Lining the underside of the roof

[MHAD]

Hi.

I have a 1930's semi. The roof is tiled directly onto the timbers (no felt in those days I gather). There is wadding / horsehair & plaster type mix that was used throughout the roof on the underside of the joins between tiles.

I want to line the underside of the roof (or part of the roof) to prevent the heavy rain of dust and dirt that comes down from ruining anything I store up there.

Whatever I use will need to be fixed to the underside of the roof timbers.

A neighbour has used plastic sheeting for this purpose, however I'm nervous of restricting ventilation to the timbers by doing the same.

I've bought some breathable roofing membrane from Screwfix (Item # 95917), which is described as:

"Breathable, high-performance pitched rool underlay made from polyolefin materials, producing high vapour permability and water-resistance. User friendly.

* Eliminates Roof Space Ventilation
* Energy-Saving"

The idea is to staple gun this to the underside of the roof timbers, for about two thirds of the roof.

My question is ... what considerations should I make when fixing up the membrane, ie: is it better to have the waterproof side on the inside or outside face... I can see arguments for both ways and keep going round in circles.

The last thing I want to do is introduce any kind of mould problem to the roof timbers.

Any advice would be most appreciated.

Thanks very much.

 

[MHAD]

Having read a few more posts on the forum, it looks like the membrane may be OK.

Should I fit individual pieces between the joists, or is it safe to just run the sheets across the lot?

 

[freddiemercurystwin]

http://www.blinkinglamp.co.uk/documents/Roofers Choice.pdf

I'd think under would be fine especially as its breathable. However if in doubt giv'em a ringo!

 

[MHAD]

Thanks very much for the link. I'll give them a ring I think, just to see if it's breathable in both directions or only in one.

If it's in one direction only, I'm still not sure which way round to fix it up. Gut feeling is for it to be a vapour barrier to any moisture in the loft space to prevent it getting onto the timbers?

 

[troy.mclure]

This is just what I've been wanting to get an answer to! I've just moved into an end terrace property which is a pre-war build, and I too have no felt liner between the tiles and joists.

I would be interested to know what you found out about how to apply the liner (stapled along all the joists, or just strips inbetween the joists).

Cheers,
Mike

 

[Deluks]

You could fix it between joists with a couple of battens, or just tack it to base of the joists.
This is not a proper substitute for underfelt as leaks in the tiles means your timber still gets wet. It'll work for dust and draughtproofing only.

Re: installation. Tyvek (for example) is always used printed side outwards, in fact many experienced builders and chippies have told me that it must be used this way. A look on the Tyvek website though says that it works either way, it's waterproof and vapour permeable in both directions. I believe the goretex and similar stuff used in jackets and suchlike only work in one direction.

 

[troy.mclure]

This is not a proper substitute for underfelt as leaks in the tiles means your timber still gets wet. It'll work for dust and draughtproofing only.

Thanks for the info. I realise that the joints will still be prone to leaks, but Im reluctant to splash out on a complete re-roofing just to get some underfelt put under what I believe is a waterproof roof. The reason Im thinking about adding underfelt is I want to put some electics up in the loft (just some flooring and lighting etc), and Im wondering if the absence of and underfelt will cause problems with the electrics (moisture in the air etc) - and if adding the underfelt to the 'back side' of the tiles will suffice as protection enough for any electrics that are up there.

Sorry if some of that is talking rubbish, I'm a bit new to this household stuff!

Cheers

 

[Deluks]

This is not a proper substitute for underfelt as leaks in the tiles means your timber still gets wet. It'll work for dust and draughtproofing only.

Thanks for the info. I realise that the joints will still be prone to leaks, but Im reluctant to splash out on a complete re-roofing just to get some underfelt put under what I believe is a waterproof roof. The reason Im thinking about adding underfelt is I want to put some electics up in the loft (just some flooring and lighting etc), and Im wondering if the absence of and underfelt will cause problems with the electrics (moisture in the air etc) - and if adding the underfelt to the 'back side' of the tiles will suffice as protection enough for any electrics that are up there.

Sorry if some of that is talking rubbish, I'm a bit new to this household stuff!

Cheers

No, lack of underfelt is not a problem if the roof doesn't leak, and if it did leak you should be getting it sorted quick-sharp anyhow.
Just bare tiles in our roof, been there 70+ years and no leaks.

However regarding your electrics and floor and 'new to this household stuff' comment. I'd suggest you have a browse through the floors, stairs and lofts section of this forum, here's one to get you started.

 

[troy.mclure]

Thanks Deluks - looks like I've got some reading to do! As far as I know the roof doesn't leak, so I'm in particular rush to use the loft for anything- good job too, it may take a while to figure what I can / want to do!

 

[Gees]

How about the spray on stuff. my slate roof is 110 years old, no leaks , but lets lots of heat out even with a great big wad of loft insulation?

 

[noseall]

How about the spray on stuff.

nooooooooooooooooooooooooo

 

[memor maplin]

GEES Don't do it covering up the(posibly still damp) battens and rafters in foam leads to wood rot.
You'd be amazed how quickly it can take hold.

Memor