Thursday 26 November 2015


The subfloor is finished and we thought we'd let you know how we went about it. 
We installed 120x35 H3 pine joists to support our floor and attached these with joist hangers directly to the trailer. We could have had steel joists welded in when we had the trailer made, but we wanted to reduce both costs as well as thermal bridges as far as we could, so opted for the timber joists for additional support.
Tabea installing a subfloor joist

We then attached 0.4mm galvanised sheets to support our insulation batts. Even though it was extremely awkward, we decided to install the sheets from underneath. This way we can access the subfloor from the outside, if we ever needed to for maintenance. The 0.4mm sheets were the thinnest we could get and while they do feel a bit wobbly, they are sturdy enough to do what we need them to. Working with the galvanised sheets was unpleasant and noisy and we're glad that we picked timber and not metal as our main building material!

Not very pleasant: 
Working with galvanised sheet 
metal in confined spaces

Very pleasant: 
Working with fluffy 
sheep wool insulation

We painted the plywood that we used for the subfloor with a borax solution before installing it. We read that this would deter termites, but hopefully they shouldn't find their way into our subfloor anyway, as everything below will be sealed and out of metal and H3 (external-grade) timber. We're also not sure how effective the borax solution would be long-term, but we had it sitting in the cupboard anyway and it's a natural product, so we thought we'd just do it. Luckily, the termites here are not as aggressive as up north, so we should be fine as long as we regularly check around and underneath the trailer. Fingers crossed.

Borax mixed with hot water
On the photos you might have noticed that our joists are not evenly spaced. This is because we needed extra support in spots where we'll be putting braces and and an internal wall. Other joists had to placed where the standard-sized plywood sheets for our subfloor would meet, so at just under 1.2m apart.

We left 2mm gaps between the plywood sheets to allow for expansion. In hindsight, we should have added those 2mm to the 1.2m joist spacing. 
We then sealed those expansion gaps with caulk, both to increase airtightness at a later stage and because we were worried about rain or bugs getting into the subfloor insulation during construction. Now that the subfloor is finished, we have a clean slate to build our tiny house on!

Cutting the plywood to size.


  1. Hallo ihr beiden lieben, prima daß ihr schon mit dem Bau eures Hauses starten konntet, die Isolierung mit der Schafwolle ist uns sehr sympatisch. Sicherlich seit ihr schon ein ganzes Stück weitergekommen und wir freuen uns für euch, gutes Gelingen, alles liebe aus Göttingen Mama und Andreas

  2. Absolutely awesome you it!!!! :-)

  3. Hi - how is the sheeps wool doing in the subfloor? I am considering using wool in the walls, but was thinking about going with rigid foam in the floor for moisture control reasons? What's your experience so far? Thanks.

  4. A joist is a horizontal structural member used in framing to span an open space, often between beams that subsequently transfer loads to vertical members. When incorporated into a floor framing system, joists serve to provide stiffness to the subfloor sheathing, allowing it to function as a horizontal diaphragm.Timber Frame Manufacturers