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  1. #1
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    May 2011
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    Philadelphia, PA
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    Adventures with Radon & Humidity: Is Pos Pressure a Solution?

    Hi everyone,

    First, let me say thanks for all of posts over the years. I have been using this forum for research over the past several weeks, and have learned so much. The amount of [free] knowledge and experience on here is amazing. THANKS!

    Now on to the issue I am facing. I live in Southeast PA. 2400 sq/ft house built in 1950s is wood framing on second floor, and block in basement and first floor. I have one walk out basement (~700 sq ft) and two enclosed crawspaces. Craw 1 has access thru main basement. Craw 2 has access through exterior. All basement and crawl areas are unfinished and on concrete slab with block walls. Basement blocks walls are sealed with "dry lock" or similar water impermeable product, and basement slab is painted with a thick enamel paint. Joints between blocks and slab are sealed. No visible cracks. Never had any water issues.

    That's the background. Now the challenge: I am trying to finish the basement and confront two problems: (1) Humidity (55 w/ two portable dehumidifiers running continuously during rain -- 45 with continuous operation during non-rain) and (2) Radon. Pre-radon mitigation: basement and crawl 2 are ~20pci/l. The combination of the two is proving especially difficult.

    Remediation company #1 hired. Post "mitigation": basement has >10pci/l; Craw 1 has radon at 4pci/l; Craw 2 has radon reading ~8 pci/l. They are unable to lower it further, even with 4+ suctions points and 2 fans. Slabs are over dirt (not stone), so getting good sub slap suction is difficult. They've been out 5+ times and ended with "trial and error at this point."

    Remediation company #2 hired. Locates source of radon behind two block walls. Conjectures radon is travelling up voids in the hollow block via stack effect and entering near rim joints (joists sit on hollow core blocks). Sure enough, my continuous radon meter indicates 35+pci/l at rim joist, and a camera snake can see most of the way down the voids of the blocks. Basement has significant negative pressure (leaking unsealed HVAC return panning). The recommended solution: add some suction into the wall and seal any cracks. This is scheduled for the next few weeks.

    I have already sealed the rim joists with foam. Same area that was registering 35+ pci/l is now leveled off at 7 pci/l. Good start. I am also getting ready to seal the leaking HVAC returns in the next few weeks. I am considering two additional "backup" options I could use input on, as I am skeptical that additional suction alone will solve the problem (of course, I will give it a chance):

    (i) Generating positive pressure in basement by adding fresh air intake into HVAC return. Using continuous radon meter, opening my exterior basement door takes the radon count to 0.5pci/l. Suggesting that positive (or even neutral) pressure might do the trick. But I can't very well leave my basement door open: so I need to experiment with the necessary amount of ventilation. I don't want to spend $$$ if 100 cfm of continuous ventilation doesn't work.

    In the coming weeks I will experiment with: (a) hooking a blower up on the exterior of the basement window and pushing 1500+ cfm thru over several hours; (b) adding supply air from the A/C to the basement (currently none); (c) ducting 6" round from outdoor air to A/C return.

    *IF* this works (and 100cfm-200cfm of continuous fresh air does the trick), based on this forum, I think the "permanent" version would be a ventilating dehumidifier that is ducted from first floor and outdoors, and dumps into the basement (solving humidity issue too). However, I am not keen on continuous ventilation during Winter. Especially since we use the basement for a kids play area. This is also not a cheap fix --either upfront, or through ongoing energy penalties. I've ruled out HRV/ERV as the ones I've looked at can't be rigged to generate positive pressure.


    (ii) More extensive sealing, plastic barrier over slab and spray foaming all walls. The initial cost is larger (>2x), but there are no energy penalties or subsequent variable costs. However, I have heard of cases where this actually makes the problem worse. The intuition is that the foam insulates the basement, raises temperature and exacerbates stack effect (my intuition tells me this would only exacerbate the issue if the sealing was incomplete). I was thinking to try this for Crawl 1 or Crawl 2 just to explore proof of concept.

    ...So that's where my brain is at. I would *greatly* appreciate any thoughts or comments. Both cases entail significant expenditures, and option (ii) is effectively irreversible.

    As things progress, I will keep the thread updated.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by airinsam View Post
    Hi

    (i) Generating positive pressure in basement by adding fresh air intake into HVAC return. Using continuous radon meter, opening my exterior basement door takes the radon count to 0.5pci/l. Suggesting that positive (or even neutral) pressure might do the trick. But I can't very well leave my basement door open: so I need to experiment with the necessary amount of ventilation. I don't want to spend $$$ if 100 cfm of continuous ventilation doesn't work.

    As things progress, I will keep the thread updated.
    A small whole house dehumidifier like the ULtra-Aire 70h with 80 cfm of outside fresh air and 70 cfm of mainfloor air going through the UA 70H which includes a MERV 13 filter supplying the basement space will slow radon in and change air while maintaining <55%RH in the lower levels.
    You may not need that much fresh air with the pressure from the main floor air.
    Ultra-Air is site sponsor.
    What town are you in SE PA?

    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
    Join Date
    May 2011
    Location
    Philadelphia, PA
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    Thread Starter
    Hi Teddy -- That is what I was thinking. I was looking at some UA units and Honeywell units earlier today.

    Sounds like I just need to experiment (perhaps with a 100cfm fan mounted in a 6" duct) to see if 100 cfm of outside fresh air will be enough to drop the radon. If it is enough, then I can avoid the spray foam, and just purchase and rely on the UA product to supply enough ventilation to dilute the radon to safe levels. Alternatively, if 100 cfm of fresh air isn't enough to dilute it to safe levels, I'll need to spray foam and seal up the area first. Then re-test radon, and if still elevated, re-test whether 100 cfm of ventilation will do the trick. I am hoping not to have to do both ventilation and foam ($$$$) but I may end up needing to.

    Town is Broomall. 13 miles West of Philly. Send me an email if you have recommendations specific to my area...I'll probably be looking into which contractors in my area deal with UA products.

  4. #4
    Join Date
    May 2011
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    Philadelphia, PA
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    Thread Starter
    I promised a follow-up, here it is...

    The radon and humidity problems are solved. The solution was to sprayfoam all basement walls and place vapor barrier on floor. Laminate floor pad on top of vapor barrier, then finished laminate plank floating floor. Crawlspaces have spray and barrier too.

    Active subslap radon vent reduced from 35pci down to 5pci. Combined with sprayfoam and vapor barrier it is between 0.5pci and 1.5pci.

    The foam dropped humidity in the basement and crawls, but not enough. Added a small dedicated dehumid to each crawl and tied into gravity drain. (crawls are <1000 sq ft). Whole home dehumid with dedicated ducting for main basement.

    Not for the budget conscious, but love the setup and more importantly it solved radon, humid, and mold issues, ... and keeps unconditioned basement at a nice 68 deg year round (in PA) using residual energy thrown off by main HVAC unit.

    Adventure ended. Problems solved.

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