Now we come to the first stage of actually constructing the inner room. All the steps so far have been alterations to the existing garage shell - and although the removal of the purlin hadn't been completed yet, I decided to start on the framework at this stage to avoid delaying the build any further.
To do this, I opted to make the framework in 2.4m sections (of 2by4), so that I could manoeuvre them around by myself, and also so that I could move them out of the way if necessary. Then I also needed some smaller sections to fill gaps of less than 2.4m. Because of the heavy load expected on the stud wall (due to the double layer plasterboard ceiling), I chose to have my studs at 40cm centres, i.e. the centres of the studs were 40 cm apart from each other.
To begin with, I made a simple box shape from lengths of 2by4 , and then used a mock up of a rafter joint (circled in red in the image below) to work out the height that the upright studs would need to be in order to give a 5cm air gap between the top of the rafter and the future outer room ceiling. As 2by4 is almost 5cm in thickness, I used a piece of 2by4 fixed on top of the rafter segment to represent 5cm air gap as you can see in the circle. After several attempts at designing the correct mock rafter piece (you can see the one in the image it labelled 'E', but the final one was 'J'...), I finally worked out that my upright stud height should be 175.5cm:
You may also notice that I chose to use a crown plate (a further 2by4 running on top of the "top plate" of the stud framework): this would help tie all the individual frame parts together, as well as absorb any slight differences in height between frame pieces. Therefore, I had to take the double top plate into account in my height calculations.
At last I began manufacturing the sections of framework to fit the perimeter of the room, leaving myself an 18cm clearance from the wall at all points. Some of these sections can be seen below.
For the corners, I used Californian Joints, which basically entail an extra piece of 2by4 lined perpendicular to the end stud, giving enough surface to be able to fix plasterboard onto both sides of the corner. This is shown below - the '175.5' piece lines up flush with the back of the right framework, leaving some of the stud marked '91.4' free to fix plasterboard to on the right hand side.
Thus, when the frames are in position, they look like this:
I found the easiest way to construct the studwork was to lay it out flat on the ground on top of two chocks , i.e. two pieces of pre-laid out 2.4m lengths of 2by4. This helped me to get everything level as the garage floor was fairly uneven. This layout can be seen below:
And here is a closeup of a completed frame ready to be moved into place:
In terms of process - I first marked the centres for the studs (every 40cm) on both the top and bottom pieces of the frame section, then laid out all my uprights on the chocks, allowing me to get them fairly square straight off the bat. I then used a set square to ensure each joint was a 90 degree angle, and stood on the joint to keep it in position while pre-drilling and screwing the timber together with 5x80mm screws.
For the noggins (the shorter, horizontal members that prevent the uprights from buckling), I chose an arbitrary value of 7cm and staggered them above and below the frame's midpoint by 7cm each time, alternating up and down. This allows for easy drilling into them from the side, as the next noggin isn't in the way of the previous noggin during assembly.
The whole framing work took me about 6 full days - after I had worked out a process, I managed to cut and construct about 2-3 sections of 2.4m a day. To me this felt like fast progress, although a professional would have undoubtedly been much much faster. Seeing the frame pieces all upright and in position (albeit only temporarily), really made me feel like I was finally getting somewhere!
