Table of contribution to air leakage from different building components (C) Solar Age Steve Bliss - Daniel FriedmanAir Sealing Strategies for buildings
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How to find & fix building air leaks to stop unwanted heat loss or heat gain:

This article discusses air sealing strategies for building retrofit to save energy costs and stop air leaks & forms the home page for our series of articles on how to find and stop both air leaks & un-wanted heat loss or heat gain in buildings.

The sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Guide to Strategies for Sealing Building Air Leaks

Window air leak seal procedure © Daniel FriedmanThe question-and-answer article about strategies for sealing air infiltration leaks on buildings (or air exfiltration leaks, i.e. heat loss), is provided in full-text below, and discusses steps to take to be sure that the energy retrofit cure is not worse than the disease, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Here we discuss: Estimates of before and after building air leaks and air changes per hour for older homes. Estimates of cost savings from sealing air leaks. Other indoor air quality problems that may occur when air leaks are sealed. Table shows relative importance of various building air leaks

Air Sealing the Building Shell to Save on Energy

In most cases, the most cost-effective energy-savings retrofit - after installing a low-flow showerhead (very inexpensive) - is to air-seal the building shell. If you are planning to add insulation to uninsulated wall and ceiling cavities, then air sealing is essential to reduce the risks of moisture damage and to be sure that air leaks do not overwhelm the benefit of the new building insulation.

A sophisticated survey of a building to find its main heat-loss points can be done most-effectively in cold weather using techniques such as those we discuss at THERMOGRAPHY IR Infra Red & Thermal Scanners.

But a direct physical examination of even one window in an older home can point out original construction details such as un-sealed or un-insulated space around these openings. If you find this condition at one window opening it may make sense to start a project of sealing these leaks at all building openings even before a winter-time thermal scan of the building.

Our photos (left, D Friedman) demonstrate a common point of air leakage around windows on a New York home constructed in the 1960's. Taking advantage of a project to install new interior window trim, we found, insulated, and sealed these 1/4" to 1/2" air gaps around the building's windows and doors.


To ensure success with energy retrofits to reduce heating or cooling costs for a building, you have to consider the whole building as a system and you need to coordinate different aspects of your work. Otherwise you may not get the energy savings and other benefits that you expect. In the worst cases, you can worsen existing heating or cooling cost problems, or create new ones.

For example, if you add insulation to a house with a wet basement [see WATER ENTRY in BUILDINGS] and fail to seal off airflow paths from the basement to the attic, you are likely to find a frosted attic ceiling, and even wet ceiling or attic insulation, or worse, a costly mold contamination problem.

At ROOF ICE DAM LEAKS we describe heat loss and ice dam formation at the opposite end of the building, it's attic or roof.

At the outset, then, you should assess the building's energy efficiency problem ascribed to air leakage and then plan a strategy.

This will vary depending on the building type, site conditions, and the idiosyncrasies of the particular building. You will need to determine the major paths of air leakage and the major paths of moisture transport in the building. At the same time, you need to identify any problems that air sealing might cause or exacerbate. Based on this analysis you can plan a reasonable course of action.

Find the Air Leaks in the Building

Window gap seal project (C) D FriedmanThere are two main types of air leaks in buildings - direct leaks through the exterior walls or ceiling to the outdoors, and indirect air leaks through interior partition walls, ceilings, or stairwells and plumbing chases.

Sometimes there are surprising air leaks into a building's air duct system as well. In many cases the indirect air leak paths account for more leakage (and energy loss) than is evident, particularly in older, balloon-framed homes.

See FRAMING METHODS AGE for an explanation of balloon framing

A trained eye can pick out many of the obvious air leaks - around heating baseboards, door casings, doors and windows, attic access hatch or stairway, and at electrical receptacles. Less obvious are air leaks around bathtubs, built-in cabinets, kitchen soffits, medicine cabinets, and interior stairwells. Depending on their location, these may leak either directly or indirectly to the outdoors.

Where possible, indirect leaks are best dealt with at the source, which may be accessible in the basement, crawl space, or attic. Plumbing and chimney chases, open-topped partition walls, and stairwells are often the main culprits. These should be sealed off in both the basement and attic where possible.

Other building air leaks are not so obvious and require a thorough understanding of the structure of the building. Many of these leaks are unaffected by the presence of a polyethylene air/vapor barrier unless the barrier itself was meticulously sealed at corners, intersecting walls, and wire and plumbing penetrations. Otherwise, breaks in the poly line up nicely with breaks in other building components to encourage aggressive air flow where you might not expect nor want it.

Listen to the building occupants' observations regarding drafts and cold spots. They can clue you in to which retrofit measures will most affect their comfort, though these are not necessarily the ones that will most affect heating or cooling costs for the building.

To track down the more tricky air and heat leaks and to evaluate the real effect of your efforts, expensive monitoring equipment - fan door (blower door) and infrared scanners (thermography) are available.

In lieu of a blower door test, an attic fan can be used to pinpoint leaks with a smoke gun, a cigarette, or even talcum powder. Even with top equipment, though, judgment and experience are needed for success in stopping air leaks and reducing building energy costs.


see HEAT LOSS DETECTION TOOLS for more sophisticated and accurate methods of detecting points of un-wanted building heat loss or heat gain.

At THERMAL TRACKING & HEAT LOSSwe describe other visual clues that can help spot points of significant air (and heat) leakage in buildings.

At ENERGY SAVINGS RETROFIT CASE STUDY we include the air sealing results for an older, costly-to-heat home for which simply adding insulation didn't do the trick.

Articles With Details on Fixing Building Moisture Problems

At the same time, the contractor should be keeping a lookout for evidence of existing or potential building moisture problems. Telltale signals are peeling paint on the building exterior:


and in extreme cases, mold - see MOLD in BUILDINGS

or building rot - see ROT, TIMBER FRAME.

First you must find the source of the moisture. Often you have to look no further than the basement.

If surface water is leaking in, often rerouting a downspout or a little judicious grading around the foundation can do wonders to stop basement water entry and even to cure high basement moisture levels when you don't actually see water on the basement floor.


Also prevent water from entering in the vapor state. If there is an earth floor in the basement or crawl space, cover it with heavy poly. If you have a porous foundation wall (unprotected concrete block or stone), patch it, then paint (using a moisture barrier paint such as ThoroSeal™) or poly it.

If free water seeps through the foundation wall it's best to find and fix the outside water source; temporarily, if you can't stop the basement water entry, isolate it from the building interior air and conduct the water away.



If you're dealing with a wet or damp crawl space, see CRAWL SPACE DRYOUT - home.

Next you want to keep the basement moisture from rising into the building wall cavities and into the attic or under-roof space. For the most part, the same measures taken to control indirect air leakage will control moisture transport into the roof cavity of a building. Pay attention to chimney and pipe chases and cavities that extend from basement or crawl space into the building attic.

One caution: if you are unable to keep the building sill area relatively dry, be careful about enclosing it since the free air circulation is probably what has prevented serious insect or rot damage to that part of the building structure.

Inside the building, the stack effect will be carrying moist, household air up towards the attic through any available openings in the ceilings such as at the attic entry hatch, ceiling light fixtures, and plumbing penetrations. Pay special attention to sealing these. A fire-retardant foam is a great material to use for smaller openings around pipes or electrical wiring.

Other Building Problems Related To Air Leaks, Air Circulation and Moisture

Reducing the rate of air circulation in a building will increase the level of indoor humidity and indoor pollutants. Since most leaky homes in cold climates are too dry in winter, the extra moisture might be welcome and might eliminate or at least reduce the need for mechanical humidification.



Other airborne pollutants, however, will also increase in concentration. The ones that have received the most attention up through the 1980's and before the public became quite concerned about indoor mold and allergens, were formaldehyde [FORMALDEYDE HAZARDS], radon [RADON HAZARD TESTS & MITIGATION], and combustion gases.

If you have reason to believe that these or other pollutants may be trouble, exercise caution.

Pay attention to potential problems such as an attached garage, basement workshop, or photographic darkroom, and attend to un-vented kerosene heaters and gas ranges. Isolate these and ventilate these spaces if necessary.


Beyond some threshold, combustion and draft air for atmospheric heating equipment can become a problem in tight homes. The interactions with other ventilation and exhaust systems becomes complex and critical. Other than switching to an induced-air or direct vented unit, there is no foolproof solution to these problems.

In some cases it is feasible to supply air to an enclosure built around the boiler or furnace.


Predicting the Savings from House Air Leak Corrections

A house, or any building, is a complex system with many interactive effects. Altering one function or component generally affects others. Predicting the full effects of your energy-savings intervention in a building with certainty is no more possible than predicting the weather. In fact, many of the same forces come into play.

In the weatherization and energy retrofit business, it pays to be cautious and, if warranted, advise the building occupants of signs of heating system, indoor moisture, or air quality problems. In most cases, problems will not occur. Old houses have a lot of forgiving qualities (including leakiness) and such buildings are rarely tightened or sealed to a hazardous level. Most often, the indoor environment will be more comfortable and healthier than before the energy-savings retrofit.

Typical Air Change Rates in Homes, Typical Energy Cost Savings from Sealing Air Leaks

In a 1979 study by Richard Grot and Roy Clark of 250 low-income households, the mean natural air infiltration rate was 0.86 air changes per hour (ACH), as measured by tracer-gas decay. In all, 40 percent fell in the 0.5 to 1 ACH range. Assuming that typical building air leak sealing work cuts the air leak rate by 30-perdcent (we're told that this is a fair estimate), this would result in a winter heating cost savings of about 8 MMBTU for a 1500 square foot house in a 6000 degree day climate.

When oil heat was $1.25 a gallon (1980's prices), this represented an annual savings of about $115. With a home using electric heat at 10 cents/KWH, the annual heating cost savings increased to ab out $240.

Building comfort is increased at the same time, due to fewer drafts and higher indoor humidity. And rather than creating moisture problems, a well-planned energy savings retrofit air sealing project can cure what had been a chronic moisture problem.

Finally, by blocking the routes of cold-air flow through the building, the savings from retrofit air sealing may exceed that predicted solely by reductions in air infiltration. That is due to the reduction of convective airflow through building cavities that robs the building of heat and robs fibrous insulations of their insulating value.

Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Original article


Continue reading at AIR BYPASS LEAKS & THERMAL TRACKING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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