Waterproof membrane for shed roof

Lemo

I need to do some work on my shed roof which is tiled but with nothing underneath, meaning that it leaks. I want to put a waterproof layer beneath the tiles.

Felt is an option but the neighbours had an extension done a while ago and I noticed the builders used a thin membrane beneath the tiles which looked a lot easier to work with than felt.

I asked about this in a builders' providers but the guy didn't seem to sure what I was on about. He said they had a "breathable membrane" which was €160 a roll. Since he wasn't sure if it was waterproof and it was so expensive, I just left it.

Anyone know what it is I'm looking for or suggest an alternative?

Liam

PS I miss RooferPete at times like this :-)

Sonnenblumen

Felt is cheap and easy to install, wht you noticed in neighbour's sounds lkike a fleece, which has good thermal/insulation values.

There are different felt grades availble so be sure to ask for underlay more specifically for under tiles. A few tack nails and a good stanley knife should see you finished within 1 hour. Do not be too mean on your overlaps, 6" is better than 2".

Lemo

Thanks. Do I need to use adhesive on the overlaps? I would make the overlaps pretty generous anyway.

Sonnenblumen

A good overlap and use felt nails to fix. Good luck

Vexorg

Hi Lemo

I did a short roofing course in the Uk a couple of years ago. What you are looking for is a sarking felt. Sarking is just a generic term for the 2nd line of defense after your tiles. This can be anything from the old bitumen based felt to newer polycarbonate lightweight membrane to the more expensive breathable membrane. The breathable membrane allows moisture from the inside to escape (essentially water vapour) but remains water proof externally, keeps the rain out should your 1st line of defense be damaged. Felts were cheaper, but more difficult to work with, are heavy and I found in my inexperienced hands, could tear, meaning starting again. The lightweight polycarbonate was easier to handle and its was much lighter.

So if you have a leak now, you could try to locate this.

If you are going to remove all the existing tiles, you will need to remove the battens also, as you fix the felt/membrane to the rafters and the batten go over the felt. Starting at the bottom, (the gutter end) and working your way up the roof. The amount that the next layer overlaps depends on the pitch, the steeper the incline, the lower the requirement to overlap as the lower the likelihood of wind driving the rain up the gap. On the course we were told you cant go wrong if you alway use a 9 inch overlap or 225mm and is the requirement for a roof with a pitch of less the 22 degrees. Remember to fix a batten about 1 inch / 25 mm above the bottom of the overlapping membrane to help hold in place.

Vertical overlaps were all 4 inchs or 100mm in Irish.

if you want to know the other overlaps and pitchs let me know.

If you have Hips or an apex, you need about a 600mm overlap which was the width of the felt rolls we were using. So on the apex (the pointy bit) and Hips, we un rolled a full roll along the apex/hip and let half fall either side.

After that refix the orignal battens in their original locations and then fix the tiles to the battens. I found the location of the battens closest to gutter were the trickiest to get right. But of you measure all the existing batten locations and put them back exactely the same, your tiles will go back up no problem.

Remember that the membrane is only a 2nd layer of defense, your tiles should not allow any water penetration.

Hope this all makes sense:) my notes were a bit rough. If I can clarify anything let me know. Hopefully some of the more experienced people here will add to this, Its a learning experience for most of us.

V.

Lemo

That's great, Vexorg. Thanks.

SoBe

nice post "roofer" vexorg,you covered everything in that one

delly

SoBe wrote:

nice post "roofer" vexorg,you covered everything in that one

Just saw the thread and was about to make a similar reference to rooferVexorg .

roofer

hi all vexorg has it covered.check your tile spacings. if the roof is tiled right it shoud`nt leak.