I just purchased a new townhome and noticed a crack that runs from front of the house through the back. it's a poured concrete slab that is shared with
6 other townhomes. the builder assured me that it's not structural however he also told me that the house would settle and that I will start to notice cracks along the doors and wals (seems like a cover-up). although I haven't noticed any cracks on the walls, doors and anything else. I know cracks on concrete is normal but a crack that runs from the garge to the back of the house? is that normal?
I just wanted to verify what my builders is saying, and to see if I should get someone to inspect it.
Your builder is full of shit. Cracks in poured slabs should be minimized and directed via control joints and expansion joints between built structures.
If it's a crack in your floor slab as I surmise, then it's not going to be a big structural deal & I wouldn't lose any sleep over it. Yes, settlement is normal and so are cracks in concrete slabs. In the design of slabs, care is usually taken to control the location of cracks, but it is virtually impossible to prevent them. It sounds as though your builder may have cut a corner, or maybe not. It's possible this simply falls under the "shit happens" clause. A bit more settlement of one side than the other is enough to cause a full length crack.
In that your townhouse is newly-built, I'd lean toward accepting the builder's explanation. Settlement happens. OTOH, if the settlement is bad enough to cause such a crack, it's also apparent that somebody screwed up. Possibilities include:
Poor geotechnical engineering. At best, however, soils engineers can only interpolate the soils conditions at any point on the site from a series of widely spaced borings. If there's an anomolous soft spot on the site, it could easily be missed without the soils guy being negligent. It's not an exact science.
Poor site preparation. My #1 probablility. It costs time and money to properly grade a site, especially when fill areas are included. The moisture content must be correct, proper materials must be used, and the fill must be placed and compacted in layers to adequately prevent excess settlement later. Given that the better the preparation, the lower the profit for the builder, it's a prime shortcut.
Poor engineering of the slab. Inasmuch as settlement and cracking are inevitable, proper crack control design and reinforcing should have forced that crack to occur in a less objectionable location rather than in the middle of your floor. OTOH, the engineer relies heavily on the geotech info and on a reasonable belief of contractor execution in designing his work. Depending on the sixe & configuration of the project, the calculations may have indicated that his precautions were adequate.
Poor quality materials. We're back on the builder again. Like site prep, proper concrete materials, mix designs, and placement cost money. Maybe the specs called for 4,000 psi concrete, but that doen't necessarily mean you're going to get it. Too much water in the concrete, too much heat, cold weather, trucks arriving late to the site can all affect the final product, and mitigating any problem subtracts from the bottom line. Chances are, however, that bad concrete wouldn't have caused your crack, though it could affect its location. Concrete will crack at the weakest point, and if a bad pour is weaker than a control joint, that's where it's going to fail.
Sorry, that's an awful lot of info just to say don't worry about it. As with other things of this sort, however, it's always a good idea to talk with your neighbors. If you have an isolated problem, well, it's kind of the luck of the draw. Also, while settlement is normal, cracks at doors and windows should not occur if the structure was properly designed and built. If there are chronic problems that indicate negligence or shoddy construction, that's a different ballgame.
the builder assured me that it's not structural however
Asking the builder if his building is ok is like asking a new car dealer whether or not you need a new car. Practically all end-to-end slab cracks
*are* structural. Forewarning you of interior cracks is the topper. That would suggest he expects major differential settling, but wants you to stay put long enough for any warrantee to expire. Check your warrantees, get expert independent help from a structural engineer, and prepare to bail, move, or take someone to court.
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