The membrane forms the water tight barrier ?

[Post and beam]

My understanding is that the roof membrane actually forms the watertight barrier from Rainfall. And that the tiles are there to protect the membrane.

Am i wrong please?

 

I have a little potential issue with the membrane and battening on the roof that the roofers are half way through. They have now broken up until the new year but i have a couple of small areas where rain has got in. Dormer valley for one of them and near to the gable ladder area for the other.

 

I would rather my mind was put at rest and this be addressed before they crack on in the new year.

 

Thanks in advance

 

keith

[ProDave]

I have always understood tiles and appropriate flashings collect all the water and send it to gutters etc.

 

The membrane is only there underneath to catch a leak if it occurs and catch any condensation that may form under the tile and trip off.

 

But it is good to test how watertight the membrane is before the tiles go on so you know it is a good backup.

[Temp]

+1

Tiles and flashing should collect all the water. Membrane is just a backup.

[joe90]

Yes, if the membrane without tiles leak I would not be happy. This needs pointing out to your roofers on their return (don’t be fobbed off with “the tiles will sort that out.)

[sgt_woulds]

The tiles and flashing form the primary waterproofing layer.  In older houses this is also the only waterproofing, which is why traditional buildings have slates or plain tiles, both of which have greater overlaps and can resist wind-driven rain quite well.

 

Wooden sarking boards were introduced in high exposure zones to prevent wind from blowing through one side of the roof and lifting tiles on tiles on the other.  These were gradually replaced with paper and bituminous membranes that performed the same function but were cheaper and quicker to fix. 

 

As modern interlocking tiles were introduced, wind-driven rain became more of an issue, and the membranes became important as a secondary weathertight barrier.  They became standard fit in all situations, but gradually changed to the breathable types.

 

The membrane should provide good weather tightness until the roof proper is on but are not 100 % proof thanks to nail holes etc.  The better types will have tape at the overlaps and a conscientious roofer will ensure there is a slight 'droop' between the rafters to ensure good runoff and tape penetrations and abutments if leaving exposed.

 

In certain situations the membrane can be deleted, e.g. wood fibre insulating sarking boards above the rafters on a warm roof.  Tiles still provide primary weatherproofing and the hydrophobic coating on the woodfibre is the secondary waterproofing layer. 

 

In any case, whatever is under the tiles is only ever a backup.

[Beau]

I would expect the membrane to be watertight in its own right and the tiles to do the same so you have two levels of protection

 

Many years back our old place didn't have any felt or membrane. We had a blizzard of very powdery snow and we had proper drifts in the loft as it blew in under the the slates. I was only young but remember moving the snow out of the loft into the bath before it brought the ceiling down or melted

[sgt_woulds]

A valley is a likely area to leak due to the amount of water it will see.  Have they fitted the dry valleys yet?

 

Gable ladders are a strange location for issues unless the undercloak is not in place.

 

As ever, pictures speak a thousand words...

[saveasteading]

1 hour ago, sgt_woulds said:

conscientious roofer 

And knowledgeable.

I've met some very ignorant roofers who don't understand lapping and flashing. Absolutely not a clue, and if was as easy to do it right as wrong.

They were roofers because they didn't mind heights and the money is good.

(And ceey few clients check the work).

All the above advice is good....it must not leak at this stage.

Post a couple of pictures and you can honestly say you've had it looked at by experts and they have to sort it and spray test while you observe.

[ToughButterCup]

2 hours ago, ProDave said:

...

But it is good to test how watertight the membrane is before the tiles go on so you know it is a good backup.

 

Now he tells me ... 6 years bloody late.

[sgt_woulds]

1 hour ago, saveasteading said:

And knowledgeable.

I've met some very ignorant roofers who don't understand lapping and flashing. Absolutely not a clue, and if was as easy to do it right as wrong.

They were roofers because they didn't mind heights and the money is good.

(And ceey few clients check the work).

All the above advice is good....it must not leak at this stage.

Post a couple of pictures and you can honestly say you've had it looked at by experts and they have to sort it and spray test while you observe.

 

Too true - too many monkeys not enough craftsmen.  The adage 'never do to a customer's house that you wouldn't want done to your own' is one I've always worked to and tried to instil in apprentices, but I've worked with many so-called tradesmen of all types who couldn't give a toss as long as they got paid.

 

Having said that, I've yet to come across any roof that is 100% waterproof but a properly installed and detailed membrane should keep out 99.99% 🙂