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I'm looking at buying a CBH house that is on a slab, instead of raised floor or crawl space. I'm not from the area and concerned with this type of construction because it is not the norm for the area.
How stable is the ground and do I need to be concerned with cracking?
What about comfort and insulation? I know the weather can get cold, will the slab suck the heat out of the house?
What about talking to local structural inspectors about the pros and cons of slab foundations in that area? How stable the soils at an individual house's build site happen to be can vary just as the quality of the ground prep for construction can. Slabs can be frost-proofed/insulated just as the vertical walls of a dug foundation are. Local building codes may require it. A structural inspector could help you evaluate the house you're considering. Are you using a buyer's agent? An agent who knows the local market well may also have some insights.
We lived on slab foundations in Oklahoma City and Albuquerque, NM. They tend to be harder floors, so kids fall harder (adults too). You're walking on concrete with a little carpet padding and carpet, or wood, tile, linoleum. You're not falling on plywood that might have "little" give to cushion the impact. Of course that's only on the first floor (we had a ranch in both locations).
Both were comfortable heat/cold wise. The HVAC system goes through the attic and you have ceiling vents into the rooms, so make sure they have good ceiling insulation. In Oklahoma we added R-20 blanket insulation over the blow-in to cover the HVAC lines for the summer A/C season.
Another issue is the vapor/water barrier under the concrete foundation. Absolutely you need to make sure the builder puts this down. in Oklahoma the builder did not put in a barrier (we didn't know any better at the time). Basically thick plastic sheeting. We had moisture problems seeping up through the porous concrete. We moved away, but I'm guessing some owner after us likely had mold issues, same with lots of houses in the neighborhood. Here in Idaho it would be radon working it's way through the foundation. Most crawl spaces have this barrier in place in this area for the same reason.
Soils issues will effect slabs, stem-wall-on-footer type foundations (your crawl space foundation), and a full basement. So I would not worry about the stability for just a slab; it applies equally to all. So-called expansive soils are most common concern for foundation problems due to soils and that is not common in the Boise area. So that particular probability is low, though no one cannot say 100% for sure without know the exact area.
Other potential issues are with site preparation, and the laying in and packing of the gravel and soil under the slab. If this new house is in a tract where the same builder is right now building other houses, you can drive by those slabs being prepped and make observations, and ask questions. Questions to the builder may get answers too.
The comments about them being hard are right, we owned one slab home, in IN, and it was indeed harder to walk on, etc. Ditto for the vapor barrier, that can be critical for any type of foundation. You need to ask the builder of one was put in, and at the same time, you can cask about the foundation insulation.
Being cold depends totally on how the slab design to address any under-slab freezing and how it has been insulated. The idea of a slab being insulated underneath has both pluses and minuses. With insulation the slab is going to feel warmer on the 'human' side. But it will not allow heat to go into the soil under the slab, and so other insulation, like at the slab edges and a few feet out into the yard under the surface are needed. IDK what is standard for Boise but the soil does not freeze too deep in that area.
Any mistakes in plumbing will require a jackhammer to get to for fixes. That part of slabs really stinks In-slab heat ducts are sometimes used, and can be sources of water leaks and moisture accumulation if not sealed well and the insulation has to be done right. That is one area that I would look into: how/where the heating ducts are run in this new home.
As for any foundation, look around the yard and carefully observe where the surface water is draining. Being at the base of a slope, without an adequate drainage slope way from the house, is a good source of problems. This is the type of thing that you can observe yourself.
Not sure how much this has helped; there are a number of things to consider, and without details, it is hard to say a lot more.
I currently live on a concrete slab and never again on my next move and house. I don't have air conditioning but when it gets hot the slab retains the heat then at night it gets real real hot when the heat soak rises into the house.
I live in Palmer, AK. I have a multi level home, 4 levels total, and the house is slab on grade. Built in 1985, it has seen some pretty big quakes, and the foundation is still in 1 piece. The concrete foundation needs to be engineered for the area. More rebar, thicker concrete, saw cut to relieve stress rather than letting it crack on its own.
It may be slab due to high groundwater, which is typical in this area, especially Meridian. There's a new housing development across from me and someone ordered a home with a basement. They have to run a sump pump 24/7 to keep the basement dry. Also plenty of homes with crawls that also have water issues(and I'm talking up on the bench, not in the floodplain (Eagle). It might also be slab as crawl spaces cost more, and building materials increases are eating into builder's margins, especially those companies that tout themselves as "affordable". Watch out for CBH homes, they are not known for their quality, use your own inspector.
I have a CBH home with Slab/Slab Wall construction and it's better than a crawlway and a lot less problems IMO. You need to understand the differences. Old school construction was to have a utility crawlway underneath the house with vents low on the side of the house for air flow and utilities. Lots of spiders and pipes underneath the floor in the crawlway which is typically a very uncomfortable space. CBH homes builds a slab wall and then infills this outline with cement to form a solid slab with no crawlway and all utilities are on the surface except for water/sewer/power which hopefully is "forever" under and inside the slab. As far as I know the slab foundations are not pre-tensioned with rods or cables but are poured inside of a reinforced wall ~6" thick which has all the utilities and risers (water/sewer/power) already positioned and ready to be cemented into place. I don't know of any problems with this type of construction in the Boise area.
I have a CBH home with Slab/Slab Wall construction and it's better than a crawlway and a lot less problems IMO. You need to understand the differences. Old school construction was to have a utility crawlway underneath the house with vents low on the side of the house for air flow and utilities. Lots of spiders and pipes underneath the floor in the crawlway which is typically a very uncomfortable space. CBH homes builds a slab wall and then infills this outline with cement to form a solid slab with no crawlway and all utilities are on the surface except for water/sewer/power which hopefully is "forever" under and inside the slab. As far as I know the slab foundations are not pre-tensioned with rods or cables but are poured inside of a reinforced wall ~6" thick which has all the utilities and risers (water/sewer/power) already positioned and ready to be cemented into place. I don't know of any problems with this type of construction in the Boise area.
That is correct: there are no pre-tensioned cables in a residential slab-on-grade; just re-bar and/or grid wire. The 'hopefully forever' condition of the under-slab utilities is usually not a problem; but it is quite a headache if it ever is. I don't like crawl spaces but I'd rather do repairs there than take a jackhammer to the slab, haul the debris out, mess with the dust inside, do the reapir, and then restore the concrete. Of course, most homeowners won't ever deal with it.
There are millions of slab homes in the US, with good results. However, there is nothing 'old school' about a crawl space; millions are still being built nationwide.
BTW, does you CBH home have the HVAC vents all in the ceilings and walls? If so, that is good, and would be useful for the OP to know.
Yes my ~2 year old CBH Home has all the HVAC vents inside the walls/ceilings and no floor vents or anything HVAC related under/inside of the slab. This seems to work well and uses as single AC Unit. But in a 2 story home you need to adjust the vents between the upstairs and downstairs to divert airflow where it is needed.
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