Roofing mystery

[EricP]

Last night at 11pm we had water coming through the roof hatch. Water was pouring through a hole in the membrane lining just under the ridge and directly over the hatch.

The roof is an 80's tiled one over the membrane and quite steep pitch.

It has been raining for days and is still raining as I type. The water poured for about 10 minutes and then stopped, no more has come through and the bowl under it is bone dry.

There didn't seem to be a wind of note when it leaked, and it is quite gusty at ridge height at the moment, but no water coming in.

So the question is does water normally get under tiles and run down the membrane? Is that how a tiled roof works?

Would it be sensible to patch the membrane and leave it as a one off mystery event?

Or patch and get the roof examined later as an expensive maintenance exercise?

We are baffled.

[EricP]

And I keep banging my head on the open hatch hanging down. It hurts!

Please help

[Dave]

cant help, but I had something similar. but oin a much smaller scale

in 1999 weeks after we moved in, we had a small leak dripping from the bedroom ceiling near the front of the house. It dried out. Checking it out was on a "to do" list. we forgot to do it and it has never happened since!

[The Natural Philosopher]

Ah.

membranes are not there to stop water coming in.

That is the job of the tiles.

The membrane is to stop the tiles being sucked off in a strong wind.

The tiles rely totally on being a series of overlapping 'umbrellas'.

This works fantastically well as long as :-

- water is not blown sideways with enough force to rise up 2/3rds of the tile height and blow over the top.

- water does not accumulate to a similar depth in a pool.

I suspect that in this case, during the dry weather detritus has accumulated, and the rain has caused it to form a dam somewhere..then enough rain breaks the dam and washes all the crap into the guttering system, where it generally blocks the gullies instead. Moss is a prime culprit quite often, but dead leaves and bits of birds nest and twig are pretty good as well.

[keith_765]

Wrong!. The underlay membrane, or felt as it used to be called, is purly a vapor barrier>

Before felt was used tiles were touced with cow hair mortar on the inside on the back and down to the lath or nailed every 5th course

[The Natural Philosopher]

Er, no, its not. Not much point in having a vapour barrier in a 'cold' roof where the wind whistles in at the eaves and out again.

I don't really care..felt was introduced to stop tiles being blown off. That is a fact. Plenty of slate rooves have none, and are fully rainproof

[EricP]

Many thnks for the input people. :)))

[roybennet]

If you have a chimney check the flashing as it is probably the most likely culprit. Check the mortar where the flashing is joined to the chimney stack for condition.

Roy

[keith_765]

CUT.

Oh yes its is. The underlay is there to stop the driven snow and the penetration of frost condensation through the slates or tiles. Felt was never designed to hold tiles on a roof from being suck or blown off. The wind that blows through the attic via the eave vent system is to act as a anti condensation in the loft area . All this condensation problem as come about by filling the loft with insulation and banging the central heating on in the winter.

Two nails per slate, they only slip or get suck or blown off when the nails become worn where the shanks goes through the back of the slate and the lath.

[keith_765]

Roof underlay has been assessed to confirm its suitability for use in pitched roof construction, under slates or tiles as a secondary weather resistant layer, for protection against wind driven rain and snow and ingress of dust.