Cavity Tray at roof abutment

[MortarThePoint]

I find that often when you are asking merchants about a product and you have to explain what it is, it means you may be trying to do something odd. Neither SIG nor Jewson seem to carry stepped cavity trays which I find strange as don't they get used a lot?

 

We've got various roof abutments that as far as I understand need these:

1. single storey side room that meets main house
2. hipped roof above a bay window
3. porch roof between two returns
4. hipped veranda roof

 

The architect has drawn them on all of these (example below), but I was wondering if they are actually needed for [3] and [4]. The cavity trays make sense to me when the wall below the roof is going to be internal and therefore you can't have weeps lower down. The porch and veranda are open to the outside world below the roof so the cavity trays seem pointless.

 

[MortarThePoint]

I'm tempted to go for these which look good. Has anyone used them or have anything to suggest?

 

http://www.glidevale.com/uploads/a241ee6cbc0b69457c89339f2886b778.pdf

 

[Mr Punter]

I think the bricklayer can make these from DPC but better just to buy the pre-formed ones.

 

They are good if there is a decent area of exposed brickwork above, but the building inspector may want them in any case.