DIY How to Board a Loft

Ensure your loft floor’s structure will be sound. If you're adding a loft to a garage or making better use of existing living or attic space, existing joists may be strong enough only for ceiling support. Depending on local building requirements you may have to replace them; some loft conversions require reinforced steel joists. In many cases you can reinforce existing joists by bolting them to sturdy “sister” wood or laminate joists to create a load-bearing floor frame.

Measure the entire length and width of the loft area. Multiply these measurements to get the floor’s total square footage. This will allow you to buy just the amount of subflooring you need, as well as final flooring material. Also, measure the height or depth of the rafters, so you can figure out how many layers of insulation you have room for.

Add insulation between all floor rafters, to insulate the loft space for both heating and cooling efficiency -- and also to help with soundproofing. Lay insulation batts to the full depth of the rafters, working around wiring and plumbing where needed. Mark the locations of all with electrical wires and plumbing lines, so you can avoid hammering nails into those spots when you board the loft.

Lay out the boards. Most CDX plywood comes in 4-by-8-foot sheets that fit together with tongue and groove, for a very sturdy floor base. Ensure subflooring seams line up exactly on joists -- meeting in the center -- for optimal strength. Lay down boards with the best surface facing up and the grain running at right angles to joists. Start in the loft’s center, lining up the center of the first board at the room’s center point, and work outward. Stagger the plywood, as you would lay masonry, so four corners never join.

Attach the subfloor boards to the rafters. To prevent squeaking floors later, Hosking Hardwood Flooring recommends applying a thick bead of subflooring adhesive caulking to the top of every floor joist before laying down the floorboards. Screw the subflooring to the rafters and joists every 8 inches along most joists, with deck screws, and every 6 inches around the edges of each plywood sheet. Allow one-eighth inch between plywood boards, to allow for some expansion and contraction.