The short answer
A commercial re-roof usually runs through four stages: survey and ordering, setting up, stripping and laying, then details and handover. The laying itself is often the quickest part. What stretches a programme is the condition of the deck under the old covering, the lead time on materials, the weather, and whether the building is trading while the work goes on. A firm programme comes after the survey, not before.
The stages of a commercial re-roof
Every commercial roofing re-roof follows the same order, whatever the building. What changes is how long each stage takes.
Survey and quotation. We study the roof covering, the deck below it, the outlets and the way in, and photograph what we find. The quote follows, with a method and a programme.
Ordering. Membranes, insulation boards, metal sheets and lead are ordered once the specification is agreed. Lead times vary by product, so this stage can sit alongside the paperwork rather than waiting for it.
Setting up. Access is arranged: scaffold, edge protection, a loading area, a skip, and a route that keeps staff and visitors clear. Where the roof has fragile rooflights, covers or nets go on before anyone walks on it.
Strip and lay. The old covering comes off in sections, the deck is checked and repaired, and the new system goes on before the end of each working day.
Details and handover. Upstands, flashings, outlets, rooflight kerbs and gutters are finished, the roof is cleaned off, and the area is left clear with all waste removed.
Why the laying is rarely the slow part
A single-ply membrane, a torch-on felt system or a new metal sheet can be laid across a large area quickly once the deck is ready. What takes time is everything around it.
Details are slower than field areas. A plain run of membrane goes down fast. A parapet, a box gutter, a rooflight kerb or a pipe penetration takes careful cutting and sealing. A roof with many of these, such as an older industrial unit with a sawtooth profile, carries more of that slower work.
A roof built in sections, or one with different levels, also needs more than one pass. Steps and upstands each have their own flashing, and every junction has to be finished before the next section is closed in.
Drying is another factor. Insulation boards and decks must be dry when the membrane goes over them. Trapped damp shows up later as blisters and as condensation, so a wet morning can shift the day's plan. Our page on commercial roofing in winter covers how short days and cold affect what can be laid.
What lengthens the programme
Most delays come from five causes, and a survey can foresee most of them.
- Deck condition. Rotten timber, corroded steel or damaged boards under the old covering have to be repaired or replaced before the new system is laid. This is the most common surprise and the one we look for hardest at survey.
- Weather. Wet or windy days stop work on exposed membranes and sheets. A programme needs some slack, and a realistic one allows for it.
- Material lead times. A specified membrane or a particular profile of sheet may take time to arrive. Ordering early removes the risk.
- Hidden asbestos. Older roofs may include asbestos cement sheets, which need careful handling. See our note on asbestos on industrial roofs.
- Extra scope. Rooflights, new gutters, safety systems or solar fixings added mid-job all stretch the time. Deciding on them up front keeps the programme realistic.
A safety system is a good example of an item to plan early. Our page on roof fall arrest systems explains why it is best fitted while the roof is open.
Working around a building that is still in use
Many commercial re-roofs happen while the business carries on underneath. That is usually possible, but it changes how the work is staged.
Work proceeds in sections, and each one is closed in before the crew leaves for the day. Waterproofing goes down as the old covering comes off, with a temporary seal at the end of each day. Noise and dust are planned for, which means deliveries and the loudest work are timed around opening hours where the building needs it.
Access routes and loading areas are marked out so that customers, staff and vehicles keep clear of the work. In some buildings, certain areas such as server rooms, food production or stock stores need extra protection under the roof line. We note these at survey and agree them with you.
All of this adds some days compared with an empty building, but it avoids closing the business. Our guide to roof work while the business stays open sets out the planning in more detail.
Repair, coat or replace
Replacement is not always the answer, and the choice changes the time involved. A repair or a local patch may take days. A liquid coating, where the existing roof is sound enough, takes less time than a strip and relay, though it has limits. Our answer on whether a roof can be coated instead of replaced sets those out.
Steel roofs add a particular question. If the sheets have corroded at their cut edges, the repair needed depends on how far the rust has spread, which affects both the cost and the time. See cut-edge corrosion for what we look for.
We repair where repair works. If a roof can be kept going for several more years with targeted work, we tell you, and give a view on when replacement will become the better use of money.
Getting a realistic programme
Ask for a programme in writing that names the stages, the access arrangements and the assumptions behind it. Treat any promise of an exact finish date given without a survey with caution, since nobody can know the deck condition from the street.
Following our free survey, the fixed price in writing comes with a programme that shows where the uncertainties lie, usually the deck and the weather. Should the deck prove worse than it looked, we tell you before extra work starts, with photographs, so that you can decide what to do.
Tell us early about trading hours, access restrictions, planned shutdowns and any dates you cannot move. Those facts shape the programme more than the roof does, and we can often plan the noisiest stages around them.
