We build our wall frames using 140x38mm SLS beams. We first build or two short sides flat on the ESB boards and later lifted them up and screwed them on the floor. We gave them extra support by adding a diagonal beam on each side. Next we covered the inside of the two walls with 12mm ESB boards. We screwed them onto the SLS beams using 30mm screws that we placed every 15 cm. We made sure each screw was about 1-2 mm inside the board, to help us clean up these holes later. We marked with pencil where the windows were overlapping the boards so we could take them out again and cut this part out with a circular saw.
Once the two small walls were completely covered with ESB panels we started building the back wall frame on the floor. We then lifted this up as well and screwed the outer beams of this frame against the two small walls. We then did the same for the front wall frame. Afterwards we covered both walls with ESB panels on the inside that we screwed to the beams every 15 cm. We filled up the screw holes and seams between the boards with putty (lineseed oil + chalk). This will make the surface more smooth but will also increase the air tightness to some degree.
