Putting a hat on any building is incredibly important and can be the one area of the building if it fails will have an enormousness effect on the rest of the building. Putting a hat on straw bale building is doubly important as the straw has little resistance to weathering, if it gets wet at any point in its life span and stays wet it will simply decompose. In this building the roof will cost more than any other part of the building and this in not normal, normally the foundation will be the most costly part of a build but as our foundation has no cement products in it and the stem wall stone was free to collect so the roof material and insulation will double the cost of the entire building.
First we have to install the rafters, these are sweet chestnut and were cut from the neighbouring forest and retrieved by hand so both inexpensive and low impact. First we laid them on flat ground to find the best orientation to give us a reasonably level line across the roof. Then we cut a flat section on the tip where it will sit on the ridge pole leaving a consistent 6cm thickness of timber again helping keep the roof-line as flat as possible.
There is a cup joint cut in to the underside of each rafter where it intersects with the outer joists/pearlings this stops it sliding off the pearling all the rafters are fixed with good sized nails at both ends. Once all the rafters are in place they are marked with a chalk line and cut to their final length.
Then its time to fix the internal layer of the roof, we are using 20mm natural edge oak boards from the local timber yard. After getting the first boards fixed to the rear of the building we spilt in to two teams working on both sides of the roof at the same time.
We managed to get the first layer in place in one day.
Here is the view from underneath.
Ready now for the first layer of lath to be set over the rafters and nailed through the broads and in to the rafters.
The first layer of rafters leaves an air gap under the multi layer foil insulation which is fitter next.
Then another layer of lath is installed to maintain an air gap on both sides of foil insulation and then the final layer of timber boards are installed.
More fun on our 2016 natural building course we still have places available for anyone interested in sustainable building and permaculture. We have a selection of courses available next year from complete houses to timber frames like this one and a permaculture design course.