Crawl Space Ventilation Tips

Posted on by Tim Carter

Tips on Ventilating Crawl Spaces

Ventilation of residential homes for many years was ignored. I believe the reason for this was based in the fact that many homes were self ventilating. Older homes had little or no insulation. We didn't have vapor barriers. Weatherstripping was unheard of 40 to 50 years ago. Drafts were common.

Basically, as we made our homes more energy efficient over the past 20 years, we have created moisture problems we never really had before. This is also true of crawl space ventilation. 

Homeowners, builders and remodelers have known for years that crawl spaces, especially in moist climates, need to be ventilated. Those that were not ventilated suffered. It was not uncommon for the wood subflooring, floor joists and any other wood framing member to begin to rot. Excessive moisture would cause hardwood floors over these spaces to cup and warp. All kinds of problems were noticeable.

Foundation vents became the standard ventilation technique. These vents often had sliding mechanisms which allowed them to be opened or closed. But when should you do what? Should they be open in the summer, the winter or year-round?

Well, there is no one answer. It depends on your climate. Homes in colder climates would benefit by having the vents closed in winter. This would help keep the room over the crawl space warmer. Homes in warm climates could keep the vents open year-round.

With the evolution of the high-performance vapor barriers, these foundation vents may prove to be a thing of the past. Numerous room additions in Cincinnati are now built without foundation or crawl space ventilation. The building code permits it as long as the crawl space is tempered.Tempered crawl spaces are those that are slightly heated. In other words, they are similar to a basement. Think of it. In a regular house with a basement, you don't have vents. The basement may have one slightly opened heat duct. Or it may get its heat from the leaks in the heating duct trunk lines or the heat radiating from the boiler pipes.

In any event, a crawl space can be treated the same way. Eliminate the foundation vents, install a high performance vapor barrier, and then have the heating person dump a little bit of heat into the crawl space.

This can work to eliminate many problems. Often there are plumbing lines that travel through crawl spaces. People are constantly trying to keep these from freezing in colder climates. The crawl space can now be used as a realistic storage area. Dampness will be negligible. Temperature swings will be a thing of the past.

If you have an existing crawl space that is ventilated, you may consider switching to an unventilated one. There are distinct benefits.

In the event you wish to keep your crawl space ventilated, the more air movement within the crawl space the better. This is true if you currently have a low performance vapor barrier. Don't count on the vapor barrier to solve your problems.

Treat your crawl space like your attic area. The more air the merrier! You can't have too much air change in your crawl space, especially if you have a poor vapor barrier.

If you decide to install a high performance product, be sure to follow the instructions. The vapor barrier is only as good as the installation! Be patient and take your time.

Author's Notes:

I received this email from Michael P, Cincinnati, OH. Here's how he helped with his crawl space problem.

"I live in Turpin Hills and wanted to thank you for your advice for sealing a crawl space. This is our third winter in our home and the basement is always much colder than previous basements from other homes. I did as you suggested and put heavy duty, thick plastic on the gravel and put doors on the opening of the crawl space. It's been a few weeks and I can see water droplets forming under the plastic. I may put a second layer of plastic for good measure. The basement is warmer and so is the room above the crawl space. I don't smell the mustiness either. Thanks again for the tip."

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Brick Veneer in Cold Weather

Posted on by Tim Carter

Dear Tim: I have asked you for advice in the past and it was dead on - so I thought I would try you again. I am building a new home in Chicago. The problem is the timing might require brick work to be done in the winter months. I have seen this done at job sites around Chicago and all seems well. Some guys use tarps and heaters when applying the mortar and probably add some type of additive for the mix -- is this an acceptable practice? Is its skill dependent on the brick laying team? Finally, if I were to see failure in the mortar due to the weather, do you think it would occur within a year or something that would gradually occur and not become a significant problem for a few years? Maury P.

Dear Maury: Brick can be installed in cold weather but there are very strict guidelines as to how it should be done. The biggest problem is that the water in the mortar mix can freeze before it has a chance to develop into hard crystals that interlock the sand, cement paste and brick into one homogeneous unit.

There are additives you can blend in with the mortar mix to work at or slightly below freezing temperatures. These additives are very effective when used exactly as directed on the product labels. Problems happen when the masons stray from the temperature ranges that are suggested by the manufacturers.

Another trick real craftsmen use is to warm up every component used in the process. With proper planning, a tent can be built over all of the materials and the brick, sand, sacks of mortar and water are heated so they think it is 60 F or higher outdoors. Raising the temperature of all of the materials is very effective and can make all of the difference.

The best solution is to tent the entire house and create an artificial environment where the entire house and all of the materials think it is 45 - 55 F. This enclosure will be expensive to build and maintain, but if you leave it up for three days after the last brick is installed, you should never have problems.

If the mortar does freeze, failure will be immediately visible. The mortar will fall apart with little effort after seven days.

Installing Drywall in a Garage

Posted on by Tim Carter

Dear Tim: I'm hanging drywall for the first time in my garage. I have completed one wall thus far. I noticed about 1 week after priming the wall that the horizontal seam is beginning to develop a hairline crack. I used 12' sheets and laid them on their sides to create fewer vertical joints. The screws are about 6" - 8" apart vertically and 1 per stud per sheet horizontally. I used fiberglass tape for this seam. Can you tell me what I've done wrong? Any help will be greatly appreciated. I hope to prevent this problem on my other 3 walls. Johnny S.

Dear Johnny: Based upon your description, it sounds like you did everything right. The crack is probably a shrinkage crack in the joint compound you used to hide the seams. If there is excessive water in the joint compound, the dried material often has small cracks from the volume loss that occurs as the water evaporates.

The crack could also be caused by movement of the walls. Some garages do flex a little bit on windy days.

High Performance Vapor Barriers

Posted on by Tim Carter

High-Performance Vapor Barriers

On more than one occasion, I have had to slither across the damp dirt in a crawl space. I would emerge from the space encrusted with dirt. Sometimes, the dirt would smell of chemicals. The air in the crawl space was heavy with a dank, musty smell.

Three years ago, a friend of mine was considering leasing a house. He asked me to inspect it, as the lease had an "option to buy" clause. The house had been vacant for approximately one year. As I crossed the threshold into the home, I knew instantly that this modern house had been built over a crawl space. I asked him about this. He said that there was a lower level storage area. The house had been built on a hillside. We went around the back of the house. Yes, there was a storage area alright. The entire house was constructed over a giant walk-in crawl space. I guess you would call it a walk-space in this instance. In any event, the musty odor was overpowering. There was gravel spread throughout the entire area, however, there was no vapor retarder beneath the gravel. Needless to say, my friend decided against leasing the house.

Water Vapor Retarders

When water evaporates, it is attracted to warmth. This happens because warm air has the ability to hold more and more water vapor. Just visit New Orleans or Houston in July and you will know what I am talking about. This same thing happens in your house on a smaller scale. Do you live in an older home, say one built before World War II? If this house has a basement, I'll bet that there is a good chance that the basement always feels slightly damp. Why? Because vapor retarders were not used back then. In fact, the widespread use of vapor retarders didn't begin until the mid 1960's.

Unless you live in a desert climate where the soil is extremely dry, water is constantly leaving the soil and evaporating into the air. It does this in your house as well. Water from the soil will saturate concrete foundation walls and basement floors. This water evaporates when it is exposed to the air in your basement. If you have a crawl space, the water leaves the soil and looks for warm air. The warm air acts like a giant magnet. The water vapor will penetrate wood flooring, insulation, carpeting, etc. It will do just about anything to get into the warm air of your living space. When it gets there, it brings along any musty odor as well.

Stopping the Flow

Virtually every builder I know uses polyethylene sheeting as a vapor retarder. You have probably seen this material. It is usually either clear or black. It comes in rolls usually 100 feet long. Often it is available in different widths ranging from 8 feet to 20 feet. It is also available in different thicknesses: 2 mil, 4 mil or 6 mil. Here in Cincinnati, everyone calls vapor retarders 4 or 6 mil 'poly'. I used this material on all of my jobs. I used to think it was very effective. I recently found out that this material has its limitations. It is not nearly as good as I thought it was.

Apparently, many of these products are made from low density polyethylene resins. The material used to manufacture them is often scrap or reprocessed resins. Fillers are sometimes added. Pinholes can exist in the material. What's more, this material can actually degrade or break down when it comes into contact with certain alkaline soils.

The Right Stuff

As it turns out, there are high performance vapor retarders. These materials are made from polyethylene. However, it's very different from the previously described polyethylene.

The high performance materials are made using virgin high density polyethylene. When they are made, most of them are cross laminated. That means that two separate sheets are fused together with a hot melt resin at a 90 degree angle. The process is very similar to the way standard plywood is made. The net result is that there are no pin holes and that these materials are often 50 times better at resisting water vapor transmission!

They are very resistant to tearing and punctures. Special pressure sensitive tapes are made which allow you to seal overlapping joints. These vapor retarders materials are unaffected by most soils.

Where are They Used?

There are a variety of places you can use these high performance vapor retarders. They make an excellent cover over dirt in crawl spaces. You can and should use these same materials beneath concrete slabs in basements & garages, exterior wall vapor retarders and as an exterior vapor retarder around foundation walls. You simply use them anywhere you wish to stop water vapor transmission.

Are They Worth It?

Often people shy away from high quality materials because of their high cost. I can understand this when you are dealing with cost differences of hundreds or thousands of dollars. For example, you may want granite countertops which can cost thousands of dollars. But, because of budget restraints, you must settle for a less expensive top.

Vapor retarders are often a one shot deal. That is, you only put them in once. For this reason, you must not let price affect your decision. You probably think I'm setting you up for a major price increase. Surprise! Yes, the high quality vapor retarders do cost more than the poor performance polyethylene products. Often they cost 5 times more. But wait, let's see what this means in an ordinary job.

Let's say you need to install a vapor retarder in a crawl space. The crawl space measures 14 feet by 20 feet. So, you buy an 8 by 100 foot roll of low density polyethylene. Here in Cincinnati, this would cost you $16.00 plus tax. This stuff sells for about $.02 to .03 a square foot.

The high quality vapor retarder, on the other hand, sells for about $.09 a square foot. This would cost you $72.00 plus tax. So you spend $56.00 dollars extra for a high quality product. Big deal! Not only that, you have over 75 percent of the roll left over for another project!

Author's Notes:

I received this email from Michael P, Cincinnati, OH. Here's how he helped with his crawl space problem.

"I live in Turpin Hills and wanted to thank you for your advice for sealing a crawl space. This is our third winter in our home and the basement is always much colder than previous basements from other homes. I did as you suggested and put heavy duty, thick plastic on the gravel and put doors on the opening of the crawl space. It's been a few weeks and I can see water droplets forming under the plastic.  I may put a second layer of plastic for good measure. The basement is warmer and so is the room above the crawl space. I don't smell the mustiness either.  Thanks again for the tip."

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Mold Information Websites

Posted on by Tim Carter

Mold Information Websites

These website links worked for me when this bulletin was published. Sometimes web pages disappear so if you get an error message make sure the link is exactly as it appears below before you give up.

http://www.aiha.org/
This website is the home of the American Industrial Hygiene Association -
1-703-849-8888.
You can find environmental consultants/contractors here.

http://www.cdc.gov/health/mold.html
This website is the home for Centers for Disease Control and Prevention (CDC), National Center for Environmental Health Questions and Answers on Stachybotrys chartarum and other molds.

http://www.cal-iaq.org//iaqsheet.htm
This fact sheet from the California Department of Health Services provides information to people who have experienced water damage to their home and presents the health concerns related to mold exposure. It also provides general guidelines on mold detection, cleanup & removal of mold contaminated materials.

http://www.ehib.org/html_entity.jsp?bcc=papers&paper_key=FUNGI_INDOOR_1996
This web page from: Health & Environment Digest Vol 10, No. 2, pages 9-12, May/June 1996 titled Fungi & Indoor Air Quality written by Sandra V. McNeel, DVM and Richard A. Kreutzer, MD describes types of molds commonly found indoors in home and offices. Health effects and the physical conditions that encourage their growth are discussed. This article contains a table containing selected important molds found in damp buildings and how to prevent and control mold contamination.

http://www.epa.gov/mold/moldresources.html
This website is provided by the EPA on identifying mold, clean-up and prevention. This site also contains links to other sites including the American Red Cross, New York City Department of Health and Occupational Disease Prevention, University of Minnesota, Department of Environmental Health and Safety and the Carpet and Rug Institute.

http://www.epa.gov/iaq/schools/tfs/guideh.html
This is another website provided by the EPA and addresses mold and moisture in schools. This site goes into identifying and correcting common mold and moisture problems.

http://aappolicy.aappublications.org/cgi/content/full/pediatrics%3b101/4/712
This webpage is from the AMERICAN ACADEMY OF PEDIATRICS Committee on Environmental Health tells about the toxic effects of indoor molds. This page describes mold, their toxic properties, and the potential for causing toxic respiratory problems in infants. Also gives recommendations for pediatricians to reduce exposure to molds in infants and children.

http://iaq.custhelp.com/cgi-bin/iaq.cfg/php/enduser/std_adp.php?p_faqid=3018
This webpage provided by the EPA is about Biological Pollutants in Your Home. This page provides you with information to identify what indoor biological pollution is, whether your home or lifestyle promotes its development and how to control its growth and buildup. Gives a list of questions to ask your doctor to help determine the effects on your health that may be related to biological pollutants in your home. This is a really helpful webpage.

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Mold in the Attic

Posted on by Tim Carter

Dear Tim: We recently purchased a home in Washington State. We were here three weeks before we had any rain. The day before Easter, we got a tremendous rainstorm and high wind. When we got home late that night, we found water (about 1/2 an inch) in the first level of the home. We found huge bubbles in the walls where water was behind the latex paint and just blew it out like strings of balloons. We looked and found a lot of the ceilings were wet and dripping. We called in a company to tarp the roof. When I peeled back the foil backed insulation there was so much water up there in the attic area I got soaked.

We had to get $30,000.00 to put on a new roof. (Insurance would not cover it, they said it was a preexisting problem.) No one found any mold while doing this. They did not change out the insulation or replace the OSB. We had to have the ceilings removed because they were sagging from being damp. Now they discovered MOLD everywhere on the OSB. All work has been stopped for five weeks.

Because we are getting so many conflicting reports about cleaning OSB we are very scared. At first the insurance company was going to replace the whole roof OSB and then they said they would just clean it. We were told you can clean plywood successfully. We were also told that you cannot clean OSB successfully because mold feeds on the glues that hold the OSB together. You can only clean the surface, you can never get rid of the mold totally in OSB.

We are concerned about the resale of the house. We were told they will scrub the underside of the OSB but the stains will always be there. If I was a new buyer and saw these mold stains, there is no way I would want to buy the house. Can you please help me with advice on where to go from here and what is the proper way to clean this. Yes, there were three inspectors before we purchased the home and no one found any mold. Winnie H.

Dear Winnie: The first thing I would do is consider talking with an attorney. If I understand your story, the attention needs to be directed immediately to the three inspectors who looked at the house and did not discover the roofing flaw that caused the leakage. Some serious mistake must have been there or this rainstorm caused the leak, in which case I would think the insurance company should be holding the bag as that is what we all pay insurance premiums for.

You need professional legal advice at this point. Be sure to hire an attorney who can prove to you they have successfully prevailed in identical cases.

As for the mold, please go read my past mold columns to understand how and why mold grows. The existing mold can be cleaned and it will not come back unless the surfaces get wet again.

Gas Fireplace Installed in Existing Home

Posted on by Tim Carter

DEAR TIM: My home is three years old, when it was built I had the builder frame out for a fireplace to be installed at a later date. What else besides cutting away the drywall would it take for a contractor to install a prefab fireplace? I am looking for gas logs ventless or vented. I just want to get the feel of a more realistic fireplace not something stuck out in the room.
Phil H.

DEAR PHIL: When you say frame out, I assume the house has a wooden chimney chase installed up to and out of the roof. This means you need to purchase a prefabricated fireplace that has a metal chimney pipe that is approved for such instances. If there is no chimney chase, you are still in great shape as you can purchase a direct vent fireplace that exhausts out a nearby wall or directly behind the fireplace.

I am not a huge fan of ventless or vent-free fireplaces or gas fireplace logs. A by-product of burning natural gas is water vapor. If you burn vent-free gas logs for extended periods of time, you inject vast amounts of water vapor into the inside air of your home. This water vapor can condense on cooler surfaces, such as exterior walls or attic spaces unless you have excellent vapor retarders and fantastic attic ventilation.

Pick a fireplace that will fit your current conditions and read the installation instructions cover to cover. Then start to get bids from contractors who will install it exactly that way. Put wording in the contract that says they must follow the instructions to the letter.

Hunting for Older Building Material

Posted on by Tim Carter

Dear Tim: The upper half of my house is siding with "shake-style" aluminum shingles. My hunch is that they were installed at least 20 years ago. I have about a 3'x9' section where they are missing. I have no idea if they can be purchased any longer. If not, do you know of any place that may have used ones, etc.? Paul B.

Dear Paul: I would call demolition contractors in your area. They are always listed in the phone book. These companies specialize in hunting for building materials that people need. If you supply them with a photo of the siding and tell them what you would pay them for the rights to salvage some of the siding before they destroy the house, they will hopefully call you when they find a house like this.

I would also scout the place where you live for houses that have the siding. Ask the homeowners if they are thinking of getting rid of what they have for a new siding. If so, perhaps they will let you salvage some.

Condensation Problems

Posted on by Tim Carter

Condensation on brand new windows? You must be kidding me! It can and does happen. The frustration most people feel when condensation forms on new high performance windows is enormous. After all, they just spent lots of money to SOLVE condensation problems!

Why Me?

There are very few parts of the USA that don't have condensation problems. The first place that comes to mind is the Southwest. The humidity is low and temperatures can be high for the most part. Sure, there are parts of the Southwest that get snow and can get cold, but it sure doesn't have the humidity you find in the Midwest or Northeast on a routine basis. Higher humidity from the air and water vapor that comes up through the ground can cause all sorts of headaches inside a home.

Sources of Indoor Humidity

Plants, cooking, washing clothes, frequent showers, whirlpools, hot tubs, etc., all can liberate lots of invisible water vapor into the air of a home. Water vapor can also come from the soil around your foundation walls and under your basement floor or your slab.

In older homes, this water vapor can be hard to control. Old houses can have rock foundations or slabs that were poured directly on dirt. I used to live in such a house and the basement was constantly musty.

New houses can have vapor barriers installed on the damp side of the concrete. A simple vapor barrier on a foundation wall is hot asphalt spray. A fantastic vapor barrier AND waterproofing product on a foundation wall is rubber modified asphalt or synthetic rubber foundation treatments.

New homes can have great vapor barriers installed over the soil in crawl spaces.

Monitoring Humidity

As the outdoor temperature drops, the indoor relative humidity level must also drop, or condensation can form on even the best windows. You can measure indoor relative humidity with a hand held hygrometer.

Decent hygrometers can be purchased at stores like Radio Shack or any place that sells weather instruments. If you decide to monitor your indoor humidity, do so on a daily basis and begin to keep a log. Take readings in the center of a hallway or some location slightly removed from the places where humidity will be naturally high like a kitchen, bathroom or laundry area. Take readings at the same time each day if at all possible.

Be sure to write down the outdoor temperature on the log beside each indoor humidity reading. It would also be helpful to write down the degree of condensation on windows or lack thereof with each reading.

If you do have condensation problems, a humidity log such as this will be very helpful in trying to pinpoint the problem.

Replacement Windows

If you want minimal condensation on replacement windows, then you must buy ones that are of the highest quality. Quality can be measured fairly easily. I happen to be a huge fan of independent testing and certification. Third party labs and associations can create strict manufacturing guidelines that ensure you are getting a great window that will minimize condensation.

Continue to read about the different certified programs and the companies that make windows that meet or exceed the strict guidelines. If you buy certified windows from a top-notch company, you should be a very happy camper!

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Vapor Barrier Manufacturers

Posted on by Tim Carter

Manufacturers of High Performance Vapor Barriers

The following manufacturers make really high-quality barriers. You will not usually find these products at a large home center. It may take detective work on your part. Most large cities have supply houses which cater to concrete masons. They can often be found on the Internet by searching under "Concrete Supplies Your City".

You want a product that meets or exceeds the ASTM-1745 standard.

These out-of-the-way businesses often stock these products. Contractors purchase their products from these specialty businesses for a reason. Hunt around, you may be surprised at what you find. Also, call these manufacturers. They should be able to direct you to a local distributor in your city.

SHEET PLASTIC VAPOR BARRIERS:

    • Fortifiber Moistop: A waterproof paper with a polyethylene coating on each side.

Fortifiber Corporation. 800-442-2587.

 

  • Super Sampson: A high-density cross laminated polyethylene.
    Raven Industries. 800-635-3456.

 

  • Tu-Tuf: A high density cross laminated polyethylene.
    Sto-Cote Products, Inc. 800-435-2621.

LIQUID VAPOR BARRIER PRODUCTS:

    • Clearseal Waterbased Gloss & Seal: Acrylic Sealer.

Tamms Industries. 800-21-TAMMS.

  • Aquapel & Aquapel Plus: A silane siloxane sealer.
    L & M Construction Chemicals. 402-453-6600.

Author's Notes:

I received this email from Michael P, Cincinnati, OH. Here's how he helped with his crawl space problem.

"I live in Turpin Hills and wanted to thank you for your advice for sealing a crawl space. This is our third winter in our home and the basement is always much colder than previous basements from other homes. I did as you suggested and put heavy duty, thick plastic on the gravel and put doors on the opening of the crawl space. It's been a few weeks and I can see water droplets forming under the plastic. I may put a second layer of plastic for good measure. The basement is warmer and so is the room above the crawl space. I don't smell the mustiness either. Thanks again for the tip."

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