Most pitched roofs on Caerphilly's interwar and post-war semis are tile-covered, either with the original concrete tiles laid between the 1920s and 1950s or with later replacements. Renovation here usually means re-bedding ridge and hip tiles, swapping slipped or cracked tiles, and checking the battens and felt beneath — rather than a full strip and recover, unless the covering has reached the end of its life.
What roofs sit on Caerphilly's interwar semis?
The streets around Caerphilly, Bedwas, Ystrad Mynach and the valley estates towards Newport are dominated by semi-detached and short-terraced housing built between the wars and in the two decades after. These typically carry a dual-pitched roof with a fairly steep slope, often a small front gable or a hipped end where two roof faces meet at a corner.
The covering is usually one of two materials:
- Concrete tiles — common from the 1920s onwards, often interlocking, heavier than slate and prone to surface erosion as they age.
- Clay tiles — found on some earlier or higher-specification roofs, harder-wearing but more brittle and harder to source matches for.
Beneath the tiles sit the roof battens — horizontal timber strips the tiles hook onto — and a layer of underfelt. On houses of this age, the original bitumen felt has frequently gone brittle, and battens fixed with cut nails may be weak where damp has crept in. Ridge and hip tiles run along the top edges and were almost always bedded on sand-and-cement mortar, which is the part that fails first.
Signs a pitched roof here is due attention
These typically carry a dual-pitched roof with a fairly steep slope, often a small front gable or a hipped end where two roof faces meet at a corner.
The clearest warning signs are visible from the ground or a bedroom window. Worth looking for:
- Slipped or missing tiles, leaving a gap or an exposed row of battens.
- A ridge line that dips or shows mortar crumbling out from between the ridge tiles.
- Moss build-up holding moisture against the tile surface, common on north-facing valley slopes.
- Daylight visible through the roof when standing in the loft, or staining on the felt and rafters.
- Concrete tiles that look pitted, flaky or noticeably faded — a sign the protective surface has worn away.
The exposed, often wet hillside positions around Caerphilly mean wind-driven rain tests the leading edges and ridges harder than a sheltered town centre would. A single slipped tile in winter can let water track along a batten before it shows inside, so small faults are worth attending to before they spread.
Re-bedding ridges and replacing slipped tiles
Re-bedding ridges is one of the most common jobs on these roofs. The old ridge tiles are lifted, the failed mortar is cleaned off, and the tiles are re-laid on fresh mortar — or, increasingly, on a dry-fix system that uses mechanical clips and a ventilated roll instead of mortar. Dry-fix avoids the cracking that mortar suffers through expansion and frost, and it lets the roof breathe. A roofer should be able to explain the trade-off between traditional bedding and a dry-fix kit for a particular roof.
Replacing slipped tiles is usually straightforward where matching tiles can be found. With older concrete and clay patterns, an exact match can be difficult, so salvaged or reclaimed tiles are often used, sometimes taken from a discreet rear slope and the new tiles placed where they show least. If many tiles have slipped, it often points to nail fatigue or rotten battens rather than the tiles themselves — in which case the affected area may need re-battening.
When inspecting, it is reasonable to ask whether the underfelt and battens have been checked, not just the tiles. On a roof of this era, the materials underneath frequently dictate whether a patch repair will hold or whether a wider section needs attention.
Reviewed: June 2026