hi tinbasher and welcome,some good points there.I dont think it matters realy where the boards go cus in the end everything will be touching the soil or compost so a good coating of wood preserver every year is all you can do. buying new timber would make a big dent in your budget,Ive been thinking about a hinged roof and you have convinced me ply n felt it will be,
you could make the posts out of box section and weld small bits of flat bar pre-drilled to bolt your boards on.
got myself the gabion (pics to follow)
and you need a level to get everyhing square I know what you boilermakers are like you only use a 6" stabila
Yep, I knew I was being fussy. As you say, the posts are susceptible to rot at some point, certainly at ground level, but enough preservative and decent section timber will give a few years service at least. I made a double bin at home a few years ago (but abandoned it as it took too much room) out of old doors and salvaged 4 x 2 etc. The problem with sticky-out bits cos everything was different thicknesses was all those raised edges and non-flat surfaces. It wasn't so much compost gathering in corners as the spade or fork jarring against the sides. Nothing worse than a sudden stop as a spade jars against an obstruction. With an already aching back after hours on the land, it seems to shake your spine loose of everything else. I promised myself that the next one I build will have smooth sides and crisp corners.
Top panels to form a roof for each bay is an essential, something else I struggled with before as all the doors were different widths so I had a staggered top edge by an inch or three here & there. An angled cut on the top planks for the sides and divisions gives a slope to the roof. A couple of inches fall on a 4 foot run is sufficient.
I thought about the box section construction (with drilled 1" angle iron rather than flats, welded to the uprights) but by the time you've done it probably comes close in cost to timber. Metal is expensive now, even mild steel. It's gone up in price horrendously in the last few years due I keep being told to 'the world situation'. Expect to pay 30 quid (probably plus VAT) now for a length (24') of 2" x 2" x 3mm box section. Then there's the angle iron, the drilling, the welding, capping the posts, lashings of paint and it all has to be constructed at work and transported to site. All the timber has to be drilled fairly precisely and then you have a load of nuts & bolts to supply. You can't just bash galvanised nails in where you please as with an all timber build. No, wood is a luxury to work with after all week fiddling with steel so I'm sticking with that.
I noticed from your pics that you have gone for slatted sides and back - ie: with a gap between each piece, and understand this is because you are maximising air exposure. Am I right? I feel that keeping the heat in is more important and so am going for solid sides and back. Air can always be introduced by turning the pile and it's easier to introduce air thus rather than keeping the whole thing insulated, which is a constant requirement. I've also thought of laying a perforated plastic pipe (lengths of the yellow gas main stuff or modern large-bore water main) at ground level in each bay, through from the back, and stacking the pile over and around this. An air flow into the pile should be available with this method. I accept that each pipe should be able to be withdrawn when turning the piles occurs else you get the old 'jarring-spade syndrome' again. You should be able to get 3 or 4 foot lengths of this pipe from salvage yards or building sites.
Technical eh and we're only after making muck?