The leak in Island Bay had beaten two roofers before it got to me in August 2022. A 1950s weatherboard house on the hill above The Parade, long-run steel from a 1998 reroof, a wet patch on the lounge ceiling only in southerlies. Both roofers had sealed the ridge for good measure. I went up in the southerly at about 70 km/h and lay on the sheeting with my face 300 mm from the surface. Water was walking uphill under a lap and entering through a screw hole where the neoprene washer had split. One screw, out of roughly six hundred. That is a small roof job in Wellington: nothing to see, and a ceiling that costs NZ$2,000 to reline if left.
Why screws fail here faster
Wellington’s hill suburbs mostly sit in Very High or Extra High wind zones, with design gusts of 50 to 55 metres per second. Every gust flexes the sheet and works the screw against its hole. Over twenty years the neoprene hardens, the washer cracks, and the screw head has often backed out 2 or 3 mm so it no longer seals. Wind-driven rain in a southerly arrives horizontally and is pushed up through the hole against gravity. Nothing about that shows in calm weather, which is why two roofers found nothing.
Older galvanised screws also rust at the head, running a stain down the sheet that owners mistake for a leak higher up. A roof of that age in Island Bay or Brooklyn typically has 5 to 10 per cent of screws in a state I would replace.
The replacement job, done properly
- Back out the old screw. If the hole has enlarged, go up one gauge, from 12 to 14, so the new thread bites fresh timber in the purlin.
- Use a Class 4 coated or stainless screw with a bonded EPDM washer, not neoprene. On coastal Wellington the stainless option is worth the extra 40 cents a screw.
- Drive it until the washer is compressed but not dished. Over-driving splits the washer and you are back where you started.
- On a 1990s roof, check purlin spacing at the same time; if the sheet drums underfoot the fixings are further apart than the wind zone now demands, and adding a screw at mid-span between existing ones is cheap while you are up there.
Expect NZ$4 to NZ$7 per screw replaced including labour on a job of fifty or more, or a minimum charge of NZ$250 to NZ$400 for a small count. Most of the cost is the getting up there, the harness and the anchor point, not the screw.
Penetrations: where sealant is not a repair
Every vent pipe, flue and skylight is a hole in the roof with a flashing around it. Sealant lasts eight to twelve years in Wellington sun and salt; the flashing lasts the life of the roof. Three layers of grey silicone around a soil stack means the flashing failed years ago and each layer bought about eighteen months. The right fix is a new EPDM or silicone boot flashing, NZ$60 to NZ$150, with neutral-cure sealant only at the top edge. Acetic-cure silicone, the kind that smells of vinegar, corrodes Zincalume and should never go on a steel roof.
Ridge caps are the other small job that is not small. In Extra High wind zones the cap should be fixed at every rib and into the purlin, not only the sheet crest. Caps fixed every 600 mm lift a few millimetres in every northerly and let rain drift under.
Knowing when small is actually big
A handful of screws, one boot flashing and a resealed ridge is a morning’s work. If the screw count runs past 20 per cent, if there is rust through the sheet at the laps, or if the purlins are soft when the new screw goes in, the job has become a roofing job and the person to do it changes. The line is not about skill; it is about the Building Act, where work on the primary weathertightness of a house beyond minor maintenance is restricted building work and needs a licensed practitioner. For the genuinely small work I have described, the practical option in a place like Island Bay is a Wellington handyman with a harness, a roof anchor and the sense to go up on a still day, which in Wellington means booking flexibly.
The Island Bay lounge ceiling dried out after the one screw was replaced and forty-odd others were done while the ladder was up. Total NZ$380. The two earlier visits that sealed the ridge had cost NZ$900 between them and fixed nothing, because the problem was never on the ridge.
Frequently asked questions
How many roof screws is it normal to replace on an older Wellington roof? Five to ten per cent of the fixings on a twenty-year-old long-run roof in a Very High wind zone. Past twenty per cent the roof needs a proper assessment, not a screw run.
Can I just put sealant over a leaking screw? It will hold for a season at most. The washer has failed and the screw has usually backed out; replace it with a larger-gauge Class 4 or stainless screw with an EPDM washer.
What does it cost to replace roof screws and reseal a vent in Wellington? Roughly NZ$4 to NZ$7 per screw on a run of fifty or more, plus NZ$150 to NZ$300 for a new boot flashing fitted, with a typical minimum call-out of NZ$250 to NZ$400.