Help - Crawlspace - Sever moisture at Rim Joist

I inspected a house last week and found a lot of moisture in the crawlspace along the rim joist, floor sheathing and the end of the floor joists.

I personally believe that the moisture is from the cold air (-25C at time of inspection) migrating through the wall into the crawlspace and condesating when meeting the warm air. The crawl space has heating duct work run throughout and the ducts are NOT insulated.

I have been asked to speculate with the seller on the cause and repair of the issue. (full permission and signed release from buyer who walked away).

Any and all input is appreciated. Thank you.

Was there a vapor barrier? and how was the ventilation

If it isn’t what you brought up or some other possible interior problem then sometimes, water can first enter on the outside of the home through 1 or more openings/gaps etc above ground level such as 1+ open-cracked mortar joints,bricks…openings around windows, doors or where any service line enters on the outside.

Not at all saying its any of these at house you’ve inspected, just saying it is the problem for some people :wink:

Have had a few HO’s get water in on driving, wind blown rains through their door bell, milk chute etc.

No there was no vapour barrier or any insulation around the perimeter. It was a dirt floor crawl and had no vapour on the floor either.

The water was consistent around a majority of the perimeter. Too consistent to be associated with driving rain or snow. It was in my opinion far too consistent to even be contributed to lack of weep holes in the brick veneer.

If they do figure it out it may look like this

Ruling out water intrusion, I would say that condensation on the rim joist is exactly what is happening. We don’t get that too much in FL, but a closed cell spray foam on the rim joist might help. Even better, would be to insulate the floor system, duct work, and ventilate better to help with the warm air in the crawlspace.


Don’t agree! Encapsulate that sucker! Insulate walls & rim joist, leave ducts as is, don’t insulate floor, close off/insulate existing vents, add professional vapor barrier.

I will post some links L8R. David Valley (pretty sure its him??) has written a really good article on this & may want to check his site as well.

Thanks gentleman, I wanted to confirm mu suspicion before recommending a fix. Always helps to hear others opinions and confirm mine. Thanks again.

Joshua, i look forward to that link.

Wayne, Yes that looks identical.

Moisture is constantly evaporating up from the soil in a crawlspace. This is the source. The rim joist just happens to be the first spot which is cold enough for the dew point to be reached and so condensation occurs there first.

The solution is to prevent the moisture from entering the space through a moisture barrier on the floor and walls of the crawl and then insulate the rim joists to prevent the condensation. Closed cell does a better job of this because it changes the location of the condensation plane away from the wood components and it air seals.

Additionally, some form of ventilation should be in place, preferably conditioning the air from the inside if you choose to encapsulate the crawl as described. Exterior crawl ventilation is becoming a thing of the past IMO.

Just for clarification, the cold air is not going to be what is condensating. It’s actually just the opposite. Cold air has little moisture in it, warm air has much more and is the source of the condensation. Very little moisture is coming in from the air leaking into the crawl if the outside temp is as you say. BTW, that’s COLD! :slight_smile:](](]( crawl spaces

In my opinion, you are not there to figure out why or where it leaks. If it’s obvious to you as a knowledgeable professional, then by all means, expound. When I don’t know what caused a particular problem I simply identify that there is a problem and they need a specialist; a plumber, electrician, concrete contractor etc. The fact that you are aware and spotted a potential issue is all that is required of you.

On this issue, I would say: “water/moisture intrusion was observed at foundation/rim joist, crawl space, floor. I recommend further evaluation by plumber or general contractor familiar with water intrusion issues.”

If the homeowner comes back to you, you simply ask if they sought out a professional to address the problem. If they didn’t, then they weren’t interested in due diligence for their own benefit.

Couple of good links there, Thanks for the share !

I agree with the correcting of the moisture first. The sealing of plastic properly followed by proper insulation is a good approach. The spray foam is too expensive here and rarely done. Especially underfloor with the precautions that have to be taken the labor just drives the cost too high. Most moisture in the home moves with air currents. Heat goes to cold and high goes to low. The cold rim joist with some gaps added with a damp warm pressurized from duct leakage crawlspace is a perfect spot to condense moisture. It is below the dew point especially with it being so cold outside. So conditioning the crawl and insulating the rim with insulation tightly against it. Insulation should be at least what the walls call for in your area. Here it’s a R-20 to keep it above the dew point.

I (11) The InterNACHI member shall not perform or offer to perform, for an additional fee, any repairs or associated services to the structure for which the member or member’s company has prepared a home inspection report for a period of 12 months. This provision shall not include services to components and/or systems that are not included in the InterNACHI Standards of Practice.
From International Code of Ethics for Home Inspectors - InterNACHI

I see this ALL the time here in Pagosa Springs, CO. 7000+ feet above sea level, subzero temperatures at night. I usually take a RH reading and closely examine Northern rim joists. If there is no vapor barrier and poor ventilation (or they’ve sealed the ventilation to save $$$) I take all kinds of pictures and usually the cost is $8K and up for the repair. I’m blessed to have a friend that is a moisture remediation expert, he comes in and fixes them. The fix is usually removal of all rotted rim joists, floor joists, subfloor; mechanical abrasion of any thick mold growth, removal with HEPA vac, coating with anti-microbial. Installation of new structural components; lastly installation of drainage, sump pump, 6-8 mil poly barrier that is seam-sealed, and sealed to stem wall around perimeter. He then does a mold spore air sample and remediation report to document for the client.

Here’s last month’s pictures with frost (north side):