Membrane at ridge, Gap or lap ?

[chriz1]

what do you suggest I do woth the roof membrane at the ridge? I'm fixing a dry ridge system and see conflicting comments saying to leave a gap at ridge of 10mm plus and others say to lap the membrane over the rdige from each side. I know that lapping it means better to protect from water ingress. But the gap helps vent the roof ? 

 

 

[CC45]

the roofers I used just lapped it over and then cut a slit with a knife.  You can feel the breeze from inside.

 

 

[nod]

I lapped ours over 

BC said I could cut a slit later

If need be 

Onsite they are pretty keen to leave a minimum 25 mil gap

[chriz1]

Thanks guys 

[Temp]

If it's a vapour permeable membrane then there is no need for a 50mm ventilated void below it - so no need for a vent gap.

 

If it's a traditional non permeable membrane it will need the ventilated void and gap.

 

Although if your loft insulation is on the floor of the loft you only need vents at the eaves.

 

Edited September 10, 2020 by Temp