Recommendations for breathable roofing membrane?

[Crofter]

Wondering if anybody had any preferences or advice on choosing breathable roofing membrane? To be laid directly atop OSB sarking boards, followed by battens, counterbattens, and box profile steel. I plan to lay it vertically so that every joint is battened- this will also be much easier for me as I am likely to be working on my own.

 

Anyway, there seems to be a fair bit of choice available, and the stuff is variously referred to as breather, felt, membrane, etc, which complicates the search somewhat.

Finally, is there any advantage to the shiny 'thermo' versions? How would this affect U-values? I presume they don't have any actual insulating properties but is the emissivity different?

 

[ProDave]

We used Protect VP400.  It was chosen by our builder as in his opinion it was one that would stand up to being exposed to the weather for a long time before being covered. It's a non tenting breathable membrane laid in our case onto the wood fibre board.  Non tenting means it can be laid direct on the board and water won't come through (as in you touch the inside of a tent and it starts to leak)

[Crofter]

Thanks Dave, I'll look it up.

[Crofter]

Blimey, how many different types of roofing membrane does the world need! Certainly plenty of competition in the marketplace. Might go with Cromar Vent 3 Pro as it looks nearly as good as the VP400 but significantly cheaper, and has a 4 month exposure rating which is as high as I can find from anybody.

 

On a related note, it seems that I will need to fit eaves guards- guessing that these go between the membrane and the battens?

[ProDave]

7 hours ago, Crofter said:

On a related note, it seems that I will need to fit eaves guards- guessing that these go between the membrane and the battens?

Do you mean this?:

What we have is the fascia board set at a height so that allowing for the ventilator strip, it is at the right height for the bottom tile to rest onto.

So that usually means the top of the fascia board is higher than the sarking board would be if it carried on down.

Some roofers will cut the sarking board just below the bottom batten and have the bottom section of sarking angled onto the top of the fascia.

What I did was bought plastic eaves boards (not the proper name but I don't know what the proper name is).They are as cheap as chips from TP something like £3 per 1.5 metre length.

So the plastic eaves board fixes to the top of the fascia, and the plastic extends up the roof by 8" or so giving the "kick up". the membrane lays down over the top of this. Then the vent strip goes on and the edge of the membrane then gets trimmed off with a sharp knife leaving the edge of the membrane securely fixed and the plastic eaves board directs any water out into the gutter.

[Crofter]

How do you secure the membrane over the plastic guard- just nail through both layers?

I think the purpose of the eaves guard is to keep the UV off the membrane at the very edge, where it is exposed.

I'm planning a rather simpler design where the sarking board angle remains constant and overhangs the edge of the fascia, so the plastic strips would just be to add a UV layer. Would also help hide the cut edge of the OSB.

Haven't considered how to deal with the edge of the box profile- I know you were asking about that very issue so I'll dig up tat thread again...

[ProDave]

So you are proposing putting the plastic strip on top of the membrane. So any water running down the membrane would run UNDER the plastic strip, and drip off in an uncontrolled fashion and may or may not drip into the gutter, it may just run onto the cut edge of the OSB?

By putting rhe plastic under the memnbrane, any water running down the membrane passes through the slot vents over the formed edge of the plastic into the gutter, keeopnf the fascia (and any exposed cut edges of sarking) nice and dry.

The edge of the membrane is sandwiched in between the plastic strip and the plastic slot vents, and secured by the nails holding the slot vents that go through all 3 into the top of the fascia board.

I have detailed a similar thing for my box profile roofing which I will take a picture of and post it here later.

[ProDave]

I have just updated my other roofing thread with this picture.

This is the detail I ended up with for my sun room roof. Almost identical except it is set slightly lower, so the roof profile (as mocked up here by the spirit level) does not quite touch the ventilator strips.  the filler profile for the box section roofing will fix (glued?) to the top of the ventilator strips.

[Crofter]

Thanks, it's all becoming a bit clearer now.

Is this is sort of thing I need? https://www.roofingsuperstore.co.uk/product/rigid-eaves-protector-15m-packs-of-10.html

And yes I guess the membrane has to go on top of it!

[PeterW]

Yep that's the ones..!

[ProDave]

Yes those are the things. I am sure they are even cheaper than that at TP, I was surprised just how cheap they were (though it might be a long drive to TP from where you are)

[DavidFrancis]

Any other suggestions for a roofing membrane?

 

We're about to have our slates relaid.  The roofer normally uses Easy-Trim's Maxi membrane.  Having compared he BBA certificates of a few I'm thinking of asking him to use the Vent 3 Pro as it's stronger, albeit £10/roll more expensive.

 

We live in south Lancashire so our wind exposure is not high.  Easy-Trim's factory is in Lancashire whereas Cromar are in Yorkshire, which might affect some Lancastrians' decisions perhaps!

 

Thanks in advance for any comments

[PeterW]

I used MKMs own brand which is made by Cromar. No complaints either from me or the roofers 

[DavidFrancis]

Thanks Peter.

[DavidFrancis]

An oberservation on membranes now our re-roof is mostly done.  I was suprised by the amount of wear the membrane got from boots whilst the roof was going on.  Our roofers walk up and down the roof along the rafter lines as I imagine most (all?) roofers do and their boots scuffed up the membrane to a fair degree.  As we're having a re-roof there were quite a few nails left in the rafters after the old battens were removed.  These were then just hammered into the rafters and if any of these had been left with a bent head I imagine there's some probability the membrane could get torn.

 

So I reckon its worth going for a pretty good quality membrane to ensure it's all in one piece by the time the tiles/slates are on.

 

One caveat: we have a double roof and our roofers got to the inside (valley) pitches from the outside pitches, so maybe our membrane got more wear than the average membrane.