Timber and water are like a good chef and a hot pan. Used properly, there's no issue. Leave it unattended and something gets burnt. Well-designed timber buildings last for centuries. The ones that go wrong almost always go wrong at a handful of predictable places.
I spend a lot of my time on moisture and durability in timber buildings, and three locations come up again and again.
1. Wet areas over timber
Bathrooms sit on top of timber floors in every timber apartment, hotel and aged care building. A shower seal fails, a pipe weeps behind a wall, a tap is left running. The water finds the timber below, and because it's hidden under tiles and screed, nobody sees it until there's a stain on the ceiling downstairs.
What we recommend:
- Two lines of defence, not one. A waterproofing membrane is the first line. Add a second: another membrane layer, preservative-treated timber under the wet area, or a moisture monitoring sensor that raises the alarm early.
- Prefabricated bathroom pods or trays. A factory-made tray brings its own waterproofing and keeps wet trades off the timber.
- Set-downs planned early. Wet areas often need a lower floor level for falls. In timber that's a structural decision, not a finishes detail.
2. Balconies
A balcony is a timber floor that's outside. It gets rained on, it holds water against its surface, and it's exposed to the sun's heat cycles. It's also where the building's waterproofing turns a corner, which is where membranes fail.
CLT balconies can be done, but they carry a long-term risk that's hard to inspect and expensive to fix. Our default is to keep the balcony out of the timber structure:
- a steel or concrete balcony bolted back to the timber, with a thermal and moisture break at the connection, or
- a lightweight balcony on its own frame, standing in front of the building.
Either way, the timber stays inside the building envelope where it belongs.
3. Cores
Lift and stair cores look like simple boxes, but they're where timber meets everything else. If the core is concrete, the timber floors around it shrink and settle while the core doesn't, so connections, lift doors and risers have to allow for that movement. If the core is CLT, it moves with the rest of the building, but some lift suppliers have firm views on fixing rails to timber, so check early.
Cores also sit open to the weather longest during construction. A CLT lift shaft can act like a chimney for rain. Covering it, or installing the core last, saves a lot of drying time later.
The fourth place: the building site
There's one more location that catches people out: the construction phase itself. Mass timber goes up fast, often before the roof and façade are on. A week of heavy rain on an unprotected floor can soak the timber, and trapped moisture under finishes causes problems for years.
The fixes are simple and cheap compared with the alternative: tape the panel joints, use temporary membranes, sequence the roof early, and measure moisture content before closing anything in.
Design it out, don't detail it out
Every one of these risks is easier to solve at concept stage than later. Moving a bathroom, changing a balcony system or choosing the core material costs nothing on a sketch. On site, it costs a fortune.
That's why every Timber Concept report has a durability section that flags these locations on your actual plans. If you'd like that for your project, send it through.