This is where it needs to go, in front of the living room french windows:
The window/door arrangement was inherited with the house, and frankly should never have been built the way it was - in the summer, the thermal expansion makes horrible creaking noises with the occasional bang thrown in, and when the wind gets up in the winter, the whole assembly shakes and rattles. It's just too big for the materials used. Part of the brief, therefore, is to provide (at least once the plants have grown around it) some degree of shade and wind disruption to mitigate those flaws, without preventing the light from getting in through those top windows. Another part of the brief is to preserve the view from the window.
Those requirements lead us to four posts at the corners, horizontal beams running parallel to the wall between them, and 'rafters' notched into the top of those beams, with the roof structure at the level of the divider between the doors and windows above.
She's got the village handyman on retainer for a morning a week to do whatever garden work she can't manage any more, so the current suggestion is that he dig out and concrete in some 100x100 metal post footings that I can place the timber into once it's done. This is attractive to me because he's more familiar with concrete work than I am, lives an awful lot closer, and is in much better physical health than me. If there's preparatory work that can be done in advance to reduce the amount of time I need to take off work and go and stay, that's only an advantage.
Size wise, it needs to be (approximately, plus or minus 300mm) 4.2x3.3m in footprint. That's to (a) span across the windows, which are around 4m wide, and (b) give room for the table and chairs in the photo. For scale, those are roughly 600mm paving slabs, and the outer posts will be set into a bed that's yet to be dug adjoining the patio edge.
Questions in my mind at this point are mainly the following. Obviously many of them are interrelated:
- Is the plan to have post footings in place beforehand a sensible one?
- Will 100x100 posts look too spindly in a structure this size? If yes, will it be viable to use larger posts and shape them down to 100x100 at the base to fit into a post footing?
- What size section will I need to avoid noticeable sag on the cross beams, spanning 4.2m or thereabouts?
- Assuming diagonal braces between the posts and the cross beams, what degree of bracing will be needed in the other plane (perpendicular to the wall) to prevent racking in that direction, and how is that best arranged when there are only 'rafters' running that direction, no beams?
- Do I actually need to include larger beams in that direction as well as those making up the roof, in order to brace them?
- If the 'rafter' pieces are notched into the tops of the beams, what's the traditional method to fix them in place? I can't really see how you'd drawbore a half lap, and this location gets non-trivial wind on a regular basis.
It's all very much an idea at this stage. With any luck, if what we're thinking above is remotely sensible, I'll start looking for timber suppliers and tools and we'll be looking at starting in a month or so.