Roof decking removal

Damaged decking is hard to spot from outside because the covering hides it. The warning signs usually show up in the loft or on the top-floor ceiling. Look out for these:

• Dark stains and damp patches on the timber or ceiling
• A musty smell that stays even after airing
• Soft or mouldy boards
• Daylight showing through
• Fine wood dust below small holes in the timber

The wood dust usually points to wood-boring insects such as woodworm or house longhorn beetle.

If the damage is in one spot, for example after a falling branch, replacing a few boards is often enough. If the timber is damp and affected over a larger area, patch repairs rarely last and the problem comes back. In that case the whole decking is removed.

Proper removal is more than ripping off boards. Each step builds on the one before. If the preparation is rushed, the rafters suffer and the budget usually suffers too.

1. Inspect the roof and loft. The carpenter assesses the decking, rafters, purlins, membranes and timber moisture, and sets the scope of work.
2. Secure the site. This means scaffolding or fall-arrest systems, roof ladders and harnesses for the workers. The area below the roof, where material may fall, is fenced off.
3. Remove the covering. Tiles come off row by row, metal sheets are unscrewed and bitumen felt is cut away. Covering in good condition can be stacked and reused.
4. Remove the decking. Boards are prised off gradually and carefully so the rafters are not damaged. OSB sheets are cut into smaller pieces where needed so they can be lowered safely.
5. Pull out or cut off old nails in the rafters so they do not get in the way of the new decking.
6. Check the exposed roof structure. The carpenter looks at timber moisture, insect attack or rot, cracks and the condition of the joints. Damaged members are dealt with before anything is covered up.
7. Cover the roof temporarily with a tarpaulin if the new decking is not going on the same day.
8. Sort and remove the waste and clean up the site.

Why check the roof structure at this point? It is the only time the whole of it is visible. Once new decking is on, hidden rot is much harder to deal with.

Older houses usually have decking made of boards roughly 20 to 30 mm thick. With close boarding, the boards sit tight against each other. With spaced boarding, there are gaps between them. Boards can be replaced one at a time, but they take up moisture more easily.

Newer roofs often use OSB sheets. They cope with short-term damp, but long-term leaks make them swell and lose strength. The sheets are larger and heavier than boards, so handling them on a roof takes more care.

On a flat roof, the decking carries the waterproofing and often the insulation as well. These layers are usually bonded or mechanically fixed together, so they do not simply come apart. Before work starts, a specialist should decide which layers can stay and which must come off completely.

Pitched roofs often have a breathable membrane or bitumen felt on or under the decking. It tears easily during removal. If it is meant to stay, it has to be handled very carefully. If it is old and brittle, plan to replace it from the start.

The size of the roof is only part of what decides how much effort, time and cost the job takes. These factors matter most:

• Pitch and shape of the roof: a steep roof with dormers, valleys and chimneys takes longer to strip than a simple gable roof
• Access to the house: whether scaffolding can go up and a skip can be placed right next to the building
• Type of decking and how it is fixed: dense nailing and bonded layers slow the work down
• Condition of the timber: rotten boards break and have to come out piece by piece
• Roof covering: asbestos cement slates or corrugated sheets may only be removed by a contractor licensed for asbestos work
• What the quote covers: scaffolding, waste removal and rafter repairs may be included or charged separately

When you compare quotes, look closely at what each one actually includes. A quote without scaffolding and waste removal can look cheaper than it really is.

In practice it often happens that work on the decking starts without a thorough inspection of the roof structure. Once the roof is open, damaged rafters turn up and the job stops until someone decides what to do with them. If the damage is missed and covered with new decking, the renovation may be wasted within a few years.

Another mistake is cutting corners on safety. Walking on exposed rafters without fall protection is dangerous. It also risks damaging the rafters and the ceiling below. Work at height belongs to professionals with scaffolding and fall-arrest equipment, which is why there is no DIY guide for this job.

The weather is often underestimated too. A single shower on an open roof without a temporary cover can soak the insulation and ceilings. A sensible contractor only opens up as much roof as can be covered again the same day.

Finally, there is the vague agreement. Wording such as "removal as required" leads to disputes. The contract should state the scope of work, the schedule and how extra work is handled. A typical example is replacing rafters found to be damaged during removal. The contractor should tell you about any such work in advance and agree it with you in writing.

Replacing decking like for like, without changing the shape of the roof, is usually treated as maintenance. The rules depend on your local building regulations, though, so check with your local building authority. Contact them before work starts in these cases:

• The pitch, shape or height of the roof will change
• The load-bearing structure will change
• The building is listed or in a conservation area

In a block of flats, the roof is a shared part of the building. Decisions about the work rest with the building management or the owners' association, not with an individual flat owner.

Timber from the decking is bulky construction waste and usually goes in a skip. Old timber treated with preservatives may count as hazardous waste. Your local council or recycling centre can tell you how to dispose of it. Asbestos roofing is disposed of separately, and only through a licensed contractor.

Once the removal is complete, walk the roof with the carpenter before the new decking goes on:

• The decking has been removed to the agreed extent
• Rafters are not cracked or needlessly damaged by prising
• Old nails have been pulled out or cut off
• The contractor has shown you the condition of the roof structure and pointed out damp or affected members
• Any extra work has been agreed in writing
• The membrane is either intact or its replacement has been agreed
• The roof is temporarily covered against rain
• Covering to be reused is stored where it will not get damaged
• Waste has been removed and the area around the house is clean