Insulation & Weatherization

Q. What does the term "R-value" mean?

A. 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.

Q. How much insulation should I have in my attic?

A. Attics should be insulated to R-38 whenever possible.

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

A. Most homeowners find it easiest to use batt insulation. Always use unfaced batts, as the paper of 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, by pouring it and leveling it with a board or other implement.

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

A. Exterior walls in new homes should be insulated to R-15 or higher. 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.

Q. How much insulation should I have under my floor?

A. 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.

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

A. With slab construction, there is no way to insulate under the floor. In cold climates, new homes typically have the perimeter of the slab 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 usually makes it impractical. In warmer climates, slab perimeter insulation is not considered cost-effective, and in locations where termites are a concern, it is not recommended as the insulation can provide a path for termites to enter the structure.

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

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

Q. Is it a good idea to add additional insulation to my walls, and how is this done?

A. 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.

Q. Can I compress 6" R-19 batts to fit into a 2"x 4" cavity, and will it be more effective than 3 1/2" batts?

A. While insulation batts are easily compressed, the R-value will be significantly reduced - it is best to use the correct thickness and not compress the insulation. You should also avoid storing heavy materials on top of attic insulation for the same reason.

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

A. 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.

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

A. 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.

Q. What is a "vapor retarder" and how important is it?

A. A vapor retarder is a material which resists the movement of water by means of vapor diffusion. A properly installed vapor barrier can minimize the chance of water vapor condensing inside your wall insulation, which not only reduces the insulation's effectiveness but can also cause damage to your home. In a hot and humid climate like the south, we recommend installing the vapor retarder on the exterior of the wall framing.

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

A. With new construction it is highly unlikely that you will build your house too tight 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 for acceptable indoor air quality. If you do significantly reduce leakage in your home -- which is good -- you should consult with your HVAC Contractor about introducing some fresh air to the return side of the central heating and cooling system. This will create a slightly positive pressure and enhance the IAQ and sustainability of the home.

Q. What is the best type of insulation to use in my attic?

A. Either loose fill (typically fiberglass or cellulose) or batt insulation (usually fiberglass) will work well. Batts are easier to install yourself, while many contractors find loose fill easier and less expensive to install.

Q. Which type of insulation is better for your walls?

A. As a general rule, blown insulations are easier to install properly because the gaps, voids and compressions common to batted insulations are eliminated. Blown insulations allow for better coverage around plumbing as well as electrical wiring and fixtures. Although R-values for blown and batt insulations are similar, blown applications usually offer reduced infiltration that result in better performance.

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

A. 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.

Q. How much ventilation should I have in my attic?

A. 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.

Q. How much ventilation should I have in my crawlspace, and should the vents be closed in the winter?

A. If the crawlspace has a dirt or gravel floor, you should have one square foot of vent area for each 150 square feet of crawlspace area, unless you have a waterproof ground cover, in which case one square foot for each 1500 square feet is recommended. Vents should not be closed in winter. If the floor over the crawlspace is uninsulated, you should have it insulated to reduce heat loss through your floors.

Q. What is the best way to ventilate a cathedral ceiling?

A. Cathedral ceilings should have continuous soffit vents and a ridge vent to allow air circulation between the insulation and the underside of the roof. Insulation should be installed with at least 1 inch of clearance from the underside of the roof. There are plastic baffles available that can be used to maintain this air space. A continuous vapor retarder is also recommended to minimize migration of water vapor into the insulation.

Q. Can I insulate over recessed lighting fixtures?

A. Only if the fixtures are designed to be covered with insulation (these fixtures are referred to as "IC Rated"). Otherwise you should maintain three inches of clearance around the fixtures and leave the top of the fixture uncovered to avoid potentially hazardous heat buildup within the fixture.

Q. What is a "thermopane" window, and how does it work?

A. 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.

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

A. 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.Selecting a Window with performance U-Factors and Solar Heat Gain Coefficients (SHGC) of .4 or less will ensure the best results in summer and winter.

Q. Why does moisture form on the inside of my windows in winter, and how can I minimize the amount of moisture?

A. 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 and keeping it in the range of 40 - 50% will also help.

Q. What are "Low-E" windows?

A. "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. Selecting a Window with performance U-Factors and Solar Heat Gain Coefficients (SHGC) of .4 or less will ensure the best results in summer and winter.

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

A. 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.