Flat roof extension - what would you choose?

downshifted

We have a choice between high performance felt, fibreglass membrane or rubber coating, does anyone know the pros and cons please? It will have a velux or similar

EssexExile

Personally I'd go for rubber, flexible and long lasting.

donemedosh

I would also go for rubber. It can last for 30+ years if done right

ritesh

Hi All,
This has always been an interesting topic. I did a three garage conversion about 7 years ago, converting to a office/man cave. After much debate we opted for the GRP on a warm deck roof. The cost for 42m2 was just over £3200. The use of EPDM worried me with all the local cats using it as a route to get to their destinations and the thought of their claws digging into it. The GRP is still looking good. I inspect it every year and just give it a wash with a soft brush and soapy water.

My neighbour has got a small extension on which he laid EPDM and not had any issues with it. I guess it comes down to good foundations and having it installed properly, no matter what it is, to ensure it will last.

Jeepers_Creepers

x 2 for GRP.

Which one would you walk across? I'm not saying you would'should walk across any, but which would you happily walk across if you needed to?

Correct.

A product like Res-Tec FlexiTec 2020 is pretty much state of the art. It's also the sole product amongst these that can be formed seamlessly around raised plinths, skylights etc.

Jeepers_Creepers

'High performance felt' - not sure what makes it 'high performance', but I know some folk swear by this traditional method, and when carried out by an experienced roofer it can look very neat indeed and last well - what sort of warranty is being offered? However, it has seams, and forming it over raised plinths and awkward shapes is tricky and requires more cutting and 'gluing'. And, it does kind of carry a stigma of a 'shed' roof and I bet it'll raise eyebrows when you come to sell if used on a new extension - it'll likely be seen by some/many as the 'cheap' option. I'm afraid I'd be one of them.

'EPDM' - can look very neat when - again - installed well by pros. It has the same issues as felt, tho', when it comes to things like raised plinths and corners - it needs trimming and bonding. The main reason why I wouldn't entertain it, tho', is because it is vulnerable to tearing if something lands on it. I investigated a leaking roof at our local Sea Cadet unit a couple of years back, and we found a series of scuffed tears in a line heading away from an edge. The cause remains a mystery, but our best guess was that a football landed on the roof from the local park, and its recovery was made by using a stick or pole which resulted in the damage. Even walking on it makes me feel uneasy - I keep checking my boots to see there's no chippings or anything caught on the soles.

'GRP' - surely the best of all worlds? Tough, durable, seamless, and just looks very professional. Should come with a solid warranty too. Ours is 20 years.

downshifted

Thank you for all your replies. I’ve just been chatting to a builder’s referee who chose to have felt on his extension on the basis that if anything went wrong in his lifetime (we’re both retired) felting is easier and cheaper to repair, whereas fibreglass or rubber would be more difficult, does anyone have a view on that please?

Slinky

I'd go for whatever you think will outlast you then it won't be your problem!

Jeepers_Creepers

downshifted said:

Thank you for all your replies. I’ve just been chatting to a builder’s referee who chose to have felt on his extension on the basis that if anything went wrong in his lifetime (we’re both retired) felting is easier and cheaper to repair, whereas fibreglass or rubber would be more difficult, does anyone have a view on that please?

Presumably he means that he could repair the felt himself?!

Ok, I haven't felted, EPDM'd or GRP'd a proper roof in my life - a small garden shed doesn't count... But I do have a pretty good idea of what's involved with each. (Eg. GRP, temp usually above 10oC min, OSB to be primed, correct quant of catalyser, etc etc.) For each of these materials, however, I'd follow the same process - educate myself (thank you YouTube), make sure I was confident about tackling the work, and then go for it. Guess which one I'd be most apprehensive in tackling? Yup - felt! Why? Because it uses flames and scary stuff like that.

Which one would I be most happy playing with? GRP. Why - 'cos I've built a couple of kit cars, and patched up plenty of rust holes.

What I'm saying is, for any one of these three products, you need to be competent in order to repair it correctly. You can 'patch' anything, but 'repair' takes the necessary skills.  Yes, I could repair a felt roof too, but I'd do so using cold adhesive - so not the best/correct way.

I don't think this guy's logic holds out; I think he is simply used to working with felt.

And, which of these surfaces is least likely to require a repair anyways? Yup - GRP :-)  

This is only my opinion, of course.

Slinky

I don't get the impression the OP or the 'builders referee' planned on doing the work themselves.

Jeepers_Creepers

In which case I find the BR's comments even more strange.

All of these roof surfaces could be 'repaired' by slapping on a coat of fibrous roof sealant. To repair them 'properly' would presumably require a blow torch (felt), adhesive (EPDM) and a GRP kit (GRP). The BR reckons the former is somehow easier. I can't see much to choose between them, and I would personally rather fix the GRP as it's the one I'm most familiar with.

In any event, GRP will withstand more abuse than the other two, and is less likely to require this repair in the first place.

I would also consider resale value, and GRP usually brings with it nods of approval. Felt is seen by many as 'old-school' and a cheap covering, and EPDM is known to be fragile and susceptible to being punctured, scuffed and torn.

I know what I did chose for our extension, and why^. (Another factor for us was that the upstairs bedroom has French doors that now give access to the roof. There's only one of these surfaces that I'm happy to walk across and also enjoy sitting on.)

Downshifted will make his own choice based on accumulated info.