House built on a slab (midwest climate)

[icyappraiser]

We are exploring some housing options and looking at a new build that is on a slab foundation. In our area (north-ish midwest USA), it is probably 80% basements, 15% crawlspaces, and only the rare slab home so we are a bit uncertain about the foundation but really like the floorplan (3 story home - 1st is attached garage + storage/mechanical area, 2nd is living/dining/kitchen, 3rd bedrooms).

A quick google indicates the following pros/cons to a home built on a slab, but I don't know what I don't know. To someone with more knowledge/experience than I, how many of these items are real, and things we should be concerned about? Are the pros true?

Pros
1. Don't have to deal with basement water / moisture issues (common in our area)
2. Less likelihood of rodent/pest issues
3. More efficient / lower energy costs
4. Lower build cost (reflected in price of home)

Cons
1. Cracking / foundation issues due to freeze/thaw cycles in our area (builder says the slab is 6" deep with 46" deep perimeter footings, with steel reinforcements for movement/cracking. Google says frost line is 42" here)
2. Utilities running through slab can make fixes costly down the road (In this house, no utilities run through slab except main sewer line, but this is usually in concrete basement floor anyways. All plumbing is accessible through ceiling of first floor as if it were a basement)
3. Cold floors - though main living space is on 2nd floor so this shouldn't be an issue)
4. Lower resale value (hopefully offset by addition of 1st floor which acts as basement and attached garage which is uncommon in this neighborhood due to small lot size)

[Dee18]

If you do buy a house on a slab get a secure place for tornados.  I have friends who had a shelter installed in the floor of their garage. 

[AccidentialMustache]

I mean a basement is just a subterranean slab. Any issues with one of those will still apply to an at-grade slab.

They like to condense water in the spring, when humidity is up but temp isn't, so have a plan for dehumidification that isn't air conditioning unless you like living in an ice box. Which is just saying you haven't fully avoided water issues.

Rodent/pest is really a matter of sealing the building properly as far as I can tell.

[roomtempmayo]

We rented a 90s-era house on a slab about 10 years ago, about 75 miles south of the Canadian border.  It had in-floor heat throughout the main level, which was nice. 

The downsides I can recall were that anywhere on the main floor with hard flooring felt, well, like you were standing on concrete.  Not a huge deal if you like carpet, but noticeable in the kitchen and baths.

Also, if you're used to having a basement, don't overlook the need for storage.  Our place had an extra deep attached garage, along with excellent closets.

Nothing in our experience would make me averse to owning a house on a slab if the heating and storage were well thought out.

[AMandM]

Our previous house was built on a slab (mid-Atlantic climate). The tiled areas did have cold floors, and we had a costly repair when a pipe in the slab leaked, but these problems don't apply to your house. We also had issues with ceramic tile cracking after the repair, because it turned out the slab repair was not perfectly level.

I mean a basement is just a subterranean slab. Any issues with one of those will still apply to an at-grade slab.

They like to condense water in the spring, when humidity is up but temp isn't, so have a plan for dehumidification that isn't air conditioning unless you like living in an ice box. Which is just saying you haven't fully avoided water issues.

I don't really agree with this. A slab avoids most of the water issues of a basement. In a basement, condensation happens where the air hits the inside surface of the wall. Floor slabs don't have this problem because the slab is covered by subfloor or tile. Also, a slab doesn't permit water to accumulate because it's at grade, whereas a basement can flood if it doesn't have a drain/sump pump.

Rodent/pest is really a matter of sealing the building properly as far as I can tell.

Agree with this.

I don't know about energy efficiency. Lots of basements don't have heating or AC, so I'd guess their energy costs would be lower than a first floor that's part pf the house.

Presumably the lower price and lower resale value go hand in hand. The increase might be the same. In any case, I'm in the camp that you don't choose your house on the basis of its value as an investment.

[AccidentialMustache]

I mean a basement is just a subterranean slab. Any issues with one of those will still apply to an at-grade slab.

They like to condense water in the spring, when humidity is up but temp isn't, so have a plan for dehumidification that isn't air conditioning unless you like living in an ice box. Which is just saying you haven't fully avoided water issues.

I don't really agree with this. A slab avoids most of the water issues of a basement. In a basement, condensation happens where the air hits the inside surface of the wall. Floor slabs don't have this problem because the slab is covered by subfloor or tile. Also, a slab doesn't permit water to accumulate because it's at grade, whereas a basement can flood if it doesn't have a drain/sump pump.

We put down some of the foam interlocking standing mats on our old house's raw concrete basement floor, away from the walls, on top of a scrap of carpet that was there. Also a bookshelf, as well as boxes of storage. Minor water damage to all of it. And yes we did have a basement dehumidifier and yes it was working. I assume this was just water migrating up through the concrete with nowhere to evaporate at the surface due to our impermeable obstructions. Subfloor/tile wouldn't stop that, it'd just hide it longer so you have a bigger and more costly "surprise!" moment when you find out.

Our at-grade garage floors (eg, slabs) are happy to condense in the spring in the midwest. Boxes are not to be set on the slab along the walls for storage, because they'll just wick/rot. Pour one big slab for the garage and 1st floor house storage/mechanical and you're going to get that everywhere as cold and water migrate through the concrete.

Hopefully the builder is smart enough to pour two slabs and insulate the house's from the garage. They should anyway, garage should be "outside" the house envelope, but a lot of builders build to code and not an inch further.

[nereo]

Among the green building community new construction homes on slabs are vastly preferred over ones with basements.

One consideration not mentioned is that basements tend to be the most expensive floor to build per square food. Excavation, frost walls below frost line and curtain drains /. Radon systems all are expensive (and carry large carbon footprints). A basement also tends to be the least desirable room to be in. Egress can be a tricky issue if it’s a finished space.

Most of the “pros” for basements involve a place to put mechanicals. That’s less of an issue now with boilers giving way to mini splits (far superior ) and large ducted hvac now replaced by ERVs that can be ducted between standard wall cavities.   The slab *should* be well insulated, but it’s good to check as it’s an area many builders skimp on because it’s impossible to check post concrete pour. Flooring options are just about anything, including LVP, hard wood, engineered wood, tile or polished concrete. Some will require additional subfloor treatments but as long as the slab is flat (which it should be) installation should be easier than most ply-over- joists that are rarely completely level. You can even install underfloor heating (if not integrated into the slab itself)

Cost seems largely an artifact of how we categorize homes. If it’s 2,000ft of living space PLUS a large unfinished basement of course it will lost higher than a 2000ft on slab. Compare apples to apples here.

[Sibley]

I've seen various houses built on a slab. Some were fine, others had problems. Needing to access buried plumbing is a nightmare, and it will happen at some point. Water intrusion was a problem on several.

I also have a garage on a slab where the slab is cracked and shifting. The foundation has failed and there's no fixing it. Tearing down and rebuilding a garage is one thing. The house is a much bigger deal.

[AccidentialMustache]

One consideration not mentioned is that basements tend to be the most expensive floor to build per square food. Excavation, frost walls below frost line and curtain drains /. Radon systems all are expensive (and carry large carbon footprints). A basement also tends to be the least desirable room to be in. Egress can be a tricky issue if it’s a finished space.

A radon system isn't expensive to put in. We did it at our old house for under 1.5k I want to say, that's including the plastic on a small amount of crawl (~100 sf) by the garage. Maybe 30' PVC, a low power fan and that's it. And that included having to route it through existing house/slab/roof/etc.

The biggest cost to me of it is really the roof penetration maintenance, which might have been avoided had it been in from the get-go (go out an outside wall rather than the roof, and then go up).

[roomtempmayo]

I don't know about energy efficiency.

Our place on a slab was incredibly expensive to heat, about $500/mo in the winter.  A house of a similar size with a natural gas forced air system was ~$200/mo in the same region.

It was some sort of electric in-floor system supplemented by electric radiators.  I suspect the insulation was really bad, as the house was generally built cheaply.  There were lots of things that could have been contributing to the heating bills, but I've stuck with a natural gas furnace since.

[ChickenStash]

Resale would be the largest concern in my area. Basements are >90% of the homes and selling one with just a slab can mean a long wait or lower price depending on the market.

IMHO, basements are too useful to pass up, particularly for homes with smallish sizes. The extra space to handle the utilities is a wonderful thing. I lived in a small slab house for a while and it was very annoying dealing with the noise from a washer/dryer running on the main living level and difficulty accessing utilities that were buried in the slab. Easy access to most of the wiring, plumbing, and HVAC for repairs and maintenance in the basement has made the less-fun parts of homeownership a lot simpler. Then there's just having the extra living space. I'm not a fan of fully finishing basements but even without that the extra space for storage, workshop, gym, etc. is great.

Like anything, the cost is a consideration. Talk to the builder or general contractor to get their opinion before deciding. Many of the variables you'll run into are going to be local, possibly even specific to the site. For example, in my area footings already need to go down at least 4ft due to frost lines and we have fairly easy to dig ground making a significant dent in the extra costs.

[sonofsven]

Slab on grade homes are looked down on in my area, for all the reasons you mentioned. Another issue if you have a forced air furnace is that the registers and ducting can't be placed in the floor, but in the wall, or even worse, the ceiling. Typically they'll run ducting through the attic and then down, which is less efficient.
I've never built one, and we don't build basements often, either, unless it's a full walkout lower level built on a slope.
I live in earthquake county and the expense of concrete and the associated steel and engineering is high, so the most cost efficient home is a crawl space with a perimeter foundation and a highly insulated first floor.
When we've built homes with hydronic in floor heat we've done it on a crawlspace home as well by keeping the floor framing lower in those heated areas and running the pipes then pouring a mix of gypcrete over them.
Building on a slab doesn't really solve any issues, it's just the cheapest way to build, but at a cost of less insulation and potential issues down the road.