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Question DetailsAsked on 7/24/2016

Seasonal cracks in the ceiling

My living room shows 3-4 cracks in the ceiling that become bigger in the summer (up to 1/4") and nearly disappear in the winter. The cracks seem to run along joists. Usually, the cracks begin to grow as the temperature outside reaches 102 F (Mid-July here in TX), the cracks subside by the end of November. I think as the house/attic/roof expand in the summer due to hot temperatures, the ceiling drywall sheets separate and this action seems to be fully reversible and season/temperature dependent. I asked an engineer, his response was to add a couple of vents to the roof. I am not sure it will help. I would appreciate any advice as to how to stop these seasonal oscillations and cracks.

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Here are some similar previous questions with answers FYI, emphasizing causes of this -

Since these joints are closing back up in the winter and reopening in the summer, definitely not due to a structural collapse or sagging of the attic floor joists because that would be progressive, not seasonally reversed.

Normally these ceiling-under-attic cracks, which rarely get even 1/8" wide (usually pencil tip maximum), run CROSSWISE to the joists and are caused by the joists shrinking and swelling as the wood picks up moisture and loses it, so getting longer and shorter while the drywall is much more dimensionally stable and does not change length along with it - the shrinking occurring in the winter in most areas as humid summer moisture in the wood dries out in dry winter air - though can be related to dry and wet seasons in warmer climes.

But you say the cracks appear to run ALONG the joists, assuming by "along" you mean the crack parallels and runs under the overhead joists or trusses. This is presumably occurring at the nailing line along the joint between sheets, and might run a good distance across the room or be limited to 4' width (4.5' occasionally) and 8, 9, 10, 12, 14, or 16' long runs when it hits a staggered-pattern sheet so runs out of joint. [Drywall commonly comes in 4 and 4.5' widths, and 8, 9, 10, 12, 14, 16' lengths so staggered-pattern layout can be any combination of those - or joints can be continuous all the way across room if not staggered layout].

This means the cracks are opening up 1/4" wide right between two rows of nails or screws (one on each adjacent sheet) located only an inch or so apart across the joist - assuming the sheet boundaries are properly located centered on the joists, that is pretty hard to imagine. Therefore, would likely be because either it is really short on fasteners so the edges of the sheets are pulling away from the fasteners, with the fasteners pulling through the material - in which case you would expect the sheet edge to crack off along the fastener line, or the joint is not on a joist so the fasteners (or many of them) missed the joist, so it is held together only by the joint compound and seam tape - not likely either.

One thing that might be the case - and if you get on a chair or ladder and push up against the ceiling with your shoulders gently (don't move it a lot), it might be that one sheet at the open joints is nailed to the joist, but the other sheet's fasteners missed so there is nothing holding that edge of the sheet - though in that case you would usually see about 1/8-1/4" mid-sheet sag along that line too. The latter you could check in the attic to see if the joint is visible from above or a row of fasteners are sticking up parallel and next to the joist in the crack area.

NOTE - be careful not to trip on or step on electrical wiring if the attic was used for wiring runs (undoubtedly some at least for ceiling lights), and step only on joists or truss lower chords - not on the drywall because it will usually just break away under you.

One thing I can think of that would cause this ALONG the joists, and considering your location a rational reason - but you would have to accurately measure the distance from wall to wall at the ceiling height during both seasons to see if the room is actually getting wider (perpendicular to the cracks) by the amount the gaps are opening up. If you are in expansive soil and it is shrinking and swelling with the wet and dry seasons (or you are using a weep system to try to keep it stable), the house could be arching its back basically.

For instance, let's say these cracks go the short distance across the house - if the long sides of the house that the cracks are perpendicular to tended to stay in place more or less when the soil shrank, but the short ends of the house sank some as the soil dried and shrank, then the "drooping ends" would leave an arch in the center of the house, making the ceiling effectively "wider" - pulling the ceiling apart between the joists. The roof might not display any effect because of the much stronger nailing in the sheathing holding the roof together as one unit, so the bottoms of the joists or trusses would just tilt slightly from side to side over the seasons while the tops stayed put under the roof. Usually if this is happening to a slab-on-grade house you would see creasing or cracking in hard or tile flooring or bare concrete floor.

In a house with basement you would normally see substantial cracking in the foundation wall in the same general location along the outer wall as the overhead ceiling cracks, wider at the top than the bottom.

This can also happen in expansive soils with seasonal groundwater changes - arching the house up in the wetter (higher groundwater) season and letting it back down in the dry season, though in cases where the basement slab is keeping the soil damp under it year around, the walls of the house can droop down in the dry season and lift up in the wetter seasons, under natural conditions. Expansive soils (mostly from well into Canada to near the GUlf coast along the East side of the Rockies and for about a few hundred miles east of that - MT/ND to Texas basically plus some local areas mostly in the West) can do a lot of weird things as they dry and then reswell when they get wet.

The engineer's thoughts had to be related to temperature-related expansion and contraction - which could explain cracking transverse or perpendicular to the joists (especially if poorly insulated) but not really the other way. However, just assuming normal softwood framing, 150 degree temperature change over the seasons in the attic (say 150 to zero F summer to winter) and 30' joist/truss length, that only works out to about 1/8" TOTAL length change due to temperature - not 1/4" plus. And again, that would be LENGTH change causing cracks ACROSS the framing, not along it. While roof venting (eave and ridge vents make the most sense and work well in typical ridged roofs) does make your attic cooler in the summer (though also in winter when you might appreciate the solar heating of the attic), the venting will only drop Texas attic temps by maybe 10-30 degrees - so not likely to have any measureable impact on dimensions of lumber.

Likewise, humidity changes, especially causing cracks along the framing, would not open up 1/4" unless the framing was getting basically saturated with water and REALLY swelling up - and unless you have a leaking roof or an A/C unit in the attic draining condensate onto a vapor barrier lying under the joists so they get feet-wet from it, not likely - and easy to check out by digging down through any insulation and seeing if the bottom of the joists are wet at the crack locations. Also, if the timber was swelling and shrinking this much you would likely be hearing some pretty distressing noises in the attic as the joists/trusses readjusted.

Short of solving the WHY, the question of what to do about it remains - depending on how finecky you are about appearance, I would just take a long-life high extension paintable silicone caulk and clean out the crack with compressed air or a fine brush and caulk it, trying to match the surface texture if any, then after a week or so of drying paint it to match. Might eliminate the crack, or make it less visible hopefully - or might not work well at all. I would use either a paintable silicone high-extensibility caulk like Bostick 91261 (though I don't remember if that is the paintable product number), Dow 795, or Sashko Big Stretch. Or maybe a Dap 18096 Concrete Crack FIller and Sealant or or Sashko Flexx concrete / masonry crack filler, though those tend to be not such high extensibility so less likely to remain adhered to both sides as the crack opens up. Other problem with this - it the crack actually closes almost fully in the winter, it will extrude the caulk that you put in it in the summer, so you might have to put it in during the sort of mid-range of the opening/closing to hope it adapts to both conditions.

One totally different approach - might or might not solve the problem - maybe try one place initially to see how it works. Remove the paper joint tape (if that is what you have) and replace it with the high-strength USG Sheetrock Joint Tape to retape the joints with drywall compound - though if it actually moves 1/4" it might just tear through the joint compound or drywall paper and leave the tape hanging. (Existing tape is obviously ripped along the joint, assuming you have joint tape on there - which could also be part of the issue if not). You would want to do the taping when the joint is near its tightest condition, because do it when the joint is open and the tape will undoubtedly buckle and bulge as the joint closes up.

One other fix I did on a resort building (100' / 30m truss span, so a LOT of roof truss movement over the seasons), from minus 40 or so in the attic in dead of winter (was closed and unheated in coldest months) to 130 or so in the summer, and RADICAL moisture changes in the wood, was to caulk the joints to provide some ability to expand and contract without opening up a crack, then 1x4's were nailed with single row of nails in a grid pattern covering all drywall joints (which had not been stagger patterned so easy to do on 4' grid) as a facade to cover the cracking. But the primary problems in this case was snow loads (typically 6-10 feet) and the local wood used for making the trusses - it had a terrible air moisture absorption problem which we mitigated the decay damage from by treating the trusses in-place with preservative, but would not stop the seasonal movements. The pity was the drywall ceiling which they wanted for heating reasons, but really took away from the beauty of the quite old rough-hewn long-span natural timber trusses.

So, if your problem proves really unsolvable, you could do a decorative frontier or Mission ceiling like one of the following links over the joints on a grid pattern - you just have to be sure to chalkline the center of all framing first, then figure the grid spacing and pencil the nailing centerlines of the grid, being sure before starting nailing that all the boards can be nailed into the framing successfully - will result in at least some off-center nailing likely. Also, only works well on fairly flat ceiling without heavy texturing, and the boards have to be put up cupped-side-up to minimize visible gaps along the sides -

Or put a "floating" suspended ceiling under it.

Answered 4 years ago by LCD

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