Any of the users here had a chance to have the Basement Systems company come out and give them an estimate on sealing and closing off their dirt crawlspace? These are the guys who claim to specialize in "All things basementy". I have them coming next week to give an estimate. I have never been a fan of vented crawlspaces and in general think they are a dumb idea. Not sure I know enough to know if they are going to take me for a ride. Any thoughts and experiences would be appreciated. thanks in advance.

The simple cheap thing to do is to cover the dirt with 6-10 mil poly sheet. What more makes sense depends on your climate, your radon levels, etc., so it's hard to know what more to suggest in your case. Reading this might help:
http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

Well I live in the middle of NC so it is hot and humid most of the year. Polu sheet on the ground decreases vapor from the ground but the vents still let in all that humid air under the house.

In the middle of NC you're on the boundary region of US climate zones 3 & 4:



Under IRC 2012, for new construction for unvented crawlspaces it would take R5 continuous insulation on the crawlspace walls to meet code in zone 3, R10 in zone 4.

You could compromise and go with 2" of EPS (R8-ish) , or go all-in with 2" of foil faced polyiso (R12-ish), either of which is a fairly easy DIY.  

In many ways it's easier to go with a fire-rated 2" foil-faced polyiso like Dow Thermax, since you wouldn't be required to use an intumescent paint or install a thermal barrier against ignition. It's also easier to air-seal the seams of foil facers, using 1.5-2" temperature rated foil tape (eg: Nashua 324a, carried by most box stores.)

First put down the ground vapor barrier, lapping it up at least 8" onto the CMU wall taping it in place. You can then put the cut foam overlapping the vapor barrier.  You can use foam board construction adhesive in hazelnut sized blobs to put up the foam initially, then come back and affix it to the CMU with 2x4 furring through screwed to the block.

In termite areas it's standard to leave a 3" termite inspection strip at the top of the foundation.  You can cut in strips of R15 rock wool batt to insulate the inspection strip in a manner that's easy to remove & replace for inspection. (A bread knife works great for making clean cuts in high density batts.)

You'll also want to insulate & air seal the top of the foundation, the foundation sill and band joist.  In your climate it's fine to seal all the seams between the framing with a high quality caulk or with can-foam, and trim R15 batts to fit.

In flood plane areas codes sometimes  require vent openings on CMU foundation to relieve flood pressures to keep the water pressure from breaking the foundation.  In that case you'd have to cut the foam at the vent and re-insert the rectangle as a snug-fitting plug, making sure that it won't be so snug as to not pop open under hydro pressure.

Hey Dana1

Thanks for the detailed response. Currently researching your suggestions and figuring out the costs. I think my appointment with the crawlspace guys is the 16th. I'll report back on the cost estimate for anyone that is interested.

dbm300,
I live in W-S and used Basement Systems on Griffith Rd a few years ago for Radon mitigation. I am a NC Licensed Builder, have no connection with them and I can tell you I am extremely satisfied with their work ethic, attitude, follow up and professionalism. My son had a different company do his 2 years ago (because they were chosen and paid by the seller of the home). They were good, but I don't think they were as good as Basement Systems. The motor on his unit went bad just after one year and they wanted more $$ for a new one than was reasonable. Took me 15 minutes to replace it for about $100. I don't remember their name.
Too bad you're not in GA; I have a friend/business associate there who is extremely well educated and licensed in Building Science and does crawl space sealing and seeks perfection on his jobs.
Call me if you want.
Rich Melius

dbm300,
Update on their name : TARHEEL Basement Systems.
RichM

They are coming tomorrow morning to give an estimate. It should be interesting anyway. With all the rain the crawlspace was still dry so I am interested to see if they recommend an interior perimeter drain or not.

So the short answer is $7500 without the insulation and $10,000 with their Silverglo R-11 insulation. Still trying to decide if I want to spend the money on it and trying to figure out if it would actually save me any money on heating and cooling. Any more thoughts from you fine folks?

1266 sq of clean space liner
15 wrapped piers
16 vent covers
April Aire 1850 dehumidifier
and Silver Glo insulation ($2500 add on)

this is their blurb on the Silverglo

SilverGlo™ is an expanded polystyrene foam insulation that's been infused with graphite during its creation to improve its insular ability by 24%. Combined with its silver radiant heat barrier on the visible surface, it provides an insulation rating of R-11 on your crawl space walls. This insulation can be customized for special projects or local code requirements, making it a versatile, effective solution.

If you're interested in keeping your crawl space dry to help prevent mold, rot, and musty odors, this is the product for you! SilverGlo™ also creates a vapor barrier on your crawl space walls that keeps moisture from making its way into your crawl space, where that moisture would help mold, rot, and mildew grow.

Graphite infused polystyrene is one of my favorite kinds of insulation. Great stuff. I think they are giving you 2" thick R-9 foam, and then counting on the radiant barrier for an extra R2, which is a reasonable estimate--other people over state the benefits of the radiant barrier but that's not far off.

What they are proposing sounds good, but it does a little pricey for a pretty simple project. And if you are going to invest in a high-end dehumidifier, the ones from Thermastor are certainly more efficient and maybe more reliable.

http://www.thermastor.com/residential-dehumidification/

i was just introduced to this discussion by a fellow reader. I am BPI, HERS, and a GC. But in this application, perhaps more importantly, a Certified Mold Remediation Supervisor and Radon Specialist. I consult on these matters throughout the SE, and my company actually performs remediation and crawl space encapsulation work throughout GA. We'll soon be expanding into NC. There is some good advice given in comments above, but a few things need to be added.
First, regarding pricing---So long as clearance is adequate, if I were quoting his 1200sf crawl in GA, the price would be in the neighborhood of about $5500 for the encapsulation, including insulation around the perimeter walls, but not including the dehu. The April Aire dehu your company quoted is about $1200 on line. I like Dri-eaz but everyone has their favorite brand. So $6700 would be approximate market price if I were quoting it here. Your guy quoted 10k for everything. That’s pretty steep.

Second---encap scope must refelct a comprehensive approach. obvious implications are related to IAQ and moisture management. Secondary to those issues is energy efficiency. Not every crawl space is a good candidate for encap. Yes, you can properly encap every crawl, but some require other accommodations.
For instance if there is mold or other sources of contamination, then those have to be accounted for before you bring the crawl space inside the envelope.
If mold exists on joists (it almost always does) then it must be remediated before encap.
If there's a furnace with 80% AFUE or if a gas water heater exists in the crawl, then you must account for combustion (make-up) air and also power vent the flue gases.
After encapsulating, you must test for high radon levels in the home. If elevated above 4.0 pci/L, then you must install a mitigation system.
If there are gas lines, then they should be tested for leaks.

These things among others should be accounted for on EVERY crawl space job.
Many companies don’t worry about them, BUT you should be aware before deciding on a contractor and a proper scope.

Excellent points, David. Thanks for joining the discussion. And it's great to hear that it's reasonable to expect better work at a lower price.

There doesn't seem to be any problems with the crawlspace per se. We had over a foot of rain 4 weeks back and there was no pooling of water or anything. But like everything in the south, humidity was 70% in the crawlspace. In my mind, crawlspaces are just not a correct way to build a house. So for all the obvious reasons, I am working toward fixing that. I've got a second contractor coming out Tuesday to quote the job.

HVAC and hot water heater are electric - no gas or propane. Units are 12 years old. Probably will need to be replaced sooner rather than later.

Radon I suppose could be a concern but it's not at the top of my list. But since you did mention it I ordered the short term tests from NC Heath and Human Services. $5 for the test.

http://www.ncradon.org/Home.html

those short term tests are fine. just take a duplicate and send both to the lab.
many are not aware of the very real danger that elevated radon can pose. EVERY house should be tested...it is better to know. as a building scientist i was promoting testing long before i started offering radon testing and mitigation services. It's part of the comprehensive approach to good IAQ. having all electric appliances and no significant bulk water intrusion, sounds like with a good encap and the radon testing, you are on track. good luck!

Second quote came in at 6500. I will probably go with them. Since the crawlspace will be sealed up, are there pros and cons to removing the insulation on the crawlspace ceiling?

once you fully encapsulate with insulation around the perimeter, the thermal advantages of insulation in floor are minimal. insulation of course will give some noise reduction, but that's not usually a factor. the main factor regarding whether to keep or dispose of it is the degree of mold contamination. fiberglass is synthetic and not organic so mold doesn't metabolize the material. however, if there is significant contamination, there will be an elevated concentration of mold spores and the insulation will harbor that heavy dose of spores, so IAQ suffers. are any of these guys you've had over Certified Mold professionals? do you have a reliable assessment? when performing remediation in a crawl, almost invariably the proper scope would be to remove and dispose of all insulation.

It is looking nice down in that there crawlspace. :-) I am doubting it makes much difference in heating and cooling but I am happy I did it. since I just moved in the house I don't have any previous data on the energy use of the house before I moved in so I can't really compare.

Radon report came back:

Radon Test Result: 1.8 ±0.2 pCi/L

INTERPRETING YOUR TEST RESULT
The US EPA action level for indoor radon is 4.0 pCi/L. The EPA indicates that there is
little short-term risk with test results in this range (0.6 to 1.9 pCi/L). However, because
radon levels fluctuate daily, as well as seasonally, you may want to retest during another
season. Additionally, if you make any structural changes or start to use a lower level of the
building more frequently, you should test again.
You may be able to obtain additional information about radon related subjects by calling
the "Radon Fix-It Line" at 800-644-6999 Monday thru Friday between NOON and 8 pm