A: Adding an additional layer of plywood will definitely help with the bounciness and, to some degree, with sound transmission. Size matters; the thicker the new plywood, the more benefit you will derive. Yes, you can screw the new plywood to the old. You will need to find the old nail patterns in the original plywood (every 16 inches) when you remove the carpet. The aim is to get every new screw into a supporting joist. This will help eliminate the squeaks, and also laminate the two layers of plywood into the floor frame.
Screwing and gluing the plywood will help the bond even more, but have pity on the next poor sap who pulls this floor up: Stick with screws. Few things are worse than dealing with a glued, screwed and tattooed floor!
Don't get cheap on the screws. This is not the place to save money. Put a screw every 4-6 inches at the seams, and every 6-8 inches in the field — this will make all the difference in the world. Assuming you have 5/8-inch or ¾-inch plywood now, use screws at least 2-½ inches long to get a good grip below. Please make sure you have no plumbing or radiant heating lines beneath.
In my experience, ½-inch plywood added over an existing sub-floor will strengthen it noticeably. It's good to stagger the seams from the original floor, but this is not so important due to the tongue-and-groove fully blocked construction beneath. Consider cheaper facings on plywood to counter recent price increases. For example, CCX PTS does well where an "A" grade would normally be required. And OSB works well under carpet.
The biggest issues here are the rooms in which you will be performing the surgery, and the floor coverings to be used. Any room where vinyl/linoleum flooring or tile/stone is to be added (vinyl/linoleum to bring it up to correct height, and tile/stone for water resistance and rigidity) will need a third layer of particle board, plywood or cement board — plus the thickness of the flooring.
In the carpeted areas you may simply have to adjust (read "cut") closet and swing doors to fit. But raise the level of the carpeted areas and you will have built an unintentional "carpet shelf." Easy enough, you say, just do the same thing in the kitchen and bathrooms, right? Not so fast, Turbo, we have appliance issues.
The dishwasher, for example, may not fit without surgery to the counter. Get out the tape measure and get busy. Stairs are another nightmare. To prevent trip hazards, the building code requires no greater than a 3/8-inch difference between stair heights, and no step may be greater than 8 inches high. If you add plywood only to the floor at the top or bottom step, you may be exceeding these limits. Now you need to add plywood to the stairs to even it out. Yikes.
This simple tightening of the floor has migrated into a major remodel, with all the accompanying worries. So tread carefully, and think it through completely.
Q: I have a single-family home with a mother-in-law unit downstairs. What is the most effective method to cut down on sound transmission through the floor, besides telling the mother-in-law to "be quiet"? I've heard that blowing insulation between the joists is good. Even better is putting in a false acoustical ceiling. What about just adding a layer of drywall to the basement ceiling?
A: All of the above are effective, especially the "be quiet" part. Anything that can absorb sound, add mass, block or radiate sound, or physically separate the adjoining areas will help.
Sound board is another readily available sheet product that can be added between a false ceiling and insulation, giving you a fairly affordable and moderately effective do-it-yourself solution.
Darrell Hay answers readers' questions. Call 206-464-8514 to record your question, |
