Few months ago they noticed a crack formed in the concrete of their driveway.  Not long after they noticed a cracks in the downstairs marble flooring.  The cracks inside the house run directly in the same line as the crack that formed on the driveway.  Is this an indication of damage to the foundation of the home? 
This is a 2-3 yr old construction on a view lot in TR.

We had a similar problem in our rented Woodbury house a few months ago. I started a thread on this (that got some really knowledgeable answers) you can find by looking at my handle. I’d provide a link but I’m not sure how to do that and don’t have time to look through the tech support thread just now. Since the house was <2 yrs old the builder hired contractors to pull up the tiles in the house, seal the crack in the underlying concrete, and re-tile. They left the crack in the garage though.

NewToOC’s previous thread:

Woodbury Construction Issues

acpme, builder’s rule of thumb: if you can stick a quarter in the crack, that’s a warranty issue, they need to call the developer/builder.
In my experience, any kind of cracks are bad, and there are three times as bad if the house was built on fill, that means it wasn’t compacted properly and the house is now settling.
You said it is a view lot, is it on the hill? If so, it could be both downward and side movement, never a good thing. That’s why I like Irvine, because most of it is flat, which means fewer foundation problems.

When a crack is parallel to slope contours or rear property line it is an indicator of land settlement. If the crack is perpendicular then it is usually an underground drainage path eroding away the ground beneath the foundation. Builders have been using post tensioned slab to hide the land movement issues. When you see a crack in recent construction it is serious matter. All view pads are manufactured to maximize lot count. When one buys a view property always inspect the before and after topo maps. Less modification to existing contour lines is good indicator and usually means the land is stable. Your cut pad means the homes at the upper tier slide down toward you. A filled pad means your home could potentially slide downhill.

Astute Observer - 29 October 2008 02:34 AM

Is it true that minor cracks are acceptable in post-tensioned slab, or the PTS should never have any crack at all, period?

Concrete cube is a material that you can put 30 tons compression weight on and the cube will stay intact but if you lift the cube from the top and the cube will detached and fall apart due to its own weight.

Concrete performs well in compression and poorly in tension. The post tensioned tendons are embedded into tubular sleeves and tighten to many thousand PSI by machine after concrete is cured. The tightening of the steel tendon cables keeps the concrete in compression from edge to edge. Never drill through the post tensioned slab because a severed tendon will shoot out from the edge of the slab faster than 2x of the speed of a bullet exiting the gun.

Any sagging from land settlement or sinkhole the slab can span over the land movement without cracking. Hairline cracks are caused by contraction and expansion due to temperature change and it is perfectly natural. Due to the compression forces cracks should be faint.

bkshopr’s explanation is a very good one, completely agree. What is “cut pad” and “filled pad,” don’t think I quite understand the terminology.
I’m just a layperson when it comes to construction, so forgive me if I’m not accurate in this description: I actually saw once how builders put the posttensioned slab in, it is pretty cool, unlike traditional foundation which is like one-piece thing, a posttensioned consists of several small sections that are filled with concrete and that have some sort of cables in it, we were told by the builder that it is a very good method compared to the old ones. But I guess it does hide soil problems, b/c if soil starts to move, only a small section of the slab would show it originally.

blackacre-seeker - 29 October 2008 04:35 AM

bkshopr’s explanation is a very good one, completely agree. What is “cut pad” and “filled pad,” don’t think I quite understand the terminology.
I’m just a layperson when it comes to construction, so forgive me if I’m not accurate in this description: I actually saw once how builders put the posttensioned slab in, it is pretty cool, unlike traditional foundation which is like one-piece thing, a posttensioned consists of several small sections that are filled with concrete and that have some sort of cables in it, we were told by the builder that it is a very good method compared to the old ones. But I guess it does hide soil problems, b/c if soil starts to move, only a small section of the slab would show it originally.

Cut is when dirt is excavated from the hillside and exported to make a flat pad. Fill is when the dirt is imported to make the pad flat. A flat pad on a hill often is created by a combination of cut and fill. The dirt excavated from the up slope is piled to the downhill edge to form a flat area. The flat portion of the site created from excavation is studier than remaining flat portion created by the piled dirt. This is a problem with a house sits on 50% solid ground and the rest 50% sit on loose dirt. Post tensioned slab will mask the problem but the problem of settlement continues to erode beneath the house without any warning signal.

The diagram below shows a existing hillside with a dark line and the proposed dirt excavation to be used as fill in forming a flad pad. The center line where the fill and excavation met is call the daylight line “cl”. It is often the case along this “cl” line where the crack occured on settled foundation.

Concrete plaza in public places designers specify a deliberate line pattern scored on wet concrete or saw cut on cured concrete. These control joints are the places of weakness so the hairline crackings could occur there in avoiding a bunch of 2mm unsightly and distracting cracks at random directions. These cracks are harmless.

In a situation of settlement there should be just one crack and the crack would separate at increasing intensity over time as most of the stress of movement converge to the point of weakness.

Generally, if I see a lot of crack in a house I more associate the problem with chemical dependency issues for the folks there.  I suspect that Irvine may see some growth in this sector of the economy as things slow.

Does a raised foundation resist ground settlement/movement better than a concrete slab?  Why do so few modern houses have raised foundations?

High Gravity - 29 October 2008 09:01 PM

Does a raised foundation resist ground settlement/movement better than a concrete slab?  Why do so few modern houses have raised foundations?

Older houses with raised foundation negotiated with hillside contours better than a modern superpad slab construction. Older homes nestled into the slope while newer homes are imposed on the slope. Raised foundation cost more because the framing of an entire floor on the first floor while new constructions the slab is the floor. Raised floor in the old days was to avoid flooding. Nowaday city mandates many drains on the street. Raised floor minimizes subterranean termite and other insect damages. Due to floor deflection tile installation must be prepared with a sub-base mortar bed.

Raised floor does not resist ground floor movement and neither a slab foundation. If the ground decides to shift then nothing can hold it back. Both systems will fail. Raised foundation however would allow you to add or jack up the area that is settling so the house can remain level while other remedial measure could take place to slow down erosion of the ground.

Due to high labor cost raised floor is not practical today. Check out the aesthetic below between the two.

Raised floor looks better from the street when the front door is elevated with steps and especially the one with a raised porch for privacy.

raised foundation with porch allow steps, the changing of paving materials, and plant palette to enhance the visitor experience.

Slab foundation with porch has no elevation opportunity and the flatness is not condusive to the layering effect of paving and plant materials.