The Roof

At this stage Almost all of the main brick work was complete together with the top cavity closed. It now was the time for the wall-plates to go on. One around the house just under the windows and another on top of the new outer walls. A 100mm x 50mm tantalised timber was used. I could have gone for a thicker 75mm however I had to strictly keep the 15 degree angle so I went for the 50mm instead considering I had Marley Medip tiles in mind. I had to first estimate the highest point the wall plate against the house could go keeping in mind that the tile and lead flashing will be going above the rafters. I marked out around the bay window first, next I placed a rafter into position just so i could roughly check the angle. I had an android mobile app which worked like a charm. I got a 14-15 degree angle.

I also had to take into consideration the maximum height of the wall-plate as I wanted the lead flashing around the chimney to look good from the street. I thought of 1 brick above the roof line. Keep in mind not to forget the thickness of the tiles at the lower end of the chimney.
I then attached the wall-plate using just two 4 inch screws temporally and cut a rafter at 15 degree. To keep the strength in the rafter, the notch should be no more than one-third into the joist.
I placed another length of wall plate with 3 pieces of slate under to allow for the space of mortar of approx 10-15mm. When the wall plate had been mortarted down. I roughly marked where i could cut into the rafters and left 5m around the notches.
Another view of the markings.
At the corner I cut a lap joint and screwed it together. I will be placing shorter straps just above the openings for extra support.
Using a 48″ square I marked where the 2 rafters will sit. Nice and square. Check the timbers as some will be slightly warped. Use you eye or string line.
At this stage it looked like loads of work. Using a sliding compound saw i planned to cut 10 joists at a time. I ordered about 60 joists. I found that they were 2 pallets of joists each with approx 5mm difference in size. At this stage it best to separate them and use them were best, ie odd sizes or warped ones for the garage and the better ones for the kitchen/lounge. According to building regs the 4m span I required 50mm thick joists at 450mm centres.