Advice needed before hiring a roofer...

Redland

3. UNDERLAYS.
The primary purpose of a roofing underlay is to reduce the wind load acting on the roof tiles by taking a significant proportion of the wind load itself. To do this successfully, it must not stretch to the point where it can touch the underside of the roof tiles when subjected to wind pressure.
If a roofing underlay does stretch, or “balloon”, so that it touches the back of the roof tiles, then it ceases to perform this primary function with the full wind load transferred onto the roof tiles.
The tile manufacturers’ fixing specifications do not allow for this additional load and roof tiles can be blown off the roof even if they are nailed and clipped.
A related problem concerns the bursting open of unsealed underlay laps when subjected to wind pressure which can also cause the removal of roof tiles. Both the old and new Code of Practice recommend an additional timber batten be installed over the horizontal lap between courses of underlay to prevent the risk of this happening. While this is recommended practice many roofing contractors do not like installing these additional battens and they can cause a trip hazard.
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More here http://www.monier.co.uk/bs-5534/underlays.html

I've have just come off the phone to MarelyEternit.

Main question; Are your double roman's weather proof if they are laid on a roof without an underlay? Yes, subject to pitch and headlap.

I won't waste our time posting what else was said.

I can post a couple of photo's later of a roof in wisbech with sandtoft double pantiles that has no underlay and yet it hasn't leaked in almost 15 years.
 
The problem with that subject to pitch and rafter length baloney is they do leak without a membrane underneath.
 
catlad, your reply is worse than woody's.

A roof tile does not leak due to a lack of membrane. And headlap has nothing to do with rafter length.

If you two were correct this roof in the fens would leak.
Double pantile out.png
Double pantile underside.png
 
So, Redland will guarantee their interlocking tiles to keep the roof below waterproof without an underlay below then. Did you ask Marley that on the phone too?

Oddly, there are more buildings in the UK without an underlay than with, and yet I don't see or hear of those tiles being deposited on the streets and gardens below very often.

Could it be that the introduction of underlays being recommended by the tile manufacturers came in at the same time as the introduction of concrete interlocking tiles. I wonder. I also wonder why. Do you know why AJ?

BTW, Redland's advice you quoted there contradicts with the advice from the manufacturers of breathable membranes. Come to think of it, how does a breathable membrane resist wind pressure anyway?

Hmmm, too much knowledge can be a bad thing eh? :rolleyes: SMH
 
The other thread you're posting on woody. Why doesn't the membrane keep the water out :whistle:

Edit: And lightweight membranes are proving to be a little more troublesome than 1f ever was.
 
^woody^ said:
So, Redland will guarantee their interlocking tiles to keep the roof below waterproof without an underlay below then. Did you ask Marley that on the phone too?
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Weather tight is not the same as waterproof, You couldn't invert a tiled roof and sail up the canal in it.

Oddly, there are more buildings in the UK without an underlay than with, and yet I don't see or hear of those tiles being deposited on the streets and gardens below very often.
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Lightweight membranes ballooning have anything to do with that I wonder.

Could it be that the introduction of underlays being recommended by the tile manufacturers came in at the same time as the introduction of concrete interlocking tiles. I wonder. I also wonder why. Do you know why AJ?
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My guess it's to do with air tight building causing condensation problems in the roof space.

BTW, Redland's advice you quoted there contradicts with the advice from the manufacturers of breathable membranes. Come to think of it, how does a breathable membrane resist wind pressure anyway?
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It doesn't if it baggy as fook. The membrane manufacturers give differing advice.

Hmmm, too much knowledge can be a bad thing eh? :rolleyes: SMH
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I noticed yours hasn't improved since you first posted about membranes back in 2007:p
 
Ok guys, am I missing something here or are you commenting on another job you've done /issue you disagree on and not adding anything more to my thread? I'm not seeing any connection? I saw the first post mentioned my post but it veered off after that.

Anyway I've selected my roofer now and for the price at £1100 for lead valley, renewed ridge 5m, replacement fascias at back, sorting of any other bad works done previously on odd tiles.

I'm also getting them to get more photos of the bonding gutter along the front and back of the main roof. I'm pretty concerned about it if it's not recommended and could cause issues over coming years, especially with the neighbour having paid for a new roof.
 
Fishwalker said:
Ok guys, am I missing something here
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Yes

The problem with water coming into your house is that the roofing felt is defective, not just the tiles.

Any "roofer"that just wants to refix or replace a few tiles or suchlike, and does not recognise the importance of the felt in keeping water out, is not a roofer. And that is the "Advice needed before hiring a roofer"
 
I found this today. I just can't understand why it hasn't been leaking as it's been like that for ten years according to the home owner.
1f.JPG 49\'s.JPG area below felt.JPG

Marley Eternit plain tiles, interlocking tiles, slates
and fibre cement slates are designed and
tested to minimum rafter pitches, below which
a build-up of surface water may cause the
product to leak.
If the design rafter pitch is less than the
minimum recommended rafter pitch for the
particular tile or slate, then they can only be
considered to have an aesthetic function.
In such cases, the true weatherproofing of the
roof system must rely on a fully supported
waterproof membrane with an uninterrupted
drainage path between counter-battens to the
eaves gutter. Details of the full specification for
such a roof construction can be obtained from
the Technical Advisory Service.
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Bonding gutters! I've got that down as my pension plan, I am going to buy a new van get it sign written. Bonding gutter specialist.
 
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