Have I missed anything or a lot .

[Under450]

Hi guys
Family member needs help with a roof problem. He has a pitched roof over kitchen in an old two up two down. It is slate roof but in v bad condition.

He has asked my help to redo it in felt.

Is there anything else I need to look out for, things i think are required etc: breather membrane nailed down onto 9mm boards, felt (anything special required here) folded at edges, left to flow into guttering, top of roof placed and mortered under next doors roofing tops and house side of felt placed under existing lead flashing that seems ok.

Help appreciated as you can tell novice... Be gentle!

 

[freddiemercurystwin]

You're gonna replace a slate pitched roof with felt?

 

[Under450]

That's want he wants to do for cost saving I've tried to say its not a good idea but there you go!!! It's not that big only above kitchen about 7ft wide by 6ft.

 

[RedHerring2]

IMO, for what it's worth, no reputable builder or even DIYer would give advice on such a patch-up.
The cost of replacing it properly is probably less than twice the expected cost of felting (materials only) but it would have probably something like a three-fold or even four-fold lifespan.

 

[Under450]

Yes I've told him that, he won't listen so I said I would help him!
Back to the original Q, what else would he need, I'm trying to turn up there with a bit more knowledge to help.
Cheers

 

[RedHerring2]

I'm not going to give much advice on this one 'cos it should be a non-starter but:
what's the point of using a breathable membrane under felt?
use up to three layers of felt. Correct underlays first. Topped with correct top layer.

 

[ladylola]

I don't know where in Staffordshire you are Redherring but you may know the area not far from me of Walsall Wood where there are several houses with pitched roofs done completey in felt. The outside layer is green mineral felt and I always wonder when I pass them as it always seems a strange idea .
If the owner of the op house wants to go ahead then your suggestion is about right, he should treat it as a flat roof for all the constructional details.

 

[Under450]

Thanks guys, yes he got the idea for this from his next door neighbour, who has had this done. I thought about the breathable underlay because it is a pitched roof with no vent etc. and there is a void underneath before it hits he kitchen ceiling, so several layers of the underlay and then one layer of top felt. Personally I think he is on a hiding to nothing but can't let him do it himself

 

[RedHerring2]

If there is no provision for ventilation in that roofspace, you may be creating as much of a problem as curing one.

 

[Under450]

What would be the answer with a felt roof to stop the condensation etc as you mention, cheers

 

[^woody^]

It seems that you are effectively doing a flat roof - ie sticking the felt down?

9mm boards will be too thin and will sag between the rafters. Use 18mm or add extra noggins/supports

No need for a breather membrane (it wont be doing anything), you can just felt the boards with suitable felt - either a 2 or 3 layer system or one layer of torch on or self adhesive

The problem will be that there is much greater chance of the felt or the laps, being lifted by wind suction when felting at a pitched angle. So it may end in tears

There will be a need for ventilation, but its very hard to say how this can be achieved. Having said that it will be the least of his worries so could probably be not bothered with

I would get him to consider EPDM instead

 

[RedHerring2]

Ventilation top and bottom.
Bottom easily achievable with eaves vents.
Top, depends on whether it's a ridge or flashed upto a wall.
If it's a ridge, then ridge tiles. if it's flashed up to a wall, I don't honestly know. Maybe someone else will.

 

[Under450]

Thanks guys, so far thinking of the thicker boards, self adhesive felt built up with four alternating layers, the top of the roof has ridge tiles, so how is it best to fit vents with ridge tiles. Cheers

 

[^woody^]

There was a good post on here a year or two ago from one of the regular roofing people and it showed how to make abutment ventilation from timber

Edit

If it is a ridge, there are proprietary ridge systems, and you will have to screw these down rather than use mortar. Google Danelaw or Klober

 

[RedHerring2]

so how is it best to fit vents with ridge tiles.

Fit the appropriaye style of vented ridge tiles.
They're not cheap, about £45 each.
Or a dry ridge system which may be cheaper and easier.

Sorry woody, your edit beat me to it.

I'll back out of the discussion.