I’m carving out a small space in my garage attic to transform into a man cave. The attic walls and ceiling are already drywalled. I have to get electric cables into the new partition wall. It appears that the easiest way to do that is through the floor. The trouble is that the subfloor in the attic is tongue-and-groove oriented strand board (OSB). Removing a piece in the middle of the room will give me all the access I need, but how do I do that without ruining the subflooring? Are there other added benefits to doing the job this way?
— Perry B., Providence, R.I.
Each job is different and presents its own set of pros and cons with respect to how best to get from Point A to Point B. This sounds like I’m dodging you, but I’m not.
In your case, it might make sense to bring the electric cables up from the garage ceiling into the floor cavity. The floor joists of the garage attic might run perpendicular to the direction you need to extend the cables. If that’s the case, it makes sense to remove a piece of the subfloor.
Many electricians have great skill in fishing cables from one point to another in a house. If you know of any, it might pay to ask them for advice before you make the effort to remove the OSB. Always keep in mind that it’s a trade-off of time and effort. You might discover that it takes only 15 minutes to remove and reinstall the piece of OSB.
A second method — making numerous small holes in the finished walls and ceilings to run the cables — might create an hour or two of repair and refinishing work. What’s more, your drywall repair skills might be not as refined as your rough carpentry talents.
I’ve removed many sheets of subflooring in my career. The degree of difficulty depends on how they were installed in the first place. I discovered many years ago that it’s a good idea to screw down sheets of attic subflooring. Some carpenters prefer to use nail and glue, but that presents huge obstacles when you need to remove a piece of subflooring. Using screws without glue enables you to remove a piece in short order. The screws also allow future easy access to the underside of the attic floor.
To remove a piece of tongue-and-groove OSB subflooring, first determine how thick it is. You can do that by drilling a small hole along the seam you’ll be cutting. Carefully slide a toothpick to the bottom edge of the subfloor. Mark the top with your finger and measure how much of the toothpick comes back out. Most subflooring is either 5 / 8- or 3 / 4-inch thick.
Look at the long edges of the OSB. One edge has a tongue and the other a groove. The tongue of one piece of OSB slides into the groove of another as the material is installed, which prevents the long edges from sagging in between the floor joists. You need to make a cut line down the long edge between two pieces of subflooring to disengage them from one another.
I cut the tongue with a circular saw, adjusting the cut depth to one-eighth inch less than the thickness of the OSB subflooring. You never want to cut into the top of the attic floor joist or the attic truss bottom chord. That will weaken the wood framing member.
Once the tongue has been cut on the two long edges, the next step is to remove the fasteners. I’m hoping the carpenter who installed your OSB used just a few nails and didn’t use a nail gun. Nail guns tend to countersink the nail heads below the surface of the OSB. That makes it difficult to pull the nails.
Use a wet-dry vacuum to remove all sawdust from the surface of the OSB after cutting away the tongues. Sweep the entire piece with care. That will help you see the fastener heads that were used to attach the subflooring to the floor joists.
I’ve had great success with two demolition tools when removing nails from wood. The first tool is called a cat’s paw. The tip of the tool has a V groove that you drive with a hammer under the head of the nail. Once the nailhead is engaged, you apply sideways pressure on the tool to extract the nail from the subflooring.
When all of the fasteners have been removed, it’s time to pry up the subfloor panel from the floor joists. If no glue was used between the subflooring and the floor joists, the panel should pop right up.
I use a flat demolition pry bar to help start this lifting job. Drive one end of the tool into the open seam between two floor joists and use the tool as a lever to lift up on the piece of OSB you want to remove. If you meet resistance, it means you missed a fastener or two, or glue could be your next obstacle. If it’s glue and the glue has a great bond, you might have to cut out each rectangle of OSB in between the floor joists and do a creative job of patching the floor later.
When it’s time to reinstall the cut-out piece of subflooring, you’ll have to cut and nail pieces of 2x wood blocking under the long edge on each side. The blocking takes the place of the tongue you cut away. Remember: You must slide it under the pieces of subflooring that you didn’t remove but that are next to the piece you took out.
Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site at www.askthebuilder.com.