Longevity of a Victorian slate roof

[Tony Williams]

I have a mostly original late Victorian slate roof (1888). Some patching where a chiney has been taken out and a few tiles replaced over the years. It has no felt. But it's dry. Joists are good. I had an "MOT" a few years ago to make sure it was sound.

 

I am exploring the fitting of solar panels and some contractors (by no means all) are baulking at fitting on such a roof.  One has cited the 2010 Building Regulattions Part C -

 

6.2 Roofs should:

a. resist the penetration of precipitation to the inside of the building; and

 

b. not be damaged by precipitation and not carry precipitation to any part of the building which would be damaged by it.

 

6.4

Any roof will meet these requirements by being weather resistant and is backed by a material which will direct precipitation which enters the roof towards the outer face as with roofing felt and membrane.

 

I thought OK, I'll get some quotes for a new roof. I'm in the process. But I also find from a bit of research that old slate roofs have quite a long life, and new roofs less so. 

 

I'm puzzling over what sort of a gamble I am taking here. Stick or twist?

 

I'd be interested in people's reactions to this dilemma.

 

Kind regards

 

Tony

[FarmerN]

I can’t help on fitting Panels on old roof , but we had a 1890 roof retiled a few years back, no felt etc .

It was bone dry in the attic and very well ventilated ! Roof only lasted 120 years!

Timbers all very sound, the bit that was failing were the batten nails. You could see the odd bit where whole battens were sliding. This would be my worry with putting panels on an old roof.

 

Just built a new house, the bit that annoyed me about the new roof was the battens were  nailed on with a nail gun, OK they were galvanized nails , but the nails were so thin and the coating very thin compared to hammer driven roofing nails. I think they will slip a lot sooner than the roof, on the old house. They used Copper nails for the slate but that seemed almost pointless as it will be the batten nails that fail.

Edited Monday at 08:37 by FarmerN

[-rick-]

Can't comment on water proofing or anything but I believe its fairly common that the roof structure of old roofs isn't necessarily strong enough to support the added weight of solar panels, so may need redoing for that reason alone. I'm not sure the environmental benefits of solar would really stack up if you have to replace a perfectly good roof to install them (maybe if you re-used the slates).

[nod]

If you look at the PV adds online None of them use cat ladders and walk all over the roof If it ain’t knackered now It will by the time there size tens have trampled all over it 

[MikeSharp01]

5 minutes ago, nod said:

walk all over the roof If it ain’t knackered now It will by the time there size tens have trampled all over it 

This would be my worry also.

[Tony Williams]

What is the received wisdom on how long to expect a Victorian slate roof to be serviceable? I have seen figures of 140-180 years cited, but no source given. In comparison, how long would I expect a replacement roof using modern materials to survive? This is what I think I need to understand to make an informed decision. Grateful for anyone who can give me some insights.

[Conor]

Nobody can really give a useful option without knowing more about the roof in question. Photos would help a lot. Is there sarking? Are the nails copper? what condition is the timebr underneath? What aspect is the roof? How exposed to wind is it? What % of the roof so you intend to cover? Is the building in any way protected or in a conservation area?

 

Lots of factors! If timbers are in good condition, but slates iffy with corroded nails, my instinct would be to strip the roof, refelt and batten, and install in roof trays, keep the best of the slates to do the remaining roof. if everything is generally iffy and near it's end, wouldn't go near it.

[torre]

In your situation I'd only consider two options:

1/ do nothing and you may get another 10+ years just replacing the odd slate. Solar will be cheaper next year anyway

2/ do the job properly as @Conor described and end up with a new roof and better solar install

 

Installing solar over the existing will inevitably cause a bit of damage and if the roof starts failing due to age anyway, all that solar may have to come off for proper repairs

[SteamyTea]

When we used to fit PV back in 2012, we had to install on dozens of old slate roofs (they are pretty common down here).

Nearly all got damaged and most had to be reinforced.

 

As I was the 'engineer' for the company, I suggested to the sales team that they either said no, or doubled the price.

Thankfully the company went bust, so they only ruined about 30 houses.