Building materials for Queensland storms: what we specify and why

Every summer Brisbane gets hail, wind gusts that take trees down, and rain that falls faster than the gutters can move it. The city is not in a cyclone region, but the building standards that apply here are still written for those storms, and the difference between a house that shrugs them off and one that leaks, lifts or floods is mostly decided in the specification and the fixing, not in the materials alone. This is what we specify and why.

The roof

Colorbond steel is the roof for this climate. It is light, it sheds water fast, it does not crack under hail the way tiles can, and it lasts forty years or more if the right grade is used. What matters as much as the sheet is what holds it down: screws at the spacing the wind rating requires, into battens that are themselves tied to the rafters, which are tied to the wall frame, which is tied to the footings. That chain of tie-downs is the standard, and an old Queenslander often has gaps in it that we close when we re-roof. Sarking under the sheets is a second skin against wind-driven rain and it also cools the house.

Gutters are where a summer downpour first overwhelms a house. We size them and their downpipes for the rainfall intensity Brisbane actually gets, put overflow slots in the front of box gutters so the water goes outside rather than into the ceiling, and keep the number of internal gutters as low as the roof form allows.

Windows and doors

The openings are the weak points. Aluminium frames have the strength and need no maintenance; timber suits a character house and needs paint. In both, the glass should be laminated or toughened where it is large or low, and the seals and flashings matter more than the frame. Sliding and stacking doors need drained sills and a proper threshold or they will let water in during a horizontal storm. Garage roller doors want wind locks, because the door blowing in is how a roof starts to lift.

Walls and cladding

The oldest Queenslanders in Brisbane are clad in hardwood weatherboards that have taken a century of storms. What fails is not old hardwood but untreated pine and unpainted timber. Where we replace boards we use hardwood or fibre cement weatherboards, which do not move in humidity, do not rot and take paint well. Brick and rendered masonry take impact and hold heat, which is a virtue in winter and a liability in a west-facing wall in January. Behind any cladding we want a breathable wall wrap that keeps rain out and lets moisture escape.

Under the house

A raised house is the best flood defence Brisbane ever invented, and it works only if the water can get away underneath. We grade the ground under a house to fall out, keep the subfloor ventilated and put the drainage in before anything is built under. Where the lower level is enclosed, the floor sits above the flood level council sets for the site, the materials near the ground are masonry, tile or treated hardwood, and the electrical is kept high. Carpet and solid timber flooring do not belong in a flood-mapped lower level, and we will say so.

Fixings and frames

The strongest material fails at its connection. Galvanised or stainless steel bolts, straps and brackets at every joint in the load path; treated timber or steel for anything touching the ground; concrete footings sized by the engineer for the soil, not by habit. This is the part of a house you never see and it is the part the storm tests. Our engineering sits inside the plan stage so the tie-down detailing is on the drawings before the price is fixed.

The garden

Water has to go somewhere. Permeable paving and gravel let it into the ground; a wide concrete driveway sends it at the house. Retaining walls in masonry or concrete sleepers with drainage behind them; garden beds graded away from the walls; no loose pebbles under the windows where a gust can pick them up. Trees trimmed back from the roof before November, every year.

Maintenance, once a year

Before storm season: clear the gutters and downpipes, check the roof screws and flashings, look for cracked paint on timber, re-seal any door or window that has started to whistle, and walk the yard for anything that could fly. Half an hour on a ladder in October saves a ceiling in January. If your house is due for that walk-around and you would like a builder's eye on it, a free meeting at the studio is a good place to start.