Low pitch, slate roof leak

[fatsheep]

Hi Folks,
My kitchen roof is very shallow pitch, old slate.
Leaks from (mostly) last two rows of slate at gutter side. It appears that wind and rain cause water to puddle on the felt and then enter via nail holes on battons.

Very badly advised by builder. any ideas other than taking down walls to lower the pitch?

Cheers
David G

 

[Feltwell]

There is a minimum advised pitch for most roofing materials, but with slates you can of course vary the amount of overlap between courses, which I would say must influence the pitch you can use. I know very little about using slates, all my properties have been tiled, so others may have more information.

You shouldn't be getting leaks through the felt, the whole idea of the felt is to stop any water getting through that has made it past the slates!

One way I think you would cure it (although someone else may have an easier suggestion) is to strip the roof of the slates & battens, replace the felt with a breathable roofing membrane such as Proctor Roofshield. When this is put on it should be allowed to sag slightly between the rafters, so that if any water does make it through it is not then trapped behind the battens and it runs down the centre line between the rafters. I've had this membrane as my only roof (no tiles!) for 3 months in winter, no water came through.

The lowest run of membrane is often replaced by a more rigid material to then drape out and above the gutter - sometimes this is a plastic tray on new roofing jobs, sometimes a very heavy grade of felt is used. This sits under the last run of membrane to ensure that any water that runs down has a path to exit. Did your roofer do this, or is it that your roof pitch is so shallow this is not working?

 

[MdB]

I'm considering building an extension on the back of the house and a low angled roof is one option. To make this water tight, one option is to use a flat roofing technique to make the roof water tight and then fit a "fake" tiled roof on top. It was suggested by a roofer mate but I've no idea how practical it is.

 

[fatsheep]

Hi,
Thanks for replying.
The builder didn't add anything extra to the lower courses. Would this be something like a plastic tray which slides under the slates?

I got into this situation by employing the firm to rebuild the roof on the barn I have turned into my kitchen.
Pitch was fairly shallow and new timber will have made it a bit more shallow. I was concerned that this would not work. I was assured that it would. It doesn't!
Obviously, I am pursuing the builder but in the meantime I am looking for a solution that doesn't involve a rebuild as until I can get the guy to cough up I can't afford it.

I appreciate any ideas.
Cheers
DaviD g

 

[Feltwell]

David,

The tray sits under the felt - see the link below, the curved bit is what hangs out & above your guttering.

http://www.screwfix.com/prods/36622/Building/Roofing-Insulation/Felt-Support-Tray-1-5M-Pack-of-5

They help stop the water "ponding" on the felt at the bottom edge of the roof.

To fit them you'd need to strip the bottom couple of rows of slates out first. BUT - without having seen your roof I couldn't really say if this will sort your problem or not.

 

[Moo]

- without having seen your roof I couldn't really say if this will sort your problem or not.

Cue the ritual appeal for photographs!

 

[CatherineB]

I'm considering building an extension on the back of the house and a low angled roof is one option. To make this water tight, one option is to use a flat roofing technique to make the roof water tight and then fit a "fake" tiled roof on top. It was suggested by a roofer mate but I've no idea how practical it is.

Our current kitchen/dining room extension has this. It was built in the early 1980's, and has (we recently discovered) a "proper" flat roof, underneath a very shallow tiled roof. We have always known that the tiled roof was "too shallow", but had no problems with leakage at all until 2 years ago, when melting snow penetrated to the kitchen ceiling.

We discovered that the flat roof was under the tiles only when we went to repair the roof. We decided to leave it as it was (once repaired, obviously!) as it had worked perfectly well for 30-odd years, and I hope now repaired it will do so for another 30-odd.

Not sure how that timescale compares with "properly built" tile rooves, but not unfavourably with ordinary flat rooves, I think?

 

[Feltwell]

Not sure how that timescale compares with "properly built" tile rooves, but not unfavourably with ordinary flat rooves, I think?

Tiled roof - depends on the tiles, location etc - but you should get 80-100 years with only minor repair before major work is needed, it can be much longer.

Flat roofs - varies hugely, 30 years is OK though. As your roof is fairly well protected by the tiled roof I would expect it to last longer. The only concern I would have is ensuring that the void between them is very well ventilated!

MdB, I'd say a chat with your Building Control officer is needed before anything else, to see if they are happy with this rather un-orthodox approach.

 

[MdB]

MdB, I'd say a chat with your Building Control officer is needed before anything else, to see if they are happy with this rather un-orthodox approach.

That was very much the plan. The shape of the roof is going to be a nightmare so BC and planning are going to be very much involved.

 

[fatsheep]

Pictures

http://s249630285.websitehome.co.uk/assets/images/kitchen_046.jpg

http://s249630285.websitehome.co.uk/assets/images/001.JPG

Hope this works
David G

 

[MdB]

Put image tags around your links at it will make them show up here:

[img]http://s249630285.websitehome.co.uk/assets/images/kitchen_046.jpg[/img]

[img]http://s249630285.websitehome.co.uk/assets/images/001.JPG[/img]

In my book, that is far too flat for the slates to do very much and the roof is relying on the felt to keep the water out (which it isn't).

 

[Feltwell]

In my book, that is far too flat for the slates to do very much and the roof is relying on the felt to keep the water out (which it isn't).

Absolutely. Forget my felt tray link posted up earlier, they won't do anything (looks like the builder may have already used them anyway). That just looks like way too flat a pitch for those slates - water gets in then cannot drain off the felt properly due to the very low pitch.

The document below may be of interest - it states "At pitches of less than 300 the weather tightness of the roof becomes questionable irrespective of the lap" - I think that's an error, I think they mean 30 degrees. What is the pitch of that roof? I'd guess at 10 degrees or so from your picture, your main roof only looks to be 25-30 degrees.

http://www.stoneroof.org.uk/stone_slate_roofs_tcm2-27954_tcm9-15988.pdf

As for your options - hard to say. The "make a flat roof under the slates" approach may work. What was on there before, and did it leak? Much as I hate the stuff, "corrugated iron" would work much better on that very shallow pitch - check with the manufacturer, but it can go as low as 5 degrees I think. Some on here love the look of it, some hate it.

 

[Gareth Hughes]

That's not a roof, it's a patio, laid in very small steps. I suspect most of the slates are flat, if not actually sloping in towards the building.

 

[fatsheep]

MdB Thanks for the picture thing.

I think the first picture is distorting the look of the pitch on the main roof which is actually ok. Try this;

A side view of the problem, barn roof;

Corigated iron or any other roof covering is a no no. National park, conservation area and SSI. So its old slate or nothing.
It was a barn before it was a kitchen. The slates are mostly original. There is no tray thing under the slates, what you can see is, I think PVC.
I know now that the pitch is too shallow, I know now that I was a fool to believe the builder. What I'm looking for is any alternative to lowering the front wall to increase the pitch. As well as the cost, I think this would mean the barn roof rising above the level of the house roof where they meet.

Thanks for your help Guys.

 

[Gareth Hughes]

The work must have involved Building Control? so there's them to take to task (as the building regulations guidance includes minimum pitches, and I could wish they were as keen on enforcing those as they are on the guidance about double glazing), plus suing the builder for what is clearly an inadequate piece of work.
As to what you do practically, metal roofing of various sorts is an entirely traditional solution to the problem, going back centuries, so the National Park argument wouldn't seem to hold all that much water. Unlike the roof.

 

[middi]

These kind of problems are not unusual where lised buildings or in a conservation area is concerned.

I have sympathy for everybody concerned. In this particular instance ( and being the builder) I would have advised the owner that in order to keep the existing elevation intact whilst trying to achieve a weatherproof building ,suitable for living accomodation, it would necessitate a correct pitched roof according to the type of roof cladding used.
Unfortunately to change roof angle elevations would require the necessary approvals from the authorities concerned. If an existing barn, or ancillary addition to it, is required for living accomodation it would also require change of use consent.
I would presume the existing elevations of the building in question has just been re-rooved, like for like, which would have pleased the conservation authorities. The same cannot be said for planning permission, as this is required to put parts of the building to a different use to which it was originally intended. This would automatically require building regulations and therefore correct roof pitches etc..
Someone, somewhere, has missed the point.
Short cuts, lack of planning permissions, and ( worst of all ) bad advise from builders lead to these kind of situations, I am sorry to say.
If the roof leaks, because of incorrect pitch, there is no other choise but to correct the pitch ( which may involve permission) or to remove the existing slates and battens, reline with swimming pool style membrane and relay slates above this . If this is done, correct attention has to be given to ventilation and insulation within roof void .
Middi

 

[Feltwell]

I think the first picture is distorting the look of the pitch on the main roof which is actually ok. Try this;

Always a bit hard to tell from pictures, but I've not long finished a roof at 35 degrees - I'd say your main roof is at 30 degrees, which clearly works fine but is probably about the minimum you want to be at. Plain clay tiles have to be at 35 degrees (certainly if using Victorian reclaims), a couple of new brands I found had been approved at 30 degrees. Bearing in mind they are a consistent, manufactured product unlike your slates, that stone roofing guide saying 30 degrees minimum with plenty of head lap sounds like a reasnoble bottom limit to me.

I can't see any easy or quick options to sort your problem out. I'd say your choices are:-

- Keep the slates as a "true" roof but change the pitch - which realistically can only be done by lowering the front wall which I presume will dramaticaly compromise the headroom internally. Raising the back section against the main house and building a vertical wall would look awful and I doubt you'd get permission. Alternatively put a new ridged roof on the barn (running the same way as the main roof) and form a valley against the main building, again this would need permission. Could look OK but will be very expensive and introducing roof valleys is something you should avoid if you can, they are always a weak spot in any roof structure if maintenance is ever neglected in the future.

- Keep the appearance as it is now but construct a "flat" roof underneath the slates - the slates will leak as they do now and will be purely decorative, the "flat" roof underneath will be what actually keeps the building dry and will of course need to be arranged so it drains OK. No difference to the appearance of the outside of the building so should be OK with the planners, but Building Control will need to be happy (it would be an unorthodox solution) and if the building is listed then the CO would need to approve. The existing roof will have to come off first without question, so there will be cost involved. The void between the slates and flat roof would need to be very well ventilated else you could end up with major timber rot problems in the future. If this is what you want to do then I'd suggest the first step is speak to Building Control and (if building is listed) the CO, to see if they would in principle approve this. This at least wouldn't cost you anything if they said "no".

- Move to a different roofing material that does work at that shallow pitch. You say that a different material is a complete "No" with the authorities, but have you tried? You have an ex-agricultural building there, within the park there must be many similar buildings still in agricultural use with corrugated iron roofs. I've yet to visit any farming area where they didn't use corrugated iron to repair old farm buildings at some point, it's a quick and cheap repair and farmers are busy and mean! It may take some persistence to gain approval. This would be the cheapest and quickest way to permanently resolve the problem I'd say.

By the way, your picture of the main roof shows that your builder did use a breathable roofing membrane rather than impermeable felt, which is a good thing. He has definitely used something at the roof edge - you can see it's a different material - either a tray like I posted, or some heavy felt, either of which is fine.

Good luck with getting this sorted. Not a nice situation to be in. Lovely looking building by the way!

 

[Moo]

A silly idea, no doubt, but in view of the fact that it's a kitchen with cupboards and worktops along the outside wall, would it really matter if the ceiling height were to be reduced there?

 

[Penners]

David - it's easy to look at the unslated roof pitch and get lulled into a false sense of security. Slates as thick as that are "laid back" by the slate beneath them, greatly reducing the pitch, not so much of the roof itself but of the individual slates. As others have commented, on a pitch that shallow, with slates that thick, you have, to all intents and purposes, flat slates. Added to that, the roughness of the slates is causing considerable gaps underneath some of them, which I'm sure will be allowing rain to be blown underneath.

Would you be allowed to use ordinary slates - thin ones? If so, they might just restore enough pitch to the roof to achieve an effective run-off. And their smoothness would allow them to lie more snugly, to help prevent wind-blown rain.

But I don't offer any kind of guarantee with that tentative suggestion! As others have said, I would also ensure that there was a truly watertight sarking underneath the slates.

The only other solution I can see would be, as you originally suggested, to lower the height of the wall, in order to increase the pitch.

 

[Moo]

The only other solution I can see would be, as you originally suggested, to lower the height of the wall, in order to increase the pitch.

"As you originally suggested".
There - I knew it would turn out that I'd not read the thread carefully enough.
And I've assumed, rather rashly, that your kitchen units run along that outside wall.

But, since Penners has made the suggestion too, I stand by my idea of reducing the wall height if it's practicable.