Asbestos potential. The wall framing may not support a second story. A tear down and rebuild may be cheaper depending.

also local codes may consider this a new build if more than some percent of the structure changes. In which case anything you have currently would need to come up to code.

we were thinking of adding a second story to a 1940s home. Wound up tearing down and rebuilding as it was much cheaper. Our house had no historic value

Most one story houses are built with an attic "floor" on top of rafter ties. Rafter ties are smaller dimensions than floor joists because they only serve to keep the rafters aligned, and provide a place to attach the ceiling below.

If you are going to add a second story you would need to upgrade to whatever size floor joists are needed for the 2nd floor, and also ensure there is a load bearing wall on the first floor that will properly transfer the load to the basement below and to the footings. In some houses it might be fairly straightforward, but in others it would require a lot of new framing.

Bruce

Thank you, very helpful. What do you recommend as the first step to this project; designer? architect? builder?

personally I would try to get a builder first. We did architect first but then the builder suggested taking the house down and we changed directions. That was ok though as it was early in the process. You will want to hear from builders whether it’s worth trying for an addition or doing a tear down. Also to get a price ball park.

We've done a number of bungalow top ups (as well as 3rd floor additions on two-storey houses) and we've found them generally to be quicker and easier than rear additions (chiefly because there is no excavation and footing/foundation work). You also have the option to raise the walls when the roof is off the add ceiling height to the ground floor. Also, by using modern truss joists (the ones that look like I-beams), you have the opportunity to have a completely open plan ground floor with no load-bearing interior walls.

We've never had any concerns raised by the architect, structural engineer or building inspectors with respect to the bearing capacity of the existing foundation of any homes we have worked on. A house built in 1974 will almost certainly have a foundation capable of carrying the weight of a 2nd storey addition (as long as it isn't finished with brick, which adds a lot of weight).