I moved here late last year, this is a century old home that had an addition done in maybe the 1960s/70s, it has a half basement and half crawlspace (crawlspace under the newer addition) I had an energy audit done and no surprise the air change rate was 17.68/hr @ 50Pa, with much of it coming from the crawlspace openings (there are many, i am slowly sealing them) and both the intake and hot air ductwork throughout the house and which run through the crawlspace and i recently learned there is a large open vent in the crawlspace. I'm not sure where in the crawlspace the air comes in to the house though, i have not ventured inside it yet because i would be doing a lot of crawling and banging my head on the ceiling. I assume i had little radon since the 80% efficient furnace was drawing indoor air for combustion (as is the chimney vent hot water tank) and i was using 18 m3 of natural gas per day on average last winter.
I recently upgraded the furnace to high efficiency which will have a pipe going outside for combustion air, and i would like to dig out the crawlspace so i can at least crawl inside.

If the crawlspace has been leaching radon for the last 50-60 years it would have likely been sucked into the furnace and pumped out the chimney (basement was never finished), but my question is what is the half life of the elements that create radon? Also if i dig out the top few feet of the dirt will i be creating more radon problems by exposing dirt that is currently buried or has the buried dirt been leaching radon into the house already (does radon move through several feet of soil easily)?

Thanks in advance for your replies.

I'd insulate, seal up and put plastic on the floor of the crawlspace and test again to verify success. Test for radon vs guessing about levels.

Not insulated is a galactic understatement, the basement is brick (and dirt), the attic is bare and the walls are hollow, and there are no basement headers, i can look up them all the way to the base of the attic

I'm very strapped for cash so this year i have done the efficient furnace and will insulate the attic, next year i hope to tackle the walls.

The plastic will block out radon?

Radon-222, the most prevalent radon isotope in the environment, results from the decay of uranium-238. That decay occurs regardless of whether the soil is exposed at the surface or not. The half-life of U-238 is 4.468 billion years, so it will be continuing to emit radon for a while.

I would suggest digging our the crawl space, and then putting down some gravel covered with 10-mil plastic with the sheets taped to each other and sealed to the walls of the crawl space. The plastic will prevent radon from passing through into the house.

You don't provide a measured value of radon. It is fairly inexpensive to get a kit that can be used to sample the indoor air for a few days and then sent off for analysis. The EPA spec is a maximum of 4.0 picocuries per liter. You might check out this site for more info http://www.epa.gov/radiation/radionuclides/radon.html

I have not tested for Radon so i don't know if there is any at this point, i've been doing more immediate repairs and analysis, the energy audit was one i wanted to get done quickly, a few insulation quotes i got suggested spray foaming the crawlspace with plastic put down first so it would get foamed to the walls, but what is the purpose of the gravel you suggest?

I think that the first thing to establish is whether or not you have a radon problem. If not, the plastic alone still might be useful to protect against moisture coming into the crawl space and the house. If you have a significant radon problem, then you should consider both plastic and a radon remediation system. Putting down gravel first, say 8" thick, would allow you to bury one or two 4" diameter PVC perforated pipe(s) to collect the gases, and then a vertical 3" or 4" non-perforated PVC pipe going upward through the roof would allow for passive flow of the gases from below the crawl space to above the house. If this passive approach were not sufficient to get rid of the radon, then adding some blowers to the vertical pipe(s) would improve the efficiency of the radon removal system. In my case, I had a passive system with verticals of only 2" diameter, but the radon level was about 8 picocuries per liter, so I added blowers in each of the two vertical pipes and reduced the radon level to 1.3 pC/l. The EPA spec is 4 pC/l.

Posted By Lee Dodge on 17 Aug 2014 06:31 PM
I think that the first thing to establish is whether or not you have a radon problem. If not, the plastic alone still might be useful to protect against moisture coming into the crawl space and the house. If you have a significant radon problem, then you should consider both plastic and a radon remediation system. Putting down gravel first, say 8" thick, would allow you to bury one or two 4" diameter PVC perforated pipe(s) to collect the gases, and then a vertical 3" or 4" non-perforated PVC pipe going upward through the roof would allow for passive flow of the gases from below the crawl space to above the house. If this passive approach were not sufficient to get rid of the radon, then adding some blowers to the vertical pipe(s) would improve the efficiency of the radon removal system. In my case, I had a passive system with verticals of only 2" diameter, but the radon level was about 8 picocuries per liter, so I added blowers in each of the two vertical pipes and reduced the radon level to 1.3 pC/l. The EPA spec is 4 pC/l.

I will look into it, thanks for your replies

Passive radon systems such as Lee describes are required by code in some areas.

The volume of combustion air for space heating & hot water equipment are nowhere near radon remediation volumes. In very cold climates with leaky crawlspaces the whole-house stack effect infiltration drives probably pulls more air through the crawlspace than the gas-burners, but if you have leaky ducts in the crawlspace the duct leakage infiltration drives could even outstrip the stack effect.

A plastic vapor barrier DOES dramatically reduce the rates of radon migration, but isn't an automatic cure-all. Think "Necessary, but not sufficient".

Converting the crawlspace into an insulated conditioned crawlspace (with a very modest amount of HVAC air) would be well worth it in most locations, including an insulated rat-slab. A ~2" non-structural slab with 1-2" of SHEET EPS (any density) under it, more if you are in a cold climate protects the vapor barrier, and improves the thermal performance, which becomes useful even in temperate climates when you are promoting air movement under the slab for radon remediation purposes.

If the foundation walls are brick it may be worth parging them prior to insulating over them. The details of how to most cost-effectively insulate the crawlspace walls without creating mold issues varies with local climate- where are you?

This house is a work in progress, about 50 years of updates and repairs need doing so i am starting with the low hanging fruit and will work up to radon (i was thinking way ahead when i started this thread). I don't spend much time in the basement, only for repairs and laundry (not even storage) so i am concerned but not worried because i spend little time in the lowest part of the house and there are no air intakes into the furnace downstairs (there is a heating vent going to a bedroom that broke apart inside the crawlspace so its getting a lot of heated air till i fix it) . I was trying to find out how much combustion air the old furnace was using in order to try and calculate savings from the upgraded high efficiency version, i found one source (without any citations) that says 1m3 of natural gas requires 9.5 m3 of air for combustion, at 18m3 of gas per day average last winter that makes 171 m3 of air per day (approx 6,000 cu ft) going up the chimney, and i calculated the house to be approx 10,000 cu ft of volume. Also most of the outdoor air infiltration comes into the house from the crawlspace (the furnace sucking out so much air may somehow explain why the humidity is so low in the winter, i needed an army of humidifiers to get the humidity to 30%). In summary i suspect most of the combustion air is coming from the crawlspace, and its volume is probably 500 cu ft, so that would mean maybe 10 air changes per day its getting but won't this winter because of the new 2 pipe furnace.
I do plan on testing for radon, and i am located in Ontario Canada, similar weather to Detroit MI or Buffalo NY
I am planning on insulating the basement, but right now my focus is the attic and walls, the basement will be insulated last since i would need to do a lot of prep work and it will be pricey, move electrical wires, possibly duct work and plumbing. I am not sure how i will insulate it, spray foam was recommended but i am not sure if its a good idea if htere are effloescence deposits, but that is something i am not thinking about right now.

You will find that wintertime humidity levels will rise as you tighten the house. The dryness is directly related to infiltration.

Posted By Bob I on 20 Aug 2014 01:57 PM
You will find that wintertime humidity levels will rise as you tighten the house. The dryness is directly related to infiltration.

That is good news, thanks

Southern Ontario is roughly the boundary between the warm edge of US climate zone 6 and the cool edge of zone 5:



In that climate it makes sense to insulate basements & foundation walls to about R15-R20 whole wall (with all thermal bridging accounted for), but without creating moisture traps.  The cheapest way to get there is probably going to be 2" of rigid  EPS trapped to the foundation with a 2x4 studwall insulated with unfaced rock wool batts (eg R15 Roxul), and NO interior vapor barrier.  The seams of the EPS can be taped with housewrap taped, and air sealed with can-foam at the seam at the top of the foundation.  Cut'n' cobbled 1.5-2" EPS over any ledge to the foundation sill & band joist is recommended, also sealed with can-foam. The ground vapor retarder can be sealed to the wall EPS with duct mastic.

Don't cheap out on the foam thickness- in a zone 6 climate you need at least R7.5 on the exterior of the batts on the above-grade portion of the foundation to mitigate condensation events. (See chapter 7 of the IRC.)  If you go thinner you'll have to use an interior side vapor retarder, but NOT polyethylene, since that would create a moisture trap on the below grade.  "Smart" vapor retarders such as Certainteed MemBrain can work, but when it's all said an done putting at least 2" (about R8) of EPS is probably going to be both cheaper and better.

Since the studwall is not structural, 24" on center spacing and single top/bottom plates are fine.  Putting at least 1" of EPS under the bottom plate is recommended as both a thermal and capillary break to keep the bottom plate dry year-round. (If you're putting in an insulated rat-slab, run the slab-foam right up against the wall-foam before installing the studwall and it'll be fine to put the bottom plate on the concrete.)

Detail drawing courtesy of Building Science Corporation:



Since you are starting out at 17.68 ACH/50 I'll BET that the wintertime air was bone-dry!  But if you can get that down to 3-4ACH/50 it will be quite a bit better.  Using humidifiers can be bad news for your house, since it increases moisture accumulation on the exfiltration paths.  Humans are pretty healthy &  happy between 30-50% RH, but it's better for your house if you keep it in the 30-35%RH range during the cold winter months.

It was bone dry in winter, it was my first winter living here, the humidity was often near 20% and raising it was a fools errand. When i got attic and wall insulation quotes i also got basement insulation quotes, most people recommended 2lb spray foam directly on the brick foundation covered with a cement type coating so no framing and drywall would be needed (monokote or something like that).

I opened up some of the ring joist covers (someone made fitted wood ones), and there is no top to them, i can see all the way up the walls to the base of the attic. Someone put a batt of fiberglass in each one going up about 12 inches, they did nothing, the base of all the walls were cold (i only found out the fiberglass was there when i opened up the ring joist covers).

I am being recommended cellulose for the attic and walls, they are plaster and lath so i am not interested in ripping out walls to insulate (too expensive) otherwise i would consider 2lb spray foam for the walls. There is no attic opening so i am going to cut one in a closet in a few weeks, i am being recommended cellulose for the attic as well, is 3 inches of spray foam better then R50 of cellulose? I'm not sure what the price difference would be but i will look into it (quotes were about $800 for cellulose in the attic).

Using 2lb foam is more expensive, and has to be done in 2" lifts, but it air seals very well.

Mind you, most 2lb foam is not very green, and is best used sparingly. The vast majority of 2lb foam in N.America is blown with HFC245fa, which delivers a lifecycle global warming hit ~1000x that of CO2. The (rare) exceptions that are most likely to be available in Ontario are Icynene's water blown 2lb foams, MD-R-200, and MD-R210, either of which would be fine in this application. Unlike the HFC-blown goods these water-blown products run only about R5/inch, so you'd want at least 3", and probably 4".

Alternatively, you can frame out a studwall 1.5" from the brick and spray-foam the brick with 1.5" of 2lb foam, then drop in R15 batts. R15 rock wool is a legal & legitimate thermal barrier against the ignition of the foam all by itself- you don't need interior gypsum. But you would want to put up some type of interior side air-barrier on the studwall (just not a vapor-barrier).

R50 cellulose for the attic is the right solution. A shot of 3" of 2lb foam would cost about $3-3.50/square foot, and it would have 2.5-3x the heat loss of the cellulose. But air-sealing the attic floor is a necessary first-step before piling on the fiber.

The basement insulation is an academic discussion at the moment due to my financial circumstances.

The attic is the current focus, i am assuming there is nothing up there at all (i will find out in a few weeks hopefully), what should i air seal it with before the cellulose?