Flat roof

[^woody^]

If you taper 2" or notch 2" off a 9" joist, it performs as a 7" joist, so you need to confirm that it will still be suitable for the span.

Bear in mind that the 2.5m limit is eaves height, not roof height.

 

[Selfbuild2345]

Looking at span table my 9 x 2 will be able to span to nearly 5m so 7 x 2 is really what i could of got away. I messed up basically forgetting about the slope on roof.

 

[tony1851]

Screw a temporary batten to the side of each joist and using the c/saw, cut down to 200mm at the top and 150 at the bottom. If they are C24s at 400 centres, they will be fine.

 

[tony1851]

If you taper 2" or notch 2" off a 9" joist, it performs as a 7" joist,

Really!?

 

[Selfbuild2345]

What you mean 200mm from top and 150 from bottom?

 

[Notch7]

Really!?

I have quite often designed glulam beams with cut outs at the end - say to go in steels etc.

The structural Engineer always passed them - he did tell me once how big a chop out is possible - it's quite a lot, something like a 1/3 (can't remember the length) before it lowers the beam stiffness.

 

[tony1851]

What you mean 200mm from top and 150 from bottom?

 

[^woody^]

Really!?

True story bro.

 

[tony1851]

True story bro.

So you're saying that if you have a 9" deep joist and notch it 2" at the end, you've turned it into a 7" deep joist??? Hmmm...

 

[JohnD]

I have quite often designed glulam beams with cut outs at the end - say to go in steels etc.

The structural Engineer always passed them - he did tell me once how big a chop out is possible - it's quite a lot, something like a 1/3 (can't remember the length) before it lowers the beam stiffness.

Cut outs from the middle?

Or cutting the top or bottom edge?

 

[^woody^]

So you're saying that if you have a 9" deep joist and notch it 2" at the end, you've turned it into a 7" deep joist??? Hmmm...

Did I say that?

A notch is a notch, there is guidance for notching.

Reducing the depth continuously via a taper is completely different.

 

[tony1851]

Silly me - my most sincere and humble apologies - I mistakenly thought you said:

"If you taper 2" or notch 2" off a 9" joist, it performs as a 7" joist"

 

[Notch7]

Cut outs from the middle?

Or cutting the top or bottom edge?

Top or bottom edge.

Quite often I designed orangeries with glulam beams.

Typically the beam would be 90 x 405 and cut down to 300mm at each end -sometimes a metre long.

Basically the 300mm section was the flat roof perimeter and the 405mm was the lantern upstand.

 

[^woody^]

Silly me - my most sincere and humble apologies - I mistakenly thought you said:

"If you taper 2" or notch 2" off a 9" joist, it performs as a 7" joist"

Apology accepted.

Btw, it was notch who suggested notching the ends of the joists over the plate that's the notching I referred to.