Moisture protection for wooden houses: the details that keep the structure dry
A wooden house lasts when water can neither get into the structure nor stay there. That is decided by a handful of details: the base of the walls, the facade, the layers in the wall, the roof edges — and how the house is protected while it is being built.
Geoniks works with wooden houses only — log, timber frame and CLT homes, cabins and villas. We can’t help with concrete, steel, apartment or office buildings.
At the base: lift the wood off the ground
- Build the wooden walls on a concrete, stone or masonry base, with the bottom of the timber well above finished ground and splash water.
- Put a damp-proof course between the base and the bottom plate or first log, so moisture cannot rise into the wood.
- Use preservative-treated timber or durable species where wood is close to the ground, and keep soil, gravel beds and plants away from the cladding.
- Slope the ground away from the house and lead downpipes away from the base.
The facade: rainscreen and ventilation
External cladding is a rainscreen, not the waterproof layer. Behind it a ventilated air gap — typically 20–30 mm, open at the bottom and the top with insect mesh — lets water that gets behind the boards drain and dry out. Behind the gap a vapour-open wind barrier protects the insulation. End grain of cladding boards is cut with a drip edge and kept off horizontal surfaces.
Inside the wall: vapour control on the warm side
Warm indoor air carries moisture. If it reaches a cold layer in the wall it can condense. The rule is to make the inside of the wall more vapour-tight than the outside: a vapour control layer (or an airtight board layer) on the warm side, vapour-open layers towards the outside. Its joints and penetrations — sockets, pipes, beams — must be sealed, which also makes the house airtight. A blower-door test checks it.
With Geoniks: Each wall in the Geoniks editor has a section with its layers and U-value; check the build-up before you ask manufacturers for a price.
Open the 3D editor →Roof edges and openings
- Generous roof overhangs and gable overhangs keep rain off the walls and are the cheapest long-term protection.
- Window and door sills with flashing and a slope that leads water out; sealed joints between frame and wall.
- Gutters sized for the roof area and kept clear.
During construction: keep it dry from day one
Most moisture problems start on site. Store timber off the ground and under cover, close the shell quickly, protect CLT panels and log walls from standing water, and do not close wet timber into walls. In winter, dry the house out gently; heating it too fast can make logs and boards crack.
Pests: termites and insects
In warm regions with termites, local practice uses soil barriers, termite shields at the base and treated or resistant timber in the bottom plates. Everywhere, dry wood is far less attractive to insects; the same moisture details that prevent rot also prevent most insect damage.
Frequently asked questions
How do you stop a wooden house from rotting?
Keep the structure dry: a raised base with a damp-proof course, ventilated cladding, a correct vapour control layer on the warm side, roof overhangs, good flashings — and dry timber during construction.
Does a timber frame house need a vapour barrier?
It needs a vapour control layer or an airtight layer on the warm side that is more vapour-tight than the outer layers, with sealed joints. The exact product depends on the climate and the wall build-up.
Why is cladding ventilated?
Rain that gets behind the boards drains and dries in the air gap instead of soaking the wall. Ventilated cladding also dries itself and lasts longer.
How high should a wooden wall be above the ground?
High enough to stay out of splash water and snow — national guidelines and manufacturers give the minimum for your climate; a stone or concrete base under the timber is the usual solution.