Any flat roof experts out there?

When I started work in the roofing trade in 1954, all felt roofs had the outlet standing up about 1"or 25 mm to retain a wet surface, then came the idea of lime stone chipping and now theve gone back to just plain mineral felt as in the 50s. Flat roofing felt as change over the last 50 years so a drop os water wont hurt only in your dislike of seeing it there.

Keith.765

Thanks for the reassurance Keith/Tony.

If there is no join near (for capilary action) or under this water I'd not be to worried. But if it's new felt bonded onto the old and the water is lying along that join I'd not be happy about it lasting long. The action of heat from the sun and water getting in and freezing will soon open up that join.

In message , tony green writes

Which is ok until a leak somewhere occurs...

hmm, very much a case of it depends I think.

We used to have a fair amount of standing water on our flat roof. The roof was surrounded by a low parapet wall and the felt went up onto this.

This was always a weak point IMO where the felt bent upwards. The joints would gradually open. In winter the water would lie for months against this bit of the roof, freezing and melting, leaking through the rof here was pretty much a certainty.

We solved it when the roof was redone, by levelling out the roof a bit, and by putting in a sort of 'gutter' at one side of the roof.

Keeping the roof wet stops degradation of the felt in the first place. A wet roof is much better than one that is kept dry, bakes in the sun, expands, contracts and subsequently cracks. If its is properly done in the first place, not covered in sharp stones and not regularly walked on they can easily last 40-50 years.

No.

Covered in chippings. AH! You mention that! Why the D- do they do that in the first place? Grr.

To reflect the heat and so keep the felt cool - something water does a bit better.

Also to damage the felt when some clod-hopper goes up there in his latest CAT boots and stumps up and down. To be blown off into gutters and bung up drains. To make re-felting more expensive. To make felting more expensive in the first place. "Reflecting the heat". Garn.