Fix a sagging drywall ceiling

Remove and replace, or install new layer?

By Paul Bianchina
Inman News™

Q: We have a large living room that needs all the ceiling drywall replaced because it is sagging. We believe it is sagging because there was not an adequate number of drywall screws put in, plus there was insufficient insulation with no vapor barrier installed when the house was first built. About five years ago, additional insulation was put in correctly, with the Kraft paper touching the top of the drywall plus more insulation on top.

Our question is: When this new drywall is installed, what is the best way to remove the old drywall, without having all the insulation fall into our living space? –Chris A.

A: Since you have batt insulation between the joists with additional blown-in material on top, removing the old drywall without creating a horrendous mess is going to be pretty difficult. Once the supporting drywall is removed, the weight of the blown material is going to cause the batts to sag into the room. Even if it doesn’t come crashing down into the room, as you install the new drywall, you’ll have a very tough time pushing all that material back up into the attic. The result could sags and irregularities in the new drywall.

You have a couple of options. Working in small sections, you can rake the blown-in material out of the way, remove the batts in that section, remove and replace the drywall, then reinstall the batts, rake the blown-in material back into place, and proceed to the next section. This would obviously be a pretty tedious operation.

A better suggestion is to just leave the old drywall in place, and install a new layer over it. You can work your way around the room and re-screw the old drywall to stabilize it, then install new 5/8-inch material with longer screws that will penetrate through both layers.

If the ceiling is currently too uneven to get a smooth finish by installing directly over it, then you might want to install wood furring strips over the old drywall, then install the new drywall directly to the furring. Install the wood furring perpendicular to the way the joists run, and use shims as necessary to get the furring even.

With either method, since the old drywall is already taped to the walls in the corner, there would be no need to tape the new drywall to the walls. Instead, cover the wall/ceiling joint with crown molding, which will enhance the look of the room and save you the time and labor needed to tape the corner joints.

Q: Thanks for your informative article on attic ventilation. My question is: Do gable vents count as inflow (low) or outflow (high) in the NFA (net free area) calculation. I want to re-roof and replace my current box vents with ridge venting, but I also have gable vents. I think, but am not sure that my outflow NFA would be a combination of the ridge vent NFA plus the gable vent NFA. –Wayne D.

A: Gable-end vents would almost always be considered high vents, as they are typically located near the top of the gable-end wall, which would place them relatively close to the ridge. As a rough rule of thumb, if you visualize a line cutting your attic in half horizontally, anything above the line would be considered high vents, and anything below the line would be low vents. Of course the higher or lower the vents are, the more effective they’ll be.

In your case, assuming the gable-end vents are relatively high on the walls, you are correct in assuming that your high venting would be a combination of the ridge and gable vents.

Q: I just read an article about using pressure-treated wood for decks. I believe it is illegal — at least in Los Angeles; it should be everywhere. To be pressure-treated, the wood is injected with poison. This makes it dangerous to have exposed. We are allowed to use it internally only (i.e., for studs in enclosed walls). If I remember the newspaper article correctly, a number of years ago someone made a swing/play set for their kids and one of the children chewed on the wood … another possible Darwin Award. I have seen it used on trail fence rails in Laguna Hills, Calif. — hello, horses chew on wood!

Or is there some “new” kind of pressure-treated wood that doesn’t pose this issue? –Candice H.

A: Pressure-treated lumber used to be manufactured with chromated copper arsenate (CCA). The arsenate is a form of arsenic, which is probably the poison to which you’re referring. However, there were concerns about the arsenic in the wood leaching into the surrounding soil, so in 2004 the Environmental Protection Agency and the wood-preserving industry jointly agreed to change the chemicals being used in the process. Today, the pressure-treated lumber and plywood available in local lumber yards is typically made with copper azole (CA-B), or with alkaline copper quaternary (ACQ), neither of which contain arsenic.

While CCA-treated lumber is now used only for very specific and limited applications, I am not aware of any code-related restrictions on the use of the newer treated materials.

Remodeling and repair questions? Email Paul at All product reviews are based on the author’s actual testing of free review samples provided by the manufacturers.

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