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Question DetailsAsked on 6/1/2016

after having our attic space renovated into 726 square feet of living space, crack on ceiling in bedroom below

The larger crack in the corner and the drywall strip goes the length of the ceiling. The tape is separating and will need to be fixed. Should I be concerned that the structure is not properly supported? Or is this normal settling? The drywall tape is peeling away and the crack is about an 1/8 of an inch wide. Thanks

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Unlikely a problem IF you had an architect or engineer doing the redesign of the attic - and if you did, you could ask them to come back and look at it. But if you did not have a professional do the design, you could have been caught by a common error - most attic floor joists are designed for only 5-10 psf (pounds per square foot) - just enough for a laydown plywood floor to walk on or store a few empty boxes or seasonal decorations on, whereas a normal residential floor is designed for (depending on use and age of building) between 20 and 40 psf. Most attic roof support trusses are designed for essentially NO floor loading - just a typically 250# concentrated weight anywhere along their length, to simulate a worker walking the trusses to work in the attic, plus an assumed minimal weight of ceilig drywall, insulation, and maybe a few planks on top of the bottom chords to walk on - hence a typically 2-5 psf or so number.

Therefore, if you put in a finished room up there, just the weight of the new walls and flooring and furnishings alone can overload the support framing and start noticeable deflections - commonly starting with cracking of ceiling drywall joints and of the seam along the top of walls where it can delaminate the tape in the joint or cause crushing of the drywall (also commonly preceded by spalling of the tape from the joint).

However - could just be creep sag as you thought, because you have probably added about 10 psf dead load up there in addition to the very few it originally had, so one would expect it to sag a bit more over time with the added load. Wood floor joists, even for floors designed for significant loads, can sag an inch or two in the center of a typical 16-20 foot span over the years, without any structural risks or damage.

One other thing I would be looking into is how were the utilities run - a normal 1/2" or less hole through the center of 2x6 or 2x8 floor joists is normally acceptable - not so much if talking 2x4 trusses, and larger openings for plumbing DWV pipe or HVAC vents are generally a real no-no if the structural impact of such large holes is not ldeliberately designed for. I have seen retrofitting of homes (and large housing buildings and hotels and such) where major structural members were cut through willy-nilly by contractors, causing major structural damage.

So - no guarantee whether this is or is not a problem of note. You also don't know (wihtout tearing it off) whether the ceiling drywall tape was done right or not - done poorly, especially without pre-mudding, and it can peel loose at a whim. Done properly, and generally it will not peel free at all - will tear and shred before peeling off.

You could contact a structural engineer (or your project architect if you have one) to look at it and confirm in writing that it is not a structural issue, or you could wait a bit and see if it continues to sag more and more or exhibit additional short-term (weeks or a few months versus years) cracking and sagging. I am not advising one way or the other - but my inclination would be (assuming no cause to suspect significant structural issues) if only center-of-ceiling cracks at ceiling drywall sheet joints running transverse (crossways) to the attic floor joists were involved, I would probably take the wait and see if it gets worse attitude if it were a hairline crack. If it opened up to more than about 1/8" open gap I would be getting concerned. If I saw cracking along the edge of the room at the walls or any through-sheet or diagonal cracking I would be more concerned. This of course assumes there are no significant signs of structural distress in the attic framing or newly built walls. Also, if the amount of sag across the length of the room is not over L/360 or even L/240 (so 1 inch per 30 feet of span or per 20 feet respectively) I would tend to be less concerned - if over L/120 (1 inch per 10 feet of span) I would definitely be looking for a serious structural problem or overload. In between is a gray area where such deflections in the larger range might not be of as great a concern if occurring over decades, but definitely would be if a short-term effect.

Answered 2 years ago by LCD

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