Felting a Shed Roof....

[Umy786]

Decided to bite the bullet & have another go at getting my shed watertight - thought about going the EPDM route but been advised against it due to 3 huge sycamores behind it & constantly falling branches, not to mention the local cats seem to use it as a hang out so I don't think a barely 2mm rubber sheet will last long.

Guy who built the shed laid the roof & it leaked the following week so I ripped all that off & put some corrugated bitumen sheets down with the plan to get it sorted in a year or 2.

Fast forward SEVEN years & it's still outstanding -it has gradually gotten worse & would like to get it sorted this side of winter as I’ve got some very expensive tools in there which I want to keep dry!

This is my initial plan for the roof covering:

Re-board with 18mm ply

Want to go with a belt & braces approach & put 3 layers of torch on felt IKO / Andersons

Shed is just a ply roof with no insulation but seen there's vapour underlays available, not sure if they're needed?

If anyone could point me in the right direction as to the best application I’d be hugely grateful as it’s gone on too long and I really want to get it sorted before the weather gets any worse!

Many thanks guys

 

[Bankrupt]

Have a look on YouTube - Some very good videos on there about re-felting your shed. Three layers of torch-on felt ? ? Sounds a bit excessive ! Good idea to use torch-on felt instead of that flimsy rubbish that the sell in the DIY sheds for garden roofs, but one layer should do the job !

 

[Bosswhite]

You may find it difficult finding someone that does " Torch on " Felt these days .A good quality felt " cold Fixed" and Battened would last years .

 

[Umy786]

Any ideas on if a vented underlay is needed, called up a few places, one suggested vapour barrier is needed, the other didn't & on another forum I saw roofers arguing about the layers being crossbonded or not ???

 

[Umy786]

You may find it difficult finding someone that does " Torch on " Felt these days .A good quality felt " cold Fixed" and Battened would last years .

Would you mind explaining in a bit more detail please

I'm more than happy to do whatever is viable but more importantly will last at least 10 years

 

[oldbutnotdead]

If the pitch is low enough you could use GRP. Be funny watching the cats try and grip that, and a lot safer than waving a blowtorch at your timber roof.

 

[Umy786]

Interesting you say GRP as almost everyone has said to stay clear due to the boards expanding and the GRP consequently cracking

 

[oldbutnotdead]

Interesting you say GRP as almost everyone has said to stay clear due to the boards expanding and the GRP consequently cracking

Depends how big your shed is, its the joints between boards where you could get problems if the roof joists are a bit puny (as sheds often are). Plus if you work in there when its raining the drumming might get on your nerves.
If its an apex roof you'd be wise to use a trim over the apex- you can mat over that sort of angle but its tricky to get it neat.
TBH shed felt is OK if its not too exposed, the felt on my 3m shed blew off after about 10 years, replaced it in 2016 & its still keeping the rain out.

 

[Harry Bloomfield]

As an alternative, take a look at modern box corrugated sheets. They are galvanised, then painted in several colours and two or three thicknesses and screw down with special self-sealing screws. They also last for decades, plus especially easy to fit.

 

[oldbutnotdead]

As @Harry Bloomfield ,you can get insulated versions of wrinkly tin as well (which you could fix over the top of your existing roof)

 

[Umy786]

Depends how big your shed is, its the joints between boards where you could get problems if the roof joists are a bit puny (as sheds often are). Plus if you work in there when its raining the drumming might get on your nerves.
If its an apex roof you'd be wise to use a trim over the apex- you can mat over that sort of angle but its tricky to get it neat.
TBH shed felt is OK if its not too exposed, the felt on my 3m shed blew off after about 10 years, replaced it in 2016 & its still keeping the rain out.

There's pictures attached on the thread - I don't know what you'd call this type of shed? Lean-to? Even though it's not leaning on anything lol ?

Shed is roughly 5m wide & 4 meters long

I had a look at box sheets, seemed almost identical to the way I laid these bitmen corrugated sheets with the nail fasteners etc, I was told those nails were sent sealing to so have gone right off anything that claims to be self- sealing hence advocating for what is probably an over the top felt roofing system

 

[Harry Bloomfield]

I had a look at box sheets, seemed almost identical to the way I laid these bitmen corrugated sheets with the nail fasteners etc, I was told those nails were sent sealing to so have gone right off anything that claims to be self- sealing hence advocating for what is probably an over the top felt roofing system

The correct screws/ bolts for the box sheets, are certainly not nails - they are a substantial hex headed wood screw, with a proper seal under the head. From memory, I had to drill a 6mm pilot hole through into the timber joists, to be able to screw them in. It is over 10 years since I did my 16 x 12 workshop and my 24 x 12 garage with the box section. I have had zero issues, zero leakage and zero rust.

 

[Umy786]

The correct screws/ bolts for the box sheets, are certainly not nails - they are a substantial hex headed wood screw, with a proper seal under the head. From memory, I had to drill a 6mm pilot hole through into the timber joists, to be able to screw them in. It is over 10 years since I did my 16 x 12 workshop and my 24 x 12 garage with the box section. I have had zero issues, zero leakage and zero rust.

Very interesting - would you mind giving more information on the system itself - manufacturer / supplier & if I need any kind of vent sheet / underlay / membrane on top of the ply or did you screw it straight onto of the ply

 

[Harry Bloomfield]

Very interesting - would you mind giving more information on the system itself - manufacturer / supplier & if I need any kind of vent sheet / underlay / membrane on top of the ply or did you screw it straight onto of the ply

Sorry it was too long ago to remember any details, but many builders merchants will supply them and there is a manufactures website around somewhere, which explains how to fit them. I just fixed mine direct to the joists. I was a bit wary of missing joists due to slight bows over the lengths, but it worked out fine, just running a string line across from one end of the joists to the other.

 

[oldbutnotdead]

Tekscrews are what you need for the fixings, there are different types (some designed to self-tap into pressed steel purlins, some to go into timber battens).I used them on my garage roof 5 years ago, no leaks, no movement.
Single pitch roof, ideal for sheet coverings. If you fix slate battens to the existing roof that'll give you an airgap (thus avoiding any probs from condensation under the tin sheets). You'd need the trims to finish off at ridge and sides, can't remember the proper name for them