Thread: Wavy Drywall Ceiling!

Good Morning All,

Has anyone ever seen drywall bow and wave between the trusses on the ceiling before? House was built 1978, 1/2 drywall, truss spacing 24", no obvious signs of was staining or exposure from the roof. My first thought was moisture from condensation over time has softened the drywall to cause it to sag. It is firmly attached to the trusses and that is what you see holding the high point then sagging between. There is about 8" of blown in cellulose insulation on top. This is odd and have not seen it before. I have already written my report noting this and my thoughts but any additional info would be great.

I thank anyone for their input. T



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Yes, I see it every so often, always on 24" joists. Cellulose seems to be involved frequently also.
Cellulose is a poor choice for this setup IMHO since it is the heaviest per inch. If there is 8" now, there would have been much more in '78, maybe even double that. Throw in high humidity and the Sheetrock is pushed past its limit.

I wonder if they used 3/8" sheetrock instead of 1/2". I have seen that on rare occasion.

Nowadays, we should warn people that the popcorn texture probably has asbestos in it as well.

That old drywall will be costly to dispose of.

Originally Posted by John Kogel

Nowadays, we should warn people that the popcorn texture probably has asbestos in it as well.

That old drywall will be costly to dispose of.

See wavey ceilings a lot,spacing to far apart to support drywall at 2 feet on centres,especially if humidity levels are high,gravity takes over.

Originally Posted by Lon Henderson

I wonder if they used 3/8" sheetrock instead of 1/2". I have seen that on rare occasion.

Most use 1/2" on the walls and 5/8" on the ceilings here.

Thanks for the responses guys!

Were I am at in CO the humidity is very low, but in the winter times when cold the heat and condensation from the living areas can cause moisture build up at these areas. We have alot of 24" oc truss installations and 1/2 for a single family home is not uncommon either especially with older installations. I think this is a unique scenario but all conditions have contributed to this outcome. As for the asbestos, any house built prior to 1980, I provide my asbestos disclosure and in Colorado if any remodeling is done to a house built prior to this time they have to get an asbestos test and abatement if asbestos is found prior to remodeling.

Originally Posted by Vern Heiler

Most use 1/2" on the walls and 5/8" on the ceilings here.

That's what I thought too. 1/2" on ceilings if rafters are on 16" centers.

Is this above a garage or 2nd level? Might be a symptom of high humidity do to lack of attic ventilation. You sure it's 1/2 inch drywall?

Jeff, it is on the 2nd level but adaquate ventilation.

The only requirement I found tor 5/8 drywall is ceiling of the garage with living space above it and has to be 5/8 type X. On the nailing scheduale it can be installed with sheets running perpindicular to the framing.

Originally Posted by Jim Luttrall

Yes, I see it every so often, always on 24" joists. Cellulose seems to be involved frequently also.
Cellulose is a poor choice for this setup IMHO since it is the heaviest per inch.
.
.
Throw in high humidity and the Sheetrock is pushed past its limit.

Precisely, except that will also happen with fiberglass batts too, but just not as pronounced as with cellulose - because of the weight difference in the two insulation materials.

Originally Posted by Terry Sandmeier

Jeff, it is on the 2nd level but adaquate ventilation.

The only requirement I found tor 5/8 drywall is ceiling of the garage with living space above it and has to be 5/8 type X. On the nailing scheduale it can be installed with sheets running perpindicular to the framing.

I doubt that you can find a requirement that it be flat either!

1/2" drywall back then should not have been used for 24" centers. It's in their specs to use 5/8" for 24" centers. That being said, there is a newer board out that is lightweight and can span the 24" just having the 1/2" thickness.