The houses in our estate have all cross supports in the attic, see below. It makes moving around up there not ideal. Are they really needed?
Yes.
They are needed until you get the attic professionally converted as they tie the roof on one side to the floor, so that the roof loads are all fully supported and balanced. If they were removed the base of the roof on both sides would shift outwards and the roof would collapse.
A professional conversion would gain you all of that storage space and you wouldn't have to go whole-hog and make it livable.
Interesting build, so it looks like the struts are nailed to every fourth roof rafter and not fixed to the purlins as is the norm, with the purlin being a substantial piece
Are the struts all onto walls below?
I don't share 10 10 20's analysis of their purpose as if you look at the loads, the joists are the bottom chord of the triangle and are thus in tension and are holding the triangular truss together
The purlin is there to reduce the bend in the rafter, also allow the use of a smaller rafter, and the struts transfer the weight of the roof to the house walls.
This is not advice, as noted earlier a profession experienced chippy will know what can/cannot be done
Do we know that those joists run continuously between the outer wall plates?
Hi Lumen.
I'm not sure I understand? Looking at the full length there are 9 on one side and 8 on the other
Short Answer - Yes they are needed.
Longer Answer - That looks like a cut or 'custom built' roof which puts you in a better position than if it was a truss or 'pre-assembled' roof. If you're going to go at them then make sure you get in a builder or carpenter who knows what they're at. A truss roof should never be altered - they can be but you're looking at a much more expensive operation to get them done properly. The roof you have looks like it could be altered but it's not just a matter of cutting out the bits you don't like !! Get somebody suitably qualified to have a look at it in person. Don't use a handyman or some fella down the pub who said it'd be grand.. If your builder / engineer / carpenter says no then stick with that. I'd be confident though that yours could be altered to create a decent usable space.
If you look at the image in post 4, Lumen is asking about the joists, which are the bottom chord of the triangle, which is in tension, tying the two wall plates together.
He is not asking about the struts
Hard to tell from the pictures but I dont think your floor joists are designed to take any great loads (they look undersized to me)
So you would need to be very careful if you are going to make more space up there for storage, your attic may not support large loads (boxes of books etc)
get an engineer, simple as
Yes it is interesting, and you've hit the nail on the head imo. The fact the struts are fixed to the rafters rather than the purlin means they are supporting the ceiling joists rather than the rafters. The rafters are 9x2 and with a purlin, which isn't actually supported, aren't going anywhere. The uprights are probably doing the same job. It's ripe for conversion if 9x2s were installed alongside the ceiling joists and fixed to the rafters with a ridge collar above.
Of course this is just opinion, OP should engage a professional before doing any work, but it's how i would see it.
I checked that out over the weekend Lumen. For 2/3 of the attic length it goes between the outer walls, for the remainder, one side is over a hall space.
OK, the reason I asked is because roof loads act to push the external walls apart, so an important component of a roof structure is the bottom "chord" which acts in tension to stop this from happening. If the horizontal timbers are carrying that load only to interior walls, and not fully across the span, then the diagonal struts might be doing the job instead (in addition to providing some vertical support of the roof), and so you can't replace them with posts.
Sometimes (e.g. with a vaulted ceiling) there is a collar tie which does the same job further up, but obvs that's not ideal if you're wanting a usable room.
This is very much not qualified engineering advice!
