# Membrane for flat roof – what to use?



## boots (5 Jan 2010)

Firstly, apologies for the two new threads in one evening - I know its probably not in the spirit of AAM. I promise to make some contributions if I can!

My qestion is- Has anybody built a house with a flat roof recently?


I am currently gone to tender for a roof membrane as follows:


Single Ply roofing system with standing seam profile 'Sarnafil' or equal approved
on 120mm Kooltherm K7 & 80mm Kooltherm K7 insulation 
on vapour control layer supported on 1.2mm gauge metal decking
The Sarnafil type product is the Architects input from planning stage, the insulation is from my research and the vapour layer and decking is from the Engineer.

This does sound ok, or would anybody have any suggestions?

Thanks for any responses,
Boots


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## onq (5 Jan 2010)

I recently used a proprietary system supplied by the contractor on an extension.

Its basically a fibreglass roof membrane with a special paint finish on Superply laid to falls on a steel and timber composite roof with Kinspan HD insulation between and plasterboard faced HD insulation below the joists.

The important thing is to ensure the 50mm air gap is included to allow air to circulate per TGD Part F of the Building Regulations, Diagram 6 Page 11.

http://www.environ.ie/en/Publicatio...ng/BuildingStandards/FileDownLoad,1647,en.pdf

I was a little paranoid about this suggestion at first and I quizzed him about possible problems with damage or cracking. He pointed out that its a fibreglass roof - the paint finish can be prepared and painted over while the membrane itself is repairable like boats or surfboards are repairable and of acceptable appearance.

I then asked the age old question of the 15-20 year lifespan and renewal problems with removal and replacement. He smiled and pointed out that its a fibreglass roof of 3mm thickness.

The longest he had installed was 14 years old and still going strong, but he was of the opinion that if it needed renewal it was only 3mm thick and quite light so the simplest thing to do would be to clean, key, prepare and install over the existing roof.

We also saw two examples of this kind of roof done by the builder with rooflight lantern lights installed and they looked very well I have to say. He was also the lowest tender by a mile.

I can post contact details if you want them or you can PM me.

HTH

ONQ

[broken link removed]


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## Towger (6 Jan 2010)

Fiberglass its self is not waterproof, in boats the outer gelcoat (couple+ of mm thick) keeps out the water and the fiberglass just gives it strength/structure. The gelcoat breaks down with age/bumps/flexing/bad workmanship/ice etc with allows water to enter / pass through the fiberglass leading to [broken link removed]


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## onq (6 Jan 2010)

Towger said:


> Fiberglass its self is not waterproof, in boats the outer gelcoat (couple+ of mm thick) keeps out the water and the fiberglass just gives it strength/structure. The gelcoat breaks down with age/bumps/flexing/bad workmanship/ice etc with allows water to enter / pass through the fiberglass leading to [broken link removed]



Thanks Towger,

Bookmarked for future reference.
I hadn't been aware of the osmosis issue before.
Fair comment re the gel, but I assumed this was understood.

My wife and I have a little experience with repairing fibreglass hulls.
We actually repaired a 27-foot cruiser on our honeymoon on the Shannon.
Wild weather hit in the middle of Lough Derg and we had a rough pier to moor against.

Amateur placing of the fenders [moi] allowed us to roll a little and a projecting stone holed us above the waterline.
Off we went to the local garage who gave us some fibre mat and a half full can of gel for free - we were chuffed and set to with a will and returned safely.

Thankfully the builder on the recent job had a lot of proprietary information and the workmanship looked okay.
The existing installations we had seen were in perfect condition as well.

FWIW

ONQ.


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