These pictures are above my two car garage. I would like to build an attic space here. I am guessing the middle vertical supports are critical, and can’t remove those. But can work with that. The question is: Can I remove the diagonal supports and put down plywood?
Thank you!
Picture one - left side - circled supports I want to remove
Picture two - right side - circled supports I want to remove
Unless you want to make the roof collapse, absolutely no.
This part of the construction pushes on parts above it in a sideways manner and there is no other element that could be used instead of that. If you remove it, the vertical beams will be easily pushed to the side – and that will result in collapse of the truss system.
Depending on the climate at your location, the roof can be expected to support not only itself, but also a significant weight of snow and wind loading. Always consult such modifications of constructions with professionals, not only on the Internet.
Also, note that there is no thermal insulation except the floor. You would have to add thermal insulation just below the roof if you want to use this space.
As already mentioned, they are a critical part of the structure. If the house was being designed for attic storage, it would have a different truss system without those members.
Having said that, they can be replaced with other supports. You need to consult an Engineer.
Again, as mentioned, the truss is not designed to have load on its bottom member. Many people, including myself do use it for storage. What I do is either use decking timber to span the trusses, or particle/chip board or plywood. But the load needs to be diverted to the studs underneath. And you can only store light stuff such as empty suitcases and boxes.
In my previous house, I had the builder put beams on top that went on top of the wall below. And then put sheets of particle board on top.
As things stand (no pun intended) those pieces are critical.
However, that DESIGN of truss is not critical. A good engineer would be able to redesign the trusses / roof to give you the space you desire. Without doing some extensive calculations, no-one on here is going to be able to tell you exactly how eye-wateringly expensive that would be, or how disruptive. (Worst case is the whole roof needs to come off. Best case you just need to double up some of the remaining structure.)
However, any such change is going to increase the total weight of the roof, even before any added load. The walls of the building may not be strong enough to take it...
