Continuous Attic Ventilation

Posted on by Tim Carter

I'll never forget that day as long as I live. It was a typical late July day here in the Midwest. I was in the midst of a remodeling job that was running slightly (right, give me a break!) behind schedule (typical). Anyway, I had to cut a hole in a roof to extend a new plumbing vent stack out to the atmosphere. For some reason, I waited until after lunch to tackle this project. What a mistake!

I poked my head above the scuttle hole. Immediately I was enveloped by hot air. I mean really hot air. It was difficult to breathe and within a period of 30 seconds I began to perspire profusely. This particular house had no attic ventilation. The air was stagnant. It took 15 minutes to complete my task. Those 15 minutes seemed like 3 hours.

I would have sworn that it was 150 degrees F or better in that attic. The homeowner happened to have a highly accurate thermometer which we used to check it out. It turned out I was wrong. It was only 134 degrees F.

Why no Ventilation Fifty Years Ago?

That's a very good question. If you are a student of older housing, you will notice that older homes rarely incorporated ventilation as a part of the roofing system. Occasionally you would see tiny gable end vents. I don't know of one old house I have ever worked on that had any form of soffit or eave ventilation.

Ventilation of homes began in earnest during the 1970's. This coincided with the increased efficiency of doors, windows and vapor barriers. We simply began to build tighter houses.

Prior to the 1970's, houses used to breathe (lose energy) very easily. Who hasn't been in a drafty old home?? Energy costs were lower. It didn't seem to matter that the old gas conversion furnace was only 45 to 50 percent efficient. Old double hung windows had no weatherstripping. Many old houses had no insulation. Air could move freely between the inside and outside of these old houses. We actually were ventilating old houses quite well. However, we found out that it was expensive!

Times changed. The energy crisis of the mid-70's shocked us into reality. Windows and doors began to be built using very good weatherstripping. Insulation and vapor barriers were applied to outside walls. Within the past 15 years entire houses have been 'wrapped' with air infiltration barriers. All of those previous paths for air exchange have been blocked. Within a matter of years, problems began to develop with houses that were suffocating. None of these problems had ever been seen before.

Old vs. New

Thousands of other people have experienced the hot attic temperatures that I encountered on that hot July afternoon. Old houses have always had the same problem. However, because air conditioning has only been around for the past 40 years or so, hot attics were simply accepted.

The same is true for older houses in colder climates. These houses rarely experienced any attic problems in the winter months. If you are building a new home or are improving and upgrading an existing older home, you can expect trouble if you do not provide adequate ventilation for your attic.

Last Chance for Air

Unless you have a state of the art air exchanger, attic areas of today's house's are the only place where air can be exchanged with outside air. It is here that today's houses must breathe. This is one of the reasons continuous attic ventilation is so important.

There are lots of other reasons why ventilation is important. Continuous ventilation helps to reduce cooling costs, validates the warranties of some asphalt shingles, reduces heating costs in colder climates, reduces chances of moisture buildup in attics, etc. Trust me, continuous attic ventilation is the only way to go.

Continuous Ventilation

If you are not familiar with building or remodeling, you might be easily confused with continuous ventilation. Older homes, and even many modern homes have used different types of vents to exhaust air from attics. A common form is the triangular gable end vents found in many older homes.

Many people have metal 'pot' vents on their roofs. These vents simply cover holes cut into the roof.

Continuous ventilation products are different. These products began to hit the market approximately 15 to 20 years ago. The first ones were metal contraptions that replaced the cap shingles at the top ridge of your roof. Besides being unattractive, they often leaked.

In addition to the ridge vents, a continuous metal strip was often (and still is) placed in the soffit or under eave area to provide a place for fresh air to enter the roof. These strips of metal would run from one end of the soffit to the other in a continuous fashion, just like the ridge vent. Is it a little clearer now?

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Ventilation Primer – How Much is Needed?

Posted on by Tim Carter

How Much Ventilation?

Probably less than 3 percent of the homes standing today (new and existing) have proper attic ventilation. Those that do can achieve this goal in several different ways.

The houses that have proper ventilation do so in the following way. Continuous or ample singular vents are placed at or near the top of the roof. A similar system of vents is then placed at the bottom or under side of the roof. This system works like a forced air heating or cooling system in your home. The air that leaves the upper vents is replaced by the same amount of air at the lower vents.

It is extremely important to have both upper and lower vents. This is what produces the flow through and continuous air flow in your attic. Furthermore, the vents should be installed in a specific fashion. Sixty percent of your venting area should be in the lower vents, while the remaining 40 percent should be at the top of your roof.

OK, so you understand that. Well, how much ventilation is required? Simple. The number (or ventilation area) is directly related to the size of your attic. In other words it is a simple ratio.

The amount of ventilation required depends upon whether or not you choose to use continuous or flow through ventilation. It is possible to achieve attic ventilation without flow through or continuous methods, but it is not as effective.

Let's assume you decide to go with continuous ventilation (Smart move!) Just about every model code, the Home Ventilating Institute and the FHA state that the minimum amount of ventilation required is a ratio of 1:300 (net free area). Hold on, I'll explain both.

The ratio 1:300 can be explained readily. It means simply this: for every 300 square foot of attic floor (in reality this equals the ceiling area of all insulated ceilings in your house) you need 1 square foot (free net area) of ventilation space.

Net free area is also easy to explain. Just about every ventilation product, whether it is a metal pot vent, a gable end vent or a continuous ventilation product has some type of screening or barrier which prevents insects from entering these 'holes' in your house. Well, you might not believe this, but the screening restricts or slows the movement of air through the ventilation product. So the manufacturers calculate the real air flow that goes through the hole. It will always be less than the size of the hole when using a non-powered ventilation product.

For example, most common metal pot vents that you see on roofs have a net free ventilating area of only 50 square inches. On the other hand, most continuous ridge ventilation products have a net free ventilation area of 18 square inches per lineal foot of vent.

For the formula of how to calculate ventilation area of a house, click here. This explanation illustrates how to determine the ventilation area needed for a typical ranch house.

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Calculating Ventilation Area of Attic

Posted on by Tim Carter

Calculating Ventilation Area

OK, to determine how much ventilation area you need for your house, all you need to know is the square foot area of the attic to be ventilated. Let's use the following simple ranch house for an example.

The house measures 30 feet by 50 feet. There is a 22 foot by 26 foot attached non-heated garage. In reality, the garage doesn't figure into the calculations. That doesn't mean you shouldn't ventilate it, it just means that I will not include it in my calculations:

30 feet X 50 feet = 1,500 square feet

OK so now we know the square footage of the attic area to be ventilated. Now, let's figure out how much ventilation space we need. Remember, the minimum area requirement when using a continuous system is a ratio of 1:300. So, in our example, we will divide the 1,500 square feet by 300.

1,500 square feet / 300 = 5 square feet

See how simple that was! We know we need 5 square feet total of ventilation area. Based upon just about everyone's recommendations, 60 percent (or 3 square feet) of this should be in the soffit area and the remaining 40 percent (2 square feet) should be located at the ridge of the roof. Let's see how a standard ridge vent product will calculate out.

Standard ridge vent produces 18 square inches of ventilating area per lineal foot. Our roof is 50 feet long, so using a standard product we will get 900 square inches of ventilating space. Nine hundred square inches equals 6.25 square feet. So the ridge ventilation has exceeded the minimum requirement. That's great! But what happens if we choose to use those individual metal pot vents instead? The calculations before indicated that we needed 2 square feet of ridge or upper roof ventilation. Two square feet equals 288 square inches. A normal metal pot vent produces only 50 squares inches of free net area. So, we would need at least six metal vents in addition to the lower soffit ventilation to meet minimum ventilation requirements.

If you choose not to use continuous ventilation, guess what? The required ventilation area doubles! This means that you would not have any soffit ventilation. It then means that you would need a total of 10 square feet of ventilating area. How many metal pot vents you may ask? Believe it or not, you would need 29 of those individual metal pot vents to meet minimum requirements. Have you ever seen that many on a roof before? I know I haven't!

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Continuous Ventilation Products and Information

Posted on by Tim Carter

Manufacturers of Continuous Ventilation Products

The following list indicates companies that make and/or sell continuous ventilation products. Many of the ridge vent products are ones that hide beneath the cap shingles of your roof. In other words, you don't really see them from the ground. Quite a few of these perform well in all situations (heat, blowing rain, & blowing snow). Some of these manufacturers make a hidden soffit or eave vent (Mid-America Building Products Corp.) These might appeal to you if you either have no soffits or have soffits and do not prefer to look at the continuous metal strips. Mid-America makes perhaps the best designed hip ventilation product. It is the one I am using on my own home.

When I built my home, there was not a great hip-roof ventilation product. I happen to have a cathedral ceiling in my Sun Room and to complicate matters it is a hip roof. This means each roof-joist cavity needs to breathe, because the roof sheathing and the finished ceiling material make a closed system.

If you have a similar situation, you need a great hip-roof continuous ventilation strip. Mine is well hidden under the cap shingles that run up the hip..

In any event, check out all of these manufacturers and read their product literature. I am convinced that you will be impressed.

Good luck! Call me with questions.

  • Air Vent
    ridge vents and soffit vents

  • Alcoa Homes
    ridge vents and soffit vents
  • Benjamin Obdyke
    ridge vents and soffit vents

  • Builders Edge 

  • Butler Ventamatic Corp.
    ridge vents and soffit vents
  • Cobra Ventilation Products - GAF Materials Corp.
    ridge vents and soffit vents

  • Cor-A-Vent
    ridge vents and soffit vents

  • Mid-America Building Products

Ventilation Association

If you would like some really great information concerning attic ventilation and any other ventilation (bath, kitchen, whole house fans, etc.) consider contacting the following organization. They have a wealth of information that they will share with you.

  • Home Ventilating Institute

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Attic Ventilation Alternatives

Posted on by Tim Carter

Continuous ventilation products are all static devices. This means that they are powered by Mother Nature. They are either wind driven or simple heat convection which pulls the air from your attic. You can also remove air from your attic mechanically, that is, by fans.

But be careful about putting too much faith in many continuous ridge ventilation products. The way they are designed is that hot air must flow down the ventilator to exit under the cap shingles. I don't know about you, but hot air rise, it doesn't want to naturally flow down.

There are powered roof ventilators, whole house fans and solar powered roof ventilators. The requirements for these are quite different than the continuous ventilation products.

In fact, some powered ventilators can pull air-conditioned air from the inside of your house into the hot attic. This is a bad thing. If you decide to install powered attic ventilators, you must have superb soffit ventilation so cooler air flows into the attic space from the outside of your home, not the inside.

The Home Ventilating Institute has a great booklet available for free download that gives an overview of the entire subject. It is called the HVI Ventilation Guide. Keep in mind that the powered attic ventilators can actually suck air conditioned air from your house into your attic if they do not have adequate soffit intake vents. If this happens, then they actually can cost you lots of money to operate by making your air conditioner work harder and longer!

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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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