Is there a truss I can install that later could be altered to become the floor of the next storey?

Q: I have a cabin in Invermere, BC that has a shed roof that I intend on removing, replacing the rake walls with regular walls and then replacing the roof with new trusses, etc. Someday I might want to add another storey to the cabin, so my question is: is there a truss I can install that later could be altered to become the floor of the next storey? Perhaps a combination of I-beams and trusses?

A: This is a very good question and before I answer it there are some points to consider. First, I see you’re building in Invermere so ground snow load will be a concern. Second, the span of the truss may limit you to what you can do.

Roof trusses perform just great when they’re used as roof trusses but when floor loads are added, suddenly things become a bit more difficult. It sounds to me like you would want to build a flat truss for now that will act as a roof truss and when budget permits, this will become the floor truss for the next storey. This will work and a roof/floor truss design could be used but I’m not convinced that it’s the most cost effective way to complete your project. You will have a set of trusses that will be the roof of your cabin for now then you will have to get another set to form the roof when you raise the walls.  With that said let’s just assume that this is the way you want to proceed.

The depth of clear span floor trusses is governed primarily by the load they support and the distance between supports. If your span is not too long then you can probably be happy with a floor truss that is designed to carry both the intended floor load and additional capacity to handle any snow that will accumulate. Again, depending on the clear span you could be looking at depths from 16” to 24”. You would have to give some consideration to the type of roofing material that would be used so that it can easily removed after when you go to start phase two.

So, building a set of clear span floor trusses with roof loads on them is really no big deal. The span will determine the depth and you can use 1 inch of depth per 1 foot of span as a guideline.

If you need a more definite answer, please forward a sketch of your proposed cabin with dimensions and I would be happy to give you some more advice and possibly a solution.

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