Breathable membrane installation (Scotland)

[lc155]

Hi,

Got a dormer window in a bay shape that needs work done to the roof framing of it, as the flashing on the sides has failed over the years as well as the mortar that sealed between the slates at the peaks. Will involve ripping the slates off and repairing any sarking/framing that requires it along with replacing flashing. At the same time, I figured putting down a breather membrane would be a decent idea while I'm at it, as due to the roof age, it's just bare slate nailed into the sarking boards.

Question is, can I get away with installing the membrane straight onto the sarking boards? Was thinking of using Cromar Vent3 Pro (I'm in climate region 4 for wind uplift) but all the installation instructions I look at when it comes to membranes always seem to just talk about using battens on top like how they do in England.

So, can I just staple/nail (which is preferable?) the membrane directly to the sarking boards, tape the laps as what seems to be required for my region, and then just nail the slates on top? Is that sufficient or will wind uplift still be a problem there?

Thanks.

 

[robinbanks]

Difficulty you have doing that is you then need to walk on a "plastic" sheet (because you don't walk on the slates) that is stapled to a potentially smooth wood surface, many meters above the ground. When you step on an end, carrying 50kg of skates, and every staple rips out cartoon stylée and you're dumped off the side of the building you're injured or dead

I'd batten, and counterbatten, it for no other reason than to give myself something to walk on, while preserving the integrity of the felt.

If you're in a terrace with neighbours and hence cannot have a change in height, I'd consider either glueing it down (spray adhesive) or don't bother installing it ; it'll be full of holes by the end of the job, having been tromped all over, had slates rested/dropped/cut on it, and two nails per slate banged through it.

I see often people trotting out some "wisdom" that a membrane is needed to make a roof watertight; it ain't true - keeping water out is the slate's job