Shed Roof Covering

[Duncan A]

The felt roof covering on my tool shed needs replacing.
It is a near flat roof with a pitch of 5 to 10 degrees.
The present covering is roofing felt over some sort of black plastic sheeting onto tongue and groove boarding and seems to have worked well until coming off in bad weather - probably 15+ years old.

Does anybody know what the plastic sheeting should be if I replace the felt? I can't see any writing on it at this stage, possibly just damp proof membrane i.e. impermeable. Should I be using a permeable membrane between the felt and the boards?

Should the boards turn out to be rotten, I'll probably replace with OSB3 and put an EPDM covering on it. Has anyone experience of this material? The shed is under a couple of trees and gets a fair amount of twigs etc falling on it - nothing heavy.
If I go down the EPDM route is it worth buying the proper trim for the edges, gutter drip etc?

All advice welcome
Thanks
Duncan

 

[Fitzroy]

EPDM on my shed and also recent dormer flat roof. Great material, easy to diy install. Dormer was done with proper edging, shed was just battened on the edges with timber strips.

I like the two part edge seal (Link). One part is screwed in place and the second part clips in holding the EPDM. This type has no penetrations of the EPDM which I think is best.

Fitz.

 

[Marineboy]

+1 for EPDM. Beware though, if it’s a big shed the material is very heavy

 

[MikeG.]

EPDM is a wonder material. It is truly superb, and cheap. However, the plastic trim around the edges costs a fortune and is .....well.......plasticky, flimsy, unconvincing. If I were you I would think very carefully about producing your own overhangs and drips using treated timber and contact adhesive, but think carefully about water paths, wind, moss growth, and so on.

 

[Duncan A]

Thanks guys
Problem at the moment is availability of all the bits and pieces required.

EPDM looks good but for approx 3m x 3m with trim and adhesive cost is around £300 plus 2 sheets of OSB - which I would somehow need to get home.
The eBay link for trim will certainly help if I go for EPDM - thanks.
EPDM with timber trim is prob the way to go - if I can get the OSB and treated timber.

Mike G: if, for the sake of getting the job done asap I re-felted, what plastic sheeting should I lay under the felt.
I have the felt already, and the plastic sheeting is still available in Screwfix so all I would then need is the clout nails and some flashing. I could treat some trim myself and that'd do for a year or two.

Duncan

 

[MikeG.]

I haven't done anything with felt for years. Decades even. But from memory and from logic I can't think that there is anything to be gained from putting anything under the felt. I've never seen a membrane under felt, either.

 

[Marineboy]

Thanks guys
Problem at the moment is availability of all the bits and pieces required.

EPDM looks good but for approx 3m x 3m with trim and adhesive cost is around £300 plus 2 sheets of OSB - which I would somehow need to get home.
The eBay link for trim will certainly help if I go for EPDM - thanks.
EPDM with timber trim is prob the way to go - if I can get the OSB and treated timber.

Mike G: if, for the sake of getting the job done asap I re-felted, what plastic sheeting should I lay under the felt.
I have the felt already, and the plastic sheeting is still available in Screwfix so all I would then need is the clout nails and some flashing. I could treat some trim myself and that'd do for a year or two.

Duncan

I’m surprised at that price for the EPDM. Rubber4roofs where I got mine from are currently quoting around £8 per m2.

 

[MikeG.]

I always use Rubber4Roofs too.

 

[Duncan A]

I did wonder what the plastic was for and whether necessary and I suspect it's largely to cover the gaps in the T & G roofing boards, as well as "belts and braces"

I have had some quotes from Rubber4roofs amongst others and they start at around £100 for the EPDM alone but the full kit quotes are for ClassicBond, inc trim. Some include water based adhesive and contact adhesive for the edges and some just include the contact adhesive.

I've got some 18mm shuttering ply at home, may use that instead of the unobtainium OSB3, even though it's not really the best thing.

Duncan

 

[Sideways]

Another vote for EDPM here. I built "Bunty" (google it - hilarious !) the shed last summer largely based on Mike's design and topped it off with EDPM over OSB boards. Buy the waterbased glue they sell to stick it down, don't buy the crazy priced plastic edging. You can go the whole hog with timber, gutters, downpipes and a pair of water butts for less than that plastic !
The only precaution I took, necessary or not, was to glue down a 4" wide rubber offcut along the apex of my roof before I put the seamless sheet over the lot. I just figured it would soften a possible point of stress in the future.
Garage flat roof will be next.

 

[Fitzroy]

Another vote for EDPM here. I built "Bunty" (google it - hilarious !) the shed last summer largely based on Mike's design and topped it off with EDPM over OSB boards. Buy the waterbased glue they sell to stick it down, don't buy the crazy priced plastic edging. You can go the whole hog with timber, gutters, downpipes and a pair of water butts for less than that plastic !
The only precaution I took, necessary or not, was to glue down a 4" wide rubber offcut along the apex of my roof before I put the seamless sheet over the lot. I just figured it would soften a possible point of stress in the future.
Garage flat roof will be next.

One of my corners wore through after I left the edges hanging in the breeze for a couple of weeks prior to contact glueing and battening down. I think a strip of rubber over sharp edges would be a smart move.

 

[Duncan A]

Thanks again gents, it'll be EPDM over OSB. I can cut down the OSB in the Wickes car park and get it into the car; just need to do a few measurements to work out the most efficient sizes. The shed is not rectangular - and neither is the car!
Sideways - a useful warning, I had wondered whether to soften the edges of the timber, seems like a good idea after your comments.
Duncan

 

[Fitzroy]

Knew I had the photos somewhere.

Edge was softened with a bead

Corner was obviously too sharp

EPDM was left hanging for a few weeks with the tarp pulled over the top. When I came to finish the roof the corner was worn through.

My trim battens were machined with a drip edge. They are screwed in place every 30cm.

Fitz.

Sorry photos are all in odd orientation but I can never get them correct on here.

 

[MikeG.]

Useful photos, Fitzroy, and that all looks very neat and tidy. I try to have the rubber form a drip, lower than any of the timber, just so that water can't seep or get blown up into any crevasses. Even a 5 or 6 mm downstand is enough to get most of the water off the rubber without coming into contact with wood. Fold the bottom edge under and glue to achieve this.