Home Inspection FYI

Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

Home Inspection FYI - Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

Tag Archives: building envelope

Blower Door Testing

Blower Door Test and Energy Audits

What is a Blower Door?

blower door2 Blower Door Testing

A blower door is a powerful, variable-speed fan that can be temporarily mounted into an exterior door frame to provide controlled air flow for analysis.  The way that air flows through a building can have a serious impact on air quality, comfort and energy expenses.  The use of a blower door allows air flow through a structure, and the resulting loss of heat can be immediately quantified, providing a way to pinpoint the location of air leaks.

The blower door was originally developed in the 1970s for use as a research tool.  As technology has evolved, allowing for the development of more portable equipment, the blower door has transitioned into use as a valuable field tool, as well.  The first portable blower door weighed as much as 200 pounds and took up quite a bit of space, and were also very expensive.  Today, a blower door is much more affordable and are built lighter and smaller.  The reduced set-up time allowed by their more compact designs has led to the standard use of a blower door as part of energy audits for measuring air flow.

How a Blower Door Works

When air pressure and air flow are controlled and measured, they can provide data about how airtight a building is.  The three variables involved are pressure, flow and holes or leaks.  A change in one of these factors will produce a change in at least one other factor.  Since the goal of a blower door test is to locate air leaks in the building envelope, data regarding air pressure and flow can provide information about the holes, which may otherwise be tough to find.Door Blower Blower Door Testing

The blower door utilizes controlled differences in air pressure to collect data.  Once the blower door is installed in an exterior door frame, the air pressure inside a building can be changed in relation to the outside pressure by forcing air into or out of the interior.  The difference in pressure forces air through holes or leaks in the building envelope.  The pressure and air flow are measured by gauges, which are part of the blower door equipment.  By measuring the pressure and air flow in relation to each other, the air-tightness of the building envelope can be quantified.  The amount of air flow needed to create a change in pressure increases as the air-tightness of the building envelope decreases.  A well-sealed building requires less air flow to generate a change in pressure.

Finding Problems With a Blower Door

During a blower door test, the interior air pressure needed to be maintained in order to gather useful data is 50 pascals, which is roughly equal to the pressure created when a 20-mph wind hits the building.  The blower door equipment has a gauge to indicate when this pressure has been achieved, as well as a gauge to indicate the cubic feet per minute (CFM), which is the standard unit of measure for air flow.  Air flow in a well-sealed building will generally be less than 1,500 CFM at 50 pascals.  Air flow above 4,000 CFM would be considered leaky.  This is valuable data that can be acquired in about half an hour with the use of a blower door.

Since the blower door forces air through cracks and holes, the locations of the leaky spots can be identified.  The draft of air entering through the holes can often be felt with the hand.  Smoke and infrared imaging can also be employed to locate smaller, more subtle leaks.  It is often assumed, especially by homeowners, that poorly sealed windows and doors are the major culprits of air leaks.  In reality, leaks in other areas are usually much more significant.  The difference in air pressure between the interior and the exterior is greater both at ground level and up high, so leaks in basements and crawlspaces, as well as in attics, are the most important to locate.

When looking for air leaks, check through basement rim joists, holes for plumbing traps under tubs and showers, cracks between finish flooring and baseboards, utility chases, plumbing vent-pipe penetrations, kitchen soffits, fireplace surrounds, recessed can lights, and cracks between partition top plates and drywall.  These are all common places where significant leaks can develop.

FYI; Accounting for Outside Factors

Wind and temperature can have an effect on the blower door test data.  Wind blowing on the outsipressure gauges Blower Door Testing de of the building can add to pressure differences between the interior and exterior.  It can also affect the flow rate of the blower fan.  It is best not to conduct blower door tests in windy conditions.  But if wind is not severe, blower door tests can be conducted at multiple points in the building and then averaged together.

Differences in temperature can create differences in pressure.  Accounting for a baseline stack-effect pressure will ensure that the test results are not skewed.  The stack-effect pressure is a function of the height of the building and the difference in temperature from the interior to the exterior.  A 15-foot tall building with a 50º-temperature difference between the inside and outside will have a 5-pascal pressure difference from the top of the building to the bottom.  Some blower door equipment has a gauge with a built-in baseline feature, so this difference can be easily determined at the outset of the test.

Temperature and barometric pressure affect both air density and viscosity, which is its resistance to flow.  Because of this, an adjustment for density is required.  Some software packaged with blower door equipment is designed to make these calculations, and if it is not available during the test, the manual supplied with the equipment should have information about making the necessary adjustments and applying it to the results.

Blower Door Preparation and Safety

In order to ensure accurate results, as well as safe conditions for performing the blower door test, some preparation is necessary before beginning.  Any fireplaces or stoves used for heating should not be operating, and all furnaces and pilot lights should be turned off.  There should be no open flames anywhere indoors.  Ashes in fireplaces or stoves should be removed so they do not get sucked into the building.  Dampers should be closed.  Every door and window must be closed tightly so that air flowing through them does not affect the test, while all interior doors should be left open.

If there is a basement, it must be determined whether this area is to be considered part of the building envelope for testing purposes.  Generally, if there is heat in the basement, even if only because the furnace is located there, it will be considered part of the envelope, and access to it should be left open during the test.  Sometimes, the test may be done both ways — with the basement access open and with it closed, and this is quick and simple to accomplish.

Since blower door testing is a standard tool used during an energy audit, it is helpful for inspectors to understand how the test works.  Knowing a bit about the outside factors that can influence the results will ensure that the test is performed correctly.  Setting up the equipment properly will ensure that testers and occupants are safe, and that the testing and results are accurate.

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Blower Door Test and Energy Audits

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U-Factor Window Rating

U-Factor Ratings for Windows

 u factor windows U Factor Window Rating
When quantifying the energy efficiency of a window assembly, the rate of loss of non-solar heat can be expressed as its U-factor (or U-value).  Understanding the U-factors of windows is helpful for inspectors performing energy audits, as well as for consumers planning a new build or updating a house with energy-efficient windows.

U-Factor or R-Value?

While windows are rated using both U-factors and R-values, the U-factor is used to express the insulative value specifically of windows, while the R-value is used primarily to rate the energy efficiency of insulation installed in other areas of the building envelope, such as beneath the roof, in the attic, behind the walls, and beneath the floors.  In order to translate a window’s U-factor into its R-value, divide 1 by the U-factor.  For example, a window with a U-factor of 0.25 is calculated as 1 ÷ 0.25 = 4, so the same window has an R-value of 4.

What is the U-Factor?

The U-factor rating system was devised by the National Fenestration Ratingnfrclabel U Factor Window Rating Council (NFRC).  The NFRC is a non-profit group that administers a uniform, independent rating and labeling system for the energy efficiency of building components, including windows, doors, skylights and attachment products.  The U.S. Department of Energy and the Environmental Protection Agency’s Energy Star Program take the U-factor into account when evaluating the energy efficiency of windows for product certifications, and federal incentive and rebate programs.
Windows that have the best resistance to heat flow and, thus, the best insulating qualities, have a low U-factor.  Less efficient windows with poor insulating ability have a high U-factor.  The combination of a window’s U-factor, air leakage, sunlight transmittance, and solar heat-gain coefficient add up to determine its level of energy efficiency.

The temperature difference between the interior and exterior of a building creates the non-solar heat flow that results in windows losing heat to the outside during the winter, and gaining heat from outside during the summer.  Compensating for this by cranking the thermostat or turning up the AC results in added energy needs and higher bills.  Greater energy efficiency calls for a closer examination of the individual building components to see how they can work individually and in relation to each other in more effective ways.  U-factor ratings can help in formulating standardized comparisons and objective evaluations.

Determining the U-Factor

The U-factor generally refers to the energy efficiency of the complete window assembly, which includes the glazing, window frame and spacer.  The spacer is the component of a window frame that separates the glazing panels, and often reduces the U-factor at the glazing edges.  The performance rating of the glazing alone, independent of the frame, is known as the center-of-glass U-factor, but use of this rating is less common.  For most energy-efficient windows, the U-factor for the entire window assembly is higher than the U-factor at the center of the glass.

The best, high-performance, double-pane windows may have a U-factor of 0.30 or lower, indicating that they are very energy-efficient.  Some triple-pane windows may have a U-factor as low as 0.15.  Manufacturers have started to incorporate low-emittance coatings and gas fills between panes in attempts to further decrease U-factors and provide an even more energy-efficient product.

U-Factors in Different Climates

While beneficial in cooling-dominated climates, a low U-factor is most important for windows in heating-dominated climates.  The following are recommendations for the most effective window U-factors based on the major climate zones in the United States.

  • In colder climates in the North that are heating-dominated, the U-factor should be less than or equal to 0.30 for windows, and less than or equal to 0.55 for skylights.  In areas where air-conditioning needs are minimal, windows that allow for solar heat gain during the day (a solar heat-gain coefficient of 0.40 or higher) can be considered energy-efficient with a U-factor as high as 0.32.  Low U-factor windows are most important and will be most effective in this colder climate area where minimizing heat loss is critical to energy efficiency.  winter U Factor Window Rating
  • In mixed climates in the North and Midwest regions that use both heating and cooling, the U-factor should be less than or equal to 0.32 for windows, and less than or equal to 0.55 for skylights.  Heating bills can help determine the importance of U-factors in this climate.  Higher bills indicate the importance windows with a lower U-factor for added energy efficiency.
  • In mixed climates in the South and central regions that use both heating and cooling, the U-factor should be less than or equal to 0.35 for windows, and less than or equal to 0.57 for skylights.  In these climates, again, heating costs can determine if a lower U-factor could be beneficial and more energy-efficient.  If costs are high and a list of factors for heat loss is being addressed, window U-factor can be taken into consideration.  A low U-factor for windows can also be helpful during hotter seasons when it is important to keep heat out, though a low solar heat-gain coefficient is more important in such situations.
  • In hot climates in the South that are cooling-dominated, the U-factor can be less than or equal to 0.60 for windows, and less than or equal to 0.70 for skylights.  A lower U-factor is still useful during any cold times of the year when heating is needed in this climate.  Such low ratings can ensure that heat is kept out on hot days when combined with a low solar heat-gain coefficient, which is the most important consideration in this climate.

Understanding the function and rating criteria for U-factors is a helpful tool for inspectors who perform energy audits.  They can then pass this information along to their clients who may have questions about their windows and their home’s overall energy efficiency.

U-Factor Rating Information

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What Is Housewrap

Housewrap Information and Uses


Housewrap is sheathing installed on exterior walls before the siding or other cladding is attached.  The term refers to all materials (made today, typically, from plastic or spun-fiber polyethylene) designed to replace tar paper, which serves the same function.  Since almost any exterior finishing material will allow at least some water to penetrate it, housewrap is used underneath to guard the building envelope against water entry. housewrap What Is Housewrap

Housewrap also serves to minimize air flow through walls, though it is not a vapor retarder.  In fact, housewrap is designed to stop liquid water while allowing water vapor to pass through.  This lets moist or humid air escape from the interior and simultaneously keeps water outside.

Homeowners may want to be familiar with the function of housewrap, especially when considering a new build, and InterNACHI inspectors can benefit from knowing more about what issues are commonly found with housewrap during an inspection.

Types of Housewrap

Tyvek® is the most common housewrap material used in the U.S.  Tyvek® is a synthetic material manufactured by DuPont.  It’s made of flash-spun, high-density polyethylene fibers.  Tyvek® is highly durable and allows water vapor to pass through it while blocking the passage of liquid.  It simultaneously resists air infiltration better than many other materials.

Other types of housewrap are made from micro-perforated, cross-lapped films, films laminated to spun-bond, non-woven materials, and films laminated or coated to polypropylene woven materials.  Asphalt-impregnated paper (tar paper or building paper) predating synthetic materials is still in use as housewrap today.

Advantages of Housewrap

  • While housewrap is used in many areas, it is most beneficial in humid climates.  This is because in areas that often experience heavy rainfall, there is a greater chance of water penetration damaging the framing of the house.  Housewrap prevents damage from water penetration.
  • Generally higher levels of moisture content in the air are also common to wet climates.  Housewrap allows moisture to escape from interiors, helping to ensure that wet conditions will not create problems such as mold growth.
  • Since housewrap helps prevent air movement through wall cavities, it also has some insulating value.

Disadvantages of Housewrap

  • Proper installation is the most important concern with housewrap.  If not installed correctly, not only will the housewrap perform less effectively, it may actually do more damage than good.  A common mistake installers make is treating housewrap as if it were a vapor retarder, and installing it accordingly, often with improper lapping.  However, because housewrap will actually collect and channel water, serious damage can occur over time if it is not installed in a manner that allows for channeled water to exit the wall system.
  • Another issue can occur if housewrap is left exposed to the elements for a long period before siding or other exterior cladding is installed over it.  This can lead to damage from wind and debris that goes unnoticed once the cladding is applied and the wrap is hidden.
  • Housewrap can sometimes be damaged by rough handling during installation.
  • Any holes or tears in the housewrap that have occurred during installation or from exposure to the elements may allow water to penetrate the wrap if they go unnoticed, negating the benefits housewrap is intended to provide.

Housewrap Tips

Here are some tips for checking that housewrap has been installed correctly:

  • Installers should follow the manufacturer’s instructions.  When installed properly, housewrap will not allow water to flow into the area behind it.  house wrap cut What Is Housewrap
  • Housewrap should be installed before windows and doors are installed.
  • Upper layers should be lapped over lower layers.
  • Horizontal joints should be lapped at least 6 inches, and vertical joints should be lapped 6 to 12 inches, depending on the potential for wind-driven rain.
  • Staples or roofing nails a minimum of 1 inch long should be used and spaced 12 to 18 inches on-center throughout.
  • Proper joints should be covered with tape designed specifically for use with housewrap.
  • A drainage provision should be installed at the bottom of the external cladding material.
  • The sill plate and foundation joint should be covered by the housewrap.

Housewrap is a useful building material that helps protect a home from damage related to water intrusion and moisture buildup.  The main concern with housewrap is proper installation.  Inspectors may want to be aware of the areas where common installation problems can be found, and knowing more about housewrap will be helpful when answering clients’ questions.

 

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