Expert: Daniel Humphrey - 1/7/2008

Question
I'm investigating the potential of constructing a second floor/attic on my 1976 modular rancher. I'm looking into removing the existing roof truss system and replacing with a higher peak and dormers allowing a second floor loft type bedroom, bathroom, and storage. Have you heard of anyone who may have completed a similar project? What should be my biggest concerns?

Answer
Dear Bill,

You will need to assess the strength of your foundation and the wall's ability to bear more weight. Modular buildings are not designed to carry a second floor. I'm not saying yours won't, but many cannot. Some modular buildings sit on blocks and have no perimeter footing, and that wouldn't work. Some modular buildings have no solid rim joist or solid blocking to allow big wall loads. A 2x4 wall at 24" o.c. would be too light, for example. Metal studs would not suffice either. You're hoping for construction details just as they would be in a site-built home.

Once you are sure the foundation and wall can take it, then you need to design a second floor system that places the weight directly above load-bearing portions of the building--weight should follow a good load path, with solid wood all the way down directly to concrete.

Finally, you need to design the new roof structure. Simply raising the peak would work, but it will not give you much usable space in that 28 feet or so, except where you have dormers. So you want the dormers as large as possible. Dormers concentrate loads at the valley intersections along the perimeter, because gable walls tend to load less than eave walls. Those points must have really good load paths.

Wish you the best,

Daniel