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joelowrider 01-11-2012 11:44 AM

crawlspace walls
 
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

AGWhitehouse 01-11-2012 02:43 PM

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?

Windows on Wash 01-11-2012 05:08 PM

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.

joelowrider 01-12-2012 08:35 AM

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

Windows on Wash 01-12-2012 09:04 PM

Quote:

Originally Posted by joelowrider (Post 820353)
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

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.

Bob Mariani 01-15-2012 08:55 AM

Vented crawlspaces are a no-no. To remove the moisture use exhaust only ventilation. Check out EZ-Breathe, works about 10 times better and much cheaper to run than a dehumidifier. The poly of the floor is the right thing. The reflective bubble wrap can come down.

Gary in WA 01-15-2012 11:21 AM

The radiant barrier is correct, it will stop the radiative coupling to the cold earth, but doesn’t warm the joist ends: http://www.buildingscience.com/docum...n-crawlspaces/

Gary

Windows on Wash 01-15-2012 12:56 PM

Quote:

Originally Posted by Bob Mariani (Post 823091)
Vented crawlspaces are a no-no. To remove the moisture use exhaust only ventilation. Check out EZ-Breathe, works about 10 times better and much cheaper to run than a dehumidifier. The poly of the floor is the right thing. The reflective bubble wrap can come down.

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?

Bob Mariani 01-15-2012 01:27 PM

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.

Windows on Wash 01-15-2012 01:43 PM

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.

CrawlSpaceMoist 01-15-2012 11:05 PM

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.

Earnie 01-16-2012 06:36 AM

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.

CrawlSpaceMoist 01-16-2012 07:23 AM

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.

Earnie 01-16-2012 08:05 AM

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.

Bob Mariani 01-16-2012 08:22 AM

I use Dow Tuff R for crawlspaces.. even their site explains it is the best way to fix a crawlspace and vents should be closed off. Also if you look it does not require a thermal or ignition barrier. http://building.dow.com/na/en/applic...tionscrawl.htm


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