Timber Frame Wall (Platform Frame)
A timber frame wall weighs a fifth of a masonry wall and insulates twice as well: yet all its value lies in two thin layers nobody sees — the airtight layer and the vapour check.
Overview
TAV. 00In platform frame the wall is a set of studs at regular centres, braced with boards and filled with insulation: the structure takes up almost nothing, and the insulation lives within the thickness instead of on top of it. It goes up dry, in days rather than weeks, and the finished floor becomes the platform for the level above — hence the name. The flip side is sensitivity: without a continuous airtight layer, moisture enters the cavity and the timber, and the advantage turns into damage.
The site score
TAV. HThe detail of the craftthe foot of the wall
The sole plate and the studs
Fixing the sole plate to the kerb over a separating membrane, then erecting the studs at regular centres.
Timber never sits on bare concrete: put the membrane in, or you'll be explaining it in ten years.site notebook — editorial synthesis
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
The invisible that counts
Why airtightness is not the vapour check
They are two different jobs, often given to the same sheet. The check slows vapour diffusing through materials; the airtight layer stops air moving through holes — and it is the latter that carries a hundred times more moisture into the wall.
Schematic. It is why the blower-door test is run with the structure closed but finishes open: if something leaks, you must still be able to fix it.
The foot of the wall
Where timber meets concrete
The point where a timber-frame house most often dies is neither the roof nor the facade: it is the first centimetre, where the sole plate meets the kerb and the external paving comes up too high.
This detail must be resolved in design together with the metalworker and whoever does the external works: it is the point where three different trades hand each other the responsibility.
How it ages (and what betrays it)
TAV. PQuestions from the site
TAV. QDoes a timber frame house last as long as masonry?
Yes, on one condition: the timber stays dry. North American and European frame houses pass a century when the base detail, airtightness and breathability are done properly. When they fail, it is almost always water, not loads.
How is it different from CLT?
In a frame the studs are the structure and the insulation sits in the void between them: a lighter, cheaper wall. In CLT the wall is a solid load-bearing panel and all the insulation goes outside: more mass, more stiffness, more cost.
How much does the blower-door test really matter?
It is the only way to know whether the airtightness was actually built or merely claimed. Run it with the structure closed but finishes still open: that way leaks are found and sealed while they are still reachable.
Doesn't a lightweight wall overheat in summer?
That is its weak point: little mass means little thermal lag. You compensate by choosing dense insulation (wood fibre, cellulose) instead of very light products, and by getting solar shading right — which matters more here than elsewhere.