Weatherization

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Weatherization (American English) or weatherproofing (British English) is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce energy consumption and optimize energy efficiency. A house with no weatherization is virtually uninhabitable.

Weatherization is sometimes confused with, but is distinct from, insulation. However, insulation requires weatherization in order for the insulation to function at full effectiveness. Many types of insulation can be thought of as weatherization, because they block drafts or protect from cold winds. Weatherization works principally to slow one kind of heat flow. Whereas insulation primarily reduces conductive heat flow, weatherization primarily reduces convective heat flow.

Weatherization has become increasingly high-profile as the cost of home heating has risen. Fortunately, there are programs available to help low income families reduce energy consumption and costs.

The Weatherization Assistance Program (WAP) was created in 1976 to assist low-income families who lacked resources to invest in energy efficiency. WAP is operated in all 50 states and the District of Columbia, and works with Native American tribes. The funds provided by Congress are used to improve the energy efficiency of low-income dwellings using the most advanced technologies and testing protocols available in the housing industry. The energy conservation resulting from the efforts of state and local agencies helps our country reduce its dependency on foreign oil and decrease the cost of energy for families in need while improving the health and safety of their homes.

The WAP is governed by various federal regulations designed to help manage and account for the resources provided by DOE. WAP funding is derived from annual appropriations from Congress. Each year Senate and House Interior Appropriations committees decide how much will be allocated.

Many state LIHEAP (Low Income Home Energy Assistance) programs work side by side with WAP to provide both immediate and long term solutions to energy poverty.

Typical weatherization procedures include:

• Sealing bypasses (cracks, gaps, holes), especially around doors, windows, pipes that penetrate the attic ceiling, and other areas with high potential for heat loss, using caulk, foam sealant, weather-stripping, window film, door sweeps, electrical receptacle gaskets, and so on.
• Protecting pipes from corrosion and freezing.
• Installing footing drains, foundation waterproofing membranes, interior perimeter drains, sump pump, gutters, downspout extensions, downward-sloping grading, French drains, swales, and other techniques to protect a building from both surface water and ground water.
• Providing proper ventilation to unconditioned spaces to protect a building from the effects of condensation.
• Installing roofing, building wrap, and siding, or making sure they are in good condition on an existing building.
• Installing insulation in walls, floors, and ceilings, around ducts and pipes, around water heaters, and near the foundation and sill.
• Installing storm doors and storm windows.
• Replacing old drafty doors with tightly sealing, foam-core doors.
• Replacing older windows with low-E, double-glazed windows.

Sometimes, people use the phrase “whole-house weatherization”. This extends the traditional definition of weatherization to include installation of modern, energy-saving heating and cooling equipment, or repair of old, inefficient equipment (furnaces, boilers, water heaters, programmable thermostats, air conditioners, and so on). The "Whole-House" approach also looks at how the house performs as a system.

The practice of installing a vapor barrier inside the house has more to do with protecting the house from itself (its own internal moisture and temperature differences) than with protecting the house from the elements. Therefore, vapor barriers probably don't belong under the category of weatherization. However, you should understand the concept of vapor barriers before installing insulation or siding, or altering the ventilation in your house. Some houses do not need vapor barriers (depending on climate, type of insulation, amount of conditioned space within house, and so on).

Sealing bypasses

A bypass is any crack, gap, or hole that allows conditioned air to leak between your home’s conditioned and unconditioned space. This includes, for example, warm air escaping from the living area into an unheated attic, or cold air entering the living area from the basement or from the outdoors. You should focus your attention at the points where the conditioned space in your house meets unconditioned space. Bypasses between two heated rooms, or between one part of an unheated basement and another part of an unheated basement, don’t matter.

Loose-fill, batt, blanket, and open-cell foam insulation will not stop air from flowing through bypasses. If you don’t seal bypasses, the insulation will only filter the warm air as it escapes into the attic, resulting in dirty smudges on the insulation.

Having bypasses:

• Puts moisture into the attic, where it condenses and causes damage.
• Allows insects, spiders, and small rodents to enter the house, travel between floors, and travel between rooms.
• Wastes energy and money. If you seal as many bypasses as possible, your house will need less insulation, because the house will be doing much of the insulating itself by preventing convective heat loss.

If you are lucky enough to buy a house that is still under construction, you can take steps to make sure the house is as tight as possible. In the case of bypasses that pass through the foundation and exterior walls, you should, if possible, seal the bypass from both the inside and the outside before the contractor backfills. On the inside of the house, seal bypasses after the ducts, pipes, and wires are installed, but before insulation is installed. Once the contractor installs insulation, seals up the walls, and installs floorboards, going back to find and seal the bypasses is extremely difficult and costly.

If you buy a house that was built a long time ago, and if you feel drafts in the house, you can sometimes locate the source of the drafts with a candle. Light a candle, put the candle down in different spots in your house, step away, remain as motionless as possible, and see if the flame distorts to one side.

Materials to use for sealing cracks, gaps, and bypasses:

• Caulk. (Pick the type of caulk that is appropriate for what you are doing. For example, use swimming pool caulk to seal bypasses in the concrete foundation. Alternatively, you could use hydraulic cement or an expansive mortar.)
• Putty or hydraulic cement, for big holes.
• Closed-cell foam, such as “Great Stuff” - especially good for rough, irregular holes, narrow gaps, and difficult-to-reach areas such as sill plate. If you’re not sure if a foam is closed-cell, check the manufacturer’s website. For example, from Dow Chemical’s website:

"Latex foams are typically “open celled” and, as a result, can take on water. In fact, the same properties that allow you to wash latex foam off your hands with water also mean that the cured foam can absorb water. This can cause wood rot or deterioration in areas where wet latex foam is next to wood, such as a window frame. In contrast, GREAT STUFF is closed-cell foam. It forms a water-resistant outer coating when cured."

• Sheet metal and furnace cement, or Roxul [link] products, for sealing around fluepipes. If you’re not sure how to do this safely, check your local fire codes.
• Rigid foam insulation or gypsum board, cut to fit, for sealing large gaping holes. Caulk around edge. Cover the rigid foam with gypsum board if it is in an exposed location, to protect from toxic fumes in the event of a fire.
• Electrical receptacle and light switch insulating gaskets, designed to fit in between the electrical box and cover plate.
• Holes in electrical boxes, and drafty oversized holes through fire-rated walls (i.e., for sprinkler pipes or wiring conduit) can be sealed with intumescent (fire stop) caulking or putty. (Does anyone know if non-flammable silicone caulk is acceptable?)

Where to look for bypasses:

• In a home with an unheated attic, you should start looking for and sealing bypasses between the living area and the attic. Most of the heat that you are losing is probably escaping through the ceiling, because heat rises. Look for gaps around the fireplace chimney, furnace fluepipe, and vent pipes that extend through the attic, and seal any gaps that you find.
• To protect from fire, don’t pile insulation against fan motors and non-IC-rated recessed lights.
• Don’t forget to seal and weather-strip the attic access door or hatch (usually in the form of pull-down stairs). An enormous amount of heat can escape through gaps around this door.
• After focusing on the attic, the next most important place to look is around exterior doors and windows. Be sure to check between the exterior window trim and the siding (especially where the siding butts against the corner of the trim).
• Apply caulk and spray foam, and then install weather-stripping on the bottom, sides, and tops of doors and windows. There are many types of weather-stripping, including rubber strips, foam strips, vinyl tubular gaskets, and metal spring-type weather-stripping. Choose whichever one(s) you think are most appropriate.
• While you’re outside, seal any other gaps in the siding, especially around outdoor electrical receptacles, hose bibbs, and points where walls meet.
• If your house is made of brick or stone, or if you have a chimney, check for gaps, and repoint with mortar, if necessary.
• Now go into the basement and seal the sill plate (where the basement ceiling meets the foundation wall) if it hasn’t been sealed already. Seal around all pipes and conduits that pass through the foundation wall. Seal any cracks between concrete blocks. Seal around any pipes, conduits, wires, or cables that pass between floors.
• Finally, go back upstairs, and seal any gaps around electrical outlets and switch boxes, and around any pipes or ducts that pass through floors, walls, or ceilings. Be especially attentive under sinks in the kitchen and the bathroom.
• Sometimes, pipes are hidden behind access panels for safety or cosmetic reasons.
• Don't forget to check for roof damage. For example, patch holes with roofing cement.
• Now and then, check if the sealants have dried up and stopped sealing the gaps properly. Reapply as necessary.

After you seal all of the bypasses that you possibly can, make sure that your house is not too tight. If a house doesn’t have sufficient ventilation, the house will trap moisture, odors, chemicals, dust, and microbes (such as bacteria and fungi spores), and the air can become oxygen-deficient. All houses should breathe. You lose some money paying for heat and air-conditioning, but that is the price you pay for not breathing stale, unhealthy air. Open some windows, operate the whole-house fan, or install more ventilation, if necessary.

Freeze protection

House features that are vulnerable to freezing:

• Fuel line of external oil tank
• External hose bibbs, especially if they are dripping and the water supply was not turned off in autumn.
• Pipes along outside walls
• Pipes traversing uninsulated spaces

Ways to prevent fuel line and plumbing fixtures from freezing:

• Drain outside hose bibbs and turn off water supply before cold weather comes.
• In an emergency, provide temporary insulation - anything from leaves, to hay bales, to sheets of plywood, to a homemade shed.
• Install electric heat wrap on the pipes.
• Replace regular hose bibbs with “freeze-proof” hose bibbs.
• Move the oil tank inside.

Make sure to protect water pipes in unconditioned areas from freezing during the winter! If the pipes are in the basement, your furnace is also in the basement and nearby to the pipes, and there are no holes in the foundation allowing outside air currents to blow directly on the pipes, they should be fine.

Drainage (preventing soil saturation)

Reasons for water in the basement:

• Saturated backfill (the most common reason). Soil saturation causes hydrostatic pressure. The pressure of the water forces the water through the foundation walls and slab floor (either through cracks, around the edges, or directly through the porous concrete). This shows up as persistent seepage.
• Blocked footing drains.
• High water table.
• Condensation of interior humidity.

The key to a dry basement is to control surface water as well as ground water. The way to tell surface water and ground water apart is that surface water shows up in one area of the basement, whereas ground water (from a rising aquifer) usually comes up everywhere all at once, and leaves uniformly as well. Often, with groundwater problems, the water doesn't come up until after it has stopped raining.

Saturated backfill causes most of the water problems in houses. Effects of soil saturation around the perimeter of the foundation:

• Saturated backfill can freeze, lifting the foundation wall and cracking the slab. This is called frost heaving.
• Gutter downspouts that drain too close to the foundation can undermine footings. Parts of the house could shift out of place.
• Moisture that enters the basement can cause all kinds of problems elsewhere in the house, even in the attic, such as warped wood, mold, rot, and peeling paint.

General drainage advice:

• Don't use black flexible corrugated pipe for drainage. This clogs easily, doesn’t allow water to flow freely, and is weak and flimsy. Instead, use some type of PVC.
• The best drainage material is crushed stone, especially if the pieces are relatively flat, such as with crushed shale. Pieces of crushed limestone are often irregular in shape, rather than flat. Do not use gravel, rounded river pebbles, item 4, or QP (quarry product) for drainage.

Ways to prevent soil saturation around your house:

• Install swales (trenches) and French drains (trenches containing slotted PVC pipe and crushed stone, underneath a driveway, for example) to intercept surface water long before it comes close to the house.
• Install footing drains using schedule 40 slotted PVC pipe, with the holes facing downward. Filter out silt by wrapping the footing drain with crushed stone, surrounded with filter fabric, surrounded with sand. Make sure the footing drains stay unclogged. Ideally, footing drains should have one or more cleanouts on the surface, and should open to daylight somewhere downhill from the foundation. Footing drains are much easier to install when a house is being built than after the house is built.
• Make sure any pipes entering the house below grade are set in impermeable soil such as tightly-compacted, "hardpan" clay (not sand) where they meet the foundation.
• The soil or material against the lower part of a foundation should have high percolability, and should have a way for water to flow away from the foundation, such as footing drains leading downhill. Ideally, you should have crushed stone against the lower part of the foundation with crushed stone and footing drains extending downhill from there. The worst type of soil to have against the lower part of a foundation is high-clay soil, because it holds water, stays saturated for long periods of time, and, when saturated, tends to cause foundations to shift, crack, and buckle inward.
• Correct settled backfill, which directs surface water towards the foundation. Instead, slope the soil away from the foundation. The soil that is on the surface around the foundation is called grading soil. The grading soil, unlike the soil against the lower part of a foundation, should be high in clay, tightly compacted, and at least 6 inches thick. Such soil is virtually impermeable to water, directs water away from the foundation, and allows air to easily pull moisture out of the soil during hot, dry weather. You can compact the soil yourself with a tamper. Make sure you compact the soil, or it will absorb and hold moisture, exactly what you don’t want.
• Do not plant large, deep-rooted shrubs within 4 feet of the foundation. Do not plant trees anywhere near the foundation.
• Water plants near the foundation early in the day, so that the soil has time to dry off before the water sinks too deep and lingers against the foundation.
• Remove tree roots near the foundation, which provide channels for water.
• Slope window wells away from the house, install bubbles over them to prevent water from collecting, or eliminate them.
• If your house has no gutters and downspouts, install them, and keep them clean and free of clogs. Repair any holes, cracks, or other damage. If the downspouts detach from the gutters, reconnect them promptly, using sheet metal screws.
• Don't use louvers to disperse water (so-called "clog-proof gutters"). They are the equivalent of having no gutters at all.
• Do not allow gutters to drain against the foundation. Instead, install downspout extensions and connect them to 4-inch PVC that is buried underground, slopes downward, directs water at least 10 feet away from the foundation, and either opens to daylight or connects to a storm drain.
• Do not tie gutters into footing drains! They will both clog.
• You can tie gutters into French drains, but don't forget to install clean-outs in French drains. Check for clogs regularly.
• Don’t install screens over the gutters or wire baskets in the downspouts. All they do is clog up the gutters.
• Repair cracks or holes in the interior foundation wall with swimming pool caulk, hydraulic cement, or an expansive mortar. Do not use "waterproofing" paints, vapor barrier paints, or moisture sealants on the interior foundation wall. Hydrostatic pressure will build up and water will find its way through the weakest spots, causing the paint or sealant to flake and peel, and causing disintegration of the underlying concrete block. (Unanswered question: If you resolve the hydrostatic pressure problem, should you then treat the concrete with one of these moisture sealant products, or should you never use one of these products?)
• If nothing else works, install an interior perimeter drain, also known as a "dewatering" or "pickup" system. This channels water, usually towards a sump pump, and is therefore usually dependent on electric power for continued proper functioning. Do not connect interior perimeter drains into the exterior footing drains – this could undermine the footings. You should never increase the amount of water next to your footings.

Sources and effects of water in a house

Water causes more damage to houses than anything else. The most important tasks in maintaining a house all involve protecting the house from the effects of water.

Paradoxically, water vapor from damp basements causes most attic problems.

Water vapor turns to liquid water when it reaches the dew point. Humid air reaches the dew point more easily than dry air.

Sources of moisture in homes:

• Dirt floor basements and crawlspaces.
• Saturated backfill, which causes seepage through foundation.
• Wicking through concrete slabs in the basement or crawlspace.
• Showers.
• Clothes dryers.
• Kitchen appliances.
• Leaking or dripping pipes (supply pipes as well as drain pipes) and fixtures.
• Leaks in roof, often near vents, pipes, or skylights, resulting from corroded, damaged, or missing flashing or shingles.
• Leaks resulting from damaged siding.

Harmful effects of moisture in a house, especially if the ventilation is poor:

• Warped wood. (Wood absorbs moisture and swells.)
• Mold.
• Rot. (Wood consistently kept at a high humidity will rot, as will wood touching the dirt for long periods of time. There are many different types of rot. Most are destructive. Those that are not, when present, indicate conditions that are favorable to the destructive types.)
• So much water can condense in the attic that it starts leaking through to the ceiling below, as if the roof were leaking.
• Ice dams and roof leaks.
• Soaked, compacted, ineffective insulation (resulting from roof leaks, or from condensation within the walls). Moisture passing through insulation will often appear as condensation on the outer, cooler edges of the insulation. Eventually, if enough moisture condenses, the water will drip down and soak the rest of the insulation.
• Moisture pushing through from the inside can cause blistered, chipped, cracked, peeling, and stained paint or siding, and popped nails, on the outside of the house. (External temperature and humidity conditions can also cause these symptoms, but excessive internal moisture drastically hastens their appearance.)
• Termites and other insects.
• Clammy feeling in the cooler months, muggy feeling in the warmer months.
• When combined with excessive heat in the attic, excessive moisture can shorten the life of roofing shingles.

Ventilation

See Ventilation issues in houses. Also be aware that poor ventilation, combined with poor insulation, can create an ice dam.

Roofing tips

Miscellaneous advice on choosing shingles and roofing material:

• If you choose to install a roof with asphalt shingles, be sure to buy fiberglass asphalt shingles. They are stronger and more durable than regular asphalt shingles.
• If you install a metal roof, you must install some kind of lightning protection, and you will need to remove or isolate all other metal protrusions to prevent the dissimilar metals from corroding each other. If damage occurs, you can solder a piece of metal to a steel roof, whereas, with an aluminum roof, you have to use mesh and roofing cement.
• The advantage of tile roofs is that they stay cool in hot weather. They are not appropriate in cold climates, because they are not designed to handle snow and ice well.
• If your roof has a low slope, you should install a rubberized ice-shield membrane almost all the way to the ridge of the roof.

Advantages of wood shakes and shingles:

• Shed water well.
• Insulate from heat and cold more effectively than asphalt shingles.

Disadvantages:

• Flammable.
• Susceptible to the effects of trapped moisture (mold, rot, insects) when items fall on the roof (sticks, leaves).
• Not appropriate on a low-slope roof.

Before installing a new roof, check the roof sheathing for rot, both on the exterior surface (the decking) and the interior surface (in the attic). Don’t just replace rotten sheathing. Also find out why the sheathing rotted in the first place. Do not install a new roof until you have solved all moisture problems.

To protect the fascia boards from rot:

• Always install a metal drip edge.
• Overlap the eaves with a few inches of roofing material.

Use roofing cement to seal around nail holes and damaged spots in the roof.

Flashing is a sheet or molded form, made of copper, aluminum, or plastic, that seals the parts of a roof where chimneys, vents, skylights, and other things penetrate or break up the roof surface. Repair holes in flashing with roofing cement. There are many different types of flashing:

• Install step flashing where the roof meets a wall. The correct way to install step flashing: Shingle, flashing, shingle, flashing, shingle, flashing, and so on, until you have wrapped around the top edge of whatever you are trying to direct water away from.
• Install “formed flashing” over ventilation pipes in the roof. These consist of molded plastic with a rubber collar that seals around the pipe.
• The best solution for the valleys of a roof is copper W-flashing.
• Flashing a chimney and the roof next to the chimney is somewhat complicated, involving base flashing, step flashing, and counterflashing (which seals other flashing). You insert counterflashing into a mortar joint in the chimney and secure it with mortar. The procedure for properly flashing a chimney is difficult to describe; refer to a roofing manual or roofing website.
• You can also create a “cricket” (a built-up ridge constructed with lumber and shingles) on the uphill side of the chimney) to deflect water and snow away from the chimney.

Skylights

Skylights can warm the house, by allowing more sunlight to come in, and can cool the house, if they are the type that you can open. Solar tubes are similar to skylights, in that they allow more sunlight to come in, but they do so differently, by collecting the light in a tube and sending it to a diffuser. Make sure flashing is installed properly around skylights and solar tubes. If you install a skylight, only install a high-quality one with an integral frame. Plastic bubble skylights tend to leak because the seam between the roof and the bubble expands and contracts over time. Pre-framed skylights are built to accommodate this expansion and contraction without leaking.

Houses in cold climates should have a narrow overhang to allow in more sunlight. Houses in warm and wet climates, on the other hand, should have a wide overhang.

Roof drain plane

If you have a relatively steep roof with few valleys, you should install a drain plane. A drain plane is a gap that you create between the roof sheathing or rigid panel roof insulation and the exterior roof surface. Functions of a drain plane on a roof:

• Allows any stray water or condensation to drain out from underneath the exterior roof surface.
• Provides ventilation to allow the back of the exterior roof surface to dry (especially important with wood shakes and shingles).
• Extends the life of the roof by keeping it cool and dry.
• Allows moisture forcing its way out from the interior of the house to evaporate quickly.

Roof insulation

If they do not already exist, you should add rigid closed-cell foam panels between the roof sheathing and exterior roof surface. You may need to modify skylights to match the new thickness of the insulation and roof. (What if the skylights do not protrude enough? Can you install some kind of protruding flashing that goes around the skylights like window casing?)

Advantages of adding rigid closed-cell foam between roof sheathing and exterior roof surface:

• Thermally insulates attic ceiling. If you install foil-faced rigid foam panels, you will also block radiative heat transfer. If you install enough rigid panels, you may not need to put any insulation between the rafters.
• Resists air infiltration (and therefore, convective heat transfer) between interior and outdoors.
• Prevents condensation from forming in the rafters by keeping the temperature and humidity between the rafters similar to that in the rest of the attic.

In the attic, you should install expanding closed-cell spray foam against the interior side of the sheathing, and between the rafters, before installing (fire-rated) drywall. (If fiberglass batts exist, remove them.) Advantages of closed-cell spray foam between the rafters:

• They keep the temperature and humidity between the rafters similar to that in the rest of the attic.
• You don't need a separate vapor barrier. Closed-cell spray foam is virtually impermeable to moisture, and acts as its own vapor barrier, preventing moisture from condensing on the sheathing or rafters. You no longer have to concern yourself with moist air leaking into the attic and condensing on the sheathing and rafters.

Once you insulate the attic with rigid panels on the exterior of the sheathing, spray foam on the interior of the sheathing, and some type of insulation in the walls, you can treat your attic as part of the conditioned space of the house. In other words, you can allow the attic to warm up in the winter, and you can more easily keep the attic cool in the summer. You will most likely not be heating your attic directly - the attic will draw heat escaping from the floors below. You no longer have to struggle to keep the attic cold and well-ventilated in the winter at the same time that you are turning the furnace up to keep your living space warm. You can insulate the floor of the attic, but since the attic is part of the conditioned space, it is not necessary.

Building wrap

A building wrap or air retarder cuts drafts and seepage that creeps through exteriors, especially at corners and around windows and doors, but allows moisture to pass through, allowing the house to breathe (similar to Gore-Tex). Building wraps do not insulate much, but they block conditioned interior air from escaping, and block unconditioned outdoor air from creeping in, especially on windy days. Thus, they reduce heat transfer, keep the house more comfortable, and save energy.

Building wrap is sometimes confused with vapor barriers.

Building wraps have permeability ratings of 5.0 or higher, to block air, but to allow moisture to escape from the wall cavities. The higher the perm rating, the more moisture can pass through. Do not use asphalt felt paper or tar paper as building wrap. Asphalt felt paper has a permeability rating of approximately 1.0, so it traps moisture against the sheathing (not very well, but well enough to cause problems).

Materials used as building wrap:

• Tyvek, 6 mil or greater in thickness.

How and where to install building wrap:

• On exterior of house, between sheathing and siding (including brick and stone). Staple to sheathing with 2-inch overlap on top, and 6-inch overlap on sides.
• Cut house wrap into framed openings for doors and windows, and tuck back and staple excess against side of framing. You can also use rigid closed-cell foam under the windowsill when installing a window.
• You don’t need to put building wrap against exposed parts of the foundation wall, because concrete does not allow drafts to pass through (as long as there are no bypasses), concrete does not rot, and concrete is porous, so any trapped moisture will eventually find its way out.

When replacing siding, you should add building wrap and insulation if they do not already exist. You install the building wrap onto the sheathing first, then install the insulation over the building wrap.

When installing or replacing siding:

• Don't bury problems under new siding. If sheathing is rotted in one area, find out why, and fix the sheathing as well as the cause of the rot.
• Always overlap siding around obstructions, so that water will not find its way in.
• Use corner boards to protect the corners of the house where siding tends to leak.
• Be aware that some vinyl siding can be insulated from behind with molded panels called backer boards.
• If you choose wood siding, apply primer to the backside of wood siding before you install it to the sheathing. Use paint, stain, or clear sealant to protect wood siding once it is installed. Stain is preferable, because moisture entering the wall from the inside can push paint off the wall, but can seep through stain causing only fading and weathering.
• If they do not already exist, you should add building wrap and rigid closed-cell foam panels between the sheathing and the siding. You attach the building wrap to the sheathing, then install the insulation over the building wrap. You may need to build out window casings to match the new thickness of the insulation and siding.

Advantages of adding rigid closed-cell foam between sheathing and siding:

• Thermally insulates wall. If you install foil-faced rigid foam panels, you will also block radiative heat transfer. If you install enough rigid panels, you may not need to put any insulation in the wall cavity.
• Resists air infiltration (and therefore, convective heat transfer) between interior and outdoors.
• Prevents condensation from forming in the wall cavity by keeping the temperature and humidity in the wall cavity similar to that in the interior of the house.

Do not put a vapor barrier in between the sheathing and siding. Vapor barriers belong on the interior side of walls.

Siding drain plane

You should install a drain plane on all walls. A drain plane is a gap that you create between the insulation, building wrap, and sheathing and the exterior siding. You create this gap by installing furring strips or plastic mesh to hold the siding off the wall.

Functions of drain plane:

• Prevents water from entering the wall from the outside.
• Helps prevent mold from growing in cellulose insulation.
• Allows any stray water or condensation to drain out.
• Provides air circulation to allow the back of the siding to dry (especially important with wood siding).
• Extends the life of the siding by keeping it cool and dry.
• Increases paint retention, since moisture will no longer force its way out through the paint.

Insulation

See insulation.

Installing or replacing doors and windows

When choosing new doors and windows:

• Replace solid core external doors with metal-clad, foam-core doors or fiberglass doors.
• Replace drafty single-glazed windows with efficient, low-E, double-glazed, insulated windows. Krypton is more insulating than argon, but windows with krypton cost more.
• Avoid metal-framed windows. Replace steel or aluminum windows with a wood, vinyl, or fiberglass windows. If you must buy a metal-framed window for some specific reason, make sure that there is a thermal break separating the inner half from the outer half.
• If you can't afford new double-glazed windows, keep your existing windows, and install year-round storm windows on the outside. You can open them and insert a bug screen in the warmer months. Alternatively, you can shrink-wrap polyethylene on the windows in the colder months with a hair dryer to trap air, you can install low-E film on the window panes, or you can install an “interior insulating window”.
• In the attic, install double-glazed windows with built-in venting around the frame, so that you can close the windows in cold weather without stopping air from flowing through the attic.

When installing new doors and windows:

• Seal the gap between the window casing or nailing flange and the sheathing by applying a bead of exterior-grade caulk before attaching the window to the framing studs.
• Seal the gap between the window or door framing and the framing studs (the rough opening).
• Make sure new windows and doors have drip caps (flashing) above them to keep water away. If there are no drip caps, install them while installing the windows or doors.
• Be aware that all multi-pane windows will eventually lose their air-tight seal. Fog that appears on the interior of the window (between the layers of glazing) is an indication of leakage.

Helpful links

• [The Weatherization Assistance Program (WAP) Technical Assistance Center (WAPTAC)]
• [The WAP System for Identifying and Reviewing New Technologies and Techniques]
• [US EPA publication on home sealing]
• [Insulation and Weatherization Handbook]

 

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