Timber Frame

Stick building with Masonite beams follows conventional timber frame practices. Masonite beams are strong, straight, light and rigid but only across their width. Across their thickness they are quite floppy (see pictures) so during construction joist, stud and rafter spacings have to be fixed by nailing temporary battens across them (small section slating batten is ideal).

Pic 3: The long beams are 12m but the trailer is only 6m. When on edge they don’t bend.

Pic 4: ...but beams on their sides just droop. These are 8.9m.

We got permission to proceed with the foundations which, when completed, served as a giant workbench on which to pre-fabricate the house.

Pic 5: Ground floor frame nearing completion. Note ‘ladders’ at gables.

Pic 6: Pre-fabbing a gable. The carpenter is standing on the completed North wall.

Preparatory to this the dimensions of all the pieces were taken off the drawings and run through a beam cutting optimiser (a computer programme. We used Cut1d). This gave us the pattern of how to cut the bits from our stock of beams with the minimum of waste. From this we printed off sheets of labels to identify the individual pieces (over 500 of them).

Pic 1: Cut beams stacked with their labels.

Here is an example of the dimensioned drawings we produced (ref).

The beams were cut on a large radial arm saw set up in a polytunnel on site with supports to keep flat the 12m beams we were feeding in.

This was laborious but not very complicated. It would have been more worth the effort if we had been building 6 houses but I still think that if we were to build another one we would buy it from Edenframes and have them erect it. Trevor Lowis from Edenframes was happy to tell us in detail how to build our frame. They are the nearest Masonite/Warmcell pre-fab manufacturers (Gretna).

Making up the panels on the flat (front and back walls plus two gable ends) was very straightforward as was the erection done by 6 people and some pulleys. Even the big load bearing studs in the gables and the ridge beam did not present any problems. The rafters were pre cut, lifted into place and nailed together in pairs with their gusset plates before being clipped to the headers and ridge beam. Throughout the erection stud, joist and rafter spacings were held by light battens temporarily nailed in place. I know I've said this before but if you miss out these temporary spacers the beams will flex and the unrestrained lengths will loose their precise spacing so when you come to nail on the sheathing (or later when you want a strong fixing for, say, a partition) you will not be able to find the centre of the stud.

The sheathing went on then the membranes then the cladding.

Larch Cladding

The TRADA Timber Frame Handbook (ref) tells you how to do wood cladding and ARCA's Timber Cladding In Scotland (ref) tells you why. What neither gives you is a step by step guide. Our experience is that painstaking setting out on the wall (and boards) avoids much redoing and frustration.

The function of cladding is described as a rainscreen, it isn't watertight but prevents rain from reaching the inner insulated shell. Careful detailing ensures that any water penetrating the cladding can drain and ventilation allows it to dry out quickly. Examples of these details include anti-capillarity gaps and chamfered tops to the battens to shed water away from the building.

We went for vertical board on board in larch with horizontal panels in the gable triangles and forming a 'skirt' to break up the visual verticals. Without these horizontal elements we thought that the house would look over-tall and not anchored. An additional plus with the 'skirt' is that it is the bottom of the cladding which perishes first and it is much easier to replace a few horizontal boards than many vertical ones which are still sound for most of their length.

Naturally we went for European larch but were unable to source any locally. Our thinking now is that species is less important than density of wood. Hybrid/Japanese larch is faster growing hence less dense so we selected trees which had grown more slowly (on north facing slopes). We have learned since that the all larch species are comparable in durability which is determined by the concentration in the wood of phenolic extractives.

The board on board has 100x18 front boards with 50x16 back boards so we get 20 overlap on each side and a 10 gap between front boards all fixed through to 22x18 battens on 600 centres.

Illustration 1: Gable showing vertical cladding with horizontal cladding above and below

The cladding is attached with Gunnebo stainless steel cladding nails. These do not stain the wood (like galvanised nails would) and have slightly domed heads so that you do not hit and mark the wood when you drive them home.


This website was produced with financial assistance from the Scottish Borders Woodland Strategy.