The Basics Part 2

Back to Insulation 101 - Part 1

So How Can You Avoid Moisture Problems?

Here are six things you should consider:

You need to stop all rain-water paths into your home by making sure your roof is in good condition and by caulking around all your windows and doors. If you are planning a new house, choose wider overhangs to keep the rain away from your walls and windows. You can also keep rainwater away from your basement walls or crawlspace by making sure that all water coming off your roof is directed away from your house and by sloping the soil around your house so that water flows away from your house. Be sure that dripping condensate from your air conditioner is properly drained away from your house. You can place thick plastic sheets on the floor of your crawlspace to keep any moisture in the ground from getting into the crawlspace air, and then into your house. These actions can also help reduce capillary water flows from the ground into your walls. You should also be careful that watering systems for your lawn or flower beds do not spray water on the side of your house or saturate the ground near the house.

You need to ventilate your home to remove the moisture that results from human activities within your home, such as breathing, bathing, cooking, etc. You especially need to vent your kitchen and bathrooms. You may be able to see mold (see a close-up view in Figure 3) that grows around your bathtub, but you will not be able to see mold growing inside the walls or in the attic. So, be sure that these vents go directly outside, and not to your attic, where the moisture can cause problems. Remember that a vent does not work unless you turn it on; so if you have a vent you are not using because it is too noisy, replace it with a quieter model. Some of the better vents are available with timers or moisture sensors so that you can be sure that the vents run long enough to remove all the excess moisture from that room. (While you are in the bathroom, it is also a good idea to check the caulking around your tub or shower to make sure that water is not leaking into your walls or floors when you bathe.)

When you think about venting to remove moisture, you should also think about where the replacement air will come from, and how it will get into your house. Many older homes have relied on leaky construction, drawing in their fresh air around window and door frames, building corners, wall-foundation joints, wall-roof joints, chimneys, etc. Air coming into your home through these pathways often travels through places you cannot see, such as wall cavities, the space between floors, the crawlspace, or attic. If this outside air contains moisture, you will effectively be pumping moisture into these unseen places. As we seal up our homes to save energy, we need to replace these uncontrolled air pathways with energy-efficient pathways. Air-to-air heat exchangers can keep the indoor air at a healthy moisture level without increasing your energy costs. In humid regions, attic ventilation may also be a moisture source because you may be pulling air into your attic that has more moisture in it than the air in your home.

It is very important to seal up all air-leakage paths between your living spaces and other parts of your building structure. Measurements have shown that air leaking into walls and attics carries significant amounts of moisture. The Insulation Fact Sheet tells you how to do this.

Plan a moisture escape path. Some moisture will always be present in your home. You can help this moisture escape with well-planned ventilation or by careful selection of your building materials. Typical attic ventilation arrangements are one example of a planned escape path for moisture that has traveled from your home’s interior into the attic space. You can also use a dehumidifier to reduce moisture levels in your home, but it will increase your energy use and you must be sure to keep

You can use vapor retarders to reduce moisture diffusion through your walls, floors, and ceilings. This is relatively easy to do when building a new house, but there are a few things that you can do for existing houses as well. The kind of vapor retarder you should use, and where you put it, depends on whether moisture is more likely to be moving into or out of your house. If moisture moves both ways for significant parts of the year, you may want to avoid the use of a vapor retarder completely.

What is a Vapor Retarder?

Vapor retarders are special materials including treated papers, paints, plastic sheets, and metallic foils that reduce the passage of water vapor. Tests are made to measure how much water vapor can travel through each material, and the results are called permeance, or perms. The lower the perm, the better the vapor retarder.

What Kind of Insulation Should You Buy?

Once you have located the areas in your house requiring insulation, and have determined what R-value is needed, you will need to decide what type to buy. Some types of insulation require professional installation, and others you can install. You should consider the several forms of insulation available, their R-values, and the thickness needed. Remember, for a given type and weight of insulation, the thicker it is, the higher its R-value.

Basic Forms of Thermal Insulation

BLANKETS, in the form of batts or rolls, are flexible products made from mineral fibers. They are available in widths suited to standard spacings of wall studs and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without vapor retarder facings. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed. Usually an inexpensive option, the drawback is its inability to completely fill all gaps and voids.

BLOWN-IN loose-fill fiberglass is blown into building cavities or attics using special pneumatic equipment, and is install by licensed and trained professional. Properly installed, BIBS (Blow In Blanket System) provides the greatest possible R-value by filling gaps and voids, preventing air infiltration. This type of insulation also provides tremendous acoustical benefits.

RIGID INSULATION is made from fibrous materials or plastic foams and is pressed or extruded into board-like forms and molded pipe-coverings. These provide thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths. Such boards may be faced with a reflective foil that reduces heat flow when next to an air space.

REFLECTIVE INSULATION SYSTEMS are fabricated from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles, or cardboard. The resistance to heat flow depends on the heat flow direction, and this type of insulation is most effective in reducing downward heat flow. Reflective systems are typically located between roof rafters, floor joists, or wall studs. If a single reflective surface is used alone and faces an open space, such as an attic, it is called a RADIANT BARRIER. Radiant barrriers are sometimes used in buildings to reduce summer heat gain and winter heat loss. They are more effective in hot climates than in cool climates. All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more).

Make Your Selection

The type of insulation you use will be determined by the nature of the spaces in the house that you plan to insulate. For example, since you cannot conveniently "pour" insulation into an overhead space, blankets, spray or board products, or reflective systems are used between the joists of an unfinished basement ceiling. The most economical way to fill closed cavities in finished walls is with blown-in insulation (Blow In Blanket System, also knows as BIBS) applied with pneumatic equipment by professional installers.

It is important to know that the different forms of insulation can be used together. For example, you can add batt or roll insulation over loose-fill insulation, or vice-versa. Usually, material of higher density (weight per unit volume) should not be placed on top of lower density insulation that is easily compressed. Doing so will reduce the thickness of the material underneath and thereby lower its R-value.

Can You Do It Yourself?

Whether or not you install the insulation yourself depends on the structural design of your house and the type of materials used in its construction.

Placing insulation in the attic floor is usually easy, requiring only laying the material between the parallel joists of the frame. Be careful about where you step in the attic. Walk only on the joists so that you won't fall through the drywall ceiling. You may need to place walking boards across the tops of the joists to make the job easier. Remember that it is important to seal up air leaks between your living space and the attic before adding insulation in your attic.

Also, bear in mind that insulation placed between joists, rafters, and studs does not retard heat flow through the exposed frame. This heat flow is called thermal bridging and is especially important in houses with metal frames or joists. In attics, thermal bridging can be reduced by adding sufficient loose-fill insulation thickness to cover the wood or metal frame as much as possible. In some houses with low-pitch roofs, it is difficult to gain access to the entire attic floor, so blowing equipment is best to place insulation in relatively inaccessible areas. In most attics, it is easier to get complete coverage with blown-in insulation. It is best to hire an insulation contractor for this job.

In existing buildings, installing insulation in the cavity of exterior walls is difficult. It requires the services of a contractor who has special equipment for blowing loose-fill fiberglass insulation into the cavity through small holes cut through the sidewall, which later are closed. When new siding is to be installed, always consider adding thermal insulation under it. Generally the services of a qualified contractor are needed to make such installations.

If you insulate a floor above a crawl space, all ducts and water lines running below the insulation should be insulated as well. Insulate crawl space walls only if the crawl space is dry all year, the floor above is not insulated, all ventilation to the crawl space is blocked, and a vapor retarder (e.g., heavy-weight polyethylene film) is installed on the ground to reduce moisture migration into the crawl space. Adding thermal insulation to the ceiling or walls of a mobile home is complex and usually requires installation by specialists. However, it is often possible to add floor insulation to such a home, just as you would for any other type of house.

If You Have It Done Professionally

You should obtain cost estimates from several contractors for a stated R-value. Make sure you describe the job in writing in the same terms to each one. You may want to ask each contractor about their air-sealing services as well. Remember that you want good quality materials and labor, as well as price. Do not be surprised to find the quoted prices for a given R-value installation to vary by more than a factor of two. When you talk to a contractor, talk of R-values. Don't forget that R-values are determined by material type, thickness, installed weight per square foot, and complete closure of all gaps and voids, not by thickness alone.

Each bag of insulating material used by the contractor should be marked with an R-value for the area to be covered. Although these figures may differ among manufacturers, the area figure will tell you the right number of bags to be used for loose-fill. Similarly, packages of other types of insulation should be identified by their R-value. It is important that you check that the proper amount is installed in your residence. Ask the contractor to attach vertical rulers to the joists prior to a loose-fill installation in your attic to help you see that the proper depth was installed. Also, the installer must provide a signed and dated statement describing the insulation installed, stating thickness, coverage area, R-value, and number of bags installed. In some areas, infrared thermography services are offered to help discover any gaps in the insulation.

Consumers may want to have their attic R-value evaluated to ensure that they are getting what they paid for. Density testing is the insulation industry recognized procedure of evaluating installed loose-fill insulation. Many independent (third-party) firms offer "cookie-cutting" density testing services to homeowners throughout the country. A good BIBS contractor will provide you with the results of these density tests.

Other Places in Your Home for Added Insulation

Don't overlook another area in your home where energy can be saved--the ductwork of the heating and air-conditioning system.

If water lines and the ducts of your heating or air-conditioning system run through unheated or uncooled spaces in your home, such as attic or crawl spaces, then the water lines and the ducts should be insulated. First check the ductwork for air leaks. Repair leaking joints first with mechanical fasteners, then seal any remaining leaks with water-soluble mastic and embedded fiberglass mesh. Never use gray cloth duct tape because it degrades, cracks, and loses its bond with age. If a joint has to be accessible for future maintenance, use pressure- or heat-sensitive aluminum foil tape. Then wrap the ducts with duct wrap insulation of R-6 with a vapor retarder facing on the outer side. (If you live in the deep South or southern California, you can use R-4 insulation.)

All joints where sections of insulation meet should have overlapped facings and be tightly sealed with fiberglass tape; but avoid compressing the insulation, thus reducing its thickness and R-value. In many parts of the country, this type of insulation will pay for itself in energy saved.

Return air ducts are more likely to be located inside the heated portion of the house where they don't need to be insulated, but they should still be sealed off from air passageways that connect to unheated areas.

Drywall-to-ductwork connections should be inspected because they are often poor (or nonexistent) and lead to unwanted airflows through wall cavities.

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