replacing Slate roof - re-use surviving slates or buy new?

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replacing Slate roof - re-use surviving slates or buy new?

Postby aggiego » Fri Jun 22, 2007 1:34 pm

Hello, I 'd be very grateful for your advice.

We are in the process of buying a fairly modest 1906 end-of-terrace house. Like many of these houses, it has a full width part for the front 2 rooms (on each floor), then it goes to a narrower part for one room (on each floor), then there is a one-storey section with kitchen and bathroom. We hope to extend at the back, by replacing the one-storey section by a two-storey, so that we can relocate the bathroom upstairs without reducing the house from 3 bedrooms to 2 bedrooms. We also need to refurbish the slate roof.

The house is gable end on to the street, ie the roofline makes a triangle when viewed from in front. That means we have our own pitched roof, separated by a parapet from the neighbouring terrace. So there aren't any issues about blending into the neighbouring roof. The one-storey section has a flattish metal roof, not slates. So the planned extension will increase the total area of slates.

My initial thought was that I would like to get the roofer to save as many of the existing slates as possible, and reuse them, and try to match them with other recycled or new slates to replace the damaged ones and extend the roof to the larger area required by the extension. But looking on this website it suggests that Welsh slates (which I assume the existing ones are) have a life of about 100 years. If the existing slates are 100 years old, and thus nearing the end of their life, would it be foolish not to take this opportunity to replace them with new and thus have a new life of 100 years? I don't begrudge paying a bit extra for a really good, worry-free roof (I hope!). We got a quick quote from a roofer before commiting to buy and this indicated about ?5000 for a new roof and an extra ?1500 for Welsh slate. In principle, even if it cost a bit more because of the extra labour involved, I would prefer to reuse the existing, (a) to keep as much of the original as possible, and (b) because it has got to better for the environment than shipping another piece of Welsh hillside to SE England. But not if it means a major reduction in the longevity of the refurbished roof.

Also, assuming we are able to re-use, but the necessary extra slates are not a perfect match, do you think it would be better to scatter the replacements randomly over the roof, or use the old slates to do the main section of the roof (assuming there are enough) and the new or recycled slates on top of the narrower section?

FYI, The surveyor said of the roof: "The roof is an original slate roof, which appears to have been in place for many years, and there is no roofing felt. The roof may possibly be the original slate coverings.
There are a number of slipped, missing and broken slates around the roof and several which are held in place with metal tags, all being an indication of accelerating deterioration of the roof coverings and the nails which fix the slates to the battens.
At the rear there are two missing slates at high level on the left hand flank of the roof and some cracked slates on the right hand flank of the roof and a number of dislodged slates at the left hand side, towards the front, around the valley gutter (which appears to have been leaking in the past).
There are also some dislodged slates on the front right hand corner of the roof and generally deterioration of the roof was noted.
The roof is now in a condition requiring stripping and recovering. This provides an opportunity to improve insulation in the roof space and also install modern breathable type roof membrane. .."
The roofer thought it could go a few more years with patching up, but agreed it would probably be wiser to do a complete overhaul at this stage.

Sorry, this is a very long post.
Many thanks for any advice.
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Postby Simon TL » Fri Jun 22, 2007 1:46 pm


A helpfully detailed post! I think the surveyor is right - it will be the original roof.

I would agree that a complete overhaul is a good idea. The problem with very old slate is that the layers start to fall apart. It may well be that the roofer can be left to make professional judgement - reuse what will say, be likely to last 20 years, and replace the rest.

As to what you use, new Welsh may be a waste if you are salvaging some; it may be better to buy more salvaged Welsh so that the overall life of the roof is similar. Scattering the batches would be good - rather than having an obvious block of new.

?5000 sounds typical. The usual approach is a Tyvek membrane - under the slates.

Good luck.
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Postby aggiego » Fri Jun 22, 2007 2:45 pm

Thank you for your prompt and helpful response!

Now we just have to wait for the solicitors to finish doing their thing and we can start getting to grips with our new home.

many thanks.
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roof update

Postby aggiego » Thu Nov 22, 2007 6:51 pm

Just thought i'd let you know we took your advice, went for re-using the slates the builder considered OK and replacing where necessary with recycled Welsh slate. Membrane underneath, and insulation above ceiling. Looks good. Not as big a hassle as I feared - there were quite a few days where we had no slates on half the roof, but the membrane seemed to do the job of keeping any rain out.

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