Moisture condensation West facing Rim Joists over 4-foot deep CMU crawlspace


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Old 01-03-18, 02:02 PM
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Moisture condensation West facing Rim Joists over 4-foot deep CMU crawlspace

Hi. I live at about 6,000 feet above sea level on a South facing hill. The winters are routinely dry here with mixed snow and sleet that sometimes sticks but oftentimes doesn't. I have a 900 square foot crawlspace on the Southwest corner of the house that has a 4-foot deep crawlspace area. My exterior is stucco (3 layers stucco/paper, with batting insulation in most of the Southwest wall area above that crawlspace area).

I've watched this area for two years as I've taken notes on it. Especially in Winter, the Sun contacts that West wall over the crawlspace and causes condensation to form on the 10" Rim Joist (about 40' of wall length), and the adjoining 6" of Sill, Joists, and Flooring that rest near that Rim Joist.

The crawlspace dirt floor doesn't get wet and I've sealed all outdoor holes, small inadequate vents (3 each) that I found with 5" of spray foam.

Should these actions likely cure the problem? I have a radon infiltration problem also in this bare floor crawlspace.

1. Put two sheets of plastic on the floor, seal it to the first 6" of crawlspace footer. This plastic would be sealed OVER the 5" radon PVC pipe that suctions from the middle area of the plastic. A high volume radon fan will extract crawlspace air from underneath the plastic and expel it upward/outward. I'm hoping with it, plenty of humidity also, because the ambient temp sits at about 58deg F year around and at about 83% humidity, constantly.

2. Dry the moist area with fans/ventilation in Summer. Clean, neutralize mold/mildew that is on Rim Joist areas, allow to dry for 3 days, paint with a mold resistant paint like Kilz, etc. Allow paint to dry for 4-5 days, and then have a professional contractor spray foam the Rim Joist and 12" of Joists, Floor, and Sill plate with two 1" layers of foam. Allowing each to cure completely between first and second layer.

Do you think this would solve the condensation problem that seems to be created by our warm Colorado Winter sun in the afternoons? I want to go as light as possible on the spray foam because my wife is mentally sensitive to petroleum chemicals that spray foam is made from, so I thought just spraying that one section of 40' long Rim Joist and 12" away from it (in all directions) might be good enough. The CMU wall that's under it is exposed to the footer and about 36" tall from footer to top sill edge. That would be helpful to spray also, but I don't want to unless really necessary because of the toxicity concerns my wife has.

I do not want to ventilate the crawlspace either. I'd like to try the radon fan and plastic to reduce any standing humidity from soil off-gasing. Most of the makeup air the radon fan would take would be from outdoors, with some coming from interior floor leaks, but most of the makeup air should be cool air from the outside.

Thank you!
 
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Old 01-03-18, 03:24 PM
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IMO you should put a couple inches of rigid foam over the joists. You should be trying to isolate the cold frosty wood from your comparatively warm, humid basement. That's what your step 2 would do.

I would worry about what your poly encapsulation idea would do to your radon collection if you think you are going to trap both moisture and radon under the poly. Bad idea imo. I would defer to a radon expert before you attempt that.
 
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Old 01-04-18, 10:22 AM
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I've researched radon extensively and honestly it seems to be a government sponsored hoax, but until that's proven I still want to reduce the levels to under 4. Currently the radon reads 26 in crawlspace and it seeps into the home on the East wall the crawlspace shares with the addition to the home. I don't have radon infiltration on the addition because it has insulation and a vapor barrier under the addition slab.

Radon in crawlspaces is treated by trapping it under the plastic and sucking it into daylight with a round PVC duct fan. I would hope by covering the dirt floor and sealing it well enough to the footers that the humid air moving from the warm earth would also be restricted and much of it sucked out as well. Time and testing will tell.

The wall rim joists that gets damp is on the warmer Westward side of the house. I have terra cotta colored stucco and the West wall gets very toasty on the sunny winter days we have. We have more sunlight than Florida here. I'm thinking the warmed sunny air from this stucco west wall permeates thru the uninsulated rim joists and cause the dampness.

Reason I'm leaning toward spray foam is because it seals air gaps much better, and my old construction there is not the easiest to work around/get a good seal.
 
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Old 12-30-18, 11:52 AM
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Wet rim

I live In jersey have lived in house for about 8 months went into crawlspace n see that I have wet floors but also that on rim joist it's soaked can it possibly be just condensation from wet ground ? Or can water be leaking in. The front of the house is stone n I have 3 ft to 4 ft over hang
 
 

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