I have loose plans to insulate the attic. I thought I'd take the opportunity to fix the floor at the same time. Currently, the floor consists of 20 mm tongue-and-groove boards directly on the rafters=floor joists, which are spaced 1 m apart. What's the simplest and cheapest way to make the floor less wobbly?
I'm only building with wood (studs/boards), as it's too cramped to handle sheets up there. The floor can't be much higher, so I can't lay a new set of floor joists on top. I can't add more floor joists to the outer wall, so everything has to hang from the existing floor joists.
Really thick floorboards might be the simplest. Tongue-and-groove 45×220 would probably be sturdy and good. If only it were available at reasonable prices.
The insulation in the floor consists of sawdust, so there’s no problem digging trenches to add more joists.
I'm only building with wood (studs/boards), as it's too cramped to handle sheets up there. The floor can't be much higher, so I can't lay a new set of floor joists on top. I can't add more floor joists to the outer wall, so everything has to hang from the existing floor joists.
Really thick floorboards might be the simplest. Tongue-and-groove 45×220 would probably be sturdy and good. If only it were available at reasonable prices.
The insulation in the floor consists of sawdust, so there’s no problem digging trenches to add more joists.
Well, I've been thinking about something similar and can't come up with anything simpler. It should become quite rigid, I think, especially when the floorboards are added and connect with the existing floor joists/rafters. Thanks.
The solution largely depends on what you will use the space for. To cope with the large distance between the trusses, it's easiest to move up to heavier floorboards, around 30 mm. There are also raw tongue-and-groove-like materials that are about 35 mm thick. In Sala, there is (or was) a well-stocked lumber company. If the problem is that the existing floor joists are too flimsy, only reinforcing these will help. Unfortunately, laying joists between the existing ones is not a solution. From your description, I get the impression that your trusses might be of the framework type. The lower frames in such structures tend to only be dimensioned for small loads, around 50 kg/sqm.
The trusses are not trusses but open. The house is from 1922, and back then people wanted an attic that could be used. The previous house had trusses, quite foolish to sacrifice so much storage to save a few bucks on the trusses. There is standing height in the space and round windows in the gables, so you could decorate extra rooms up there if you run electricity and fix a bigger staircase plus building permit. The roof is steep, maybe as much as 45°. I think the beams are quite stable, but I won't know until I open up. At least I don't experience any sway when standing near a beam, only when I'm in between. I don't think they're dimensioned for anything, just used what was common without optimizing anything.
Thick tongue and groove planks sound interesting. If you buy "real" floorboards in a thicker model, they are often exclusive in several other ways, wedge-sawn, grown in Norrland, or they've passed through all four stomachs of a 12-point elk. Even if it becomes a loft up there someday, anything that doesn't give you too many splinters will do.
Primarily, it is about insulating. Right now, it's only the wind's floor joists that insulate upwards, about 25 cm of sawdust.
Thick tongue and groove planks sound interesting. If you buy "real" floorboards in a thicker model, they are often exclusive in several other ways, wedge-sawn, grown in Norrland, or they've passed through all four stomachs of a 12-point elk. Even if it becomes a loft up there someday, anything that doesn't give you too many splinters will do.
Primarily, it is about insulating. Right now, it's only the wind's floor joists that insulate upwards, about 25 cm of sawdust.
Old roof trusses and floor joists provide much greater flexibility, so that's good. A 45° roof pitch is perfect. If you plan to convert the attic into some form of living space, it's worth checking the floor joists' dimensions to ensure they are sturdy enough; otherwise, not. I guess the floor joists are 3x7 inches, a standard dimension from that time. Fine floorboards can be ridiculously expensive and still not so nice. I would opt for 1 1/2 inch tongue and groove spruce. If they aren't available in Sala, you can check with manufacturers of garage kits. It's a common dimension for garage lofts.
Beier sells "Slätspont 33X120MM G4-2 Gran". Seems to be suitable quality and the intended use is for subfloors or flooring in simpler spaces. The question is whether you get enough stability with C-C 1 m. Maybe you can visit a lumber yard, put together some boards, and test sway a little. 