I like to reach all ICF experts with this topic: I have lived in Canada for over 20 years and crawl spaces are a mystery of the past, mainly they are ineffective regarding energy usage. I have lived in North Carolina for over 10 years now and have encountered the request for crawl spaces almost 100%. Crawl spaces harbour a lot of disadvanteges for the living comfort of the inhabitants. What do you think about the crawl spaces? I surely don't understand it - specifically in this time of technological advancement in building science. Any takers? I don't want to bash anybody's thinking or reasoning, just want to hear the different opinions of the pros and cons. Thank you.

Hi Manfred, I am not a builder but from my limited experience (I live in Anchorage AK.) Crawl spaces are common here but I may be forced to use a FPFS when I build on my lot in Wasilla only because the ground water table is high enough and the lot is pretty flat, it would be very expensive to dig a full basement needing constant pumping while under construction and then getting it completely sealed. The FPSF or frost protected shallow foundation which will be my best choice.
I guess I could go with a crawl space but don't care much for the problems with moisture, and the need for a sump pump and being pretty much unable to drain the water away from the structure.

I'm not a builder either.  However, one of the reasons many up North have basements is because they have to dig so far down to get below the frost line.  This make the additional cost of a basement very little since you essentially have the walls built already anyway.  Just add a floor and perhaps a little deeper excavation and you have a basement.   In the South the deep excavation isn't required so the cost for a basement is a lot to add the deeper dig, floor, and walls.   Also, for places like Florida with very high water tables, the cost of keeping the basement dry would be very large.

I am up North (Eastern Ontario) and I live in a wet area with a high water table. Many of my neighbours spend $15-30 K having drainage ditches/tiling done to get dry basements.

That's why I went with a FPSF. No basement, very high insulation values (R30 under slab). I am high and dry, heat my place with a candle or two  and no worrying about wet basements and moisture control.

Terry

A family member here in Kansas has a 1500sf single storey home over a vented 3ft deep crawl space and has had moisture problems primarily due to poor construction. Contractor didn't install a sump pump initially and only after much pushing. Improper grading/drainage of exterior flatwork which allowed water to work its way thru the OSB sheathing supposedly above the concrete stem wall. Wooden floor trusses too long for concrete foundation walls, so easier for contractor to remove one of two vertical 2x4s at the end of the truss to make it fit atop the stem wall. There's more, but you get the picture. I was curious about their crawlspace since I was planning our future home and discovered many of these defects. I'd say, as with any residentail system, if constructed properly a crawlspace can function well.

Virtually all houses in southern (maybe all of) Louisiana are on slabs. Basements and crawl spaces would be nigh impossible to keep dry.

With the house I've almost got finished here in Idaho the lot slopes 4' from one house corner to the diagonally opposite. My choices were a lot of fill inside a concrete retaining wall in order to have a slab, a crawl space, or a basement. Basements are loosing favor and the fill idea didn't make economic sense. That leaves crawl space. To make the best of it, and because the ICFs begin at the footer, I sealed the crawl space and poured a 2" rat slab over 3/4" blue board. I put the air handler for the heat pump in the crawl space and am using the crawl space as the supply plenum. This saved on duct work (probably not a great amount) and should give me a quasi radiant heated floor.

Western wood products was pushing a whole house plenum. a few years ago but has discontinued the program.  a lot of people have had to install ducting to get better heat distribution.  I f  you have enough floor and side wall insulation and fire protection.it should work.

Thanks for all your input. I was hoping to hear more pros and cons on the question, but now realize that I need to be more specific. Mother earth provides a lot of thermal mass. My sense is that if you incorporate the energy of this thermal mass into the heating and cooling of your house you can use the space underneath your house. This would eliminate the "air" space and replace it with an elevated slab filled with sand. During this operation you can lay multible feet of pex tubing to harvest the energy underneath the house. Has anybody thought of this before? What are your initial objections?

Be careful about using sand. Dry sand is a good insulator, believe it or not. In a restored early 1900's village near here my brother has restored an old blacksmith shop. The forge has a fire pan which is a wooden box with about 2" to 3" of sand in it. I believe it's never burned and you know how hot a forge fire can be!!!

Good point, dmaceld. So, if dry sand is a good insulator, would subscribe to the thinking that you could store energy in dry sand?

ok, just received an e-mail stating that the sand itself would not generate enough heat. What if I would inject, supply energy into the sand? Would it store for later release?

Not efficiently. When I started my house design project I was considering a geosource heat pump and wanted a system to store heat. I was thinking about using a large tank under the garage floor filled with rocks and water, the rocks to store heat and the water for a heat transport fluid to the get the heat to and from the rocks. Turns out, water is a much better heat storage medium than rocks. What you need to look at is what is called specific heat. That's a measure out how many BTUs it takes to raise one pound of material one degree F in temperature. Of all the commonly available materials water has the highest specific heat on a volume basis, i.e., BTUs per degree F per cubic foot of material.

I gave specifics in a comment in the geosource or radiant heat forum months ago. You may be able to search and find it. Sorry I don't have time right now to do so.

dmaceld, thanks for your response. I realize to store energy in any medium is a fluid/changing process. What if you took pex tubing from the roof down to your subgrade and filled it with water and circulated it at preset speed determined by temperature fractions available in the enironment (on the roof). This way you will create a heat bubble (for the lack of a better word) underneath the house which you can draw from in an continous way. Would you subcribe to this idea? Let's just take it step by step. There is more.

I can not think of a good reason to do a crawl space on new construction. On some additions yes. Either full basement or slab on grade with insulation under the slab and necessary frost-foundation. My own next house will be slab on grade with hydronic heat in the slab, which also has enough thermo-mass. Oh did I mention all the walls would be ICF?

A 5,000sf house we did recently had electric heat cables and XPS at the bottom of 24" of sand which was under the basement slab. The dry sand insulator was questioned, but if the XPS keeps the heat from going down, then it either comes up or the cables overheat. As of now I would not recommend this.

This was the same house that used 1 x 2or3s to fur the ICF walls, I spoke out against this. The designer was worried about condensation forming on the back of the drywall.

ICFconstruction, I agree with you on the crawl space. It is an unnecessary dead space in my opinion. I understand that some folks run their mechanical equipment through it - I content this could easily be done through the attic, unless you have a flat roof, in which case you have to make room for a "mechanical" room in your design. There are always reasons for this and that, I wanted to turn the question of "crawl space or not" into an exploration of what you could feasably use the space for if the crawl space was turned into a filled in stemwall. BTW, the same principle I have in mind works for underneath a basement. The reason I chose sand for the discussion is because I know how to compact it to a proctor 95% to receive a slab. Sand does better than stone, whatever kind, when it comes to energy storage. Maybe someone has another idea of how to compact a different energy friendly substrate to proctor 95?

http://ace.cte.umt.edu/documents/GeoSolar.pdf  Please read this research on AGS for heating a partially insulated on grade slab. In 3 years, the AGS sysytem (using a trombe wall) brings the soil (6' deep under the slab) from 50 degrees to 70 degrees using the hot summer sun. This heat energy is then radiated back into the slab during the winter. The slab insulation is left out of the center of the slab, enough to have contact with the warm earth. Hydronic pex tubing in the slab surface diffuses the heat. A back-up electric heater is used for any delta heat needed. This along with passive solar on the floor and the backup should heat most houses in temperate climates that are insulated and sealed against air infiltration....such as you would get with SIPS or ICF.

Manfred,
I live in an area where almost all single family housing (custom and spec), is built on crawlspaces, and almost all rental property is built on slabs. The reason is simple--expectations of the buying public. Historically, here at least, basements are dark, damp and downright wet. And slabs were for barns, and work places, not homes. This perception continues and is just now beginning to change. We won't talk about how dark, damp, and downright wet some crawlspaces are.

wes, that is my experience exactly in NC. I used to live in Ontario, Canada for 20 years and of course had basements there. And yes, an unfinished basement was still damp and cruddy. I agree with you on the public's perception, it seems the same here. I don't know whether it has something to do with stepping "up" to the front door, which will elevate you over the neighbour who steps "in" the front door.
I am on a quest to incorporate the "crawlspace" into an energy solution by taking the "crawl" out of it. I have come across an amazingly simple system to make a house a "zero energy house". Having said this, by no means am I an expert with this system, that is why I started this thread "crawlspace or not" trying to find a consensus that the crawlspace, even though used in some cases for mechanical installations, is a public perception of "a better build house" rather than, in it self, an inefficient way to build. Dmaceld brought up a good point of sand being an insulator rather than a particular friendly medium to store energy. Does anybody else have ideas on this?

Manfred,
It just struck me that the reasoning for crawlspaces is historical. The original settlers built log cabins with dirt floors. As they became more prosperous, they built bigger houses with wood floors, which had to be raised off the ground to prevent rot. The areas of NC and KY are similar in soil, lots of clay. It does not drain well, so any early basements normally had water standing in them half the year. Also, in our area, stone for basement walls is not easily available. The easiest way to put in a wooden floor was to use the fewest stone 'piers' as possible. Therefore, the protypical crawlspace was the norm. It also gave the dogs and chickens a place to live.
Heck,  I grew up in an old house built just this way. I don't know why it took me so long to realize the answer to your question.

When I started my house project I considered something of this sort. What I thought of doing was installing a typical geosource heat pump. In the summer some heat would of course be injected into the ground during the cooling phase. However, I expect cooling load to be far below heating load on an annual basis. To augment the heat movement into the ground where the loops would be I considered solar panels to capture summer sun heat and, using the heat pump loops, inject the collected heat into the ground. Because of lot size limitations I would have had to use wells which would have reached into the ground water table. Moving water would carry away heat so I had doubts about the efficacy of this approach. For loops 6' to 10' below the surface, and a water table below that level, I think it might be feasible. One of the biggest problems with using earth for a heat storage medium is containment. How do you assure the heat you inject won't just wander away?

In the end though, as maybe you've seen in other posts of mine, I dropped the plan for geosource and installed a very good air to air heat pump. That's mostly because my ICF house structure is so low in heating/cooling requirements it would be difficult to get a pay back on a costly installation just to cut my energy supply cost by 1/2 to 2/3. I'm not sure I'm going to see a great payback on my Daikin heat pump system, and at this point I really don't want to figure it out only to find it's not there!!

As noted in the two references above, and other places where I've seen discussions, the earth could very well be a viable heat storage medium, though not particularly efficient from a temp swing standpoint. And because the earth temp would almost certainly be below desired living space temp you would need a heat pump to extract it.

In my opinion your idea of storing energy below the house is not all crazy, but implementing it will not be a piece of cake.