As part of the build, significant effort was put into reinforcing the existing building shell. Because of my plan to add a false roof to the underside of the timber rafters, I had to be sure the rafters, (and the walls!) would take the additional weight. In order to best explain this, here's a closeup of the rafter structure where the roof meets the wall just above the window:
As you can see, there is a piece of timber than runs on top of the wall that acts as the bottom of the rafter structure. This is called the "top plate" or "sill plate", and is what the rafters attach to. The aim of the restraint straps that I added was to tie down the sill plate to the wall, so that the horizontal force of the additional roof weight wouldn't push the sill plate off the wall, or push out so much on the wall that it would collapse outwards.
Here is an example of what I mean - you can see the metal strap screwed to the top of the sill plate (with wood screws) and then fixed to the wall with rule plugs and screws. This holds down the roof to the wall, and distributes the load down the wall so that it isn't all concentrated on the topmost block course.
I also used restraint straps to fix the rafters at the gable end wall (the end face of a roof which looks like a triangle), to keep the roof attached to the wall. This can be seen in the closeup of the right hand side rafter below:
These straps are referred to as "Builder's Metalwork" and can be purchased at any builder's merchants. I added the longer restraint straps along all the walls at roughly 2m intervals, and then added 4 straps to both of the gable end walls.
One tip in the installation of the straps was to use a marker pen to mark the positions of the holes on the wall through the brackets as standard, but then also to mark the approximate heights on the outside with a line (as seen in image above). This allows for easier location of the smaller hole marks. I then went through the marks and added a large "X" for easier identification. Finally, I used a hammer and punch to make a small indent at the centre of the X before drilling so that the masonry drill bit had somewhere to grip and didn't slide around due to the rough surface of the blockwork. This may seem like overkill, but it actually saved me a lot of time once I had worked out the process, as it can be very hard to identify a small mark on rough blockwork when looking through PPE!