Re-screwing roofs in Christchurch: when popped nails mean repair, not re-roof

Long-run steel in New Zealand was originally fixed with lead-head nails, going back to the first nail-fixed roofs in the country. Twisted-shank nails became the common choice from the late 1990s through to the early 2010s, before screw-fixed installs took over. On any nail-fixed roof with either type, a popped nail shows as the head sitting proud above the sheet.

You will see heads that have lifted clear of the steel, often visible from the ground once several have started to go. Both nail types are prone to popping on Canterbury roofs. The most common driver is the daily heat cycle: cold nights and hot days move the steel through expansion and contraction until the nail works loose in the timber below.

Once the head lifts, a small gap opens between the head and the shank. Capillary action pulls water into that gap and holds it against the nail. Water sitting on the shank starts rusting the nail and damages the sheet around the fixing.

Any nail head sitting above the roof plane needs addressing. The hole in the timber widens through repeated expansion cycles, and on the next wet front water drives in through the lifted fixing and the hole in the sheet around it. That is where the leak starts on most re-screw call-outs.

By the time a homeowner notices a popped nail, the rubber neoprene washer under the head has usually been exposed to UV and gone brittle. Hammering the nail flat does not re-seal against the sheet.

The expansion and contraction cycles have also enlarged the hole in the purlin or batten. The nail has less grip than when it was first driven. That is why re-screwing uses a thicker shank than the original nail and coarse threads meant to hold permanently in tired timber.

We do not walk nail-fixed roofs to size up a re-screw. Foot traffic compresses the sheets and pops additional nails, which makes the problem worse before work has even started.

A qualified roofer attends site and uses drone passes from the ground to capture the condition of fixings across each roof face. That imagery comes back to the office where we build an accurate, itemised quote for the scope required.

Where ceiling access allows, we also check purlin condition from inside before confirming timber is sound enough to take a full re-screw programme.

Climbing onto a nail-fixed roof causes damage. On any roof face we access to carry out work, we replace every fixing on that face. Patching only the popped nails you could see from the ground would leave the compression damage from our access untreated.

We remove each existing nail while causing as little damage to the sheet as practical. Extracting a fixing takes force, so you may see minor scratches or light denting around some holes. That is normal on a re-screw programme.

We then install a class 5 roof screw through the same hole left by the removed nail, seating the washer flat against the sheet. The original fixing pattern stays as it was when the roof was installed.

A re-screw makes sense when the Colorsteel still has sound coating, the underlay is holding, and the problem is fixings rather than perforated steel. Done across the required faces, it buys years without stripping the cover off.

You are looking at re-roofing when rust is widespread, the coating is brittle, leaks appear in multiple rooms in one winter, or the roof is past economic repair. Screws cannot save sheets that are already failing.

If you can see lifted heads from the ground, or the rattle in a nor'wester has got louder after the last storm, book an assessment. Spring and early autumn are practical windows in Christchurch to sort fixings before the next heavy wind season.