Moisture/Frost/Condensation??? at sill

Hello all…

This one has me perplexed… i just did a warranty inspection on a 9 month old home… in the basement, at the rim joist etc… the owner is complaining about moisture. The run a DE-Humidifier nearly year round because of the lot they built on is wet and the basement while not wet, feels damp to them… hmmmm NOT at time of inspection, but the rim joist, insulation and NAILS were very wet this winter (even on dry low humidity days)… the nails showed signs of rusting…

Any thoughts on the cause and possible remedies… he wants to talk to his contractor about the issue but does not know what direction to head… added ventilation? keep on going with the dehumidifier???

any thoughts? I basically cannot advise him of much since i did not see the moisture and limited signs… my only thoughts are to look into the ventilation etc…

thanks in advance…

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Can you post a pic of the exterior of the same location?

An exterior pic would be nice. Did you note the corrosion of the anchor bolt. Most likely not stainless or double hot dipped galvanized. This bolt will not last long since the ACQQ treated wood will corrode the bolt. Give it 5 years tops. These bolts should be replaced since this work is under warranty. Call me if you need help with that.

Can’t help on the wet wood until I know what is above the area in the photo at the exterior.

Kelley :wink: :wink:

Well, lets look at the psychrometric properties of condensation.

What causes condensation to occur?

Condensation forms when air (which contains water vapor) comes in contact with a surface that is below the dew point temperature of the air (this is based on the relative humidity of the air which is the amount of water vapor that air can hold in the vapor state at a specific temperature).

What can we do to change things?

  1. Reduce the relative humidity of the air.
  2. Increase the temperature of the object condensing water, above the dew point temperature.
  3. Prevent contact of the cool object with the air.

Re: #1
You are using a de-humidifier.
This can raise the temp of the air in the crawl space increasing the capacity of the air to hold water vapor which raises the dew point temp. This means the humidifier may be too small. You can increase the dehumidifier capacity or reduce the moisture intrusion my encapsulating the soil and walls of the crawlspace.

You can increase ventilation in the winter months when the relative humidity of the outdoor air is very low. This will lower the dew point of the indoor ambient air.

Re: #2
It is unlikely that you want to “heat the rim joist”.

You can reduce heat loss, resulting in condensation by reducing conduction of the materials condensing the moisture. Exterior insulation will reduce heat loss and lower sill temps.

Remember, there is no such thing as “cold”. There is heat, more heat, and less heat. Heat or “hot” moves to less heat or “cool”. Reduce the heat transfer rate and the object (condensing the water vapor) will be warmer and stop the liquid from occurring.

Re: #3
Vapor barrier to prevent contact with the damp air.

I do not have one exactly in that area, but these two are on each side of it… Where the oil tank fill/vent is the highest grade then it gets lower… the boiler vent is about 10 feet from where the moisture levels were most prominent. Again, dry at time of inspection, but owner complained about it so I looked closer and saw the rust.

Thanks Kelley for all the offline info as well… :stuck_out_tongue:

Thanks for your input here Dave and Dave? :eek:

The dehumidifier is likely too small for the space as mentioned… the sills are insulated, we took the insul down to look… the lot this is built on is wet… the daylight basement opens to very wet area… they have filled with crushed rock…

I think this place has been wet for a while, during construction and as kelley relates is still releasing water into the air…

Kelley you should post the link to the fastener bulletin here for all to see…

thanks guys…

off for the day…

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It can be a leak in the hvac gas exhaust pipe…
Especially if the problem is worse in the winter.

I saw major moisture problems once where the flue was blocked and all of the exhaust was going into the crawlspace.


The first problem I see is the stone that is placed right next to the foundation. This will allow any rain water (in that area) to seep right down to the basement level.

I like to see grading (dirt) next to the foundation. Not stone.

Was a sill gasket used between top of foundation wall and bottom plate of framed wall? If not there could be could air leaking in.

I also notice there is no insulation nor vapour barrier in the rim joist area, nor on the wall of the foundation.