DIY Doctor

Main navigation

Felt Flat Roof Replacement .

Postby doodles » Wed Jan 14, 2009 11:40 am

Hello ,

I have seen a few posts on this subject but still a bit undecided .

I have a felt flat roof that needs replacement but dont want to replace like with like and have the same issues later or when I come to sell my property . Felt has many joins that in time will leak .

My choice seems to be fibreglass or rubber .

I have been told that fibreglass will not deal with severe changes in temperature and may crack .

This leaves me with rubber , which also seems to carry a longer guarantee .

Does this seem correct ?.
Is rubber at risk of being pierced , by a falling slate for example ?.
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Wed Jan 14, 2009 11:19 am

Postby stoneyboy » Wed Jan 14, 2009 6:35 pm

Suggest you use built-up felt with polyester reinforced felt used for the top 2 layers. This type of roof should easily last 30 years especially if the top is coated with chippings.
Get a cost for each roof type and decide from there.
Rank: Project Manager
Posts: 5520
Joined: Wed Dec 10, 2008 6:44 pm

Postby TheDoctor5 » Mon Jan 26, 2009 9:59 am

Last year 64% of the questions asked in our forum were answered within our DIY project pages at The project pages are now separated alphabetically and your answers are accompanied by diagrams and the ability to see, and buy, the tools and/or required to complete your project. Use our search box to look for your answer and save a great deal of time and money!
Posts: 1381
Joined: Tue Jan 20, 2009 9:17 am

Postby Perry525 » Sat Feb 28, 2009 8:19 pm

As you say, replacing a cheap roof with another cheap roof that will fail in a few years is a pain.

A slate roof can last 400 years.
A tiled roof perhaps 80 years.

Fibre glass roofs last forever, I have two, so perhaps I am prejudice. The summer here can run to the middle forties and the winter gets down to minus ten, a fairly normal range, fibre glass has been used to make ships hulls and lots of other things for over fifty years, lots of those old boats are still working today.
The joy of fibre glass is that if you want do something to it you go out and buy a kit and do it!
No especial skill or gear is required and it is definitely DIY.

Fibre glass can be laid flat and there is no worry about ponding, it does get slippery and you need great care when walking on it - you could slip off the roof.

Other than that its perfect!
Rank: Site Agent
Progress to next rank:
Posts: 734
Joined: Fri Jul 06, 2007 7:35 pm

Postby youasked » Wed Mar 25, 2009 3:09 pm

Liquid Rubber, from Canada, brill and used by many many industrial end users eg London Underground. No joints, 900% expansion, 99% memory 2mm thick will sui most domestic flat roofs. Made by LeFarge.
roof coaters are al over the place.
Rank: Tradesman
Progress to next rank:
Posts: 25
Joined: Wed Mar 25, 2009 2:52 pm

Postby insulationgrants » Thu Apr 23, 2009 2:43 am

I spent the best part of my earlier career in roofing approx 13 years and I have used practically every type of product there is so here totally impartial advice as no longer am in the roofing industry.

Pros & Cons of each type of roofing system I can think off.

Heat wieldable PVC, preferably a homogenous sheet minimum 1.2mm.

On my opinion the best type of product on the market and heavily used in commercial work.

Recommendation would be Sarna or Protan.

Weakness: PVC will need additional protection from foot traffic. Ideal for low foot trafficked roofs.

Felt roofs: If you get a dual reinforced polyester cap sheet and a decent contractor you will have a great roof however felt comes in a variety of qualities and prices and cheap generally means do not use.

Recommendation would be Icopal, the Andersons brand, Techno Torch is a great economy product and their higher end product Profiles is great to work with. IKO also has some good high end products. Erisco Bauder is very expensive but the quality is exceptional.

Asphalt: Great for car parks however it can crack with frost, is very heavy and need a solid deck ideally concrete and screed and can suffer from slumping and blisters in hot sun.

Recommendation do not use for domestic use and I would not recommend above anything with high humidity such as a commercial kitchen or swimming pool.

Rubber sheets such as Goodyear.

In theory it sounds great with no joints however its puncture resistance is very poor as it is unreinforced, it tends to shrink and if you do need laps then it is a disaster waiting to happen as the solvent laps are practically impossible to seal if it is below 5 degrees. An added problem is the laps vulcanize and this makes repairs more difficult than they should be.

Personally I would only be happy using rubber on water reservoirs as one sheet and covered over with soil as it will not pollute the water and also as a gas membrane again protect with soil. Personal preference would be Dunstable Rubber.

Coating systems, GRP, Polyurethanes, Spray Foams etc.

Forget it under 5 degrees and forget it if they are not reinforced.
Some of the reinforced polyurethanes are good for box gutter repairs as some stay tacky and also good for roofs with details that would be impractical to seal either due to limited access or a potential for a fire hazard such as a chemical store.

If you have clear blue skies and a nice summer’s day then this will work but unless you have perfect conditions I would not recommend either type of product as it has a habit of peeling off.

Recommendations none.

TPO roofs, basically like a PVC , but is more environmentally friendly.

I am not a fan of TPO as it is difficult to weld and has poorer fire properties. If you must use one use Sarna.

Green roofs basically a garden roof.

Very expensive, environmentally excellent and Erisco Bauder would be my recommendation.

Self adhesive felts.

The theory is you do not need a gas torch which is fine right up until the point you have to dry off some rain. You really need a new plywood deck and the weather to be sunny and above 5 degrees preferably much warmer.

Not a fan of this product as it can be rather soft to work with, of poor quality and the minerals fall off a lot more than other felt. However if your a DIY hand it could work in the right hands.

My tip is to try bonding the underlay straight to the plywood upstands without primer as in my experience it sticks better, however you could try both options and run with the one your happy with as moisture and weather will play a big part in how successful his will be.

Keep your upstand heights low as it will need mechanically fixed as the bitumen is so soft it will slump, the minimum height should be 150mm at walls.

The above is backed up with experience and what you will find in some of the BBA certificates and Building Research establishment guidelines and NFRC guidelines.


Jim Barrie

Former Estimator & Roofing Technical Advisor
Now a Government insulation grant advisor
Rank: Apprentice
Progress to next rank:
Posts: 5
Joined: Thu Apr 23, 2009 1:23 am

Postby ritchieroofer » Sun May 17, 2009 4:58 pm

hi i am roofing contractor and am a member nfrc and other member schemes, i have used lots of diiferent materials over the years, i was awarded NFRC roofing finalist 2007 and recieved pride in the job award from NHBC we only use the best products on the market and can asure you protan is not one of them! but have to say sarnafil is one quality material i served my time using this product its the most well known. We use Alwitra its also quality product and can match sarnafil in every aspect also comes with 20 year guarantee. both are very good products but would only recommend these two single-plys.

if you are using single ply membranes use: Alwitra, Sarnafil

P.S Protan is a no no
Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Sun May 17, 2009 4:16 pm

Postby insulationgrants » Sun May 17, 2009 11:59 pm

Irrespective of what anyone's personal preference of materials are if you have decent trained men they can lay any material even it you buy the cheapest material as long as it is technically up for the job.

The most important aspect is to make sure you have selected the most suitable system for the job which means no one manufacture will have the best solution at all times hence we both have used many different materials.

No system is perfect every system has a weakness, the real skill is in picking the system that has the best chance for success given the restrictions and conditions you have to overcome.

On some roofs I would not even consider a single ply membrane, it is all down to what is the best technical solution for the job.

If the budget is not available to do the job properly the best action a professional contractor can make is to not price the job.

However do not take my word for it or ritchieroofer, ask others opinions then make up your own mind.
Rank: Apprentice
Progress to next rank:
Posts: 5
Joined: Thu Apr 23, 2009 1:23 am

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics