Roof and weathertight shell: the milestone lenders and insurers watch

Getting the roof on and the windows in is the biggest milestone on site. It turns an open frame into a shell that rain cannot reach. After that the inside can dry and the interior trades can begin. It is also the stage where lenders, insurers and your own programme all ask the same question: is the house weathertight yet?

What happens in order

1. Roof structure. Prefabricated trusses or cut rafters are lifted onto the wall plate, braced and fixed down with the straps in the design. A crane or telehandler is usually needed, so book it for a dry, calm day.
2. Gables, ridge and bracing. The gable ends are built up or framed, and the roof is braced against wind.
3. Fascia, soffit and verge timbers go on, with ventilation openings left as designed.
4. Underlay and battens. A breathable membrane is laid over the rafters or trusses, then battens at the spacing the tiles need.
5. Roof covering. Slates, tiles or a metal roof are fixed to the battens, with flashings at chimneys, valleys, abutments and rooflights.
6. Rainwater goods. Gutters and downpipes are fitted, and ideally connected to the surface-water drains.
7. Windows and external doors. These are fitted, sealed and made secure, then the openings are protected.
8. Scaffold struck. Once the outer envelope is finished, the scaffold comes down. Check that the remaining trades have what they need.

The sequence of 7 and 8 varies. Some builders fit windows before the roof covering is finished, with temporary cover.

Who does what

Agree before the roof goes on who is responsible if it rains while the structure is open. In a main-contractor build the contractor normally carries that risk under the contract. If you are managing trades yourself, it is yours, and you should ask your insurer how that is treated.

The roof is often a separate trade from the walls. The truss supplier designs and delivers the trusses, a roofer fits the covering, and a window supplier fits the openings. Your designer and engineer specify the structure, and your assigned certifier’s inspection plan should include the roof structure before the covering. The lender’s inspector may separately confirm the roof stage. See the assigned certifier.

If the trusses were designed by the supplier, ask for their design drawings and any certificate, and confirm that the engineer and certifier accept them.

What to check before it is covered

Get a record of each of these before the covering hides it:

• Truss layout and bracing match the supplier’s drawings. No notch, cut or hole in a truss member without approval.
• Fixings between plate and wall, and between truss and plate, are the specified straps, bolts or clips.
• Wall plate is level and tied down to the walls at the spacing in the design.
• Underlay is laid with the right overlaps, sags slightly between rafters so water can drain, and has no tears.
• Battens are the specified size, spaced to suit the tile or slate, and nailed to the specification.
• Ventilation and insulation details at the eaves and ridge match the design. A cold roof needs ventilation; a warm roof has insulation above the rafters.
• Flashings and abutments: valley, chimney, wall abutments and rooflight surrounds, where leaks usually start.

Take photographs of the underlay and battens, and of any area that will be hidden by fascia or flashings.

Windows and doors

Think about security as well as weather. Until the external doors are fitted with working locks, anyone can walk in, so most builders fit temporary doors or board up the openings and hand the keys to one person.

Windows and doors are a major part of the thermal envelope and the security of the house. Check:

• The delivered units match the order: sizes, glazing, opening type, colour and fixed or opening panes.
• Frames are packed and fixed to the manufacturer’s instructions, not just foamed in.
• The seal between frame and wall, which affects airtightness and draughts, is the one the design calls for (tapes or membranes, in an airtight build).
• Cills, thresholds and cavity closers are in place, with a tray under thresholds.
• Glass is clean and undamaged, and labelled with the safety glass marks where required.

Window orders have lead times, often several weeks and sometimes longer. Order from the final dimensions, and measure on site if you changed openings.

What goes wrong, and what it costs

• Late trusses or windows. The shell stays open and everything behind it waits. Order as soon as the structure is fixed.
• Wind and rain on an unfinished roof. Damage to underlay, insulation and plaster is expensive. Ask what protection is on site.
• Poor flashings. The most common roof leak. Photograph them before covering.
• Roof loading mistakes. Stacking tiles on trusses can overload them. Ask that loads are spread over the walls or supported.
• Wrong window sizes or colours. Replacement means weeks and cost.
• No hold on scaffold. Taking scaffold down before gutters, fascias and render details are complete leads to expensive re-erecting.

Why lenders and insurers care

There is a practical reason for this too. Once the shell is closed, the inside can dry and the interior trades can start without fear of water damage, so the programme speeds up. Work out how many weeks you have between weathertight and plastering, because that is when delays in joinery, windows or first fix show.

A weathertight shell is a recognised milestone. Many lenders have a stage for it, and an inspector may need to see the roof. An insurer may ask whether the roof is complete when you arrange cover, because an open house is a different risk from a closed one. Tell your insurer or broker when the shell is complete, in case your cover or its conditions change. Look at your contract works policy for exclusions around storm damage or theft of unfixed materials, and keep records. See what lenders require.

Site and insurance risks at this stage

• Storm damage. Trusses, scaffolding and the shell itself are exposed. A bracing failure can bring down a roof structure.
• Water damage to insulation, plasterboard and timber frame.
• Falls from height. A serious hazard for the builder’s team and for visitors, especially children. As the client, ask how the site is secured.
• Theft. Copper, windows, tools and tiles are all tempting once the house has valuable fittings.

Make sure cover is in place for the works, the materials on site and your liability to others, and that it names who is insured. Use the cover checker to see which types suit how you are building.

Payments

If your lender pays a stage at roof level, check what the lender’s inspector needs and whether the payment arrives before the builder’s invoice. See staged drawdown explained and the stage payment planner.

Before first fix

• You know the date the shell was closed, in case your insurer or lender asks for it.

• Any storm or leak damage found while the roof was open has been recorded and either repaired or listed.

• The roof, windows and external doors are fitted and secure.

• Inspection records and photographs are saved.

• The lender’s stage evidence is submitted.

• The next stage is first fix.