Felting Shed Roof — Questions

paperclap

Hi all,

After failing to fix my ever leaking shed roof, I've decided to refelt it.

It's quite a mammoth shed, at 9.5m long by 2.75m wide.

I've a few questions.

Felt
Felt vs "Super" Felt. At almost double the price, is the "Super" stuff worth it? Also, conveniently, the regular stuff comes in 10m lengths – perfect for my 9.5m long span, with 25cm play either side for overhang. IKO do say they do the "Super" stuff in 10m lengths, but I can't find it!
https://www.wickes.co.uk/IKO-Black-Shed-Felt---10-x-1m/p/112812
https://www.wickes.co.uk/IKO-Super-Black-Shed-Felt---8-x-1m/p/117668

Felt adhesive
Has planned on using one of the following:
https://www.toolstation.com/everbuild-black-jack-roofing-felt-adhesive/p73292
https://www.screwfix.com/p/bostik-feltfix-bituminous-roof-felt-adhesive-black-5ltr/41499
Any preference on the above? Just how liberal does this stuff need to be applied?

Felt overlap
Obviously largely determined on the slope of the roof. Ours is very minimal. Not sure on the height difference between the back to front, but it works out at around a 2 degree slope. Perhaps best to just use as much overlap as my sheets of felt allow for? Will probably end up being around 25cm overlap.

Nails
The joists run width ways, at roughly 400mm centres. And I do mean very roughly (Not sure who built this thing!). Can't ensure that nails will hit the joists, so with that in mind, had planned to nail directly into the OSB. Based on the assumption that it is 12mm OSB, I'd planned on using 13mm clout nails. What is best practice for spacing? I've seen so many suggestions. And once all nailed in, is it best to dab some of the bitumen adhesive on top to seal in? I know some people dab the nail in sealant prior to nailing in, but think this is messy and horribly time consuming with smaller nails (I've done it!).

Eaves trays (?) and guttering
Had planned to run new guttering along it, as the current stuff is warped, and frankly, not been done correctly! Is it worth running some eaves trays along, and cutting the felt short of into the guttering? Our current felt has deteriorated in the gutters.

Thanks one and all!

Section62

It's a big shed, the materials and labour to cover it with felt will be fairly expensive and time consuming.

You won't want to have to redo it in three or four years time, so use the best quality felt you can afford now.

Or, a far better idea would be to forget felt and cover the roof with plastic coated steel instead.  Easier to fit and much longer lasting.  And better on a roof with minimal pitch.  A shed that size is a useful asset... no point ruining it with a poor-quality felt roof.

stuart45

You can tell the difference between the cheaper and better quality felts by how easily the cheap ones rip by hand. I replaced the felt on a roof for a friend that had.only lasted a few years. Often the sheds come with a cheap felt.

warwick2001

I have just this month replaced my shed felt with a Skyguard (other manufacturers are available) EPDM rubber one. Really easy to fit, the rubber is pretty thick so shouldn't rip, the kit I bought came with all the materials I need (adhesive, roller etc.) and as I live in the Lake District, already tested and waterproof!!

Having fitted felt in the past, IMO the EPDM stuff is far superior, but saying that I've never seen 'Super felt', so can't comment on that. Go rubber, you know you want too.....


Edited to add: I just used an online calculator to work out the cost for a rubber kit for your shed. Came out at £789.72. Maybe go with the felt......

paperclap

Yeeeah, I'm sure there are better roofing materials out there, but I'm looking for the best low-cost option... purely because I'm not sure about future plans (moving, building a new shed, tearing this one down, etc). Just want it watertight!

I've found the "super" felt in 10m length, but seems IKO only does this in the green!

Might nip to B&Q this evening and look at how the green looks. Might look alright... right? 

https://www.roofingsuppliesuk.co.uk/products/iko-super-green-shed-roofing-felt-10m-x-1m?keyword=iko super

I've also noticed that IKO recommend using an underlay if the pitch of the roof is low (below 20 degrees). Well, ours is 2 degrees! Really necessary?

Section62

paperclap said:

I've also noticed that IKO recommend using an underlay if the pitch of the roof is low (below 20 degrees). Well, ours is 2 degrees! Really necessary?

It depends whether you want to do the job properly, or bodge it and do it again next year.

Cheap DIY roofing felt works on the same principle as tiles/slates - that the pitch is sufficient so water will run down the slope and there is sufficient slope to stop the capillary/wind effects causing leaks.

At 2 degrees you are towards the lower end of the typical flat roof range - and for that you would either need a single sheet cover (e.g. EDPM or steel) or else built-up felt which is torched on.  If the roof really is only 2 degrees then I fear you'll be back here next year asking why your new felt roof has failed.

Do the job properly, or do it twice.

paperclap

Well, the reason I'm asking as to whether it is necessary is because I don't believe this current felt roof has an underlay, and where the felt isn't destroyed (torn, etc), it's performing.

I think this is the stuff to use?

https://www.wickes.co.uk/IKO-Trade-Traditional-Roofing-Felt-Underlay---10-x-1m/p/240019

twopenny

I used to do my own shed with a decent felting and Felting Tacks.

Thick and strong with big heads they look smart and don't tear  the felt. They also cover the hole the tack makes going in with the large head and fit flush so keeping it watertight. Easy to get at a local diy/building suppliers.

https://www.screwfix.com/p/easyfix-felt-nails-galvanised-3-x-20mm-0-5kg-pack/17718?kpid=17718&ds_rl=1249413&gclid=EAIaIQobChMIhcX6_e2d_wIVj_DtCh3yQgHTEAQYAiABEgKTvvD_BwE&gclsrc=aw.ds

walwyn1978

Green felt looks decent iMO, got that this time round because my local builders merchant didn’t have any black in. 

+1 for felting tacks. 

35har1old

paperclap said:

Hi all,

After failing to fix my ever leaking shed roof, I've decided to refelt it.

It's quite a mammoth shed, at 9.5m long by 2.75m wide.

I've a few questions.

Felt
Felt vs "Super" Felt. At almost double the price, is the "Super" stuff worth it? Also, conveniently, the regular stuff comes in 10m lengths – perfect for my 9.5m long span, with 25cm play either side for overhang. IKO do say they do the "Super" stuff in 10m lengths, but I can't find it!
https://www.wickes.co.uk/IKO-Black-Shed-Felt---10-x-1m/p/112812
https://www.wickes.co.uk/IKO-Super-Black-Shed-Felt---8-x-1m/p/117668

Felt adhesive
Has planned on using one of the following:
https://www.toolstation.com/everbuild-black-jack-roofing-felt-adhesive/p73292
https://www.screwfix.com/p/bostik-feltfix-bituminous-roof-felt-adhesive-black-5ltr/41499
Any preference on the above? Just how liberal does this stuff need to be applied?

Felt overlap
Obviously largely determined on the slope of the roof. Ours is very minimal. Not sure on the height difference between the back to front, but it works out at around a 2 degree slope. Perhaps best to just use as much overlap as my sheets of felt allow for? Will probably end up being around 25cm overlap.

Nails
The joists run width ways, at roughly 400mm centres. And I do mean very roughly (Not sure who built this thing!). Can't ensure that nails will hit the joists, so with that in mind, had planned to nail directly into the OSB. Based on the assumption that it is 12mm OSB, I'd planned on using 13mm clout nails. What is best practice for spacing? I've seen so many suggestions. And once all nailed in, is it best to dab some of the bitumen adhesive on top to seal in? I know some people dab the nail in sealant prior to nailing in, but think this is messy and horribly time consuming with smaller nails (I've done it!).

Eaves trays (?) and guttering
Had planned to run new guttering along it, as the current stuff is warped, and frankly, not been done correctly! Is it worth running some eaves trays along, and cutting the felt short of into the guttering? Our current felt has deteriorated in the gutters.

Thanks one and all!

20 degree pitch is recommended If less underlay should be used
Which way is the fall is it on 2.75 axis if so you could use wooden straps to secure the over lap thus avoiding the risk of a clout going  of line and damaging  the felt also it would be easier to work with 3m x1 m opposed to 9.7M x 1M which is approx 20kilos
What size are the joist will they take your weight without being supported ?
10M x !M Lifespan 5 years ?
8M x 1M Lifespan 15 years Nails or adhesive?
Screwfix both cheap and more expensive only 1 year Both 10M 1x 1M

tetrarch

Definitely EPDM. In my opinion it is a far superior material and totally everything-proof

I did my 10m x 3m shed roof in a single (65kg) sheet and it has been excellent and totally weatherproof. No need for nails and joist worries. Mine isn't even glued down but just (temporarily) held by some fixings at the edge and a couple of old joists as weights on either end

I also installed a large garage roof in 2003 in EPDM that was still going fine in 2021 when I moved

Cost wise, mine was £415 from Rubba-seal:

Firestone RubberCover EPDM Membrane 045 - 1.14mm
Width: 11.00m
Length: 3.50m
Area: 38.5m²

Regards

Tet