Felt on flat roofs in 2018: yes or no?

Felt on flat roofs have long had negative association in my head. The flat roof area I need to cover/replace the existing felt roof is c. 20sqm. However, my builder was telling me that the felt and the way it is put on flat roofs is now much better than 40 years ago or whatever. Is this true in your experience?

This article seems to agree with him, and essentially says felt roofs are unfairly tarnished by problems in the past:

Flat roof replacement

FELT ROOF
This type of flat roof still has a bad reputation with some people, but I’m going to tell you why that perception is out of date. Most people have in mind the old ‘pour and roll’ felts of yesteryear, and these were thin bitumen felts glued together with a hot liquid bitumen between each layer. They had minimum internal reinforcing, with some containing natural hessian fibres which were prone to rotting. This type of felt, sometimes known as felt paper or tar paper, would effectively dry out and crack with age or UV damage from the sun. 10 years was pretty much the life expectancy.

MODERN TORCH ON FELT ROOF
Torch on felt roofing, in case you hadn’t guessed describes the method of application. Do not confuse these modern roofing felts with the older pour and roll system. Great strides continue to be made in bitumen and modified bitumen technology such as SBS or APP, resulting in much better resistance to UV damage and cracking. This type of felt roof comes on rolls and is laid with the aid of a very large blow torch that heats and melts the rear of the felt, melting it onto the roof structure below. Typically it’s applied as a 3 layer system usually consisting of a perforated underlay, a 2mm underlay layer, then thick 4-5mm felt. These layers are all laid in a half lap manner, so all the joints are the furthest away they can be from another joint.

The thickest top layer is often a coloured mineral finish known as a cap sheet, and they are available in a variety of colours, as well as a plain felt finished with a silver solar reflective UV finish. All of these felt layers are also reinforced with strong polyester weave sandwiched in the middle of the felt, giving them incredible strength. In lifespan terms, I don’t know a single roofer that will not be happy to guarantee 10 years, because they know it will last 20, sometimes 30+. In fact we use a company that guarantees for 20 years. Not as bad as you thought is it?

Cost – By far the cheapest option see our flat roof costs page.
Suitability – Can be laid to any size of roof, or detail level without problem. Has favourable expansion and contraction properties due to modern bitumen technologies. Not best for heavy and frequent foot fall, especially during the hottest weather in summer months.
Damage resistance – During hot weather heavy or careless foot traffic may scuff the mineral surface. It is perfectly ok to walk on if you’re careful as long as you don’t have high heels, but no ladders or step ladders without protection between them and the roof.
Repairability – Repairable by torching a new patch of felt on the top of a damaged section, but it does look a bit patchy. If you have the plain felt and solar finish it’s the easiest to repair.
Appearance – Beauty is in the eye of the beholder, but a nice mineral finish is pleasant to look at, certainly prettier than a rubber roof. There’s plenty of colours to choose from like green, brown, grey and purple.
Installation issues – Make sure that any contractor carries full insurance to work with hot flames.

What's your view on putting felt on flat roofs in 2018?

Four Phucs Ache

Maybe

No.

EPDM or fiberglass.

Its like using untreated timber as opposed to paying the extra for treated timber. Sure they both do the same thing , but the cheaper timber will need maintenance,might possibly fail and ultimately will need to be replaced ALOT sooner than the dearer option.

the_pen_turner

no
if its worth putting a roof on it should be worth putting a proper roof on

felt isn't worth putting on a shed let alone anything else

if possible put a pitched roof on or one of the modern fiberglass

bleaks

Bumping up an old thread for a bit more feedback on this. Got a roofer to pop over to get a quote for replacing a flat galvanised steel roof over our garage (that's attached to the house) that we're hoping to start using as an office/usable space.

He was saying torch on felt was the way to go on this and that the other types aren't reliable. Is he being genuine or just looking for a handy job for himself? I'd like to use this space for music making too so sound proofing is a bit of a concern too. Any input, much appreciated.

Ps - if anyone has a roofer recommendation in Dublin (d12), let me know via PM.

the_pen_turner

https://www.boards.ie/discussion/comment/120779229#Comment_120779229

done right its ok. it can last years but i would never put it on anything. i would go for insulated cladding in full lengths. great stuff.

embracingLife

Appears posters don't know the difference between the different types of roof felt.

The comments claim that "felt" isn't good are referring to a cheaper type of felt called Mineral Felt which goes brittle after several years,this also is the same type used on timber garden sheds.

#bleaks: the roofer you met recommended "Torch-on Felt" which is superior felt. It's about 1 inch thick,comes in a roll and requires a blow torch/flames to heat as it's being unrolled onto the roof and also needs a liquid tar to act as glue to help the felt bond to the roof. Once it's done it will last for years, easily 30 years but it's recommended to be painted with a sunlight reflecting paint which is usually silver in colour.

#bleaks: you could have phoned your nearest builder provider/hardware shops and they'd give you the advice instead of coming on hear and listening to amateurs giving armchair opinions!

Also the fiberglass roof surfaces are prone to cracks! Which allows water to leak in, usually if the underlying timber roof surface has not been secured/nailed down properly. Nobody mentions that.

Gumbo

I’d have the modern thick felt over fibreglass myself.

embracingLife

https://www.boards.ie/discussion/comment/120860479#Comment_120860479

Why was that done? Did the fibreglass fail? Double job to be sure!

Alkers

I ha d a nightmare with a fibreglass roof, looked the business but significant cracking and delamination appeared after two years. Torch on felt over it and that's been fine so far. Doesn't look too bad either

chooseusername

https://www.boards.ie/discussion/comment/120857938#Comment_120857938

""Torch-on Felt" which is superior felt. It's about 1 inch thick,comes in a roll and requires a blow torch/flames to heat as it's being unrolled onto the roof"

A 16ft roll of that would take some handling!

Calahonda52

No

WTF are we going with 1 inch thick torch on felt?

You need to stand closer to the urinal, it's much shorter than you think

A 16ft roll of 1" is 120 kgs

Gumbo

https://www.boards.ie/discussion/comment/120864912#Comment_120864912

I’d pick felt “instead” of fibre glass based on my experience with both.

As with anything, it depends on the design of the building though. I like using parapets to avoid seeing the roof finish and keep clean lines.

chooseusername

https://www.boards.ie/discussion/comment/120868377#Comment_120868377

And the irony;

" you could have phoned your nearest builder provider/hardware shops and they'd give you the advice instead of coming on hear and listening to amateurs giving armchair opinions!"

10-10-20

On the hot-topic of torch on felt, anybody seen a warm-roof installed with torch-on felt as the VCL directly on the lower decking of OSB, then running the felt up and over the parapet wall? Thought that the VCL for this use-case pretty much had to be the adhesive silver-foil type, bonded properly to the blocks at the bottom of the parapet? Worried that felt will be insufficient as a VCL, plus the top of the parapet will end up with condensate which runs down the block and creates damp spots.

Bsharp

We were advised to use a paralon flat roof system.

It wasn't possible to do a pitched roof without lots of difficult joints.

Every builder we asked recommended against fibre glass for whatever reason, one of whom was a friends brother.

embracingLife

Boo hoo