FOUNDATIONS

Strip foundations were carefully measured out and dug down to the granite bedrock. Holes were drilled into this bedrock and rebar ‘pins’ inserted to ensure there was no slippage. Where the bedrock fell away steps had to be created that were each one block and one course high. Rebar mesh was laid and the hand-mixed concrete poured on top.

CRUCK RAISING

Cruck-raising was always a special time in the build, transforming a low boring wall into a towering structure that was reminiscent of a whale’s ribs. The full size of the houses could be better understood. The smaller crucks used on the porch worked well and provided extra support against extreme wind events and allowed all four bedrooms/bathrooms to have external windows/light. The crucks were spaced 1m apart (te length of a strawbale) and each is able to carry up to a 7 tonne load, more than adequate for the tiled roof. Many thanks go to the numerous volunteers who helped in this process for both houses.

The crucks were covered in polytunnel plastic (the tallest polytunnels in Scotland) to allow the strawbales to be inserted out of the rain. The gable end walls were then constructed with the same double-wall with 300mm of insulation between.

STRAWBALE INSERTION

Around 1,000 very dry, ‘construction grade’ strawbales were ordered for both houses from a Nairn farm and were stored in a local barn (thanks Laura and Craig!). The first bale sat on a think sloping piece of polystyrene to get it leaning slightly ‘away’ to follow the line of the cruck. After each bale was inserted a great deal of loose straw was inserted at both ends and hammered down both to keep them in place and to ensure there were no insulation weak points.

Then a wooden, T-shaped, ‘bale spacer’ would be laid across the back /top of the bale which would be screwed into the crucks. The 500 bale spacers in each house greatly help tie the crucks together and make the structure more ridgid.

Inserting the final bales at the top of the crucks was very tricky as it had to be done from the inside. A galvanised-steel mesh was added after the straw was finished which would help hold the lime mortar in place. Finally a porthole ‘truth window’ was added (two in ‘Jill’ one in ‘Jack’), as is common with most strawbale houses, to make it possible to see the straw under the lime.

LIME APPLICATION

Two layers of lime mortar were applied on the inside of the houses and a single layer of hydrated lime applied on the outside. As well as providing an attractive finish it protects the straw from mice wanted to make their home in it, it allows the straw to ‘breathe’ through it and it also acts as a fire retardant (it is nearly impossible for the strawbales to burn as they are so dense that oxgygen is unable to penetrate so in tests they just ‘char’).

The mortar was mixed with course sand and fired onto the walls using a ‘single-tool’ compressor and morta-firing ‘gun’. Needless toay this was an extremely unpleasant process as the lime can burn skin if not washed off promptly.

Lots of eye guards, protective gear, eye washes etc etc were required. Applying it to the outside of the straw was generally easier as it was being fired ‘down’ but there was the challenge of carrying it up to te roof, loading the hopper and firing it onto the straw (holding the ‘gun’ with both hands….). Great care was taken throughout the build and no major injuries were  sustained throughout the build process.

One of Brian’s best design features was the ventilation ‘chimneys’ that he created. The top of the external lime was around 50mm lower than the sarking on the roof. Air was able to pass under the gutters, through some stainless steel mesh (to exclude insects/mice) and up and across the lime to vent at the roof’s ridge. This keeps the lime/straw dry and is a vital design feature particularly in Scotland’s damp west coast. Where the porch got in the way of the bottom of these chimneys, we inserted lateral ventilation pipes within the straw (passing through the cruck’s ‘webbing’) to allow air to keep the lime dry above the porch too). Photo 8 illustrates this design feature.

ROOFING

Sarking boards were attached across the outer cruck flanges using stainess steel screws (all the screws used in the construction were stainless). Then a breathable, waterproof membrane, then vertical counter-battens and then 50x25mm horizontal battens from which the tiles would be ‘hung’. Due to the changing angle of the roof and the greater chance of water ingress towards the apex, the tiles were spaced more closely for the middle third and very closely for the upper third, as per Brian’s recommendation.

The slightly curvving, slate-coloured roofing tiles came from a factory in the west midlands. Almost 30,000 tiles were used for all three buildings. The curved nature of the roof provided an extra challenge which was overcome using a ladder tied to the scaffolding and resting on the roof ridge. Helpful family members would pass tiles to Robert and he would hang them on the battens and fix with a small screw.

INTERNAL WALLS AND FLOOR

The first floor joists were spaced 300mm apart and basic timber walls were used to construct the downstairs walls which were covered in plasterboard and taped/jointed in the usual way. Sound insulation was inserted as well.

Robert’s temporary but sturdy stairs were replaced by John’s beautifully crafted stairs that were subsequently covered in engineered oak flooring as was the rest of the house.

DECK/BALCONY CONSTRUCTION

Spare hydropower, plastic penstock pipes were used to cast the reinforced concrete pillars that the deck and hot tub sits on. The pipes also sit on concrete pads that are tied into the bedrock so they are not going anywhere. A strong steel structure was engineer designed/approved and manufactured in Fort William. The spiral staircases were found on ebay and pressure-stripped with sand and repainted.  

LANDSCAPING/OUTSIDE

A few photos to show the process of turning a building site into an attractive outside space, in particular the addition of the locally-sourced larch cladding.