Elevated Slab vs Conditioned Crawl
 

Elevated Slab vs Conditioned Crawl Space

I have been discussing this with a builder, and I thought I would ask for opinions here also.

Slab is cheaper but usually means that your utilities are not accessible.
IE: If a water line starts leaking, you may not find it until your water bill is abnormal. Then you rip up your floor covering, rent a jackhammer, and start breaking concrete.

Conditioned Crawl Space means higher construction cost and perhaps higher HVAC cost.
[edit: builder says add $15k for choosing the crawl over slab]


Is access to the utilities worth the extra expense, or are utilities so reliable that you should not have a need to break the slab in the next 30 years?


Any other pros, cons, or concerns?

after my issues with my house, i will never again get another slab. lesson learned

Does it rain much where you live? I always like the idea of living up, off the ground. But how much more will it cost?

Conditioned crawl space..definitely. If I ever had a house built, I'd want a crawl space with a slab for a bottom, lighting installed, enough clearance to be able to reach and work on everything easily...a space where a guy could go anywhere, work on everything while rolling along atop a creeper...

But, just a dream...like a garage with a lift, a rec room with 2 pool tables, etc.

Crawl spaces are awesome except for when the main sewage line cracks during the winter so everything that should be leaving your house creates a frozen lake under your house that you'll only discover as spring arrives.

Just sayin.

I like the house built off the ground but of the Millions of homes built on slabs, especially the way they are built in the last few years, the chance of a problem is very small.

thanks for tonight's nightmare scenario!!!

I have a "Un" conditioned crawl space, dirt floor. Its @3ft clearance underneath the house. Its a little damp but I rarely go under there. Just replaced all the water pipes. got a little dirty but thats it.

My friend just built a home with a "conditioned " crawl space. She has a stairway from inside the house going down. I took one look and said "Wow!". Its really nice, 3-4 ft clearance, you could probably use some of it for storage. Access to everything and you don't have to go outside.

In the long run the little bit extra that you will spend during construction will be worth it.

IMHO

As far as frozen sewer & other pipes go...most folks have learned to plug foundation vent holes & add a bit of heat when temps drop really low...

Have conditioned crawl space.

So long as your sump pump is functioning properly (fark you Ryan Homes) it's pretty darned neat. Use ours for storage. No real cold floors either. REALLY like the idea of access from inside the house....hmmmmm......

I would go with conditioned crawl space.

Full blown basements are not that much more than conditioned crawls

It's very inexpensive sq footage if the water tables will allow it.

Most slabs will crack to some degree, most of the time it's not a big deal.

Why not just put in a basement? I have a 12 coarse block walls with a concrete floor. lots of room for storage and a great place for the kids to play. Have all utilities down there with no problems getting to anything. I would never own a home without a basement, it is well worth the extra $$.

water table von. would LOVE a basement but would be a swimming pool.

Agree, 98% of the houses built if Florida are slab on grade. The chance that a problem "may" happen are very small. Building an elevated slab is a huge waste of money.

Why not build a slab with hot water or electric radiant in-floor heat and thermal mass underneath? Best of both worlds and ability to heat eliminates some of the plumbing concerns.

Guess it all depends where you live and your checkbook. In GA, NC and SC, I've built a 100 homes on unconditioned crawl spaces. With proper ventilation and a vapor barrier, I've never run into a problem. Some of the crawlspace been above ground and some dug in (and waterproofed with a drain).

Why condition the space? $15k seems like a lot to me. Is it a poured wall or a block wall?

Slabs seem to popular in FL.

No idea what the do up north.

Generally speaking conditioned crawl spaces are considered to be higher quality construction. However (as has been said) you will pay a penalty in cost - both up-front and in recurring (it costs money to condition it).

Another alternative that nobody has mentioned is having access panels or lined trenches with cover plates. Ugly as sin, yes but if you have some sort of raised floor above it with a nice finish, you'll never see it and it could potentially save you a lot of $$$.

Another nice thing about lined trenches is that they can be sloped like the piping so if there's a leak it goes away from the building, not creating a septic tank underneath it - as someone has mentioned is a potential problem with conditioned crawl spaces...

1. Potential for leaks
2. Copper piping is extremely expensive right now
3. Need for a second HW heater
4. Not cheap to run the heating
5. steel piping can rust
6. PVC piping in the slab can spall

That said, there are a lot of these sort of under-slab or in-slab radiant heating systems that work well for a long time. The type/quality of heat provided is amazing. I had the pleasure of visiting Mies Van Der Rohe's Crown Hall at IIT in the dead of winter several years ago. It's quite something to have the brutality of a Chicago winter only inches away on the other side of large expanses of single-paned glass but the radiant heat keeping you completely comfortable. It makes the experience like watching it in just enough of a detached way to make it something one appreciates without making it SO detached it's like watching it on television (which is often what the experience is like behind double and triple-paned glass and walls so packed with insulation it's like being in a spacecraft).

Efficient? Hardly. But an amazing experience. Radiant floors rock if done correctly.

Does anyone have pics/info on retrofitting inside access to conditioned crawl space?

Wouldn't have room for a proper door/stairs in our house but some sort of trap door thing could suit.

I don't know about the efficiency aspect, but PoP's experience matches mine. With a wood stove I can make my indoor temp. whatever I want regardless of the outside temp. But the house is so much warmer feeling at 68 with the floor heat than 78 with the stove. Pex tubing in concrete, earth sheltered construction, no utilities (other than spetic) under the slab.

A section of the floor joist would need to be removed, and then you double up the ones on each side, add headers to close up the box and add a trap door. Use the floor space in a closet and throw carpet over the top.

Running the heating is less expensive than forced air, if done correctly. Even thermal-mass-storage electric heating cables can be more efficient, esp when there is an off-peak rate (usually at night) when you can heat the slab/mass.

Hot-water in-floor heat (Wirsbo, et al) is usually Polyethelyne Cross Link (PEX) that should last forever with no problems. So no copper, steel, or PVC. Since it is flexible, there are no joints and laying it in place is easy and usually tied to rebar grid.

I'm really not sure where your comments are based

chef that sounds like the project in a nutshell!

Along the coast here in SC, you can't condition the crawl. Code requires so many sq inches of ventilation and vents within 12" of the ground, so water can escape in a flood.

Thanks guys... lots of good info with the opinions!

A well ventilated crawl should allow less radon gas into your home.

South Carolina | Radon | US EPA
http://www.epa.gov/radon/states/images/scarolina.gif

If this is for a home theater/ 2-channel stereo listening room go with a slab, else go with a crawl for all the reasons people are saying.

Slab makes a quieter home, thus better acoustics. It feels very solid-"constructionwise." We have a combination slab and partial unfinished basement under the rest of the house (3rd home). Most of the utilities are accessible from the basement, though there is a bathroom and septic line that runs under some of the slab.

Over our slab portion it is a one story, so the attic is available for wires. If there were a finished floor above that I think that would not be ideal.

If you are considering a crawl space, why not go with an unfinished basement. Unless you incur huge blasting fees for limestone, it is the cheapest square footage you can get.

I've had two homes with a crawl space and it bugged me to no end that the only access was outside and very cramp, actually anyone could have gotten under the house since I never locked it. But with the unfinished basement you can gain a spot for the water heater, easy access to the heat and cooling systems, pipes, wires, etc., and add a wine cellar to boot. Not to mention all the great storage space for the little lady.

My recommendation is do a combo partial unfinished basement and slab with all your utilities in the partial basement.

no kidding? when the builder threw up our 'hood with conditioned crawl spaces it was the first to have such in the area. local inspectors insisted on vents as they didn't trust/understand this new fangled idea. eventually the vents were removed and filled in so the concept could operate properly.

but now i wonder, could there have been more to the story?

but what about a sump pump? our house has one and it would pump the space dry if it were filled in a flood i suppose.

My understanding is that PEX tubing is very efficient at insulating the fluid flowing inside (I've seen it used for long runs from heat pumps to heating units and stuff like that). Based on that I don't know if it would work well for actually heating something itself - you want to transfer the heat FROM the fluid through the tubing to the slab to the space. I'm sure there are ways to do it but I've not designed or dealt with a system of that specific type.

I've seen some heated driveways that used metal pipe and they were expensive to run and eventually started failing at the penetration points (but they did last quite a few years).

I'm sure there are ways to do it - as with most things it's all in the detailing and that's just a question of research and finding the correct detail for a given situation.

If you had a well-insulated living space you might be right about it being cheaper to run once everything is up to temperature. It's very expensive (and inefficient) to heat air to blow around like with forced-air systems... I'd have to see some actual comparative data though. Extra water heaters are very expensive to run, but they might be cheaper than a furnace...

I've seen PEX used to do fairly long runs of heating water from heat pumps to area heaters - my understanding is that it affords very good insulation to the fluid inside - for this reason I don't think it would necessarily make a very good "radiator" to transfer the heat from the fluid to the slab (through the wall of the tubing). Maybe there's a way this is dealt with in those particular applications but I'm not familiar with it (would have to check). I've dealt with heated driveways which always used metal or copper piping and typically would introduce corrosion/failure loci at the penetration points (although there are probably ways to detail this to prevent it from decaying in those areas)

You might be right though - if you have a well-insulated living area and are relying on a heated slab, the cost might be less to run the associated water heater or heat pump than to run a furnace - it costs a lot (and is inefficient) to heat up a lot of air to blow around - but it is also easier to control space-by-space which is why it's typically done in large installations (VAVs, etc.)

I'd have to see a comparative analysis but my gut feeling is it'd probably be a toss-up with respect to operating cost versus a "conventional" forced air system which throws it back in the court of construction cost - probably a lot cheaper to do a ducted forced air system than a heated slab (especially if you're talking about more than one floor!)

If ya got the money though... I love the idea of radiant flooring. The quality of the heating is awesome.

Great. Greenville already has a terrible mold problem.... now I also find out that Greenville County is worst for Radon in SC. :(



Learning from your mistakes is good, but learning from other people's mistakes is better. Watching the recent housing bubble collapse, and seeing people with shattered lives, I am certain that I do not want to build my "dream home" and then have it taken from me later on.

I have set a budget for myself. It's not all I can afford... it's all I can afford if things in my life change. It's not living within my means... it's living safely below my means.

But I digress. Within my budget, I want to maximize the living spaces of my home and the quality of construction. I know a basement is cheap square-footage, but adding a basement still takes money from the actual home and also it's not what I'm looking for. And I refuse to exceed my budget to have both.

You might end up with one of those ventilating blowers with PVC pipe stacks running up the side of your house if done after the build as a fix.

This is typically a specialty item/installation, perhaps there is a way to run the PVC pipe vent inside a wall if that meets your state code.

You might be able to vent a slab for Radon the way they do for Methane (people do build on old landfills), but again you need to talk to an installer or code official about this.

Our Michigan Building Code here is based on the International Code and has a special Radon Chapter. Now might be the time to look at your code and start talking to someone local about it.

EDIT: regarding mold and concrete ground slabs..............a crawl is looking better all the time. I know that for commercial concrete counter-tops/bars in food service areas there are several additives which prevent the build up of germs. Just a wild thought and deserving of some research, perhaps there are additives in addition to the traditional vapor barriers and rigid insulation (never use expanded beadboard (white), use only extruded polystyrene pink/blue) which can be used on a ground slab in your area.

The problem with a pump is when the power goes out, there's no way to drain the crawl space. Garages are required to have certain amount of ventilation as well.

In both cases, the vent can't be the type that can be closed off, such as plastic vents that many have.

After hurricane Hugo, codes changed requireing this. Add in the proximity to the coast and Charleston being in a seismic zone, they changed a lot of things in the past 10 years.

Radon :rolleyes:

I'm not sure it is a good idea to totally write off radon's effects, but when I hear those ads (maybe they're PSA's) on the radio where radon is claimed to be the #2 leading cause of lung cancer, I wonder where that info comes from. Where do they get the data about radon caused cancer? If I develop lung cancer tomorrow, will they measure all the places I worked, lived, went to school? How could they possibly track a statistic like this?

I have had both a Wirsbo (hot water) system and an electric cable system in a poured basement slab. I had them built in both cases.

The electric cable ran $1 per square foot, installed plus the extra washed sand and rigid foam insulation around the perimeter to create the thermal mass. It was on a seperate box and meter, and our electric company had a special rate for off-peak (and even had a rebate program that almost paid for the system). It would kick on at 6pm (if needed) and run until 6am (if needed). It was toasty and took the temperature of the slab (not the air). It cost about $15 per month during the winter months and made the basement (esp the bathrooms!) much more liveable.

The hot water systems are more mainstream. They are straightforward and easy to install. They can be run with hot water heaters, or specialized heavy-duty hot water heaters, or dedicated boilers. Since PEX is designated for potable, the entire system could be integrated with your regular hot/cold plumbing. Even after going through the heating loop the returning water was still warmer than from the street, cutting down the energy needed to generate more hot water. Incorporating a geothermal heat pump and/or an auxillary external wood (or whatever) boiler can really save.

Also, if you have tall ceilings or great rooms or large vaults or open staircase, heating the floor (rather than the volume of air) makes sense.

UPDATE: 04/01/2010

Short but good article on crawl spaces in the Northeast.
Advanced Code Group CMS Page - Crawlspaces in the Northeast United States (not a building code article)

Perhaps there is another article on the website for the Southeast, I do not know but is worth checking out. This is from the forum code officials and architects use.

Thanks, Kach.

Based on the added expense of building a conditioned crawl, coupled with the perpetual expense of conditioning the enclosed space, I think I have decided to go with elevated slab.

Everything I am reading seems to indicate that the sub-slab plumbing has come a long way in dependability in the last couple of decades... so I guess I am going to take that gamble.

+1 I've lived in several homes with this type of construction. I've never heard of a problem with this method.

A basement is practical. Think of all the utilities that could go down there, even a washer and dryer, that really maximizes living space above. And if you ever need shelter from a hurricane or tornado, you're protected.

Do what makes sense, but you should at least check out the price a partial basement.

If you ever wanted a dedicated workout room, winter work shop, or media room you won't loose that precious livable space.