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Weatherizing FAQs

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What does the term "R-value" mean?

R-value is a measure of how well a material resists the passage of heat. The higher the R-value the more effective insulation is in keeping the home warm in winter and cool in summer. Insulation should always be judged by R-value rather than inches, as different insulation materials have different R-values per inch of thickness.

How much insulation should I have in my attic?

In the Midwest, attics should be insulated to R-49 whenever possible. To ensure proper levels, check your local building energy codes.

If I install more insulation in my attic, what type should I use?

Most homeowners find it easiest to use batt insulation. Always use unfaced batts, as the paper or foil vapor retarder can trap water vapor in the original insulation, causing moisture problems. If possible, install the new insulation perpendicular to the attic floor joists to reduce heat loss through the joists. Loose fiberglass or cellulose can also be used. Follow instructions for proper density.

If I install more insulation in my exterior walls, what type should I use?

Exterior wall R-values should equal R-15 or higher in the Midwest. In existing homes, insulation can be blown into uninsulated walls. Have a qualified contractor check the walls and determine the feasibility of blowing in insulation.

How much insulation should I have under my floor?

Floors over unheated crawlspaces or basements should be insulated to R-19, while floors over open air (such as overhangs) should be insulated to R-30, if possible. If your home has a basement containing your heating system or other sources of heat, you should insulate the basement walls to R-11, rather than insulating the floor above.

My home is built on a slab. Is there a way to insulate my floors?

With slab construction, there is no way to insulate under the floor. In new construction, the perimeter of the slab should be insulated to several feet below ground level. This can also be done in an existing home, but the cost and difficulty of trenching around the perimeter often make it impractical.

Is it better to insulate the attic floor, the roof, or both?

Unless you are finishing the attic for living space, you should insulate the attic floor to contain the heat within the living space.

Is it a good idea to add additional insulation to my walls? How is this done?

If your walls currently have no insulation, insulation can be blown into the cavities through holes drilled through the exterior of the home. This should only be done by a reputable, qualified contractor. If there is already some insulation in the walls, you should not attempt to add any more.

I've always heard that "heat rises." Why do I need to insulate my floors?

Actually, heat moves from warm to cold. If your home is built over a crawlspace or unheated basement, you can lose a lot of heat downward through the floors. Insulation will help reduce that loss and also make your floors feel warmer in the winter.

If the walls and ceiling of my home are well insulated, do I really need to insulate my basement?

The importance of basement insulation depends on whether the basement is heated. If you heat your basement, or if your furnace or other sources of heat are in the basement, you should insulate the basement walls to contain the heat. If not, you should insulate the basement ceiling to reduce heat loss to the basement and keep your floors warmer.

I've heard that you can make a home "too tight." Should I be concerned about this?

With new construction, it is possible. In existing homes, it is unlikely unless extraordinary measures are taken to eliminate air leakage. For an existing home, basic air sealing measures like caulking and weatherstripping will save energy dollars without making the home too tight.

Is it better to caulk my windows and doors on the inside or the outside?

Any large gaps on the outside should be weatherproofed to keep rain out, but the inside is generally the best place to caulk to keep the heated air inside, along with any water vapor that could condense in a cold wall cavity.

How much ventilation should I have in my attic?

In most cases, you should have one square foot of net-free vent area for each 150 square feet of attic floor area. Net-free area is the actual area that air can flow through. With screens and louvers, you can assume that is roughly half the gross area. If you have a properly installed ceiling vapor retarder, you can reduce the vent area to one square foot per 300 square feet of attic floor area.

What is a thermopane window? How does it work?

A "thermopane" or double-paned window has two panes of glass, separated by a trapped air space. The trapped air acts as an insulator, reducing heat loss through the glass.

My home has single-paned windows. Would it be better to replace them with double-paned windows or to add storm windows?

Both double-paned or thermal windows and storm windows work by creating an insulating air space between the panes of glass. If your existing windows are in good shape, storm windows will usually be more cost-effective. If your existing windows are damaged or if you are replacing them for aesthetic reasons, you should install good quality double-paned windows.

Why does moisture form on the inside of my windows in winter? How can I minimize the amount of moisture?

Condensation will occur whenever warm air hits a cold surface because warm air can hold more water vapor than cold air. If you have single-paned windows, adding storm windows will keep the inner pane of glass warmer and reduce the amount of condensation. Monitoring your indoor humidity will also help. As it gets colder outside, you should lower your humidifier setting until window condensation disappears.

What are Low-E windows?

"Low-E" windows incorporate a microscopically thin layer of a metal oxide which reduces the amount of heat transferred through the glass without reducing the amount of light. This coating is only used with double-paned windows.

I'm considering having vinyl siding installed on my home. Will this reduce my heating and cooling costs?

Vinyl siding is typically installed over a thin layer of foam insulation material. Although this material has some insulating value, it is minimal. You should be skeptical of any claims of substantial energy savings. The main benefits of vinyl siding are enhanced appearance, reduced maintenance, and potentially increased resale value.