More damage inside old buildings starts at roof level than anywhere else. Water gets in at the top and shows itself somewhere else entirely, often a long way from where it entered, which is why roof and chimney defects are worth understanding before they turn into structural ones.
Stone slate roofs
Traditional Cotswold stone slate roofs are heavy, handsome and demanding. The things we look for:
- Slipped and missing slates. Often the fixings have failed rather than the stone, which is a different repair from replacing the covering.
- Nail sickness. Historic fixings corrode, and slates begin slipping across a whole slope rather than in one spot.
- Sagging between rafters and purlins. The weight of a stone roof is considerable, and deflection tells you something about the structure beneath.
- Previous repairs with the wrong materials. Cement mortar, modern flashings and inappropriate replacements cause more problems than they solve.
- Torching and underlay. Many older roofs have no underlay at all, which isn’t automatically a defect but changes how the roof behaves.
Flashings, valleys and rainwater goods
In our experience, a large proportion of “roof leaks” aren’t the covering at all. They’re the details:
- Lead flashings that have split, lifted, or been replaced with mortar fillets
- Valleys that are undersized or blocked
- Parapet gutters, which are common on larger Cotswold houses and unforgiving when they block
- Cast iron gutters with hairline cracks that only show in heavy rain
- Downpipes discharging against the wall rather than into a drain
These are cheap to put right early and expensive once the wall behind them is saturated.
Chimneys
Chimneys take more weather than any other part of the building, and they’re often the most neglected:
- Eroded and missing pointing, particularly on the exposed side
- Cracked or absent flaunching around the pots
- Failed lead trays and flashings at the junction with the roof
- Leaning stacks, which may indicate sulphate attack or movement
- Redundant flues capped without ventilation, which causes condensation inside the stack
- Damp staining in bedrooms and lofts around the breast, which often traces back to the stack rather than the roof
Where the damage shows up
Water entering at roof level frequently appears as damp low down, or as timber decay in a floor. That’s why we investigate rather than treat the symptom. Our guides to damp and timber surveys and defect investigation explain the approach.
What to do about it
- Get the rainwater goods cleared and checked every year. It’s the cheapest maintenance there is.
- Deal with slipped slates promptly. One slate is a repair; a slope full of them is a re-roof.
- Use the right materials. Lime mortar and lead where the building expects them, not cement and mastic.
- Get a proper inspection if you’re buying, or if you’ve noticed staining inside. A Level 3 building survey covers the roof in detail.
How we could help
We survey and investigate roofs, chimneys and the damage they cause across the Cotswolds, Gloucestershire and Bath, on period and modern properties alike. Get in touch if you want a defect looked at properly.
Frequently asked questions
The stone itself lasts a very long time. It’s usually the fixings, battens and flashings that fail first, which is why careful repair often beats replacement.
It needs investigating. Some lean is historic and stable, but movement in a stack can also be progressive, and stacks are high and heavy.
On traditional construction, cement mortar frequently causes damage. Lime based mortars suited to the stone are usually the right answer.
