For my first internship within the Gabion eco-construction training, I am going back to Jules for the third time in order to continue to help him on his working site. Since my last stay in February 2021, the roof has been finalized. The edge and ridge tiles have been bricked up and the land behind the ruined house has been leveled. The next stage of the site is to build a small extension of about 30m2 in load-bearing straw bale. The roof will be flat to accommodate a vegetalized roof. The extension will serve as an extension to the living room and will accommodate a small kitchen. The interior will be plastered with earth or lime and the exterior will be cladding. A second extension in straw bale is planned on another side and will be coated with lime on the outside. These two extensions are used to illustrate the different eco-construction techniques and to promote straw bale construction.
I find again Jules and his team with pleasure. The weather is better than in February but it is still cool. The levelling works are finished, they are laying the foundations. Under the floor of the extension is a draining layer of stones. Everything was done by hand and with a pickaxe, the mini-excavator bought by Jules a month earlier having refused to work.
We put tar strips in place on the brand new foundations to prevent water from rising in the walls. The bottom rail is attached to the top with boxes filled with loose straw. It is on this low rail that the straw bales will be placed. We use the bottom rail as a template to prepare the top rail which will surround the top of the straw wall. Strips of textile strap and straps are inserted under the bottom rail. They will be used to compress the wall of bales of straw.
- The foundations being built.
- Installation of the capillary break (in black), a strip of tar, to prevent water from rising in the walls and installation of the bottom rail.
- A layer of lime is inserted into the bottom rail box to prevent rodent and moisture infiltration.
- The boxes are filled with loose straw and then closed.
Once the foundations finished, we begin to assemble the pre-frames, which are used to delimit the windows and bay windows. Then it is the assembly of the walls. The straw is delivered on Monday morning. The bales are very dense, denser than those used for roof insulation. Five Twiza volunteers came to lend a hand. The assembly of the straw wall is done very quickly, in one day.
Doing a load-bearing straw wall means that the straw is structural. It is it who carries the frame. There is no wooden frame. The only pieces of wood present are used for the pre-frames so that the straw does not come to push against the joinery. The wall is assembled by assembling the bales one above the other in staggered rows and inserting them on stakes (in this case cut wooden broom handles). Plugin all the holes and make it as compact as possible is required. It is often necessary to resize the bales and so a new bale of the desired size has to be “knitted” from a full bale.
Once the wall is mounted, the top rail is fixed on top. In order for the wall to be clean, the straw bales are “cleaned” using a large saw. Then the straps and textile strap are fixed over the top rail to compress the wall. The compression is done in several times in order to allow time for the straw to position itself correctly and to reach its maximum compression point. Compressing as much as possible is very important in order to prevent the bales from settling over time and the joinery rubbing against the top rail. Once maximum compression is obtained the straps will be removed while the textile straps will remain in the wall.
- Knitting a new boot.
- Foundations, straps, bottom rail and straw bales.
- Straw bales impaled on stakes.
- Fixing of the corner bales.
- Cutting of a troublesome part of the pre-frame of the bay window.
- View of the house and the extension under construction.
- Positioning of the top rail.
- Cleaning of straw walls.
- Compression of walls.
As for the bottom rail, the boxes of the top rail are filled with loose straw and then closed. Then comes on top the frame of the flat roof. It is the same system as for the floors of the house. On the ruin side, a load-bearing beam is fixed against the wall of the house. It is a little higher than the top rail in order to respect the angle of inclination recommended for vegetalized roofs to allow water to flow down. Metal brackets are attached to it to accommodate the joists. On the other side, the joists are simply fixed to the top rail. Spacers are fixed in the middle to prevent deformation of the joists. And gypsum boards close the roof of the extension from the inside.
Between the joists we add insulation. Jules had planned to do everything in chènevotte (loose hemp, very good insulation, resistant to insects and humidity) but supply and stock problems forced us to fall back on cellulose wadding to finish the roof . It is much less pleasant to work it because it makes a lot of dust. Since several months, the building sector has been facing increasingly large stock-outs. The price of wood has tripled and the waiting times are getting longer. The fallout from the covid crisis, the economic slowdown and the appropriation of resources by the Americans and the Chinese are starting to be felt. This does not smell good.
- Fixing the brackets.
- Fixing the joists on the top rail.
- Closure of the frame from the inside with gypsum boards.
- Insulation of the frame with cellulose wadding and chènevotte.
We take advantage of the last day of the week to finalize the roof. A rain screen is placed over the insulation to prevent water infiltration. Battens are put in place to allow a ventilated air space closed by OSB boards. And wooden planks acting as a parapet are fixed on the sides of the roof. The parapet (generally a small wall serving as edge of the roof) makes it possible to fix the waterproofing of the flat roof and the evacuation of rainwater.
To finish we fix with an adhesive an EPDM tarpaulin (Ethylene-Propylene-Diene Monomer, rubber) on the roof in order to protect the entire roof from water infiltration and then to accommodate the earth for plants.
I left the site, once again very happy to have learned so much in barely ten days. Jules will finish the extension then attack in the coming weeks, the second. For my part I return to Mane to resume my training. I hope to be able to come back to the site regularly during the year to follow its progress and continue working with Jules and his team.
- Installation of the rain screen.
- Liteaunage on the rain screen to accommodate the OSB boards.
- Attachment of the EPDM tarpaulin to seal the roof.
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