Materials for Flat Roof Dormers

I started talking about roof dormers in my previous post, how big can a roof dormer be? Some research lead me to EPDM, a type of durable rubber that is used instead of felt to give a flat roof dormer a longer life.

A builder also mentioned today that fibreglass is another option, and a little research revealed that their is a company very nearby that provides these roofs – RW Mouldings in Canvey Island. They say that a “properly laid GRP roof will last for at least 30 years with no measurable deterioration”. I guess that the product has not been around long enough for them to say it will last longer, but by the sounds of things, it might well last beyond my lifetime!

It certainly looks very durable in the photos. The photo here is of a fibreglass roof.

So, roofing options are:

  • Felt roof – when applied with great skill, can last for around 15 years. Could start leaking in a shorter time
  • Rubber – lifespan of over 20 years, maybe 25
  • Glass fibre / fibreglass – potentially longer than 30 years.
  • Sloped roof with tiles – but I think not possible with my roof

Obviously cost is a big deal. I have a flat roof on my single story extension, and it does not cost much for a roofer to come around with a ladder, strip the stones off and lay a new piece of felt – so it might not be economic to use anything better than felt.

But, the dormer in the loft will require scaffolding when it needs replacing and this is a huge cost. Also, repairs will not happen overnight and seeing that this is our bedroom, we might want something that is not going to leak after 5 years in the sun. The dormer will be south facing – no idea if that reduces lifespan, but something else to research.

The dormer walls

Another questions is, what to cover the dormer with. The builder today said that while tiles look nice, they can be a nightmare and are prone to fly off in storms. He suggested cladding, which can now come already coloured so there is no need to ever paint it. Sounds like a good idea.

The dormer windows

Because my dormer is now going to be on the side of the house, under permitted development rules, the windows need to be obscured glass. Rear dormers can have clear glass. I will not have much glass in the dormer because it is really there to provide additional roof space. I guess I will have a couple of small, obscured panes to make it look nicer and then have Velux and normal windows in the gables.

Guttering, Roof Trims and Fascia

Because it will be so high up, everything will definitely be PVC. I want no wood exposed to the elements at all.


Photo credit: Fibreglass roofing undertaken by Crown Building Services Halifax by Crownbuild (CC Licence)




More like this in the Planning and Design section

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