Roof valley detail?

[I'm not a robot]

Hello, just wondering what the method is for forming a valley?
Looking on the web I see some have a long valley rafter with jack rafters butting to the sides of it and others have a layboard down one set of common rafters and jack rafters laid on top of the layboard.
Is there a specific reason for having either method?

Cheers

 

[catlad]

Laying the boards on the common rafters would be if you where doing an extension.

 

[kp00110]

Something also is that the layboard option also limits useable space in your loft as the commons prevent you getting any thing past to get access into the extension are beyond etc

 

[I'm not a robot]

Yes it's for an extension so a valley needs making up to join the new pitched roof to the existing pitched roof.
So do you strip the tiles off the existing roof to expose the rafters and fix a layboard onto them first and then fix the new jack rafters onto the layboard?

 

[kp00110]

Yes thats what I did with my extension. The layboard had to be quite wide to catch the cuts of the jack rafters

 

[I'm not a robot]

Okay great, so I don't need to fix a long valley rafter from the ridge to the wall plate then?
Do I need to fix a layboard onto the new jack rafters?

 

[kp00110]

 

[cdbe]

This is mine, someone advised that a nice scaffold board is good for it:

 

[noseall]

This is mine, someone advised that a nice scaffold board is good for it:

View attachment 284609

Im a huge fan of scaffold board lay boards. At 38mm they are the ideal thickness and are often very straight. We always buy brand new which always means splinters! That and the faff removing the end bands and plates.

 

[noseall]

Okay great, so I don't need to fix a long valley rafter from the ridge to the wall plate then?
Do I need to fix a layboard onto the new jack rafters?

It depends how the roof is constructed, but generally, no.

Your layboard has to be carefully positioned so that its outer edge forms the straight line onto which the peak of the jack compound cut sits. This is usually a juggling act using a long straight edge or builders lines. It's also a faff determining the acute top and bottom cuts to the layboards. We again use a straight edge and a bevel. You have to have the ridge board set up along with a pair of full rafters (or more depending on roof length) at the gable and work from there.