need hangers ?

What hangers do you need ? for fixing into masonry or fixing into timber ?

For either scenario Simpsons Strong Tie will offer both..

 

[RonnyRaygun]

The rest of the extension roof timbers will need to sit on a timber wall plate fitted to the all of the house, but I cant get 175mm joist hangers for 75mm timbers.

So I was thinking can I cut the wall plate and roof timbers half through so the roof timber sits on the wall plate without using a joist hanger? Wont this decrease the strength of the roof joist though?

Your thoughts appreciated, thanks

As Chickenlips says, Simpson Strongtie do 175x75 hangers for masonry and timber fixing, but...

It may be possible to notch the joists to bear directly onto the wallplate. Joists are usually most highly stressed in bending, and either bending or deflection governs the design.
Shear stresses are usually so low that I don't even bother with the calc (unless there is a large point load near the end of the timber).
This means you can reduce the cross sectional area at the end by a certain amount and still be within the shear capacity of the member, but you'd need a calc to know how large the notch can be.

Better to get some hangers.

 

[noseall]

Where the 219mm in hieght lintel is going, I'm going to use some 225mm joist hangers for the 175mm timbers, so that the bottom of the timber is just below the linter and the ceiling with hide the linter totally. These joist hangers will sit on the top of the lintel.

I take this is not a concrete lintel?

Wait Im confused, if the roof timbers are sitting on a wallplate why do you need hangers ? ..

We are assuming this is a 'pole' plate i.e. a vertical plate fixed to the face of a wall.

 

[BobTheBear]

Yes not concrete, it is metal box section

By timbers sitting on a wall plate, apologies if I've confused anyone here. What I was trying to explain was the timber which is fixed to an existing wall, which the new extension roof timbers would fit on usually with joist hangers. Perhaps that timber isnt called a wall plate???

 

[noseall]

It is called a pole plate or sometimes referred to a pitching plate.