Loft Floor Construction

Lofts

• Lofts or attic rooms are living spaces that occupy the area between the roof and the ceiling of a building. They can be fully enclosed, or they can be partially open to the space below, with a floor that is supported by interior load-bearing walls, rather than spanning the entire width of the building. When they are planned during the building's initial construction, lofts are relatively straightforward to frame. However, when converting an existing attic space to a habitable loft, care must be taken to insure that the building remains safe, structurally sound and compliant with local building codes.

Joists

• Joists are the horizontal framing members that span the building at the top of the exterior walls. The primary function of joists is to tie the roof rafters together and prevent them from pushing the exterior walls outward; they are not designed to support the weight load of a living space's floor and are usually made of lumber too small to serve both functions at the same time. That problem can be solved by reinforcing the joists with supplementary "sister" joists that are bolted to the side of the existing joists to increase their rigidity and strength. Alternatively, the joists can be replaced with stronger materials, such as engineered structural timbers.

Trusses

• In the case of roofs constructed using engineered roof trusses, the potential structural problems are even more severe. Since trusses are designed to support the roof using the lightest and least material possible, removing any of the timber in a truss, such as the support members on the interior of the truss that interfere with usable attic space, or increasing the weight load on the bottom chord of the truss will compromise the structural integrity of the truss. A common solution is to reinforce the truss with stronger members, such as steel beams that span from wall to wall, so that any loss of truss strength or increased load that the truss must bear is compensated for.

Subfloor and Flooring Materials

• Once any potential structural issues are resolved, the loft floor can be finished in much the same way as any other floor, with insulation between the joists, a plywood subfloor and finish floor materials such as hardwood, carpet or vinyl flooring. Building codes typically require minimum ceiling heights in attic living spaces, so floor materials should be chosen so that adequate ceiling heights are maintained when the floor is finished.