Some homes don’t have attics, they are flat roofed, and some homes have 2-stories with floors in-between. In either case, this is a situation where there is usually 2×12 wood framing with drywall attached to the bottom and some plywood attached to the top. There is no crawl-space, it’s literally like a horizontal wall. In this case we treat it just like a wall: we drill holes and inject insulation into the empty cavities. We use cellulose because it has a higher R-value per inch and it’s the only material that can be effectively blown into a cavity.
Unfortunately, most places built in the 1970’s or newer tend to have fiberglass insulation installed in their ceiling and we can not inject additional insulation into these cavities. The best thing to do is check the ceiling to see if there is existing insulation. See How to Check for Existing Insulation, below.
How to Check for Existing Insulation
Quite often homeowners will call us and insist that their walls or ceiling between units must be hollow and they explain that they can hear their neighbor next to them, therefore the wall or ceiling must be empty. Unfortunately, most places built in the 1970’s or newer tend to have fiberglass insulation installed in their walls or ceiling and we can not inject additional insulation into these cavities. The best thing to do is check the wall or ceiling to see if there is existing insulation. There are several methods:
Make a hole. Find a closet or inconspicuous location where a small hole can be made and the inside of the wall or ceiling inspected. You can use a drill bit, knife, screw driver or any sharp object to create an opening the size of a dime. If you have fiberglass insulation it’ll be soft, fluffy and similar to cotton candy. If you can stab a screwdriver into the wall cavity that doesn’t mean it’s hollow, you need to make a hole large enough to see into the cavity.
Another technique is to remove the light switch plate or electrical outlet plate and look to the side of the box. You may have to open-up the plaster or drywall a bit to see to the side of the box, but the plate will safely cover up to 1/2-inch of any area you open-up. To the side of the box the wall will appear either empty or you’ll see a cotton candy-like material.
If you already have insulation in the wall or ceiling, we can not inject additional insulation into that cavity. Your best bet is to then have a drywall contractor install a layer of QuietRock over the wall, this sheet of dense drywall is equivalent to 7 layers of regular drywall and can help stop sound coming through the wall.
For more information on checking for existing insulation please see our video.