The shed section and frame continued
The frame for the top of the walls is made from 47mm x 75mm timber (sawn and regularized)
with the walls screwed to the 47mm edge with 1.25"x8 stainless steel panhead self-tappers (Screwfix
2573) using the pre-drilled holes at the top of the wall panels. All timber was pre-painted with three
coats of water-based green timber protector. It gives a superb finish and doesn't smell! The front of the
shed with the door opening does not have a top frame member. There would be no way to mount the
doors if you did as it would pass in front of the door tracks. The doors can't be mounted until the floor
is installed and the bottom door guide and door saddle installed. The front wall will be a little flexible
at this stage but will be strengthened later when the weather boards are installed.
Wall frame rear corner detail
The corner posts are 75mm x 75mm softwood timber. The bottoms were stood in a
petroleum-based wood preserver for a couple of weeks. Yardmaster use aluminium flat plate corner gussets
at the bottom and in the middle of the corners. These sit on the base rails and side braces and have
flanges which allow the corner wall panels to be screwed into them. These and the bottom rail design
prevent the wood corner posts from getting right into the corners. I cut out small sections in the corner
gussets to get the corner posts as far into the corners as possible. You can see a middle corner gusset in
the image above behind the corner post.
Top of wall frame rear corner detail
The top frame does sit on top of the corner posts but not as fully as I'd have liked. As
you can see I've used 100mm and 75mm angle brackets (Screwfix 4177 & 2488) to fasten them together.
With the corner posts eventually concreted into the ground and the walls screwed on to the outside of the
top frame this is, and has proved, strong enough. All the wood screws of various lengths were Screwfix's
own TurboGold screws. These are expensive compared to other wood screws but compared to the cost of the
observatory as a whole the difference is negligible. These are the best screws I've ever used, they go
through wood, even the 6x100mm ones, like a knife through butter. They are self-drilling (no pilot or
clearance holes are necessary), can be used close to the edge and they countersink themselves. The time
and effort saved is enormous on a project like this - so do yourself a favour - get them!
Preparing corner post hole
The corner posts were sunk into concrete to anchor the shed down. There were held tight up
against the bottom rails once a small piece was cut out of the corner gussets behind. The surface
surrounding the hole was prepared in the same way as the pad and lined.
A corner finished
The bottom rails were not to be secured to the concrete, they just sit on top of the pad.
However, they were secured to the corner posts with two 50mm angle brackets (Screwfix 1013). The inside
and outside edges of the bottom rails were sealed against the concrete to prevent water ingress with lots
of non-silicon-based sealer.
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