Crawl space moisture

So I'm gonna throw a question in here for @Mac5005 that could be informative for the topic at hand. I can send a pm, but it would be good info for the thread. @ProbablyBroke , I'll move to a different thread or pm if you would like.


Do you feel it's necessary to encapsulate a crawl space for a controlled environment if it's damp? I'm dealing with some moisture in mine now. One place does an internal French drain with sump and another does encapsulation with sump and dehum. Obviously, they both think they have the solution. Hell idk if i really need anything other than a better moisture barrier.


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The more the info the merrier. Makes me feel better knowing I'm not the only one. I imagine you didn't knowingly buy into your situation.
 
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ProbablyBroke said:
The more the info the merrier. Makes me feel better knowing I'm not the only one. I imagine you didn't knowingly buy into your situation.
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Well, kindof, but not to the extent that I'm taking it. I bought my house off market and we let some things go on the inspection. . Moisture was a little high, but there was a ton of missing moisture barrier. Not much to speak of for mold. Problem came when I want to install new floors and mine are crazy unlevel. So i started looking into floor leveling and moisture control. Ultimately, the floors have sagged due to past moisture. I don't think it's that bad for moisture now, but i still need to add some stabilization.

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working thru my own issues now too. Pics are not in order, but you can see start to current.
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Ok here is my personal .02 with info. I’ll try to keep it short, I can expand if requested.

Crawlspace moisture issues as I define them are wood moisture content levels above 19%.

At 23% and above MC the problem is severe as wood rot( brown mold) will occur, and fixing floor joists gets expensive.

19-23% MC doesn’t necessitate converting to a closed crawlspace but it’s definitely a good idea. If staying vented, raise the tstat during the cooling season 2 degrees.

MC under 19% during the cooling season isn’t a crawlspace moisture issue.

The way to solve a crawlspace moisture issue is to convert from a vented type to a closed or conditioned type.

I prefer a closed crawlspace with a dehumidifier. I do not recommend a conditioned crawlspace for many reasons. There are only a few unique scenarios, ie anomaly’s, that I would suggest a conditioned crawlspace.

I do not use the term encapsulated etc, as it’s not a term recognized by the NC building code. I want to be as transparent as possible. I don’t use this term as it can mean different things to different people.

To me, A closed crawlspace consists of a 100+% vapor barrier, air sealed perimeter walls, and a mechanical means to remove the water vapor from the air in the crawlspace. This dry air will then dry the wood, ductwork, and insulation.

A dehumidifier lowers the dew point of the air in the crawlspace by removing moisture vapor.

This lower dew point prevents condensation on wood, ducts, pipes, and insulation.

To work effectively and more importantly efficiently, the crawlspace MUST be completely air sealed from the outdoor environment. Same idea as not having your windows open while trying to heat/cool your house.

As far as vapor barriers,

I believe in covering all the soil in the crawlspace plus at minimum 12” up the perimeter walls above exterior grade. (Always leave 3-4” termite inspection gap at brick/block wood connection)

Overlapping the seams 12” or more, and securely fastening the vapor barrier to the soil after pulling taught.

Take notice to ensure debris under the vapor barrier is removed as to not poke holes in barrier when traffic occurs.

12” overlaps are sufficient, and taping these is not necessary, but should be done in a few unique circumstances.

Now, as far as water.

Any and all ground liquid water should be collected and pumped or gravity drained to the exterior.

If no water intrusion, nothing needs to be done to get it out.

May need a sump pump, may need a drain to daylight, may need perimeter drains and a sump pump. Depends on what the house needs.

Ground water (liquid) and dampness have little effect on wood moisture content. This is due to very little heat available to evaporate the water, compared to normal 55-60° ground temperatures. I’m not saying it doesn’t occur, only that it’s not the big factor to wood moisture levels.

In the cooling season, The big issue is moisture laden air entering the vents. This air mass is then cooled as it enters. This raises the dew point of the air mass even further than outside air.

This moisture filled air then condenses on the duct work(r6 and r8), bottoms of joists, and insulation. Any surface with a temperature below the local dew point condenses the water vapor.

The lower the temperature setting of the AC, the worse the problem will be.

6 mil vapor barrier is plenty sufficient. Especially when considering cost, as long as it’s installed correctly.

The difference in permeability between 6,10,12,20 mil isn’t enough to warrant the additional cost. The ROI of the thicker mil plastic in terms of permeability doesn’t exist.

1/2” polyiso foil faced is adequate and cost effective to seal the foundation vents. Make sure it’s cut to fit tightly and any caulk/glue/foam is only to ensure small gaps. The right fit should hold itself in the vent hole.

There is no appreciable ROI on insulating most crawlspace perimeter walls. Yes there are anomaly’s.

Once the crawlspace is air sealed, there is enough temperature loss through the ductwork insulation, and temperature input from the ground, to keep crawlspace temperatures 65-72° year round.

The entire crawlspace air mass then acts as insulation.

TL:DR version

If you have moisture, get it dry.
If you have water, drain or pump it out.
To dry it, seal the envelope of the space.
To remove moisture vapor, mechanically removed the water thru condensation.
Do all of this with the least cost to get the most return.

Conservative avg. of 10-15% energy savings from a closed crawlspace with a dehumidifier compared to a conventional vented. Some as low as 5, some as high as 25% energy savings.

This is going to make me compile my even more detailed thoughts in a dedicated thread.
Sorry it got long winded.
 
justjeepin86 said:
So I'm gonna throw a question in here for @Mac5005 that could be informative for the topic at hand. I can send a pm, but it would be good info for the thread. @ProbablyBroke , I'll move to a different thread or pm if you would like.


Do you feel it's necessary to encapsulate a crawl space for a controlled environment if it's damp? I'm dealing with some moisture in mine now. One place does an internal French drain with sump and another does encapsulation with sump and dehum. Obviously, they both think they have the solution. Hell idk if i really need anything other than a better moisture barrier.


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Click to expand...


If you have water getting in, the best is to fix and stop it from getting in the crawlspace, next best is to collect it in the crawlspace and then get it out.

Especially on existing houses, install 100% + vapor barrier fastened to walls and floor of crawlspace. Install dehumidifier that drains to daylight. Install small 50cfm or less fan to negatively pressure the crawlspace, vent the air to outside.

The make up air that enters the crawlspace will now come from 1st floor holes around ducts/popes/wires.

Dont use HVAC air to mix 1st floor and crawlspace:
1) waste of energy
2) conditioning air you don’t live in
3) HVAC is temp controlled not humidity controlled. This isn’t optimal for moisture removal
4) terrible idea for indoor air quality, ESPECIALLY on existing houses
5) the extra size of HVAC unit/run time/ energy cost negates the possible ROI on converting to a closed crawlspace.
6) did I mention it’s a bad idea to mix house air with crawlspace air?

If you do a quality vapor barrier with no means to remove moisture, or stop moisture rich air infiltration, it won’t fix a crawlspace moisture issue.
 
Mac5005 said:
If you have water getting in, the best is to fix and stop it from getting in the crawlspace, next best is to collect it in the crawlspace and then get it out.

Especially on existing houses, install 100% + vapor barrier fastened to walls and floor of crawlspace. Install dehumidifier that drains to daylight. Install small 50cfm or less fan to negatively pressure the crawlspace, vent the air to outside.

The make up air that enters the crawlspace will now come from 1st floor holes around ducts/popes/wires.

Dont use HVAC air to mix 1st floor and crawlspace:
1) waste of energy
2) conditioning air you don’t live in
3) HVAC is temp controlled not humidity controlled. This isn’t optimal for moisture removal
4) terrible idea for indoor air quality, ESPECIALLY on existing houses
5) the extra size of HVAC unit/run time/ energy cost negates the possible ROI on converting to a closed crawlspace.
6) did I mention it’s a bad idea to mix house air with crawlspace air?

If you do a quality vapor barrier with no means to remove moisture, or stop moisture rich air infiltration, it won’t fix a crawlspace moisture issue.
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Thanks for the reply
So,
1. Fix water issue
2. do the fancy sealed vapor barrier like you are going to encapsulate, but don't encapsulate.
3. encapsulation causes you to mix crawl air with home air and that's not what you want.
4. add dehum with a small fan blowing out of the crawl, basically do the encapsulation, but have the fan to pull air from upstairs out the crawl.

I was told by the encapsulation guy that you don't want a dehum under the house without encapsulation because it will pull humidity from outside. The fan would negate that, because that air would come from the living area and not outside, correct?

Just making sure I understand things right.
 
justjeepin86 said:
Thanks for the reply
So,
1. Fix water issue
2. do the fancy sealed vapor barrier like you are going to encapsulate, but don't encapsulate.
3. encapsulation causes you to mix crawl air with home air and that's not what you want.
4. add dehum with a small fan blowing out of the crawl, basically do the encapsulation, but have the fan to pull air from upstairs out the crawl.

I was told by the encapsulation guy that you don't want a dehum under the house without encapsulation because it will pull humidity from outside. The fan would negate that, because that air would come from the living area and not outside, correct?

Just making sure I understand things right.
Click to expand...

1) Do whatever is needed for the water intrusion issues.

I don’t use the term encapsulation because it means different things to different people.


2) Full vapor barrier covering all soil and extending up onto perimeter walls.

3) Air seal all foundation vents and any holes for pipes, wiring, etc in the perimeter crawlspace walls.

4) Glue the plastic onto the perimeter foundation walls leaving 3-4” minimum termite inspection gap.

5) Install dehumidifier on concrete blocks and drain to daylight.

6) Install small 50cfm fan in crawlspace and vent the air thru the crawlspace perimeter wall. Vents to exterior.

7) Gasket/hardware on access doors so they are sealed when closed but function fully.

No forced air mixing of living space and crawlspace.

In the NC code, you have 3 types of crawlspace.

Conventional vented.

Conditioned ( closed crawlspace with HVAC to control moisture)

Closed ( dehumidifier to control crawlspace moisture)

Encapsulated/encapsulation is only a term that makes things less transparent. Use it loosely.

The vapor barrier in the code is the same for all 3 types. 100% coverage. I like to exceed that into include vapor barrier on perimeter walls. This really helps with winter time condensation on the perimeter walls.

The air sealing of perimeter walls is the same for closed/conditioned.

Conditioned crawlspaces require the perimeter walls be insulated. No ROI on this.

Closed crawlspaces can have conventional floor insulation or perimeter wall insulation.

I prefer floor, it’s cheaper. In all practical aspect, it doesn’t matter once the air is dry. The air mass acts as the insulation.

I literally tell contractors, home owners, anyone. For most crawlspaces and insulation, do what is the cheapest option. Not enough temperature differences to warrant the costs. Not enough ROI to warrant the additional costs. *yes there are anomaly’s that exist.
 
shawn said:
It's just a cheap 6mil polyethylene sheet.
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By fancy, I mean wrapped and sealed on all the pillars and the foundation walls, not just laying on the floor. There isn't anything fancy about the plastic itself. I would think if you were going to glue it up and seal the whole thing, you would want more than a 6 mil plastic. That's a lot of work to have holes in it.
 
justjeepin86 said:
By fancy, I mean wrapped and sealed on all the pillars and the foundation walls, not just laying on the floor. There isn't anything fancy about the plastic itself. I would think if you were going to glue it up and seal the whole thing, you would want more than a 6 mil plastic. That's a lot of work to have holes in it.
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I thought you meant 20, 40 mil, etc. Small holes don't really matter much for vapor transfer. Diffusion can't move much water. You're looking for perm rating and percentage of coverage. It's the same reason you don't have to worry about taping the seams - the dirt is 99.9999% covered. Anything less is a rounding error.
 
shawn said:
I thought you meant 20, 40 mil, etc. Small holes don't really matter much for vapor transfer. Diffusion can't move much water. You're looking for perm rating and percentage of coverage. It's the same reason you don't have to worry about taping the seams - the dirt is 99.9999% covered. Anything less is a rounding error.
Click to expand...

QFT

Only times I recommend thicker plastic, wrapped piers, taped joints:

Known mold allergy and significant fungal growth on soil surface

Radon mitigation

Higher than normal traffic crawlspace

For the cost/price. I like the 10mil single layer installed in the same way as 6 mil.

Beware of some multilayer reinforced products. The thickness is supposed to be measured without including the nylon reinforcement.

Several competitors are selling 2 layer 7 mil and labeling it as “12” mil.

The permeability of the 7mil is worse than USA made single layer 6 mil polyethylene. It’s being sold as a competitor to raven 12 mil.
 
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I fixed my crawlspace issues by selling my house that had a crawlspace and buying one that doesn't.
@Mac5005 was a huge help when the buyers of my old house had an issue with the CS. Thanks again bruh.

Asking for a friend...what's the highest floor joist MC you've seen? It was measured at 42% at our old house!
 
When the moisture goes into the 40s the wood is saturated and water appears as droplets on the surface. Surface water will peg the moisture meter and requires a drying period to be accurate again. If my memory serves me correct 28% is the fiber saturation point but that might be for one particular species of wood. Which brings up another thought moisture meters come with a chart to make adjustments to readings to compensate for different species. My guide lines for floor joists are 19 % or less no problem. 20% -22% warning of elevated moisture. 23% - 28% surface mold can start with limited or no damage to wood. Above 28% wood destroying mold can survive. Interesting note wood submerged in water can not support mold growth due to lack of oxygen .Also termites don’t like to eat moldy wood.
 
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