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dreamercgl 07-11-2009 12:59 PM

Crack running entire length of room in new additon.

hI. We just put on a new addition 2 yrs ago. The contractor we used has been in the business for over 25 yrs, and he is very good. We added on a 40 by 32 room, one and half stories. The attic is very well insulated, the structure was very well strengthened. The ceiling in the living room is drywall with a light stucco design. Very happy until last summer. We noticed a crack going the entire length of the room in the ceiling. Come winter time the ceiling would close and you couldn't even see it. Now , summer, it is back. My husband tried redoing the stucco in the crack which made it worse as far as noticeable.

I hate this so much. My husband seems to think that it is because we have a humongous cottonwood tree that has very large roots that run under our house. But the older additon is 70 years old and no crack anywhere on the ceiling. He wants to cut down the tree. I am adamant about leaving this beautiful tree , it is 125 yrs old and shades our home and plants.

he says it is the only thing that could be causing this.. I think that if it was the tree roots doing this, the crack wouldn't close up and then reopen other times. Please help, I do not want to lose my tree. We had a concrete company pour our foundation, and inspector walked upstairs and he said it was so sturdy that you could not budge the floor at all. So I don't know what is going on. We have no water leaks or anything. The whole house has been completely remodeled. The addition where the crack is does have crown moulding, just to let you know , although I find it hard to believe that , that would have anything to do with the crack. My husband is determined to cut down this wonderful tree. Please help.

ccarlisle 07-11-2009 01:15 PM

A cracked ceiling is replaceable, a tree isn't. If he is looking for an excuse, this isn't a good one IMO.

Is the crack straight along a possible seam? at a given fixed distance from a wall, like 4' or 6'? along a joist?

Nestor_Kelebay 07-11-2009 01:37 PM


You should be aware that almost all (over 90 percent) of a trees roots will be in the top three feet of soil. I don't know how deep the foundation is on your addition.

The reason why even the largest trees have a very shallow root system is that besides anchoring the tree against wind, the job of the roots is to gather moisture and nutrients from the soil. The nutrients the tree is after are the ones that occur as a result of AEROBIC decomposition of organic matter. (That means the decay of organic matter that takes place in the presence of oxygen.)
What the roots are actually looking for is "compost" which is made by allowing organic matter to decal aerobically.

The problem is that you simply don't have enough oxygen in the soil more than about 3 feet down to support aerobic decay. You may have anaerobic decay deep down, but that doesn't produce the good stuff the tree is after. So, roots that grow downward into deeper soil don't find that good stuff, and simply don't do well.

This is precisely the reason why cities with millions of sewer pipes buried 6 to 8 feet deep and millions of trees with root systems 0 to 3 feet deep don't interfere with each other very often. Generally, the only time a tree will grow roots into a sewer pipe is because there's a crack in the sewer pipe and the soil around the sewer pipe starts to resemble the soil near the surface; with plenty of moisture, oxygen and nutrients in it. If there is no leak in the sewer pipe, the tree won't be the least bit interested in it.

What you CAN do, until you find the cause of the cracking is to paint over the crack with something called an elastomeric coating. Elastomeric coatings work on masonary buildings and roofs, and are essentially a paint made from the same kind of rubber the toy called "Stretch Armstrong" is. It's a thin rubber coating that will stretch across a gap as long as the gap is spread, and then shrink back again to it's original shape as the gap closes. Any place that sells roofing materials and/or exterior coatings for masonary buildings will know about, and can advise you further about elastomeric coatings. You don't have to paint your whole ceiling with the stuff, only over the cracked area. Essentially, you simply tint your elastomeric coating the same colour as the paint you intend to use on your ceiling. You paint over the crack with your elastomeric coating, allow time to dry, and then paint up to the crack on each side with your normal ceiling paint.

Nestor_Kelebay 07-11-2009 01:56 PM

The crack in your ceiling may be due to frost heave if your foundation isn't very deep. In the winter the ground will freeze to a depth of up to 5 feet where I live (Winnipeg, Manitoba) and shallower the further south you live.

During the winter, ground water percolating upward from deeper down will freeze to the bottom of this layer of frozen ground. As it does so, the water freezes as it expands and creates something called an "ice lens" (so named because it's shape resembles the convex on both sides shape of a magnifying glass). If an ice lens forms in the ground under your addition, or freezes to the addition's concrete foundation, then the expansion of the ice as the ice lens grows will lift the foundation of the addition, and this is the most common cause of cracked walls and ceilings up here in Canada.

Believe it or not, it's possible to prevent this from happening by insulating the heat of the Earth from the cold winter above. If you Google "Frost protection of shallow foundations" you should find a number of technical papers on how to protect buildings with shallow concrete foundations (say only 3 feet deep) from the effect of ice lens formation under or beside the concrete. Basically the procedure is to dig a 4 to 5 foot trench around the shallow foundation, attach thick extruded polystyrene insulation (like Roofmate) to the sides of the foundation, and then set thick slabs of the polystyrene insulation down on the floor of the trench before backfilling with dirt. What happens is that the thick polystyrene insulation spreading laterally outward from the building actually insulates the Earth from the cold above, and the ground under the insulation doesn't freeze in winter. It's warmed by geothermal heat. Any freezing that occurs above the insulation will, at best, freeze to the insulation attached to the foundation wall. Ice doesn't stick well to polystyrene insulation, and this insulation is thick enough that it acts as a slip-plane even if the ice does stick well to it. What that means is that the 4 or 5 inch thick insulation is thick enough and soft enough so that one side of the insulation can move up to an inch or so upward or downward without the other side moving at all. So, any relative motion between the ground and the concrete foundation is entirely accomodated by deformation of the vertical insulation layer. Thus, the insulation acts as a "slip plane".

Google "frost heave" "shallow foundation" and you should find a lot of engineering studies into how to do what's described in the previous paragraph.

Big Red 08-07-2009 07:02 AM

Well, structures move around AND you get a lot of drying of new wood and that can cause cracks. I have cracks where the ceiling and the wall meets in my new home. I attribute my situation to truss lift. The cracks get wide in winter and compress in summer, just as you describe. Get yourself some tubes of a caulk called,"Big Stretch." You can go to their website and read about it. It's the only caulk I use, anymore. It will stretch 2" without breaking, and also compresses very well. I tried it in one of the cracks I have---no more cracking. It seems only Ace hardware stores stock it, but you can by it online, also.

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