With all the clearing work we’ve been doing in the woods, there’s now a need to get all the firewood-to-be under cover to season well before use. The log store we’ve been constructing next to the main building at last has its roof – a patio area – complete. We just need to relocate the things presently occupying it – like the washing machine – which, as is the way of these things, ideally requires completion of another couple of stages in the project beforehand.
This store will provide about 12 cubic metres of firewood storage space plus room for a workbench and tools. The wood stored here will be used primarily for the rocket stoves in the kitchen and bathhouse/greenhouse, so another storage area is needed for wood for stoves in the upstairs rooms. This dovetails nicely with the final stage of groundwork and construction needed to keep the main building dry and to provide space for a toilet, a connecting corridor between the upstairs rooms and hanging space for outdoor clothing and footwear.
So the next project is to construct a lean-to roof, along with natural drainage, along the back of the building. A lean-to roof with a difference. We plan to take it right out to meet the slope behind the building, varying the pitch as necessary, and cladding it (after waterproofing) with straw and a light covering of topsoil as a growing medium. It will be left to seed naturally with the pioneer plant species – mostly carqueja (Genista tridentata), wild lavender (Lavandula stoechas) and various heathers – that thrive in the thin dry soil on the slope above it, eventually resulting in a roof that’s almost indistinguishable from the surrounding hillside. So really neither a turf roof nor a green roof, but a living, growing roof nonetheless. Minus brambles and pine seedlings though …
Two days ago, the first day of January’s waning moon, we cut some poles from the few eucalyptus trees we have growing in the woods. Apparently if eucalyptus is cut during January’s waning moon, it has much less tendency to split and twist as it dries. Although most of the eucalyptus grown in Portugal goes to make toilet paper, it can make an incredibly strong building timber if it’s seasoned carefully and kept away from any source of wetness. It’s also naturally resistant to the indigenous wood-boring insect population, so this is what we’re using for the framework for the back roof. We’ll be using the poles in the round, as we have elsewhere in this project.
To minimise the chances of the poles splitting at the ends – the end grain dries fastest – we’ll be painting the ends with diluted PVA to slow the drying process. (A handy tip thanks to Jonny from Quinta das Abelhas, the newest member of our now 4-strong part-time construction team.) As it happens, the ‘ecological’ wood preservative we used for the main roof timbers contains PVA, so is ideal for the purpose. The time of year is also on our side as we have another 3-4 months or so of slow drying in cooler temperatures and moister atmosphere before the summer heat hits us.
Once the roof is completed, I’m intending to insulate the back wall of the house externally. The building gets no sun at this time of year so we have no possibility of utilising passive solar gain. In some ways, this actually makes designing for the extremes of temperature here much simpler. The rear walls contain by far the greatest proportion of total wall area in each upstairs room, roughly equal to all the other walls combined. External insulation allows their thermal mass, together with the dividing wall between the upstairs rooms, to be used for heat storage in winter, conserving the heat we generate from the woodstoves for as long as possible. This will significantly improve winter comfort levels and energy use in the building and, with internal insulation on the remaining outside walls, prevent walls at ambient temperature from sucking all the heat out of the room. Anyone who’s lived in an old stone house without adequate insulation will know this only too well …
In summer it works the opposite way round, keeping the building much cooler, especially with the benefit of the solid rock back walls and floors on the ground floor.
I’ve looked at various natural insulation materials and focused on ‘slip-chip‘, or wood-chip light clay. It’s a flexible material with good insulation properties and a wide range of possible ways of using it. We’ll need to experiment to find the best application method – either plastering it directly into and onto the stonework or pouring into reed mat forms fixed to roof timber supports – but the raw materials can be sourced very locally and very cheaply, if not for free. A final coating of lime plaster will provide a breathable finish, and a more durable and harder one than clay plaster (which will be used internally) in an area of heavy traffic where the walls are much more likely to be frequently knocked and scraped. A smooth white-painted wall will also enhance natural light levels in the corridor, which will be lit in daytime by 2 litre clear plastic soda/water bottles filled with water fitted into the roof.
Being out of sight under the turf roof, the insulated and plastered wall won’t detract from the external appearance of the building’s traditional schist stonework either.
Well … that’s the theory anyway. No doubt I’ll stumble on many things I haven’t thought about yet along the way …