Scottish roof (ply under tiles) in England...help please!

[Allthegearnoidea]

Evening all,

 

I would be grateful for a bit of help if anyone has any knowledge in this area!  The structural engineer has specified a 12mm plywood skin on our single storey rear extension with mono-pitch roof.  I'm planning to use BMI Redland Mini-mockbond tiles, as they're closest to the tiles on the main house and can handle the low pitch (17.5°).  

 

I'm at the point of building up the facia / soffit, but with the vertical battens necessary over the ply skin, I'm struggling to visualise the facia / guttering arrangement.  My CAD mockup shows the water is going to overshoot the gutter, but if I use a taller facia board I'll be blocking the breathable membrane, which needs to sit either on top of the ply or on top of the vertical battens (it will probably be Tyvek Supro if BC are happy with it, as the data sheet shows it's used for this sort of build up).

 

 

Any of you knowledgeable folk know what to do here?

[Allthegearnoidea]

Perhaps cut a proper tilting fillet and mount the gutter to that where it overlaps the vertical battens?

[Nickfromwales]

The tile course can be set back a little, and the ply + membrane ‘fly’ over and into the gutter. 30mm or so should suffice.

A vent strip makes things look nice and stops you seeing up the ventilation void. 

 

Rain only really tends to overshoot if it’s very heavy rainfall, otherwise it holds on to the surface of the tile and pretty much falls (near) straight down.

[saveasteading]

2 hours ago, Nickfromwales said:

Rain only really tends to overshoot if it’s very heavy

And the gutter will probably ( can be) be bigger than shown. That looks small and far too shallow..... gutters seldom go in level or to a steady fall, so any dip or rise severely reduces capacity. 

[Russell griffiths]

TBH that drawing is all a bit wrong  

delete out the two battens at the bottom they won’t be there

lift the facia up to 25mm below the bottom tile

add an over facia vent on top of the facia to make up the 25mm height. 

[ProDave]

44 minutes ago, Russell griffiths said:

lift the facia up to 25mm below the bottom tile

add an over facia vent on top of the facia to make up the 25mm height. 

And the membrane comes up over the fascia but under the fascia vent.  You either need a strip of OSB or a proper eaves tray to support the sloping bit of membrane so there is not a sag to fill up with water.

[Russell griffiths]

4 hours ago, ProDave said:

And the membrane comes up over the fascia but under the fascia vent.  You either need a strip of OSB or a proper eaves tray to support the sloping bit of membrane so there is not a sag to fill up with water.

Well yea, loads of bits I missed out, but it should get him going in the right direction.