roof ventilation using breathable membranes?

[browfish]

I have just constructed a new roof on my semidetached to incorporate a new extension. I have felted it, battoned it and started tiling the.
My question is, using breathable membranes, is there any ventilation required, eg at the ridge or hips and in the soffit boards?
thanks
james

 

[Mick Leek]

Building regs cover this but NO there is no need for any additional ventilation.

 

[BOB NUTS]

lots of breathable membranes available but not many of them are the equivalent of traditional ventilation.

So you may need to use normal soffit vents to satisfy building regs

 

[browfish]

THanks
Only in the redland catalogue they seem to suggest using ventilated ridges. I guess that is for the old type nonpermeable membranes.

I used the proctor group's roofshield by the way

 

[Mick Leek]

I'm in the same boat having recently built an extension. The BCO guy asked if we were using breatheble felt and i said i hadnt decided. All he said was "well if you dont then i want vents in the soffits, if you do use it there will be no need for any additional ventilation."

Didnt you ask your BCO guy? Mine has been very helpful and offten pops round just to see how im doing

 

[browfish]

Does that mean the felt can be wrapped over the top of the ridge? I have put a seperate sheet over that overlaps both sides at the moment just to weatherproof it really and planned on cutting a strip out if needs be. I shall just lay the ridge tiles over the top then if this is ok

 

[noseall]

i use breathable membrane all the time, doesn't rip,saves on vents etc. but there is a downside, b.c. reckon if your extension roof is independent, ok to use it, but if you cut into an existing roof that hasn't got breathable felt, then it invalidates the venting properties. tyvek argue this vehemently.

 

[browfish]

That should be ok then as i have completely ripped the old roof off and replaced with the new one that covers the extension. I thought you were going to say something like it wouldnt work on a semi detached for a minute

 

[bren47]

Hi. I'm no expert on these matters but I had a new roof using a breathable membrane and found that even though vents were not required in extreme cold spells I did get some condensation on one elevation. The eaves were closed and made worse by being occluded by badly installed insulation and old birds nests. I rectified these matters and fitted soffit vents which seem to have cured the problem.
I find it difficult to believe that breathable membranes allow sufficient movement of air to completely eradicate air bourne moisture. They may allow drying if condensation does settle but I wouldn't have thought that satisfactory.
I'm sceptical (but by no means an expert!)

 

[constructionbuyer]

As a buyer for a large housebuilder, we are considering moving away from breathable membranes and reverting to standard felt with vented soffitt as there is no evidence that breathable membranes are actually any better.

 

[Owen74]

We have a small extension roof that joins into an older roof. The older one is felt, the new is supposedly breathable membrane. I'm feeling somehow the mix of both is causing problems with ventilation. Condensation is a major problem on plastic valleys where the two roofs join.

 

[noseall]

We have a small extension roof that joins into an older roof. The older one is felt, the new is supposedly breathable membrane. I'm feeling somehow the mix of both is causing problems with ventilation. Condensation is a major problem on plastic valleys where the two roofs join.

We always supplement BM with OFV's (over-fascia vents).

 

[datarebal]

reverting to standard felt

Bat friendly too

 

[Owen74]

I have just constructed a new roof on my semidetached to incorporate a new extension. I have felted it, battoned it and started tiling the.
My question is, using breathable membranes, is there any ventilation required, eg at the ridge or hips and in the soffit boards?
thanks
james

For me the answer would be yes. I have recently had an extension built on my house, with membrane. No vents. Lots of mould and condensation had built up within 1 year.