Ceiling Deflection & Sheet Rock Crack

[Cherrybark]

I've been reading the forums and believe my problem is more accurately described as a ceiling deflection rather than, as I would have formerly said, sag. I will freely admit to having little to no knowledge of framing.

Our twelve year old house has a three car attached garage. Over the years the sheet rocked ceiling has developed a crack along a sheet rock seam, that runs the full width of the garage perpendicular to the ceiling joists. The ceiling deflection seems cosmetic more than anything but I would like to correct the problem while converting the garage to an air conditioned, year around shop. The attic is a large open space so naturally the builder decked the space over the garage, tempting home owners to use it for storage. We do store light weight boxes such as Christmas decorations. I'm guessing the deflection is caused as much by the weight of the joists, the two strong backs, and the 1/2" OSB decking.

The space is an open 22" x 32" with 2" x "8 joists on 16" centers. Here in East Texas the joists are almost certainly Southern Pine. With my limited understanding of the tables, a 22" span is beyond recommended limits for 2x8 joists. Two strong backs, made of 2x8s and 2x4s, run perpendicular to the joists, dividing them roughly into thirds. The crack in the sheet rock seam is directly under the tallest vertical 2x4s running to the peak of the roof in that area of the attic.

Since it has taken twelve years for the crack to develop, and it is basically in the mud over the tape between joints, I'm guessing the deflection isn't likely to develop into a serious problem. Rather than getting involved with Glu-Lams, hydraulic lifters, and punching holes for access, I'm wondering if a third strong back, running down the middle of the existing two and supporting the vertical braces, might be an appropriate DIY solution.

Once the joist are reinforced, the space will be insulated, re-decked with the 1/2" OSB, and the Christmas decorations returned.

 

[boobag]

have you pulled a string to see if the ceiling joists are being pushed down by the 2x4 posts? those 2x4 posts are not really structural if there is no wall below to carry the load. maybe remove them?
i do like your idea of running a 3rd strong back.

also, humidity can cause joists to expand. is the attic ventilated?

 

[dodgejunkie]

So, after 12 years you have one (1) tape joint that has developed a crack in the garage? I'd say that's pretty good all things considered. Considering the moister and dryness over the years you're just dealing with normal settling. 2"x8" on non load bearing should be more than adequate for hanging a Sheetrock ceiling with that span!

 

[Cherrybark]

Hadn't thought to stretch a string to see the deflection. Obvious idea once someone points it out - thanks.

This is a corner of a completely open attic space over a 3800 sq ft home. I would say it was relatively well ventilated with five turbine vents. But it does get nice and humid during the East Texas summers.

 

[matt_i]

Are you sure there is actually tape used? I have same style crack that appeared after I started using the attic, but I can see after pulling down a garage door hanger that no tape was ever used. So, not worried.

 

[DougWil]

The space is an open 22" x 32" ......

The film Spinal Tap had a bit about that.

If I understand correctly the 2x8 strongbacks are scabbed together and spanning 32 ft,,,, can't see those carrying any load.

 

[bczygan]

Inadequate depth of members for that span. Lucky that only one crack developed.

If you are adding the weight of insulation to the mix, you can only expect additional cracking.

To properly fix the problem will require more than a strongback. It will require a beam or truss to cut the spans of the joists so the deflection is reduced or some method of reinforcing the joists or adding intermediate ones.

Did the crack develop under where that knee wall framing is? If so, it is transferring it's load and the roof load from the rafters to your ceiling joists.

I ran this calculator for #2 Hem-fir 2x8 ceiling joists spaced 16" with 10#LL and 10#DL and L/360 and got a maximum span of 19'0".
http://www.awc.org/codes-standards/calculators-software/spancalc

Bill

 

[Cherrybark]

I do agree that the tables say at 19' span is the limit for 2x8s. Wonder how much safety factor is built into the tables? Of course, it's very unlikely an engineer designed the framing of the homes in this neighborhood. Presumably an architect did the drawings, a framing crew built it the way "we always do" and the inspector glanced in passing.

I'll trip over my ignorance of framing and structures if I'm not careful here. The one long crack isn't under the knee wall framing. It developed under the tallest verticals running to the local peak of the roof. Being near the very middle of the 22' span, I would hate to guess if it is from the weight of the roof or mostly from the joist.

There is no tape along the dry wall joints. With no experience in dry wall, I don't know if that would have any bearing (weak joke) on hiding the crack.

I'm torn between considering it a cosmetic problem to be taped, floated and painted. Or going to the other extreme of beams to support the joists. A middle of the road, DIY idea would be most helpful. But I appreciate I may seem to be asking for permission to do a poor job and an appropriate response might be, "Do what you want kid."

 

[8man]

DO NOT REMOVE the 2x4 kickers. They are there to keep the rafters from sagging.

Check with the string line to see if you do have a sag, and how much sag there is. You may find it is minimal and not worth messing with. Most long spans of sheetrock in our area will eventually have a crack. So my first thought is this is a cosmetic problem.

If you have a sag that requires addressing, the simplest is from below by using a column strategically placed to support to the concrete flooring.

I have put beams after the fact, it is not going to be easy or cheap, and finding someone competent in this type of retrofit will not be an easy job.

 

[pmiranda]

I wouldn't mess with the framing unless you want to really use that attic for more storage.

 

[kerr]

Once apon a time I read , I think it was here about the strength an added flat 2x4 glued and screwed to the top of your 2x8 's . It was a great read and true to this forum , it was chewed pretty fine .

I believe the outcome was that it was a very worth wild thing to do and added mucho strength to the boards where the sheetrock was screwed to .

I cant get much out of the search function here but maybe you or someone else could dig up that thread .

Seemed it was way better than nothing fix at the least . Good luck . Use paper joint tape to finish sheetrock . The stick on mesh will be for do-do on that spot for sure and will crack again .

YMMV

 

[Cherrybark]

Crawled all wobbly kneed, despite the pads, to the end of one of the middle joists, tapped a nail into the top, made my way to the other end and attached a second nail. Then went to the middle of the joist to discover absolutely no deflection. Took a minute to realize the string was running under the strong backs and I was only measuring a run of 10 foot or so. Wobbled back to the end, put the nail a couple of inches down the side, measured, put a nail the same distance on the other end, headed back out to the middle and measure 1/4" of deflection. I mention this routine because any of you with construction experience would have cracked up watching my Laurel and Hardy drill.

A negligible amount of deflection on a central joist. I see no signs of tape on the sheet rock joint when probing from the attic. I'm going with the idea that this longest span in the house has a cosmetic crack caused by movement from temperature or humidity cycles or movement of the house in high winds. The dry mud readily cracked and abraded with little movements.

I'll have cellulose blown in, top with closed cell foam boards with radiant barrier across the joist, and put the OSB deck back in place. A trusted paint crew will sheet the walls after I've installed insulation. They can decide how to repair the crack. Should the problem return, it will give me a nice project some winter. It's just the garage and I'm allowed to make messes there.

Finally thought to include photos of the crack with objects to help judge the size.





Thanks for all of the comments and helpful suggestions. Of course, if you think I'm completely off base, feel free to jump in.

 

[Cherrybark]

Kerr,

I found that "2x4 I-Beam" thread. Long discussion and, after reading, one could leave with almost any original opinion intact.

You are right. They chewed that topic to death!

http://www.garagejournal.com/forum/archive/index.php/t-88914.html

 

[kerr]

Glad you don't really have a problem . LOL , I say you earned at least a little mess makin card ! "wink"

 

[lakeroadster]

This table from the Southern Pine website should make you feel a bit better about your ceiling joists.

Your unknown at this point is what type and grade of lumber was actually used.

http://www.southernpine.com/app/uploads/SPtable15_060113.pdf

 

[bczygan]

Here's how I would feel about it. YMMV.

It's a garage.

I don't care if there is a crack in the drywall joint that opens and closes, or just stays open. I have a half inch opening between the portion of the house with a basement under it and the portion on crawlspace and slab. It opens and closes with the seasons.

You are probably adding more than the structure was designed for. It probably wasn't even designed for the drywall ceiling, and you are adding loose fill and rigid insulation and decking and then storing things.

Who cares if the crack reappears.

Just store heavier things more towards the edges of the space and call it a day.

Are you going to hang lights from the ceiling?

BTW, the 2x4 screwed and glued to the top, does add strength to a joist. How much, would need to be calculated.

Bill

 

[Cherrybark]

I appreciate that Southern Yellow Pine web site. I won't try to grade the lumber but it is one area of the framing that has the clearest boards.

As Bill says, it is a garage. If the crack returns, I'll add it to the project list.

Found a reference saying 7" blown cellulose will add around 1# per square foot. Everything else about the twelve year old structure will remain the same. Two or three added lights around the perimeter. I'll find someplace to put the 18# extension ladder, that is currently stored on a platform in the middle of the ceiling, and call it even.

Thanks again for all of the help.

 

[Justin James]

Cherrybark,
Please don't take this the wrong way, but I have to agree I really don't think you have a problem there. I've been a residential painter for 33 years and taped drywall in a non heated/cooled garage always ends up cracking on the seams afterwhile. Told many customers to leave it alone, you can fix it but it will come back.

JJ

 

[Deej-79]

Put some caulk on it, paint it and call it a day

 

[ishiboo]

Put some caulk on it, paint it and call it a day

This.