If your windows are properly installed and flashed, a crack that small doesn't present much of a problem. I'd take some pictures of how that sub is doing it on another job; he probably did yours that way.

Bring it to the builder's attention in writing.

Joseph, thank you. The sub who did it is no longer working for the company. We did have an inspector in before drywall went up and he didn't see any problems with how the windows had been installed.

Mark, I'm way ahead of you. Definitely bringing it to the builder's attention but wanted to hear from the pros as to whether it was something we needed to be concerned about.

Yes.

Here's the section of the Builder's Performance Guidelines under the mandatory Warranty plan in Ontario dealing with your situation:

Worthy, any idea what might be causing them since they are only under the windows?

And I agree they must be fixed. What would be the best way? This is traditional stucco, not synthetic

The cracks are all very vertical and appear to be following something along the sub surface beneath the cement plaster. Is there wall sheathing used, such as plywood or particle board? Did the builder and plasterer install a backer and reinforcing before plastering? Is there a vertical joint at that point in each case?

Talk to the builder. This isn't acceptable.

I agree with Virgil, whatever they used for a substrate isn't properly installed. You're likely to find more and more of these cracks.

And yes it IS going to be a water penetration hazard.

The cracks are all very vertical and appear to be following something along the sub surface beneath the cement plaster. Is there wall sheathing used, such as plywood or particle board? Did the builder and plasterer install a backer and reinforcing before plastering? Is there a vertical joint at that point in each case?

Talk to the builder. This isn't acceptable.

Hi Virgil. Thank you. There is cement block under the stucco. The stucco was done correctly with the wire lath, etc. No wall sheathing or particle board. No vertical joint.

Thank you homechef. Ours was the three coat application. Like you, I had done the research before. It was not with the horsehair. The problem is I think the paint was ordinary house paint and not elastomeric paint.

My stucco has a mesh product (fiberglass?) applied over the scratch coat before the finish coat. Haven't seen any cracks.

However, random concrete cracks I can understand but these are definitely seams telescoping from underneath. There is MOVEMENT in that wall that should NOT be there.

I've left a message for our home inspector to come out and I've also written the builder. Will let you all know.

I've never used stucco, EIFS or traditional, other than for a few bays. But I have had concrete bricks (mimicking stone) under windows develop the same cracking after a few years. A bit of caulking disguised it fine; never a moisture problem as that's what the drainage plane is for.

All buildings are in constant motion, some large, like skyscrapers designed to sway as much as 6", some small as masonry contracts and expands by fractions of an inch depending on moisture and temperature.

Thank you. I have our building inspector coming out on Wednesday to do a final walk through and to check this out especially. It's on 5 windows.

We bought an existing stucco house in CA and we also used elastomeric paint when we repainted. Locals highly recommend the Dunn Edwards brand, which is what we used.

But I wished I had done more research on stucco when we built our guest house and retaining walls. Original stucco in this area had the last "coat" of stucco applied with the color mixed into the stucco, which is much better than applying a layer of paint. It would have worked much better on the retaining walls that get a lot of water exposure.

Not many left that know how to do the stucco the original way.

Had the engineer out and it's just normal settling. And also talked to a builder friend. He agreed. Needs to be properly caulked and sealed and then repainted.

I don't blame you for worrying and checking. Not after what you've been through!

Elastomeric paint for longevity...$$$/gallon!

Hairline cracks seem normal especially after cold temps and settling from a new/newer build

You are going to want to do a quick bit of research on elastomeric paint and application techniques. I searched elastomeric paint and a bunch of information popped up. It's a good idea to educate yourself before you take on the painter. Just about every paint and coating company will sell a version of the product. They are all tintable. It can be sprayed on with a monster sprayer and the right tip. But, it will have to be back rolled. My guys rolled it. I'm glad it's such a fixable problem. You will be pissed when you see the bill. I think the best you can expect is a no profit job and materials at cost. At least this won't stop the CO process.