In brief
- Roof sheets rarely fail in the sheet itself; they fail at fixings, laps and the purlin line that was never checked before covering.
- A supervision gap can show up as loose roof coverings that lift in wind and leak at the laps, sometimes months after handover.
- Detect the gap by walking the roof during fixing and by asking for the fixing schedule, screw samples and purlin survey before sheets are laid.
Contents
How does a roof sheet fixing supervision gap turn into loose roof coverings?
Roof sheet fixing fails quietly when nobody checks the work at the moment it is covered up. A supervisor who is not on the roof during fixing, or who signs off from the ground, cannot see the screw type, the lap, or whether the purlin line was set true before the first sheet went down. The sheet itself is rarely the problem. The covering lifts because the fixings and the supporting line under it were never verified against the specification.
A roof sheet fixing supervision gap can open in one of three ways. The fixing crew works ahead of the check, so the next bay is covered before the last one is looked at. The supervisor is responsible for several trades at once and the roof is treated as a single inspection at the end. Or the drawing detail is followed loosely because the fixing schedule was never issued to the site. Once the sheets are laid, the evidence is hidden under the lap.
Ask the contractor for the fixing records from comparable roof work, and ask what his own inspection routine is before work starts. A written routine is the first thing a gap removes.
What should be checked before the sheets are fixed down?
Set the purlin line and the fixing schedule before any sheet is laid, because a roof that is covered cannot be corrected cheaply. General practice is to check the purlin spacing and level against the approved drawing, confirm the sheet thickness and coating, and agree the screw type, washer and spacing before the first bay. Confirm the actual figures for the project against the specification and the engineer's instruction, since the required spacing and fixing pattern vary with the sheet profile and the wind loading.
The checks that catch a gap are simple and local:
- Walk the purlin line with a string or laser and record the deviation bay by bay.
- Ask for a sample of the screws and washers on site and compare them with the submittal.
- Watch the first two bays being fixed, then check the lap and the screw depth in those bays.
- Ask who signs the fixing record and whether that person is on site during the work.
If the crew cannot show the fixing schedule or the screw submittal, the supervision gap is present before the first sheet moves. Ask the contractor to stop at the sample bays and settle the detail. This is cheaper than re-fixing a finished roof.
How do missed inspections show up after handover?
A missed inspection can show up later as a lifted sheet, a drumming sound in wind, or a leak that appears at a lap rather than a penetration. Where salt and humidity are present, they can also attack a coating that was scratched during fixing, so the defect can be visible as corrosion around a screw rather than as a leak. Confirm the exposure conditions and coating specification for the project with the engineer. General practice is to check the roof after the first strong wind and again after the Gu and Deyr rains, and to record what moves.
The detective work is straightforward. A lifted or loose covering can point to screws that were over-driven, under-driven, or set outside the purlin. A leak at a lap can point to a lap that was fixed in the wrong direction, or to a sealant that was not applied. A drumming sheet can point to a missing fixing in the middle of the bay. Each of these is a fixing question, not a sheet question, and each can be checked against the fixing schedule if one exists.
Ask the contractor and the project engineer for the fixing records and the as-built roof layout. If the records were never kept, ask for a joint walk of the roof with the fixing crew and write down what each fixing looks like. Confirm repair methods with the engineer before anyone re-fixes a sheet.
What to do next
Before the next roof starts on the project, ask the contractor for a written fixing schedule, a screw and washer sample, and a named person who will be on the roof during fixing. Ask the contractor and the project engineer for the fixing records and as-built roof layout from comparable work. Walk the first two bays together before the rest are covered, and keep the photographs in the project file.
Frequently asked questions
Can you inspect roof sheet fixing after the roof is finished?
Only partially. The lap and the fixing pattern are hidden once the sheets are laid and the flashings are on. You can check for lifted sheets, drumming in wind and corrosion around screws, but the fixing depth and lap direction are no longer visible. Record the fixing pattern in open bays before the roof is closed.
Who should hold the fixing records on a project?
Ask the contractor to keep the fixing schedule, screw submittal and bay-by-bay check on site, and confirm with the engineer who signs the fixing record. If no one has the schedule, treat it as a supervision gap and settle the detail before the next bay is covered.
Local reporting: this article is written for building work in Garowe and Puntland. Ground conditions, prices and rules differ between places; confirm the details for your own site.