Structural engineer who is going through a builder to build a home. What should I expect and prepare

[gmoney731]

Hi, I’m asking because typically the main slabs on grade do not have construction joints - only the garage and patio do.

I guess both make sense, since the garage sees higher vehicular point loads, and the back patio is supporting the facade.

But why not the slab on grade for most of the house too?

Also, I didn’t see expansion joints between the house slab and the back patio slab as well as potentially the garage slab.

Perhaps all these slabs were poured monolithically, but I clearly see it as separate slabs butting up against each other.

Wanted to know if I can talk to the Super about it, or what other structural considerations I should be aware of. Thanks for your time.

 

[jerseyshore]

Are you confusing construction joints with contraction/control joints?

People usually don't sawcut interior slabs if they are going to be covered with a flooring. Garages or exposed patios should definitely get the joints though because they will develop those ugly shrinkage cracks if you don't.

 

[gmoney731]

Jerseyshore, yes, I meant contraction/control joints. Thanks for the advice.

Couldn’t short term temperature/shrinkage cracking still occur, though, up through the slab curing process, and then through the construction process?

 

[jerseyshore]

Cracking can still occur, but owners usually don't care if the floor is going to be covered because you won't see it when finished.

 

[TheDW]

We do have builders around here sawcut joints at the interior house slabs. We even give them a joint layout.

I've seen other firms plans that don't give them a layout, just say 'add control joints at 15' spacing' or something.

We had a builder a few years back that wanted to stop doing it inside, so we stopped showing it for them for a few years. They changed their minds and cut them inside again now.

It may be a waste of time, but when the floor cracks and potentially ruins flooring etc and somebody gets sued, we at least want to be able to point out what crack mitigation measures we specified.

Sounds like a regional thing. Not much you can do now that it sounds like the slab has been there for a while. Not the end of the world, and not uncommon.

 

[phamENG]

1) What kind of structural engineering do you do?
2) If you don't feel comfortable designing a house (no worries - most SEs who don't work in wood/residential shouldn't feel comfortable), why didn't you hire an SE working in residential?
3) Most of your questions are difficult to answer without a sketch, photo, etc.

My MO for slabs on grade in houses - let the contractor figure it out. The slab isn't a "structural" item in the sense that the overall structure depends on it for stability. Cracks also don't cause a life safety issue. So I instruct the contractor to implement a crack control plan as they see fit. After all, there's a whole lot more to it than just joint spacing. A properly reinforced and cured slab may have no visible cracks even with no joints. A slab with joints could have a very noticeable crack 6" away from the joint. It comes down to reinforcement, restraint, mix, curing, and saw cut timing. You can also use fibers to drastically reduce crack width. Add to that the potential issues with adhered flooring that may not be selected until during construction...I leave it to the contractor to coordinate it.

I wouldn't be worried about a lack of expansion joint material. Unless you built a 50,000sf slab on grade house, you probably don't need to worry much about expansion. Those usually act more as a bond break so, when the slab shrinks, it doesn't adhere to the first pour and develop a crack parallel to the joint a few inches away.