Flat roof re-felting advice

[robgraham]

I've a flat roof which is nominally 4m square. It is part of the roof of an extension that was built in late 1990, so is in it's 23rd year. I had a roofer check it 2 years ago and he gave it the all clear, and he has done so again this past week.

This seems pretty old for a felt roof, albeit this one does have pebbles on it to protect it. The roofer does say that he is surprised how good it is and despite doing himself out of a job, he recommends leaving it as it is. The guy is a good tradesman.

What does the collective feel about this leave alone option ? The quote is £450 to strip off the pebbles and put on a top coat of felt.

Thanks for any comments

Rob

[Bill Wright]

Does it leak? I have several flat roofs here that date from the 1980s and they are OK. If it ain't bust don't fix it.

Bill

[Frank Erskine]

What is the decking beneath? If it's real wood it can probably withstand a short-term wetting when the felt fails. Chipboard will act like Weetabix and your repair work/bills will be all that more. If it's a south-facing roof or catches a lot of sunshine you're very lucky it's lasting so long, and it's seriously time to consider preventive maintenance. A lot depends on the original felting process. A proper "built-up" felting process will last longer than a "just slap it on" felting. Normally built-up involves nailing on (with clout nails) a thin perforated layer of felt (1" holes every 3" or so, glued over by an undercoat felt using hot pitch. This allows movement of the decking due to thermal and organic movement, and allows the wood to "breathe". Finally your mineral layer is added, with its pebbles or whatever to resist solar attack. The lack of this is why, say, shed roofs fail after just a few years (if that!).

[Alexander Lamaison]

Can you inspect the timbers from below? If so, and there's no signs of damp (usually appears at edges and felt seams first), I'd leave it as it is.

It's good that you keep checking, though.

Alex

[Interloper]

That seems an incredibly good lifespan. Flat roofs on properties I've owned have generally failed in just a few years, leading me to conclude that the best thing to do with a flat roof is not have one (the same axiom applies to sliding doors!).

I increased the pitch of the flat roof on my existing property to around 17 degrees and covered the (new) wooden decking with a membrane and Alcan profiled aluminium sheets. That was 19 years ago and I've had no problems (I used austenitic stainless steel fasteners throughout).