A loft conversion is one of the most common ways to add space to a house in London and the South East. Many involve a dormer, a hip-to-gable change or a mansard. All of them depend on the existing roof.
Before you get plans drawn up or ask builders to quote, it’s worth knowing what condition the roof is in. This guide explains what to check and why it matters.
Why the existing roof matters
Most conversions keep at least part of the existing roof. If the coverings, battens or underlay are near the end of their life, it may make sense to deal with them while scaffolding is up. If you find out only after the conversion that the rest of the roof needs work, you could end up paying for access twice. It can also be harder to trace a leak once the loft has been lined, insulated and decorated.
The condition of the roof also affects how the conversion is detailed. New flashings, valleys and junctions have to tie into what’s already there.
What to check on the coverings
- Slipped, cracked or missing slates or tiles. On old slate roofs, look for signs of nail fatigue.
- The type of covering. Matching old slate or clay tiles on a new dormer can take planning.
- Ridges, hips and verges.
- Chimneys, especially any that will be removed or that sit next to the new structure.
- Flashings and valleys.
What to check in the loft
The loft space is about to become a room, so it’s worth looking carefully:
- Underlay. Older roofs often have bitumen felt or no underlay at all. Breathable membranes only appeared in the UK in the late 1990s.
- Damp. Stains on timbers, wet insulation or mould can point to leaks or condensation. See condensation or a roof leak.
- Timbers. Visible rot, splits or past repairs.
- Insulation. Spray foam on the underside of the roof can hide the timbers. See our guide to spray foam insulation.
Our survey can report what we see in the roof space. Structural design for the conversion is for a structural engineer.
Want a roof surveyed? We cover London and the South East, with written reports and photos from £150 including VAT. Book a survey or call 07833 053749.
Planning and listed buildings
Many loft conversions can be done under permitted development, but not all. Dormers on front slopes, changes in conservation areas and work on listed buildings may need permission. The Planning Portal has general guidance. Always check with your local council. See our guide to roofs on listed buildings and in conservation areas.
Shared roofs and neighbours
On terraced and semi-detached houses, loft conversions often affect party walls, shared chimneys and the junction with the neighbour’s roof. Knowing the condition of these parts beforehand gives you a record if questions come up later. If work affects a party wall, there may be formal steps to follow, so take advice early.
How a survey helps
A roof survey before you plan gives you a written record of the roof’s condition, with photographs and recommendations by urgency. You can share it with your architect and builders. After the work, a new roof snagging inspection can check the new dormer or mansard and its junctions.
Quick answers
Do I need a roof survey before a loft conversion?
It isn’t required, but it helps. Knowing about defects early lets you deal with them while scaffolding is up.
Should I fix roof defects before or during the conversion?
Often during, because scaffolding is already up. Your builder and designer can advise on timing once you know what needs doing.
Can your survey say if my loft is suitable for conversion?
Not in design terms. We report on the roof’s condition. Head height, structure and design are for your designer and a structural engineer.
Related services
More advice
- Mansard Roof Problems and What to Check
- Spray Foam Insulation and Your Roof
- Roofs on Listed Buildings and in Conservation Areas
- New Roof Snagging Checklist
- All advice
This guide is general information about roofs and roof surveys. It isn’t legal, insurance or structural engineering advice; for those, speak to a suitably qualified professional.