If you have ice dams forming on your roof during the winter, it means that heat is escaping the house and leaking into your attic. Ice dams are the manifestation of energy inefficiency in a home. They are the result of poor air sealing, a lack of insulation, and inadequate ventilation in an attic.
Warm air travels upward because of its natural buoyancy. As it reaches the ceiling in the top floor, it seeks ways to rise even higher through cracks and gaps in the ceiling and walls. Some of those pathways are obvious; many others are not. Openings around and through recessed canister lights, whole-house fan installations, attic-access hatchways and pull-down stairs, and electrical boxes in the ceiling and walls all provide conduits from the house into the attic. Additionally, heat is conducted upward through the top-floor ceiling through inadequate attic floor insulation. The result of the air leaks and conducted heat is an accumulation of warm air in the attic.
When snow falls on top of a roof, it acts as insulation, protecting the roof surface from the outside cold air. The combination of heat from below and snow on top creates conditions that warm the roof sheathing and shingles.
The warm shingles melt the snow that covers them, and that water runs down the roof, under the snowpack that lies on top of the roof. As the water reaches the roof edge, there is no longer any heat from below to warm the shingles and sustain the melting process. The water freezes along the overhangs and starts to build into ice dams.
As the ice dams build up higher over the course of the winter due to the constantly melting snow on the roof, water starts to form ponds behind the dams. Eventually, if the water level gets high enough and if the roof is inadequately protected from water intrusion, it starts to seep in underneath the shingles. In the worst cases the water can penetrate into the soffit areas, get behind the siding, and even enter the house through the interior ceilings and walls. Ice dams can be very destructive and result in millions of dollars in insurance claims every year.
The root cause of ice dams is excess heat in the attic. Air sealing and upgrading insulation will help reduce the heat leakage problem. The idea is to make the attic as cold as possible -- as cold as the outside air -- to reduce or eliminate the snow melting that starts the ice dam formation process. Additional ventilation in the attic also exhausts any heat that does manage to make it up there.
The ideal ventilation scheme involves several components: soffit vents that introduce air into the attic under the eave edges; air channels; chutes that hold insulation back from the underside of the roof sheathing and direct the air upward from the soffits into the attic; and high roof or ridge vents that convey the air to the outdoors. The chutes are important because insulation lying against the underside of the roof sheathing forms a thermal bridge that allows heat from the house below to travel through the insulation directly to the sheathing. It is essential to break that thermal bridge to eliminate the direct conveyance of the heat to the sheathing and to promote the free flow of air into the rest of the attic from the soffit vents.
Attic ventilation is also needed to reduce moisture concentration in the attic environment. Air that travels into the attic from the house below carries water vapor. Unless that moisture is vented away, it can condense on the cold insulation, framing, and sheathing. If allowed to continue, the wet surroundings can create conditions conducive to mildew and mold growth, and can even rot.
Adequate attic ventilation also pays off in the summer. Air flowing through the soffit vents and up through the ridge or high roof vents exhausts heat. Venting the attic means less heat is transferred downward through the attic floor insulation and into the house below. Therefore, the A/C doesn't have to run as often, which conserves your energy dollars.
Comprehensive air sealing, insulation, and ventilation can reduce or eliminate the formation of ice dams on your house roof in the winter while paying dividends in the summer.
Most every attic has at least some insulation in it, and that's fine. Insulation helps prohibit heat loss. It doesn't stop airflow, however, and that's a problem. The insulation lying on attic floors often conceals a very large problem -- cracks, gaps, and holes through which pressurized air from the house below is driven into the attic.
These fissures take many forms: holes drilled into the wood framing where wiring runs from a room below up into the attic; lighting fixtures and electrical boxes; areas where the tops of partition walls in the room below intersect with the attic-floor framing; bulkheads over kitchen and bathroom cabinets; exhaust vent fans; and fireplace and heating equipment chimneys and flues. It's a long list, and it's likely you can find fissures in your own attic that aren't even mentioned.
Every one of these holes represents an opportunity for warm air to escape the rooms below -- and that escaping air represents your energy dollars flying up and away as well. So, although digging through insulation in the attic to find and seal up these trouble spots is probably not anyone's idea of fun, it is time well spent.
The materials used for sealing most attic floor penetrations are caulk and spray foam. The application does not have to be neat; no one is going to come along and grade you on tidy performance. Once you foam or caulk, you'll just cover the area with insulation again. But it will behoove you to do a thorough job. Remember, any gap left unfilled will leak air.
Sealing Leaks
In an attic filled with unfaced fiberglass insulation, it's relatively easy to find spots where air is leaking upward from the rooms below. You'll often see gray, brown, or black smudges or staining in the insulation. Those discolored spots are dirt that was borne on the air leaking from below. Fiberglass insulation strains contaminants out of the air and leaves them there as telltale indicators of air leakage. Lift up the fiberglass batting at one of these spots, and you'll find an opening into the rooms below, maybe an electrical box or wire chase.
Attics insulated with cellulose fiber don't show air-leak smudges. The material is as dark as most airborne dirt, and it doesn't act as a filter. So you'll need to use your sleuthing skills to come up with places likely to contain room ceiling/attic floor penetrations. Examine rooms below before you enter the attic. Take note of where light fixtures and interior walls are located. You may even want to draw a map.
Once you locate a hole that needs to be filled, use a brush to sweep the insulation back, squirt caulk or spray foam to seal the hole or gap, replace the insulation, and move on to the next spot.
Be especially aware that many interior walls have wires running up into the attic. Foam around the wires to fill the holes in the framing. Electrical boxes should have the power switched off before you work around them. Caulking around the box where it penetrates the drywall or plaster and around the wires that run into the box will seal things as well as possible. Vent fan housings can be sealed in a similar manner.
Chimneys require a different approach. Building codes now mandate at least a two-inch gap between any flammable material (usually wood framing) and the masonry or metal. In newer homes this gap is sometimes left unfilled, leaving a hole that goes directly from the basement to the attic. A lot of warm air can rush up a hole that size. Older homes may not have as sizable a gap, but the solution for either is to close the hole with a nonflammable material and fireproof caulk. Sheet metal nailed to the framing and shoved against the chimney works well, and it can be sealed with the caulk to eliminate any of the remaining small gaps.
Securing Pull-Down Attic Stairways
A pull-down attic stairway probably represents the largest hole in the attic floor -- a hole through which a tremendous amount of air can flow in both winter and summer. Some energy experts estimate that the gap around a typical pull-down stairway system can amount to 40 square inches. You'd certainly notice if there was a hole that size in your ceiling, but many people don't connect a pull-down attic stairway with a loss of heat or cooling.
The undersides of many pull-down attic stair units is made of 1/4-inch plywood that warps away from its sealing surfaces shortly after installation. Springs that hold the stairway in place lose their resilience over time, allowing the unit to sag down from the opening and further open gaps between the plywood and the jamb. And even in the best of circumstances the entirety of the stair system is uninsulated. It's a worst-case scenario in terms of air sealing and energy efficiency.
Sealing a pull-down attic stairway is tough to do. The stairway, after all, still has to function as an entrance and exit. But adding compressible self-stick foam tape along the upper edges of the plywood door can help reduce air leakage. Adding eyehooks or another type of latching device to the door causes it to jam tight against the foam weather stripping when not in use.
A more comprehensive solution is to insulate the door as well as adding air-sealing capabilities. Several kits are available to solve this dilemma. One is called an "attic tent." It consists of a clothlike material that is caulked and stapled to the framing around the stairway opening. A zipper in the upper part of the tent can be opened for access and closed for air sealing after use. The stairway opens and closes normally underneath the tent fabric. An attic tent, however, provides only a small measure of insulative value compared to the insulation that should be on the rest of the attic floor.
Another kit version is a thick, insulated box that surrounds the stairway opening in the attic. It comes with a removable cover, which can be lifted off when access to the attic is desired, and sealing strips along the bottom of the box that contact either the framing around the stairway or the attic floor. Such a box could also be constructed by a homeowner using rigid foam board and other easily obtainable materials.
Warm air travels upward because of its natural buoyancy. As it reaches the ceiling in the top floor, it seeks ways to rise even higher through cracks and gaps in the ceiling and walls. Some of those pathways are obvious; many others are not. Openings around and through recessed canister lights, whole-house fan installations, attic-access hatchways and pull-down stairs, and electrical boxes in the ceiling and walls all provide conduits from the house into the attic. Additionally, heat is conducted upward through the top-floor ceiling through inadequate attic floor insulation. The result of the air leaks and conducted heat is an accumulation of warm air in the attic.
When snow falls on top of a roof, it acts as insulation, protecting the roof surface from the outside cold air. The combination of heat from below and snow on top creates conditions that warm the roof sheathing and shingles.
The warm shingles melt the snow that covers them, and that water runs down the roof, under the snowpack that lies on top of the roof. As the water reaches the roof edge, there is no longer any heat from below to warm the shingles and sustain the melting process. The water freezes along the overhangs and starts to build into ice dams.
As the ice dams build up higher over the course of the winter due to the constantly melting snow on the roof, water starts to form ponds behind the dams. Eventually, if the water level gets high enough and if the roof is inadequately protected from water intrusion, it starts to seep in underneath the shingles. In the worst cases the water can penetrate into the soffit areas, get behind the siding, and even enter the house through the interior ceilings and walls. Ice dams can be very destructive and result in millions of dollars in insurance claims every year.
The root cause of ice dams is excess heat in the attic. Air sealing and upgrading insulation will help reduce the heat leakage problem. The idea is to make the attic as cold as possible -- as cold as the outside air -- to reduce or eliminate the snow melting that starts the ice dam formation process. Additional ventilation in the attic also exhausts any heat that does manage to make it up there.
The ideal ventilation scheme involves several components: soffit vents that introduce air into the attic under the eave edges; air channels; chutes that hold insulation back from the underside of the roof sheathing and direct the air upward from the soffits into the attic; and high roof or ridge vents that convey the air to the outdoors. The chutes are important because insulation lying against the underside of the roof sheathing forms a thermal bridge that allows heat from the house below to travel through the insulation directly to the sheathing. It is essential to break that thermal bridge to eliminate the direct conveyance of the heat to the sheathing and to promote the free flow of air into the rest of the attic from the soffit vents.
Attic ventilation is also needed to reduce moisture concentration in the attic environment. Air that travels into the attic from the house below carries water vapor. Unless that moisture is vented away, it can condense on the cold insulation, framing, and sheathing. If allowed to continue, the wet surroundings can create conditions conducive to mildew and mold growth, and can even rot.
Adequate attic ventilation also pays off in the summer. Air flowing through the soffit vents and up through the ridge or high roof vents exhausts heat. Venting the attic means less heat is transferred downward through the attic floor insulation and into the house below. Therefore, the A/C doesn't have to run as often, which conserves your energy dollars.
Comprehensive air sealing, insulation, and ventilation can reduce or eliminate the formation of ice dams on your house roof in the winter while paying dividends in the summer.
Most every attic has at least some insulation in it, and that's fine. Insulation helps prohibit heat loss. It doesn't stop airflow, however, and that's a problem. The insulation lying on attic floors often conceals a very large problem -- cracks, gaps, and holes through which pressurized air from the house below is driven into the attic.
These fissures take many forms: holes drilled into the wood framing where wiring runs from a room below up into the attic; lighting fixtures and electrical boxes; areas where the tops of partition walls in the room below intersect with the attic-floor framing; bulkheads over kitchen and bathroom cabinets; exhaust vent fans; and fireplace and heating equipment chimneys and flues. It's a long list, and it's likely you can find fissures in your own attic that aren't even mentioned.
Every one of these holes represents an opportunity for warm air to escape the rooms below -- and that escaping air represents your energy dollars flying up and away as well. So, although digging through insulation in the attic to find and seal up these trouble spots is probably not anyone's idea of fun, it is time well spent.
The materials used for sealing most attic floor penetrations are caulk and spray foam. The application does not have to be neat; no one is going to come along and grade you on tidy performance. Once you foam or caulk, you'll just cover the area with insulation again. But it will behoove you to do a thorough job. Remember, any gap left unfilled will leak air.
Sealing Leaks
In an attic filled with unfaced fiberglass insulation, it's relatively easy to find spots where air is leaking upward from the rooms below. You'll often see gray, brown, or black smudges or staining in the insulation. Those discolored spots are dirt that was borne on the air leaking from below. Fiberglass insulation strains contaminants out of the air and leaves them there as telltale indicators of air leakage. Lift up the fiberglass batting at one of these spots, and you'll find an opening into the rooms below, maybe an electrical box or wire chase.
Attics insulated with cellulose fiber don't show air-leak smudges. The material is as dark as most airborne dirt, and it doesn't act as a filter. So you'll need to use your sleuthing skills to come up with places likely to contain room ceiling/attic floor penetrations. Examine rooms below before you enter the attic. Take note of where light fixtures and interior walls are located. You may even want to draw a map.
Once you locate a hole that needs to be filled, use a brush to sweep the insulation back, squirt caulk or spray foam to seal the hole or gap, replace the insulation, and move on to the next spot.
Be especially aware that many interior walls have wires running up into the attic. Foam around the wires to fill the holes in the framing. Electrical boxes should have the power switched off before you work around them. Caulking around the box where it penetrates the drywall or plaster and around the wires that run into the box will seal things as well as possible. Vent fan housings can be sealed in a similar manner.
Chimneys require a different approach. Building codes now mandate at least a two-inch gap between any flammable material (usually wood framing) and the masonry or metal. In newer homes this gap is sometimes left unfilled, leaving a hole that goes directly from the basement to the attic. A lot of warm air can rush up a hole that size. Older homes may not have as sizable a gap, but the solution for either is to close the hole with a nonflammable material and fireproof caulk. Sheet metal nailed to the framing and shoved against the chimney works well, and it can be sealed with the caulk to eliminate any of the remaining small gaps.
Securing Pull-Down Attic Stairways
A pull-down attic stairway probably represents the largest hole in the attic floor -- a hole through which a tremendous amount of air can flow in both winter and summer. Some energy experts estimate that the gap around a typical pull-down stairway system can amount to 40 square inches. You'd certainly notice if there was a hole that size in your ceiling, but many people don't connect a pull-down attic stairway with a loss of heat or cooling.
The undersides of many pull-down attic stair units is made of 1/4-inch plywood that warps away from its sealing surfaces shortly after installation. Springs that hold the stairway in place lose their resilience over time, allowing the unit to sag down from the opening and further open gaps between the plywood and the jamb. And even in the best of circumstances the entirety of the stair system is uninsulated. It's a worst-case scenario in terms of air sealing and energy efficiency.
Sealing a pull-down attic stairway is tough to do. The stairway, after all, still has to function as an entrance and exit. But adding compressible self-stick foam tape along the upper edges of the plywood door can help reduce air leakage. Adding eyehooks or another type of latching device to the door causes it to jam tight against the foam weather stripping when not in use.
A more comprehensive solution is to insulate the door as well as adding air-sealing capabilities. Several kits are available to solve this dilemma. One is called an "attic tent." It consists of a clothlike material that is caulked and stapled to the framing around the stairway opening. A zipper in the upper part of the tent can be opened for access and closed for air sealing after use. The stairway opens and closes normally underneath the tent fabric. An attic tent, however, provides only a small measure of insulative value compared to the insulation that should be on the rest of the attic floor.
Another kit version is a thick, insulated box that surrounds the stairway opening in the attic. It comes with a removable cover, which can be lifted off when access to the attic is desired, and sealing strips along the bottom of the box that contact either the framing around the stairway or the attic floor. Such a box could also be constructed by a homeowner using rigid foam board and other easily obtainable materials.
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