I am using 3" stainless steel, decking screws, with small Torx heads. So that [in theory] they sink neatly out of sight below the surface. It makes a pleasant change not to hear creaks and rattles as I walk about up there. It may even stiffen up the building in a belt and braces sort of way. You would not believe how quickly floorboards eat up a whole box [and a half more] of 250 screws!
Half an acre of larch boarding.Well, 3m or 10' across. You do the maths.
Now I have to go back around with the DeWalt on "drill" setting to pull many of the screw heads down. Lots didn't go into the surface even on a "15.5" maximum torque, driver setting.
I love the way the larch boards have darkened the grain pattern with exposure to UV sunlight and rain. A brand new look was never in my list of desires and modern "knotty pine" boards can never look the part. I want the floor to look "antique" and "lived in" before I even start using the observatory in earnest.
Sunday 16th. A wet morning is forecast. Persevering with floor boarding.
Monday 17th. Two sides of the veranda now boarded.
Tuesday 18th. Veranda boarding sneaking towards completing a third octagon side. It needed joist height adjustment to cater for half inch upward bowing!
Thursday: Another view from the shed end gable showing three sides of the veranda almost complete.
I have painted in the lines of the existing parallel joists in red. The run of board, end miters lies at an angle between the two joists. [Green] Even a new 2x6 joist [blue] in the middle, between them, isn't really a perfect solution.
Though it catches most of the longer overhangs. Perhaps I should use a diagonal 3x6 or even a doubled 2x6 instead? That can be fixed to the corner post later with a matching socket. The inside end can be mitered and screwed to the nearest joist beside the octagon post.
I went with the green option but had to go out to get more 2x6. The image alongside shows how I caught most of the overhanging boards with a mitered, diagonal 2x6. It is a compromise but the overhangs are all quite modest. I shall notch the outboard end into the railing post.
I don't want to start installing the corner, railing posts until I have the roof/dome on. Otherwise they are bound to get in the way of lifting the roof sections. Probably by sliding the panels up pairs of spaced ladders.