Roofing felt and OSB

[oilman]

I have a 45 deg shed roof covered with OSB. Is there any problem using cold applied felt adhesive to fix the felt on? I'll use 2 layers of underfelt and cover it with felt shingles in the spring if I don't do it earlier.

It looks easier to fit the underlays by going up and over the ridge rather than along the roof, if I did this and fixed a strip along the ridge afterwards would this be ok?

 

[masona]

It looks easier to fit the underlays by going up and over the ridge rather than along the roof, if I did this and fixed a strip along the ridge afterwards would this be ok?

Shouldn't be a problem as the roof pitch is 45 degree as long you have a good overlap on the sides. Some sheds roof do have a slight bow in the middle which might give a off line appearance by putting felt up & down. On the top ridge, you could use a plastic downpipe cutting out a 45 degree slot to fix it on top instead of timber for maintenance free.

But have you look at the Bitumen Corrugated Sheet (Black or Green, 15 yrs guarantee, I think they are about £7 per sheet) 2m x 940mm in Wickes? It will last a long time compared with roof felts problem and cheaper in the long run. You can fix the sheet using screw/caps into the OBS board & ridge tile sheet are available for this as they are flexible for most angle.

 

[oilman]

No problem with sagging roof, just put it up with 4x2 at 16 inch centres and 6x2 ridge. Sounds like over the ridge it is. I had a look at the corrugated stuff, but with felt shingles and 2 under layers, they look better and I hope will last a lot of years.

Any thoughts about the bitumen glue on the OSB, would this cause me trouble?

 

[masona]

Any thoughts about the bitumen glue on the OSB, would this cause me trouble?

I take it when you say bitumen glue as in bitumen primer then yes that's the best way. Also make sure the OSB joints is supported on the centre of the joists, if not, then something like 2"x1" timber underneath with screws on top + glue otherwise it can tend to give the roofing felt a hairline crack if not supported correctly.

Thought I mention it, have you seen the rubber roofing tiles strip that made out recycle tyres which is also ideal for shed roof.

 

[oilman]

I take it when you say bitumen glue as in bitumen primer .............

It's felt adhesive/lap cement.

Also make sure the OSB joints is supported on the centre of the joists, if not, then something like 2"x1" timber underneath with screws on top + glue otherwise it can tend to give the roofing felt a hairline crack if not supported correctly.

All the edges are over supports except where there are supports at right angles to the edges at about 14 inch intervals . This must be the way most roofs are covered, are you saying ALL the edges need support?

Thought I mention it, have you seen the rubber roofing tiles strip that made out recycle tyres which is also ideal for shed roof.

No, I'll try and find them, sounds good.

 

[masona]

All the edges are over supports except where there are supports at right angles to the edges at about 14 inch intervals . This must be the way most roofs are covered, are you saying ALL the edges need support?

No, that's fine, I meant in the middle section because I wasn't sure how big your shed roof is!

Thought I mention it, have you seen the rubber roofing tiles strip that made out recycle tyres which is also ideal for shed roof.

No, I'll try and find them, sounds good.

It's here , I can't remember the price of them as it was a couple of years ago when I've last used them.
Click at "Product range" > Ardesia

I have also use "Turicor" sheet on one of my friend shed which give a nice appeal.

Getting carried away here but maybe useful to others, another one I have use on my summerhouse roof on here. Loads of info there.

 

[oilman]

I've tried the glue on the OSB, doesn't seem to be a problem. Just hope the all over gluing doesn't give problems. A builder said it would give trouble because of expansion and contraction, but I don't know if its true. Any ideas?

 

[masona]

In theory the builder is right but it's mostly unsuitable like for laying ceramic floor tiles as the movement will loosen the tiles and the grout.

Doesn't matter what plywood or sheet you use they will all have a expansion rate, some less than others. Just read my old book regarding OSB sheet and quoted,
OSB > Leave 1/8" spacing between OSB panels to allow for expansion and contraction. To minimise the buckles on 8' sheet is to cut smaller sections. Cut edges are also prone to swelling if they get wet so seal these edges after they are cut and mainly only a problem if moisture arise.

So we are talking about a very small amount of movement, over 95% of sheds roof are fitted with OSB sheet as the thin shavings are bonded with waterproof glue and it's very strong. I not has any problem so far on shed roof area as they are on a smaller scale, on a bigger roof area may be a problem though.

Also the problem with most roofing felts they don't last forever on shed roof to external weather but are guarantee up to 20 years anyway. If you wanted it to last lifetime then there are other ways of doing it instead of roofing felts.

 

[oilman]

The shed is 20 x 10ft and I went to cover the roof today. Took off the tarpaulins and got the roof ladders in position. As I have access from one side only I have to go over the top. Looking at this and covering it with felt was a bit daunting. So I got some corrugated bitumen sheets and did it in that instead. Still took all day and I've only got one side done. The front side should be easier. It's smaller too.

 

[H.A.Ross]

I would just like to ask where you managed to get the corrugated bitumen sheets as my shed has red corrugated bitumen covering which has lasted thirty years but I think could do with replacing. Many thanks, Heather

 

[masona]

Wickes do them in black or green