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crawlspace walls

11K views 67 replies 8 participants last post by  Windows on Wash 
#1 ·
So I have a 3 foot crawlspace that is very damp We are thinking of putting a dehumidifier in it and insulating the outer walls.

Right now we have the floor joist insulated with the reflex reflective bubble wrap. Should this be pulled down left up or what
 
#2 ·
Please post useful information if you expect any answers....

Do you have plastic or some other kind of vapor retarding system on the floor now? On the walls? Is the crawl space vented? Where are you on this big blue marble? Is bubble wrap your only insulation?
 
#3 ·
Reflectix is not insulation and is barely effective as a radiant barrier...neither of which is proper in this application.


  • Where is the home located
  • What is the drainage/grade around the property like
  • What is the relative humidity in the crawlspace in the summer
  • Any utilities in the crawl
  • any additional details are useful here as are pictures.
 
#4 ·
I have a 6 mill black vaper barior on the floor. tapped and overlaped

I live in Evansville IN about 30 foot off the Ohio River.

The Grading is bad due to the fact I have a hill behind the house My house is on the low side.

We have a french drain system aroun the back side of the house (drains water 365 days a year)

We also have a tile system under the house to a sump pump That mainly runs on very rainy days.

The Crawlspace is vented and humidity can get to 90 in the summer we put a power fan on it and we can get it to 60.


All of the houses around here have sealed crawlspaces now.

So we have ordered a 20 mill vapor barior and the foam insulation we are going to close off vents and condition the space my only question is to leave the radiant barior or take it down
 
#5 ·
Neither.

Leave the space as unconditioned in my opinion and apply a continuous vapor barrier across the underside of the framing of the floor.

Batts in between the joist with a healthy layer of rigid foam (seams staggered and taped/sealed) would be my best approach.

With that high a moisture content and fundamental drainage issues, I would leave the crawl as vented and continue to manage the moisture diversions/ejections.
 
#8 ·
How do you figure in this case?

Vented crawl spaces have been used for 100's of years successfully and what difference does it make in this case if the insulation and air barrier are intact at the floor joist level.

I would agree with you that converting a crawl to conditioned is applicable in most cases, however, the homeowner in this case has noted that he has poor grading and high water table. Most moisture/rH control measures in crawl spaces are designed at handling minor moisture issues. If he has a sump and french drain combo that runs pretty continuously, I would prefer to rely on a system that just manages the bulk moisture and control humidity via insulation and air barriers.

With that high and continuous moisture issues, that EZ breathe will be running constantly as compared to the occasional cycling of the sump pump. Which one is going to be using more energy at that point?
 
#7 ·
#9 ·
the EZ-breathe will still use less energy. Bulk water however should be treated as a separate issue. vented crawlspaces have been used for years... another thing done wrong. In humid months more moisture is brought into the space, which creates a problem. The new code and informed building practices now understand that vented crawlspaces are wrong.
 
#10 ·
I realize that EZ Breathe quotes $2-4 per month in usage but I would be very interested in seeing what the current draw is and what the electrical usage would be under very humid conditions. I suspect that $2-4 is under very low cycling conditions.

I think we are debating and accepted point here. I agree that conditioned crawls are ideal and when building a home, crawls should be engineered as conditioned vs. vented.

That being said, the grading issues, the fact that this is existing construction, the high water table, and considerable moisture issues make this a good candidate to remain a vented crawl. If the grading were better, not such much bulk water, etc I would be more inclined to encourage the poster to make it conditioned.

If the insulation and air barrier details are correct across the underside of the floor, I see no additional benefit to treating this as conditioned crawl and if done right, I also don't see any energy offset benefit to the conditioned crawl.
 
#11 ·
I definitely agree it sounds like a sealed/conditioned crawl space is the way to go here.
With an exterior french drain and an interior tile to a sump pump, it sounds like you're handling the 'bulk' water. You don't really clarify what about your crawl space is 'moist' - the ground or what.
A fan that pulls humidity from 90 to 60 is amazing, but 60 is still high, depending on the temperature of the crawl and it's components. Have you taken any moisture readings in the wood of the joists?
Honestly, think about it. If you have a VB on the floor, you're handling the moisture (humidity) eminating form the floor - you're left with a circulation/humity issue. Unless it's muddy under the plastic?
I'd stay away from putting any poly on the underside of the joists. You could likely trap moisture between the poly and the floor and allow tremendous condensation issues, especially during the summer when the a/c is running.
Seal is, run a quality dehum to control the humidity in the crawl. Remember, once the humidity is controlled, the dehum will only run as-necessary.
 
#12 ·
When I moved into my house the crawlspace was like a rain forest. No poly on the floor, open foundation vents, plumbing, electrical, ducting, and HVAC air handler were dripping water. So I did some reading.

I placed 6 mil poly on the ground as required by code. A week or so later I looked in the crawlspace to now find a lake. Dripping water was now standing on the poly. Did more reading.

Next I closed and sealed the foundation vents and installed a cheap dehumififier. It took over a week of constant dehumidifier operation but the water on the poly dried. So did the insulation, electrical, plumbing, and HVAC. Did even more reading.

Next was placing foam board in the rim joist area and sealing around it. The cheap dehumidifier lasted a year. The new one is a SantaFe Compact. Right now the humidity level in the crawlspace is 54%. This is without sealing the poly to the walls, at seams, or around pillars. Found a site selling 16 mil poly. Started replacing the 6 mil.

Last project is to install foam board on the block walls. Still need to find a suitable way to cover the foam board. I will not use drywall.

So for my situation, closing the vents and starting to encapsulate the crawlspace has made a huge difference in the Rh.
 
#13 · (Edited)
If I may ask, why are you planning on covering the foam board?

And thanks for the post. one thing that's often forgotten with a crawl space SYSTEM is that the air is in balance with the dirt. Normally, especially in the South, sub-surface moisture 'breathes' out from the soil as humidity into the craw where the vents are supposed to help clear it out. HOWEVER, in crawl spaces where the humidity entering is extremely high and (typically) with poor circulation, the soil can absorb moisture from the air.
When you place a poly, you 'break' that absorption zone. it's pretty rare (in my experience), but you can have people with poor crawls, they place a poly, and it gets worse! You've just isolated your problem as primarily from the venting.
Sealed crawl is the way to go! thanks for sharing.
 
#14 ·
Why will I cover the foam board? 2009 NC Residential Code Section R314 Foam Plastic.

Specifically, R314.5.4 Crawlspaces.

"The thermal barrier specified in Section R314.4 is not required where crawlspace access is required by Section R408.4 and where entry is made only for service of utilities and the foam plastic insulation is protected against ignition using one of the following ignition barrier materials:

1. 1.5 inch thick mineral fiber insulation
2. .25 inch thick wood structural panels
3. .375 inch particleboard
4. .25 inch hardboard
5. .375 inch gypsum board or;
6. Corrosion-resistant steel having a base metal thickness of .016 inch.

The foam plastic ignition barrier is not required where the foam plastic insulation has been tested in accordance with Section R314.6."


I read it that the foam board must be covered unless tested and approved. Help me understand why protection is not required for the foam board.
 
#16 · (Edited)
I don't want to take away from the original poster question. Just adding my experience.

Bob, I don't see where the link states no thermal or ignition barrier required. Dow can state whatever it wants. The building code says different unless Dow has provided testing data and the product has been approved.
 
#17 ·
In any case you need to follow you local codes. Unfortunately they are very outdated and flat out wrong when it comes to energy efficiency retro-fits. Codes will be changing for 2012 when local officials adopt them. big changes.
1) vapor barriers are not to be used in mixed climates
2) exterior foam insulation is required to stop thermal bridging
3) air sealing and a blower door test are required
4) vapor retarders over dense packed cellulose are not required
5) Mechanical ventialation (HRV) will be required
 
#19 ·
if it not to be inspected and building science shows it is the right way, I would go with the right way. Poly on warm side of walls for mixed climates is an excellent example.. By code grow mold. As a contractor I install the poly get inspections and rip it out. Inspector knows this is being done and agrees with it. If fact it was his recommendation. code here still wants cross vents in a crawlspace. yet when doing a fix we immediately seal these off. (note DOW says to do the same thing) Building Science is relatively new. And codes were not built to local conditions. Our housing stock is built horribly as a result.
 
#20 ·
I have no problem with what you wrote but there are limits. Yes?

To the issue of covering foam board, my understanding is protecting the foam from fire and the potential gases it produces when burning.

Will those gases make it into my living space before I know there is a fire in the crawlspace? I have no idea. A smoke detector in the crawlspace (and attic) might be a good solution.
 
#23 ·
Why would a crawlspace ceiling need to be air tight if it was being treated as sealed/conditioned?

I guess you could stomach cancer is worse than lung but that doesn't mean I want either.

Code is code....and the foam is supposed to be covered. Random dismissal of a tenant in the code is not exactly advisable. :whistling2:
 
#22 ·
#24 ·
a crawlspace is normally not intentionally conditioned living space. As such it is considered outside the building envelope. The insulation (thermal boundary) and air sealing (pressure boundary) should be aligned. Also air in the crawlspace would rise due to stack effect and it is not the quality of air you wish for your family
 
#25 ·
If you turn it into a sealed crawl, isn't the pressure and thermal boundary the crawlspace stem wall at that point?

If that is the case, why is the pressure boundary required at the ceiling? At that point you are mixing layers. Air and insulation, in the same plane, is the outside wall.

As part of any crawl space sealing protocol, the floor is going to be covered an with Poly and sealed at the stem wall so there should not be any issues with dirt smells/odors.
 
#26 ·
If you're sealing and conditioning the crawl space, the air quality shouldn't be an issue.
Per the building science RR-0401:
"Crawl spaces should be designed and constructed as mini-basements, part of the house – within the conditioned space."

Since the code allows/requires conditioning, including the exchange of air between the occupied space and the crawl space, it appears the issue is not that the crawl should not be considered outside the building envelope, but part of the functioning system of the home.
 
#30 ·
We should be commenting on old construction not new. See original posters question.

In a perfect world if I were designing a new house and needed a crawlspace I would desing and build a mini-basement or "basement for trolls" as I remember it being described.

I would not overlook the HVAC requirements (heat gain/heat loss) if I planned to condition my crawlspace. So I won't be installing a new HVAC system to accomodate a conditioned crawlspace. Please don't write that the crawlspace load would be of no concern and tapping into the existing HVAC would be ok.

As to Thermax, or any other glass-fiber-reinforced polyisocyanurate, that product was my orginal choice until I read that it absorbs water. Also, the foil would not allow any moisture that enters the brick/block wall to dry to the inside. Not sure why I want that, but that was needed.

I do not have a Phd in building science. I'm a home owner who wants to know what is being done to my house and why. It's my money, my house and I live in it.
 
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