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mookie 01-21-2008 01:23 PM

Slate roof: need a few slates replaced or the whole roof?
Hi, and apologies for my first post being a question but I am really needing a bit of expert advice on my roof.

We've lived in our house for almost a year, through torrential rains and really severe cold. With no leaks or damp. However very recently, overnight a small patch of damp plaster was obvious in the upstairs bedroom. The damp patch made the paint bubble up, but although it was approximately 3-4inches square, it only spread from the join between the wall and the celing down the wall - but not along the ceiling. We've had another couple of much smaller patches at different spots along the wall but again nothing on the ceiling.

Anyhow, I've been up into the loft to have a look at the roof from the inside to see if there were any obvious leaks. It's a slate tiled roof on a house that is approximately 100yrs old, and we've no knowledge of whether it has been replaced in that time.

My observations were as follows:

- It appears that all of the major joists running horizontally across the width of the loft are damp on their top surface. These are the joists that are above floor level. They aren't 'wet', but do feel slightly damp to the touch.

- The thinner slats that run down the length of the roof, from the peak to gutter, are also damp. Some are damp all over, some again on the top surfaces only. They vary in their dampness, and I checked 3 out of the 5 or 6 up there. Again none were soggy or really wet, but mainly just again damp to the touch.

- A large number of slates are either slightly, almost imperceptibly damp, or glistening, on the loft side. Now this is only the underside of the slates on the outside of the roof, not the slates that are completely exposed to the inside of the loft. You can only see a few inches square of the damp tiles between the others where they overlap. I repeat, the vast majority of the surface area of tiles in the loft are dry - only the small overlaps between are damp.

- The roof from the outside has indeed got several cracked tiles. Some are very seriously cracked and look in some cases as if they are cracked their full width. This is my view from the road outside.

- There is no obvious signs of dripping water in the loft. The dust and grit etc on the crawl boards and junk, is also completely dry, and from what I can see the insulation is also dry - although I can't really tell right under the smallest space at the gutter side of the roof.

We've now had three estimates:

1. Full roof redone, minus felt, 2500 - "porous slates letting water through".
2. Replace half a dozen cracked tiles, 250 + VAT.
3. Full roof redone, 6000. Also offered to do cracked tiles instead for couple hundred as a short term fix.

We've got some more guys coming out to look, but as the first three have such wildly different opinions I'd just like some expert knowledge on slate roofs - specifically how they should be on the inside of the loft (should they be damp feeling? Condensation?) and could a few cracks cause this or could the whole lot need replaced due to becoming porous?

Apologies for the massive post, but any help would be appreciated!

the roofing god 01-22-2008 12:44 PM

doesn`t sound like they are all bad,you can remove all the slate refelt the deck with 30# felt(after any necessary wood repairs),reinstall the roof slate minus the bad ones,and buy new slate to make up the difference---or you can remove everything,put all new slate,or asphalt shingles if you prefer,the asphalt is cheaper,but the slate would last longer(assuming they`re in good condition)---It would be a good idea to get a camera and post several pictures of the slate from inside and out,and we could then give you a better idea

MGC 01-25-2008 03:16 AM

the problems with slate, over time is that they will seperate their layers and hold moisture..

as for the moist feeling on the overlap, since your roof is made of natural material, it will hold some moisture and when the sun comes out, the moisture trapped between the layers will evaporate at a slower rate than that in the dirrect sunlight

as for new or repair..

its mainly up to you, whats your budget? whats the style of your house/what look would u want for it.

personally i would say go for the repair of the slate, just make sure u know that a few more slate are gonna need replaced than what u see, since when u walk on them, a few will break.

replacing it is a messy dirty job!!

RooferJim 01-25-2008 07:51 AM

Sad to say a lot of pennslvania slate is inferior and will delaminate and get porous over time. vermont and canadian slate can last for centuries. Not all slate is the same.

Ed the Roofer 01-25-2008 10:41 AM

Since the described moisture seems to be prevalent on all of the interior wood as you described, I am going to also suggest proper balanced ventilation.

Before I get into this any further, please let us know where you are from. Is this the UK or Canada. You are proclaiming pricing in a different currency than the US, so the location of good higher quality materials would not be relevant if you are across the pond.


tinner666 01-25-2008 12:43 PM

I'm with Ed on this one.

MGC 02-02-2008 04:45 AM


Originally Posted by RooferJim (Post 91875)
Sad to say a lot of pennslvania slate is inferior and will delaminate and get porous over time. vermont and canadian slate can last for centuries. Not all slate is the same.

probably why there isnt much around anymore lol

it could be like that from the climate here also, freeze thaw cycles suck

RooferJim 02-04-2008 04:59 PM

The slate around here is mostly from Vermont and up state New York and looks brand new after a century. A lot of the slate from PA is poras and will delaminate and not last that long. nothing to do with ventalation at all, in fact most older homes are not very tight.

slatergrl 02-07-2008 06:54 AM

It sounds like you are possibly somewhere in europe? From your description it sounds like you have perlings for your roof deck(not a full continuous deck?). That may be part of the reason you are getting the substantial moisture in the attic if the slates are at the end of their life. I am usually always in favor of repairing slate roofs if at all possible. Unfortunately, in our area the problems have been let go for so long that the cost of repairs(replacing rotted beams, extensive new copper flashing, gutters, etc.) can often exceed the cost of an entire new asphalt roof. Observe the slate for yourself, is it soft and flaky? Can you feel the hardness of it? I would go with the repair of cracked tiles(if they are in proximity to your leak replacement should fix that problem) and some better ventilation as recommended above. Make sure you are working with someone who is used to working with slate roofs. If your slate is at the end of its life, it is extra fragile and you wouldn't want an unscrupulous roofer cracking up the rest of the roof in the process. Good luck.

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