what is the fabric for under the roof tiles?

[RobertL]

My house was built in the 1960s and like many it has heavy roof tiles that are laid on battons which are fixed to the rafters. The tiles seem to be held there by gravity alone - each one has a lip that engages with the batton. Between the battons and the rafters is a sheet of bituminous cloth (it looks like).

What is the purpose of this cloth?

Is it to stop the wind which might otherwise (1) blow water up the tiles and into the roof space and (2) lift off the roof tiles? or it is to catch any water that does leak in and guide it to the gutter.

I want to cut this cloth in order to remove as small patch of tiles so I can do some ridge repairs without having to climb onto the outside of the roof.

When I repair it afterwards does it need to be watertight or simply windproof?

Thanks,

Robert

[Andrew Mawson]

tiles

It's called Sarking felt, and is there to stop rain and snow being blown into the loft by an unfavourable wind. It also stops a load of crud being blown in keeping the loft cleaner. Conventionally it is laid from the roll parallel to the guttering, starting at the bottom of the roof. Each subsequent strip being laid to over lap the previous one by 4"-6". At the ridge, a roll is laid so that half goes down one facet of the roof and the other half down the other facet. This gives a waterproof seal so anything blowing under the tiles will run down the outside of the sarking felt and down into the gutters, as the felt should overlap the gutter board slightly and dip into the guttering.

You will find that the bituminous type will be very brittle by now and will probably crumble as you try to remove it. Modern sarking felt is a plastic sheeting, grey on one side and black on the other, with a square nylon reinforcing mesh embedded between the layers.

Although you ought to be able to remove the tiles and felt, and do your ridge repairs 'from inside' I cannot see how you can correctly replace the sarking and tiles in a weatherproof fashion from inside.

If the tiles were laid correctly every third row should have been nailed to the battens - or even every row if in an exposed position.

AWEM

[RobertL]

that's very helpful. thank you.

You are right, the cloth is very crumbly now. in fact there is a broken part elsewhere in the roof and the undersides of the tiles are visible and that's how I found the tiles were apparently held only by gravity. it could well be that some elsewhere are fixed down - I only looked at one!

I want to replace, or repair, a cracked 'curved' ridge tile. It wa spotted by workman replacing the barge boards. I though I might be able to reach it as I described, but maybe its not so straightforward in the light of your comments.

thanks again,

Robert

[The Natural Philosopher]

To prevent wind lifting the tiles off, mainly.

It somewaht reduces sucton effects right by te tiles.

Windproof. The tiles are the waterproof layer.

[Rick Hughes]

Well there is a mechanical fixing spec dependant on expected wind loading in your area .. typically something like clip every other tile in every third course, and clip all tiles in first course.

The felt is there to prevent snow & wind penetration, it is not there to prevent water .. the lap on tiles takes care of that.

If you do remove felt, then make sure you slide patch under the row above and have a good overlap. making sure at least 150mm on all side, and nailed onto rafter, with large clout head galv felt nails.