Expert: Richard Taylor, AIA - 1/19/2008

Question
5 years ago we added a room above our garage.  2 years or so I noticed minor bubbling in the texturing/paint on the inside of the garage walls.  Over time this minor bubbling is now about 2 inches below the top of the wall all around the garage.  Looks very minor, but am concerned that there is settling.  The drywall was mostly replaced when the room above it was built - was crossing fingers this is not a big deal, but was concerned about if I could just scrape and repaint, or did I need to dig deeper.  There are no cracks or any other signs in the addition itself, and nothing on the outside.  Could it be from heating/cooling (garage is subject to fairly extreme temp changes) could this be a one-time settling of the trusses onto the wall...

Thanks in advance,

Sean

Answer
Sean - thanks for your question!

From your description it sounds as though it's the paint, not the drywall, that's "bubbling";  if settling were occuring, you'd have problems with the drywall rather than the paint.

But it doesn't sound at all like a "settling" issue.

When paint "bubbles" off the inside of a wall, it's a sign there's moisture present where it shouldn't be.  You can't just repair the damage, you've got to correct the problem.

If the existing garage roof was removed to add the new room, then the connection between the new and existing walls on the exterior wasn't properly done; it may not be flashed, or the exterior finish may not have been applied properly.  Moisture's getting in where the old and new meet and is saturating the drywall - then it's trying to find its way out toward the warmer interior of the garage, and is pushing the paint off.

If the existing roof and floor system stayed in place when you added the new room, then the construction has somehow damaged the weathertightness of the exterior.  You need to find where the moisture is coming in and correct it.  The damage sounds minor for now, but over the long term moisture will rot the wood framing of the garage walls and the floor above.  You won't know it until it's too late.

If by chance it's the drywall that's bubbling, then either it's been installed or finished improperly or you're getting excessive deflection in the floor structure above.

Deflection is the amount the the floor joists/trusses "bend" when they're loaded...although this sounds like "settling" it's much different.  Settling eventually stops; deflection is a permanent condition.  If that's the case, you need to talk to your designer, engineer, and/or builder about who is responsible for seriously undersizing the floor structure.  It is possible to correct, but will be messy and expensive.  I hope that's not the case!

If you do some digging into the damaged area, you'll be able to tell if it's a paint or a drywall issue.  Remember, paint's a moisture problem, drywall's a structural problem.

Hope this helps!

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com