What size timbers for rafters?

[MikeGrahamT21]

Hi,

 

Small lean to roof, 2.4m projection with a 22.5 degree angle with 2 roof lights in and concrete tiles, what size timbers are required these days?

 

I'm thinking either 47 x 175 or 47 x 200 and doubled up around the roof lights? Just in middle of doing my plans for building control.

 

Regards

Mike

[PeterW]

150x47 C24 at 600 centres is fine. 
 

Insulation will be your biggest issue though - you may have to go up to 200x47 for the depth required unless you use PIR between and below the rafters. 

[MikeGrahamT21]

Yeah was thinking to use some insulation below the rafters, as it’ll cut down thermal bridging too.

 

ill do some calcs for the insulation and see what works best.

 

thanks for the info, I’ll get it on the plans ??