Crawl Space Condensation

Condensation in the crawl space can add to the nightmare of an all already wet, damp and musty smelling crawl space. At first the condensation might seem harmless, after all the crawl space is already damp. But left mismanaged, that condensation will induce a wide range of damage to your home. Condensation is a major factor in:

  1. Mold, mildew and fungus growth, which eats at your home
  2. Premature deterioration of wood structure
  3. Attracts wood boring insects like termites and powder post beetle
  4. In colder climates, the condensation will freeze causing the wood to split
  5. Heating and cooling duct work will rust causing energy loss
  6. Elevated moisture levels could cause bacterial growth
  7. Damage to electrical, television and phone cables

So what to do? The answer is easy and the moisture control process can be done by most able bodied homeowners. Eliminate the moisture and you have stopped the condensation. The warmer the air the more moisture it can hold, so when the warm moist outdoor air comes into the cool crawl space the moisture leaves the air and settles on the cooler surfaces like the vapor barrier, water lines, cooling ducts and just about anywhere it is cooler than the air outside. Since you can not control the outside temperatures you will have to control the moisture to get this problem under control.

The foundation vents are the biggest contributors because they will bring in the excessively moist air from outside. If you close the foundation vents without sealing the dirt floor first, you will have a completely different issue but every bit as devastating. When it comes to moisture control, whether condensation or just elevated moisture levels, you will have to commit to fixing all of the sources in order to truly prevent damage. Crawl space encapsulation is the best way to seal out the moisture from the outside and protect your home.

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Zero Perm crawl space vapor barrier

Just another marketing trick!

So we see it more and more, “Zero Perm crawl space vapor barrier”. Articles are written about it, professionals recommend it and resellers give it their own special name. For some reason companies in the crawl space industry, either just getting in it or have been in it for some time, feel they need a magical product in order to sell the job. Seems few are really concerned about results, but rather how much can they make.

The Truth

What is the most important characteristic of a crawl space vapor barrier? I will give you a hint- It’s not the perm rating. It is the quality and durability of the material you use. The codes (both IRC and NCDOI no longer site a minimum “perm rating” as they once did. Today the requirement is minimum 6 Mil.

North Carolina Department Of Insurance-
R409.2.1 Ground vapor retarder. A minimum 6-mil (0.15 mm) polyethylene vapor retarder or equivalent shall be installed and secured…

So you see not much focus on the famous “perm rating”. I will tell you why. The perm rating of an actual 6 Mil (not home center “visqueen” that product is an actual 4 mil) is between 0.1 and 0.06, of course the exact perm will depend on the quality of the polyethylene. In a 1200 sq ft crawl space with 3′ high walls the amount of moisture that will pass through that 6 Mil plastic at .06 perms, is 0.59 pints of water in 24 hours. Now that is just the plastic, not the tape or untaped seams. Simply put- if the barrier could be put in the crawl space as one piece and there were no obstacles, .59 pints of water is all the plastic would let into the crawl space each day (pressure, temperature and other factors will affect these results but unnoticeably so).

So what’s all the “hub bub” about perm ratings? The perm rating is important, its important that it is less than 0.1 perms, past that it’s just a bonus. That same crawl space above having a 0.1 perm would increase your pints per day from 0.59 to nearly 2.0, that is four cups of water in 1200 square foot. The truth behind the BUZZ about perm ratings is marketing, what else?

The Untruth

Like the “Antimicrobial” trick, the perm rating campaign is meant to prey on the ones that really don’t understand the technical side of this business. Two of the most common deceptions are:

Zero Perm & Dividing the results

1. Zero Perm-This marketing scam is the most intentionally deceptive. Just from reading this article you have some kind of idea how perm ratings are presented. They are in whole numbers or in fractions of a number displayed as a decimal. So, for example the popular house wrap Tyvek™ has a perm rating of 48.0, while the 12 Mil SilverBack™ crawl space vapor barrier has a perm rating of 0.051.

Here’s their scam- They display only whole numbers as their perm rating. While the honest guys show 0.053 perms, the dishonest guys show their 60 Mil crawl space vapor barrier as zero perm by doing this 0., instead of showing you this 0.103.

They do this because most consumers know with perm ratings, lower is better. Once they have you convinced their product is “Better” they charge you handsomely for the result of their deception. The also state 99% aluminum and that’s not true either, but I will write about that next time.

2.Dividing The Results-This one is a bit harder to catch.

It makes me cringe each someone asks me for the perm rating of our SilverBack™ vapor barrier. Not because I’m ashamed of the performance, but because I know the person asking has no idea what they are asking for. Perm ratings are given in grains of water that pass thru a square foot of material per inch of mercury every 24hrs.

Here’s their Scam-If your perm rating was 0.053 they will divid that number by 24 (hours in the day) and POOF the new perm rating is 0.0022. Who has the lower perm rating now? Of course they don’t tell you they did that, mostly because you didn’t ask. Two other scams that go with this is: companies use the WVTR as their perm rating, while others use the metric perms (which is lower than US perms).

What do you do? The answer to this question is ALWAYS going to be- Do your homework and buy from a reputable company. Currently there are no “Plastic Police” so its a bit of a free for all.

I hope this helps in your search…..


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Crawl Space Moisture Solved

Lowering Crawl Space Moisture & Humidity- Explained

Relative Humidity (RH) is the byproduct of two conditions in the atmosphere, temperature and dew point (amount of crawl space moisture in the air). To control or alter the RH you must manipulate either dew point or temperature.”Dew point temperature is the absolute measure of how much water vapor is in the air”- Source. The dew point is always less than the air temperature. The closer the dew point temperature is to the air temperature the closer the RH gets to 100%. Example- Dew point temperature 70F and air temperature 70F = 100% RH

If the home has an encapsulated crawl space, then the dew point inside the house will be different than that of outside the house. Air temperature will actually dictate what the RH is at any given dew point temperature. Inside the home we keep the air temperature at a comfortable level, say 70 degrees (which I am assuming is this case). A crawl space that has been sealed and encapsulated will maintain an air temperature similar to inside the living area. With that said, similar air temperature means about 5 degrees cooler than the living area. This is due to the consistent temperature of the earth under the vapor barrier, a geothermal effect. This is good in many ways for the home, because the air temperature will remain between 60F – 68F degrees most all of the time. Back to our RH problem, so the house (assuming ) is 70F degrees (air temperature) puts our crawl space at (again assuming but will be close) 65F degrees (air temperature). In this scenario I will need to know either the dew point or RH to figure out the rest of the equation. Once I know the dew point I can show you what is going on in the crawl space and why it’s happening.

The assumptions-

House air temperature: 70F/49% RH
Crawl air temperature: 65F (house temperature minus 5 degrees)
Crawl RH:Unknown
Dew point temperature in the living area- 50F degrees

Using a dew point calculator to figure out RH in the crawl space with this information-

Crawl air temperature (assumption): 65F
Dew point temperature inside the home: 50F (also the dew point in the crawl)
Crawl Space RH is 60%

So you can see there is an 11% difference in RH levels between the home and the crawl space. The only difference is the air temperature between the two spaces. If you raise the air temperature in the crawl space to 70F, same as the living area, you will have the same RH 49%. Setting the crawl space dehumidifier at 49-51% means it is trying to lower the dew point temperature in order to achieve a lower RH. To successfully lower the dew point temperature in the crawl space you must lower moisture for the entire house. This is quiet a task for any dehumidifier when you consider the traffic in and out of the house, the amount of showers taken, moisture from cooking, moisture in the wood inside the home and the natural moisture loss from each person living in the home. It will cause the dehumidifier to run more then 5 min an hour. If you wish to accomplish a shorter run time for the crawl space dehumidifier, then you can raise the air temperature in the crawl space. This can be done by creating a conditioned crawl space with air from the home, helping to deliver heat to the coldest places- the crawl space. Of course when you raise the temperature to control RH, you make the RH level much more critical in the mold growth equation (explained better in the next paragraph). The other option is to set the controls on the dehumidifier to a higher setting, maybe 58-60% (based on 65F degree air temperature).

There are several factors in crawl space mold growth; dew point temperature is only one of them (amount of moisture in the crawl space air), the other being air temperature. RH is simplified as a mixture of dew point temperature and air temperature. This simplification does not allow for any absolute rules, for example the myth that crawl space mold will grow once RH reaches 55%. As a convenience to avoid teaching in depth classes on dew point temperature and air temperature each time a crawl space dehumidifier is sized and installed it is widely expressed- ‘to avoid mold growth, a safe RH is below 55%’. But, once RH is really understood that statement does not hold enough information. Last week, here in Michigan, our outside RH was 85% but the temperature was 31F degrees. Mold growth is not imminent in this equation because the air temperature is far to cold, but under the understanding of “less than 55%” it would be widely considered a mold growth threat. Just like RH is tweaked using air temperature, so is mold growth. In a crawl space that has an air temperature below 70F will not generally be threatened by mold growth until the RH rises past 67%. Keeping an encapsulated crawl space that has an air temperature of 67F and an RH of 58-60% will produce excellent results in the battle against wood rot, odor, mold and mildew growth and a high electric bill caused by the crawl space dehumidifier. Of course the owner if the house has to add the crawl space to the list of maintenance duties required by the home, bi-annual crawl space inspections are strongly recommend.

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Does crawl space encapsulation really work?

Does encapsulation really work?

It’s funny because I never hear that question. There are more objections to closing the vents than any other subject. I think the question that is really being asked is; is it worth it? My answer would be; how much is it worth to eliminate the crawl space from having problems? How much does it cost to remediate Mold, or treat for termites? Is it really worth replacing your roof before it leaks? You can see where I’m going with this. You are probably here on this blog because you are having problems or you know someone that is. Aside from fixing anything that is currently wrong it really is an investment in keeping it from getting worse and costing you more. The average cost of repairing rotted joist is about $3500, now that is not for replacing all of them but it does pay for around 10 or 15 to be replaced. We did a job in Linden Michigan in the Fall of 2008 that needed 22 joist and 45′ of main beam replaced. It was a summer cabin the family used on the weekends and during Christmas time. The crawl space was 2200 sq ft and only 18″ high, a bit of a challenge I might add. The homeowner (Tom) knew it needed to be fixed and was having trouble finding a company that wasn’t trying to retire on his bank account. With this amount of damage it wasn’t hard to see why the salesman’s eyes would light up. In the end we installed a drain system and sump pump, closed seven foundation vents, our 16 Mil SilverBack™ and replaced the 22 rotted joists as well as the 45′ of main beam. The price? Well, the structure repair was $8500 and the rest was another $8000. Hardly chump change for a weekend home, but Tom really didn’t have any choice. It was that or ride it out until the floor fell in then walk away. I can tell you story after story about a homeowner that either inherited, bought or neglected a problem crawl space. Either way it still hurts.


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