Flat roof :felt or fibre glass - scot22

Knowing the wide range of knowledge and experience on the forum I wondered if anyone could give any pointers.

I have a small outdoor storage area, about 4mx2m, with a felt flat roof. This now needs replacing and I am considering having glass fibre instead of felt. I have been told glass fibre will have a life expectancy of 20 years so could prove more cost effective.

Interested to hear any views.

Flat roof :felt or fibre glass - FP

I understand that felt roofing done properly - three layers, including a good mineral topping (light-coloured stone chippings) - has a lifespan of up to 25 years.

I see some firms are offering a 40-year guarantee for glass fibre flat roofing.

The obvious advice is to get some quotations and guarantees for the work and decide which is the best value in your case. As a guide, it seems fibre glass is roughly twice the cost, per square metre, of felt.

Points like how long you intend to stay at the property will come into the equation.

Flat roof :felt or fibre glass - scot22

Thanks that's very helpful.

Interesting price comparison - got two quotes and the glass fibre is only 50% more ( known locally to be reputable). Could be the felt quote is dear. I suspect that there is a element of luck ( as in most things )

Flat roof :felt or fibre glass - primus 1

You can also get rubber roofing have you looked into this. ? Had my garage fibre glassed last year, cost me 1500 but well worth it , obviously it is a bigger area but has a 25 year guarantee.

Flat roof :felt or fibre glass - scot22

Thanks primus for the post.

Like you we had our garage roof done a few years ago. Like you say it was well worth it. This shed is not really worth spending that level of money on.

Flat roof :felt or fibre glass - Chris M

Two thoughts come to mind.

How sound is the rest of the shed?

Who is providing the guarantee and will they be there in 25 years time? Is the guarantee for the full coat of replacement should it fail after say 20 years, or will they only pay 20% because it's 80% of the way through its' expected life?

Flat roof :felt or fibre glass - concrete

Hello scot, Is it vital that your shed roof is installed to a habitable standard? If not, then there are several cost effective options you can consider. To have it felted with hot bitumen or heat applied felt is one option. This means removing the existing felt. Both types of heat applied felts go straight down onto the roof boards, which need to be in good condition. If the boards have suffered from water ingress then they need replacing. All this is a cost for only a 'shed'.

Alternatively you can cover the existing roof material. I put steel profiled sheets over mine, with an edge trim. They screw down into the roof boards or joists with self sealing screw heads. This cost me about £180 for a 3M x 2.5M shed. I had considered laying new felt onto the existing using cold bitumen but the cost was marginally more and the job would have taken longer and would have been very messy. Been on since last July and no problems at all and not expecting any. It is my workshop and tool store so I like it dry. Consider this option.

Cheers concrete


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