Attic Remodeling: Floor and Ceiling Tips – Handyman Club

An unfinished attic with plenty of headroom is an irresistable remodeling project for an enthusiastic remodeler or DIYer. It's an unclaimed space, full of architectural potential. But remodeling an attic can be tricky because its floor joists may not be up to modern rigidity standards, those appealing rafter ceilings may have low-slung collar ties that block all that apparent headroom, and the roof rafters may not have sufficient depth to accommodate the necessary insulation.

Stiffening Spongy Floors Existing attic floor joists may not be stiff enough to meet current codes for a bedroom. If you have enough headroom to double-up attic floor joists with 2x10s or 2x12s, youre lucky most of the time, old attics have 2x6 or 2x8 floor joists at best, and the joists typically have a notch cut out at the ends to accommodate the sloping rafter ceilings, which makes it impossible to insert deeper members. An obvious idea is to double up the existing joists by sistering (or scabbing) another 2x6 or 2x8 alongside the existing joists, but that wont solve the problem. Floor stiffness is a matter of joist depth, not width a double 2x8 sandwich will not resemble the stiffness of a single 2x10.

The solution to stiffening up a floor requires a combination of adding midbay joists, laminating the subfloor and possibly adding girders. Although sistering joists wont add much stiffness, reducing the joist spacing by adding new joists between the existing ones will. If you consult a joist/rafter span table (available at most lumberyards and in every building code book), you will find the maximum distance that your existing attic joists can span to meet current code as bedroom floors. (Note that bedroom floors have lower stiffness requirements than living room floors: 30 pounds per square foot (psf) for bedrooms vs. 40 psf for other living areas.) You may find that adding another joist between each pair will create enough stiffness to comply with codes: For example, 2x6s spaced 12 in. OC are equivalent to 2x8 joists spaced 16 in. OC. Even if the added joists alone are not sufficient, they may be part of a two- or three-pronged solution.

You can further stiffen the floor by adding a thick layer of subfloor, such as 3/4-in. tongue-and-groove plywood (which is lighter and stiffer than oriented-strand board) glued and screwed to the joists. I know one builder who laminates two layers of subfloor perpendicular to each other to strengthen attic floors without adding new joists. However, a structurally sound floor can still feel bouncy, and floor-joist codes are based on minimum prescribed stiffness, not just holding up the weight of people, furniture and walls.

The final weapon in the floor-stiffening arsenal is to add a beam, but not necessarily under the floor joists because that may interfere with the ceiling below. Instead, you can add a beam (or girder) on top of the joists (illustration below). This solution works best when it coincides with a wall location that can hide the beam otherwise youll trip over it. Heres how it works: Set an adequate-size beam probably a 4x10 near the midspan of the floor, where you may be building a wall anyway. Fasten the beam to the joists below using framing straps or oversize joist hangers. The beam will distribute the load across all of the joists to enhance stiffness without compromising headroom.

Sometimes youll have to transfer this load down to a bearing wall below or to the foundation by means of posts or vertical supports. An experienced carpenter with a code book in hand or a creative structural engineer can usually resolve even the surliest floor-reinforcement situations, so dont worry too much about the solution, just know that solutions exist.

Remedies for Headroom Headaches Collar ties keep the weight of the roof from spreading the exterior walls of your home. Floor joists running parallel to the roof rafters serve the same purpose, so you may be able to remove existing low-slung collar ties entirely. But you should consult with a building official or structural engineer to make sure this solution is adequate for handling snow loads, wind and other roof stressors. If youre going to install a flat portion at the apex of your attic ceiling (as seen in the photo), you can replace the existing collar ties with short ceiling joists attached to your existing rafters using plywood gussets firmly glued and screwed to both sides of the joists and rafters, essentially using your new attic ceiling as a replacement for the old collar ties you removed.

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Attic Remodeling: Floor and Ceiling Tips - Handyman Club