More Overhead Clearance in the Garage
Need more overhead space for garage storage? Tom Silva has some good advice
My two-car garage would make a nice home gym. But the 2x8 ceiling joists—there is no finished drywall ceiling—are only 8 feet above the garage floor, which isn’t enough clearance for my overhead exercises. Can I add collar ties between the rafters, and then take out the joists?
—Max Fischer, Miller Place, NY
You may be able to gain some extra headroom by reframing your garage roof, but first let me clear up some roof-framing terminology. Collar ties are horizontal pieces of lumber that connect rafters on either side of a gable roof, up near the peak. Properly installed, they do make a roof stronger and help a ridge line resist sagging. But without the joists, collar ties by themselves can’t provide enough support. For that, you’ll need rafter ties, horizontal 2xs that connect to the rafters’ lower ends. Your joists perform the same function that rafter ties would.
The position of the rafter ties and collar ties in the roof’s structure is critical. To understand where they should go, imagine a sloped roof in cross section; it forms an isosceles triangle with the roof peak at the top, the sloped rafters on the sides, and the ceiling joists on the bottom. Collar ties need to be fitted within the upper third of that cross section. Rafter ties have to go within the lower third.
I can’t say how much height you’ll gain if you replace your ceiling joists; that depends on the pitch of your roof and the width of your garage. But a quick to-scale sketch on graph paper will show you how much extra height the new framing offers.
If you do proceed with this project, check first with your local building department. You may need to submit a stamped drawing from a structural engineer.
Leave the joists in place as you add the rafter ties, one for each pair of rafters. Cut the ends to match the roof slope, then push them tight to the underside of the roof framing. Fasten each end to a rafter with six 3-inch structural screws. A joist can be taken out once its corresponding rafter tie is in place. Save the old joists to make collar ties, if you want.
Ties longer than 16 feet may sag. To prevent that, nail vertical 2x4s to the ties near the center of their span, and to the rafters directly above.
This project isn’t done yet. Taking away joists weakens a roof’s connection to the walls, and you don’t want a bad windstorm to lift your roof off the garage. One way to strengthen that connection is to nail metal hurricane clips to the wall’s top plate and to each rafter. Use only the nails specified by the clip’s manufacturer, and plant a nail in every clip hole.