WHAT THE WEATHERIZATION EXPERTS SAY
Weatherization experts agree - it is vitally important to reduce air leakage into your attic. Air leakage takes heat and moisture with it - wasting energy and leading to potentially serious moisture problems.
"An airtight building assembly is a prerequisite for energy savings, pressure control and ventilation effectiveness. Improved airtightness can be achieved through the use of the Battic(c) Door Attic Stair Cover, The Fireplace Draftstopper, and the Dryer Vent Seal."
Energy Codes in force across North America require that attic access openings be caulked, gasketed, weatherstripped, or otherwise sealed to limit infiltration and exfiltration. This is because air leakage through cracks can result in higher energy use for home heating and cooling than necessary.
Below are quotes from numerous published articles, documents, fact sheets, and websites - the full text of which can be downloaded from our WEATHERIZATION LINKS page:
From U.S. Dep't. of Energy (DOE) Office of Building Technology - Fact Sheet - ATTIC ACCESS
"DON’T LEAVE A HOLE IN THE CEILING - A home’s attic access, such as an attic hatch, pull-down stairs, or knee-wall door, often goes uninsulated, representing one of the biggest deficiencies in the thermal barrier between the attic and conditioned space. This gap in the attic insulation increases heat loss in winter and heat gain in summer, and makes indoor living areas uncomfortable. Such accesses are often not sealed properly. A ¼-inch gap around the perimeter of an attic access can potentially leak the same amount of air supplied by a typical bedroom heating duct (~100 CFM). Unsealed, the attic access in a home leaks energy dollars and causes the house to be less comfortable."
"An attic access is a big hole."
"ATTIC STAIRS - Pull-down stairs are another common type of attic access. The frame for the stairs fits in a rough opening and leaves a gap, much like that for a door or window, which must be sealed."
"To insulate attic stairs access, a lightweight, moveable box can be constructed to fit over the stairs from the attic side. Insulating kits are also available through weatherization suppliers or from local hardware stores."
From MN Dep't of Commerce Energy Info Center - ATTIC BYPASSES
"Attic bypasses are hidden air passageways that lead from the heated space into the attic. Because warm air rises, it is continuously moving up these passageways and escaping into the attic during cold weather. So even though the attic should be cold, attic bypasses make it a semiheated space, which is a waste of energy. These bypass leaks can cut the effectiveness of attic insulation by 30 to 70 percent."
"Fiberglass and cellulose insulation do not stop air from moving into the attic. They only filter and slow the air on its way out. If you have many of these air leaks into your attic, adding insulation is not going to help much. Also, water vapor carried with the escaping warm air may condense, freeze and build up in the insulation. And when this water builds up, it can soak the insulation (wet insulation has almost no insulating value), cause plaster and paint to crack and peel, and lead to rot and other structural damage."
"Ice build-up on the roof is another problem caused by attic bypasses. This build-up, called ice damming, happens when heat gets into the attic and melts the underside of the snow on the roof. The melted snow then flows down the roof, underneath the top layers of snow, until it reaches a cold spot such as the eaves, where it freezes, forming a dam, behind which more snowmelt and ice build up. The ice build-up can back up under the singles, damaging them, and allowing water to leak down to the ceilings and walls below."
"To avoid these types of water problems and to receive full benefit from your insulation, you need to plug up your attic bypasses."
From U.S. Dep't. of Energy (DOE) Office of Building Technology - Fact Sheet - AIR LEAKAGE
"WHAT IS AIR LEAKAGE? Air leakage, or infiltration, is outside air that enters a house uncontrollably through cracks and openings." "A leaky house that allows moldy, dusty crawlspace or attic air to enter is not healthy. The recommended strategy in both new and old homes is to reduce air leakage as much as possible."
"WHAT ARE THE BENEFITS OF AIR SEALING? Air infiltration can account for 30 percent or more of a home’s heating and cooling costs and contribute to problems with moisture, noise, dust, and the entry of pollutants, insects, and rodents. Reducing infiltration can significantly cut annual heating and cooling costs, improve building durability, and create a healthier indoor environment. The size of heating and cooling equipment can also be decreased, which saves additional dollars." "WHAT ARE THE PRIORITIES FOR AIR SEALING?Although windows, doors, and outside walls contribute to air leakage, the biggest holes are usually hidden from view and connect the house to the attic, crawlspace, or basement."
"WHERE ARE THESE LEAKAGE SITES? Dropped ceilings and kitchen soffits, ductwork and plumbing chases, attic accesses and pull-down stairs, recessed light fixtures, holes in mechanical room closets, and wiring penetrations through the top plates of walls represent major connections between the attic and conditioned space."
"AIR SEALING CHECKLIST: For attic pull-down stairs, make stairs airtight using latch bolts and weatherstripping. Add an insulated cover."
From ZERODRAFT Professional Weatherization Materials and Canam Building Envelope Specialists Inc.: Homeowners – Thinking about a new roof?
"Have you got a wet attic? More and more homeowners are discovering mould, rotten wood, ice damming, buckled shingles and premature roof failures. Sometimes these problems lead to interior damage. These problems happen because of uncontrolled air leakage.
Here's how air leakage causes such serious problems: Warm air in the house rises through leaks in the ceiling and walls and enters the attic. As the warm damp air gets into the cooler attic during the winter, it condenses on the wooden beams. The wood expands. When the attic gets warm in spring and summer, the wood dries and contracts. This constant process can loosen nails and cause shingles to buckle.
- Ice damming leads to serious damage.
Melting snow on the roof refreezes at roof edges and forms ice dams. These cause further melting snow to back up under shingles and enter the attic where it leads to moisture damage to ceilings and walls. Melting is caused by warm air rising from the interior of the house and also within poorly insulated and/or poorly sealed ducts located in the attic.
- Mold is very unhealthy. It's associated with respiratory problems and allergies.
Mold is something you don't find out about until you're thinking about a new roof -- after all, how many people ever go up in their attic?
- Glass and mineral fiber insulation materials not only fail to solve these problems, they can actually make them worse.
Most contractors put in insulation plus ventilation with little thought to air leakage, moisture, condensation.
- If you want to sell your house and the prospective buyer asks for a home inspection, you could be in for a major bill.
What are the real causes and solutions?
The traditional belief is that roof ventilation is a cure-all. It isn't. It can make the problem worse. Here's why: Passive ventilation doesn't move much air through the attic. In winter, outside air has little ability to pick up moisture in an attic. CMHC research shows this. Active ventilation tends to draw more warm moist air into the attic. This air may not leave the attic at all; it often stays behind and condenses on the wood -- leading to mildew, mould and rot.
How do you prevent these problems?
Ensure that warmth and warm air containing moisture in the living space cannot get into the non-conditioned space in the attic. Keep the attic sealed off from the living area below (using air leakage control measures to seal holes, cracks, gaps). Not by adding insulation on its own."
From Minnesota Department of Commerce Energy Information Center - CAULKING & WEATHERSTRIPPING
"Air leakage can account for one third of the total heat loss in an average home. Add up the small cracks and holes in your home and you could have the equivalent of a two-squarefoot hole. This is like leaving a small window open all winter! Moisture also escapes with the warm air, and if it condenses inside the walls or in your attic, serious structural damage could result."
"Determine where the air is leaking from your home. Common sources of air leakage are... Poorly fitted attic access hatch."
"Attic access hatches should be weatherstripped with compressible tube or strip products. The hatch must also be insulated adequately."
"Attic hatches should be sealed to prevent air leakage."
From Minnesota Department of Commerce Energy Information Center - HOME MOISTURE
"Attic moisture problems. Attic bypasses are areas where warm air escapes into your attic: around light fixtures, up walls, etc. Bypasses can allow enormous amounts of warm, moist air to leak into the attic. Sealing them can save on winter heating expenses while preventing some moisture damage."
"Eliminating attic bypasses is the main strategy to avoid moisture problems in attics. Seal around all penetrations into the attic".
From Minnesota Department of Commerce Energy Information Center - ICE DAMS
"A major solution to ice dams is sealing attic bypasses . . . "
"Causes of Ice Dams - Although there are other causes, in most cases ice dams begin inside the house when heated air leaks up into the unheated attic. In the winter, the roof above the unheated attic is cold. When warm air leaks into the unheated attic, it creates warm areas on the roof which in turn cause the snow on the exterior of the roof to melt. The melting snow moves down the roof slope until it reaches the cold overhang, where it refreezes. The process continues, causing ice to build up along the eaves and form a dam. Eventually this dam forces the water to back up under the shingles and sometimes into the ceiling or wall inside the home. In addition to the roof and water damage described above, ice dams may cause structural framing members to decay, metal fasteners to corrode, and mold and mildew to form in attics and on wall surfaces.""The Solution — Sealing Attic Bypasses"
"The pathways through which heated indoor air moves into the attic are called attic bypasses. To reduce ice dams, attic bypasses must be eliminated. The following areas are common sources of attic bypasses that are required to be sealed by the Minnesota Energy Code...attic access hatches."
"Attic bypasses occur when no seal or insulation is placed over the folding attic stair."
From U.S. Dep't. of Energy (DOE) Energy Savers - INSULATION & WEATHERIZATION
"Warm air leaking into your home during the summer and out of your home during the winter can waste a substantial portion of your energy dollars. One of the quickest dollar-saving tasks you can do is caulk, seal, and weatherstrip all seams, cracks, and openings to the outside. You can save 10% or more on your energy bill by reducing the air leaks in your home."
From U.S. Dep't. of Energy (DOE) Office of Building Technology - SEALING AIR & MOISTURE LEAKS
"Air leaks between your home's interior and the outdoors can be a constant drain of energy and money. The air leakage in a typical U.S. home is equal to leaving a window wide open."
"Moisture control is also an important aspect of maintaining an energy-efficient home. If humid air leaks into cool spaces, moisture can condense on the cool surfaces and cause damage. In addition, moist insulation has a lower R-value than dry insulation, so moisture problems will lower your home's energy efficiency."
"One aspect of moisture control is to seal air leaks around electrical outlets, switches, and penetrations through the building envelope for plumbing, wiring, ventilating, heating and cooling, and attic access."
From U.S. Dep't. of Energy (DOE) Office of Building Technology - Fact Sheet - ENERGY EFFICIENCY PAYS
"REDUCED AIR LEAKAGE - Excess air leakage in homes can increase heating and cooling bills by 30 percent. Although windows, doors, and outside walls contribute to air leakage, the biggest holes are usually hidden from view and connect the house to the attic, crawl space, or basement. Reducing air leakage typically costs less than $200 for the average home and is required by the Model Energy Code."
From Georgia Environmental Facilities Authority (Southface Energy Institute) - Home Energy Projects, An Energy Conservation Guide For Do-It-Yourselfers
"Weatherstrip and insulate the attic access door - Install weatherstripping all around the attic access door to reduce infiltration. Attach a batt of insulation to the door. If the attic access is a fold-down stairway, build a lightweight, insulated box to go over the stairs. Such a box can be lowered easily over the stairs as they are closed. There are also commercial products designed to insulate over attic stairs."
From Southface Energy Institute - Energy Technical Bulletin 9 – ATTIC ACCESS
"Don’t leave a hole in the ceiling. Attic hatch - A home’s attic access, such as an attic hatch, pulldown stairs, or knee-wall door, often goes uninsulated and unsealed, creating one of the biggest holes in the thermal and air barrier between the attic and conditioned space. A ¼-inch gap around the perimeter of a standard pulldown staircase can potentially leak the same amount of air that is supplied by a typical bedroom heating duct (~100 CFM). Unsealed, the attic access in a home leaks energy dollars and causes the house to be less comfortable. During winter, conditioned room air may escape to the ventilated attic, while in the summer, hot attic air (which may contain airborne insulation fibers) can infiltrate into the home."
"An attic access is often a big hole in the thermal envelope of the house. Adding an insulated cover and weatherstripping to a pull-down stairs can reduce infiltration and heat loss through this passageway."
From Southface Energy Institute - Energy Technical Bulletin 12 – INSULATION BASICS
"The R-value assumes no air is leaking through the insulation. Air leakage lowers the R-value of insulation. It is important to seal air leaks as well as install insulation. Standard density materials such as fiberglass batts and loose-fill materials do not seal effectively against air leaks."
From Southface Energy Institute - Energy Technical Bulletin 18 – ENERGY EFFICIENT CONSTRUCTION
"Air leakage can account for over 50% of a home’s heating and cooling costs, and contribute to problems with moisture, noise, dust, and entry of pollutants, insects, and rodents."
"Insulation reduces heat flow through the building envelope. Gaps in insulation waste energy and can lead to condensation which can damage building materials and cause growth of molds, dust mites, and other biological contaminants."
"It is important to seal air leaks before insulating. Commonly used insulation materials, such as batt and loose-fill products, do not stop air leakage. As air leaks through these materials, it lowers the R-value."
From Southface Energy Institute - Energy Technical Bulletin 25 – ENERGY EFFICIENT CONSTRUCTION
“Seal all attic to home air leaks, especially chases, bypasses, and furr-downs. Remember, most insulation such as fiberglass and rock wool, does not stop air flow.”
“Insulate the attic hatch or attic stair by attaching a piece of batt insulation or installing an insulated cover box.“
The full text of the above quoted documents can be downloaded. Click below to go to the "Energy Conservation and Weatherization Links" page.