Taking a break from the practical gives you the chance to give the theoretical some attention. A question I need to know the answer to is: where exactly should the green oak ridge beam sit? This is the answer.
We are aiming for a 45mm gap between the top face of the green oak principal rafter and the underside of the softwood rafters. This will take 25mm of insulation plus 12.5mm of plasterboard and leave a small gap. This 45mm gap equates to a vertical distance of 59mm (sin(50)=45/59)
The softwood ridge will sit on the green oak ridge beam and we know that this hangs 6mm below the bottom of the softwood rafters. This means that the arris of the ridge beam needs to sit 53mm (59-6) above the line of the top edge of the green oak principal rafter.
Knowing this we’ll be able to cut the ridge joints in the top of the king posts.
For more on the roof geometry, please see: Roof Geometry – green oak barn and More Roof Geometry – green oak barn.