What We Consider for New Pitched Roofs

A new pitched roof makes obvious sense for a new house, extension, garage or outbuilding. With an existing property, the decision is less clear-cut: sometimes a repair is all that is needed, while in other cases continuing to patch an ageing roof simply delays work that has become inevitable.

When is replacement better than repair?

We would not recommend replacing a sound roof because of one leak, even a serious one. A broken tile, an isolated flashing problem or a small area of storm damage can usually be repaired.

Replacement starts to make more sense when problems are widespread rather than localised. Typical signs include large numbers of deteriorating or slipping tiles, failed fixings, brittle or damaged underlay, decaying battens, repeated leaks in different places, or a roof that has already accumulated numerous patches and repairs.

The condition underneath the tiles matters particularly. The tiles may still look reasonable from the ground while the underlay and battens beneath them have reached the end of their useful life. Once those layers are failing across the roof, replacing individual tiles does not address the underlying problem.

In our experience, repeated repair costs are another useful indicator. Scaffolding and safe access make up a significant part of roofing work, so repeatedly paying to access an old roof can eventually become poor value compared with stripping it once and renewing it properly.

Any significant sagging or distortion needs separate investigation. A new covering will not correct a structural problem with rafters, trusses or supporting walls.

When a pitched roof is the right choice

For the main roof of a house, a pitched roof is usually an excellent way of dealing with British weather. The slope sheds rain quickly, tiles and slates provide a durable outer covering, and the construction can create useful loft space or accommodate insulation at ceiling or rafter level.

Pitched roofs are particularly suitable where you want a traditional appearance, a long-lasting tiled or slated covering, or a roof that ties naturally into the existing house.

A flat roof can make more sense on some extensions and smaller structures, particularly where overall height is restricted by first-floor windows, boundaries or the design of the existing building. A flat roof can also create simpler junctions in some situations. It still needs a designed fall, good drainage and careful waterproofing; “flat” does not mean completely level.

A pitched roof normally requires more height and can involve more complicated carpentry and detailing. On a new extension, it is worth settling the roof form early rather than choosing the covering first.

Roof shape, pitch and covering all work together

Common domestic roof forms include gable roofs, hipped roofs and lean-to or mono-pitch roofs. More complicated roofs may combine hips, valleys, dormers and abutments.

Complexity is not necessarily a problem, but every valley, change of direction, chimney and wall abutment creates another detail that has to manage water correctly. A simple roof therefore has fewer potential weak points than an unnecessarily complicated one.

The roof pitch also affects which coverings can be used. Roofing products have minimum pitches and required laps, gauges and fixing arrangements. We would not choose a tile simply because it looks right and then try to make it work at an unsuitable pitch.

Typical choices include:

• Concrete tiles, which provide a wide choice of profiles and colours and are widely used on modern homes.
• Clay tiles, often chosen for their appearance and particularly appropriate on traditional properties and in areas where clay roofs are characteristic.
• Natural slate, which gives a thin, distinctive covering and can provide exceptional service when good-quality slate is correctly selected and installed.
• Fibre-cement slate, which can provide a consistent slate appearance with different weight, cost and detailing considerations from natural slate.

The weight of the proposed covering also matters. Changing from one material to another is not always a like-for-like exercise; the roof structure must be capable of supporting it.

What actually goes into a well-built pitched roof

The visible tiles or slates are only one part of the system. On a typical new roof we first make sure the roof structure provides a sound, straight base. We then install the specified underlay or breathable membrane, correctly graded roofing battens and the chosen tiles or slates. The roof is completed with the appropriate ridge, hip, verge, valley, eaves and abutment details, together with leadwork where required.

Small details have a disproportionate effect on performance. Batten spacing determines the tile gauge and overlap. Eaves have to discharge water properly into the gutter. Valleys need an unobstructed route for considerable volumes of rainwater. Underlay laps and penetrations have to be formed correctly rather than simply cut around pipes and vents.

Setting-out matters too. An experienced roofer plans courses before laying large areas of tile, so that awkward narrow cuts are avoided at verges, valleys and abutments wherever possible.

Wind resistance is another area where roofs that look identical can be very different. BS 5534, the main British Standard for slating and tiling, requires the fixing specification to take wind loading into account. Modern pitched roofs cannot simply rely on the weight of the tiles or a bed of mortar to hold everything in place.

The battens themselves should also be proper graded roofing battens complying with BS 5534. This is not somewhere to substitute ordinary timber of roughly the same size.

Breathable membrane does not mean “no ventilation needed”

This is a common misunderstanding. Condensation control has to be considered as a complete system. BS 5250 covers moisture management in buildings, and the correct approach depends on factors including whether the roof is warm or cold, the type of underlay, the roof covering, the pitch and how well sealed the ceiling is.

A breathable or low-resistance membrane can form part of that strategy, but its presence does not automatically remove every ventilation requirement. On replacement roofs we also need to consider how changes to insulation and ventilation will affect an older building rather than simply copying what was there before.

The standards behind a good pitched roof

The main standards and guidance we work around include:

• BS 5534:2014+A2:2018 for slating and tiling design and fixing
• BS 8000-6:2023 for workmanship in slating and tiling
• BS 5250:2021 for moisture and condensation management.
• BS 8612 for proprietary dry-fixed ridge, hip and verge systems.

Building Regulations can also affect structural design, insulation, moisture control and fire performance, particularly when a roof is being substantially rebuilt rather than simply receiving a small repair.

These requirements explain why we look beyond whether the finished tiles appear straight. The specification of the structure, membrane, battens and fixings; the ventilation strategy; and the way the roof is detailed at its edges and junctions are what determine how the roof performs once it has been through years of wind and rain.

Written by Benjamin Brown. Last reviewed on 16 October 2026.