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Because warm air naturally rises, the attic or roof area of your home is your first priority for insulating. Insulation reduces the upward flow of heat, keeping it inside your home longer. That means you’ll stay warmer, and your heating system will not come on as often – reducing your utility costs! In Montana’s cold climate, insulating existing attics to an R-value of at least 49 is recommended. R-value is the measure of an insulation material’s ability to resist heat flow. It’s measured per inch of material. For example, glass fiber batt or blanket insulation has an R-value of around 3.2 per inch, and the R-value of loose-fill cellulose is about 3.7 per inch.
Both of these insulation types are commonly used to insulate attics. Twelve inches of the glass fiber batt insulation achieves R-38, and about 101⁄2 inches of cellulose will achieve the same R-value. How much insulation is in your attic?
How your attic should be insulated depends on how your roof is built. Common attic/ roof types are:
In these homes, the attic is not part of the living space. You can often get into the attic by ladder through a hatch usually located in a hallway or closet ceiling. Unfinished attics are generally the easiest type to insulate; the insulation goes between the framing members (joists) of the attic floor, which is also your living area’s ceiling. Capable do-it-yourselfers can tackle this job with advice from a professional. Rolls of glass fiber or loosefill cellulose have been the insulation of choice for most do-it-yourself jobs. This fact sheet primarily deals with steps you can take to add insulation to your unfinished attic.
A portion of these attics are living spaces. As a result, insulation should be placed in the exterior walls (called kneewalls), the entire ceiling and the outer floor areas – those not part of the living space. An experienced professional should be called upon for this job since it often requires the use of several insulation products and use of special insulation blowing equipment.
These types of ceilings don’t have attics above them, and due to little or no space to add insulation, it may be impossible to add insulation to this roof type. If there is space, the insulation must be blown or placed between the interior ceiling and the exterior roof. It’s very important that these construction types be well-ventilated and sealed to prevent moisture problems. They, too, usually require the expertise of a insulation contractor.
Here are the steps either you or an insulation contractor should take to insulate or add insulation to your unfinished attic:
You can put glass or cotton fiber batt insulation over existing loose-fill or vice versa. As a rule of thumb, when adding more insulation, stay with the same type and/or weight of insulation. Heavier insulation will pack down your existing insulation and ultimately reduce the R-value of what was already in place. Just make sure that the new insulation doesn’t have a vapor barrier, which would trap moisture inside the old insulation. (More on that later.) If the existing insulation is or has been wet, find and correct the moisture problem. It could be a leaky roof, or it may be caused by too much air leaking up from your living space. When warm air from your house rises into the attic, it carries with it large amounts of moisture, too. When the moisture hits the cold surfaces of your attic, it can condense and cause a number of problems:
− wet insulation does not insulate well,
− mold growth and damage to sheetrock and other building materials.
To control moisture, also make sure bathroom and kitchen vents are not vented directly into the attic. They should be vented through the roof.
If there is already insulation in your attic with no vapor barrier under it, you can paint your ceilings with vapor barrier paint – especially in high-moisture rooms such as kitchens, bathrooms, and utility rooms. If some insulation already exists, it is important that new insulation not have a vapor barrier. Preferably, the new insulation should be unfaced – manufactured without a barrier attached. If unfaced insulation is not available, use the vapor-barrier type but remove the barrier or slash it with a knife.
Vents should be located on opposite ends of the attic, with some near the top and others near the bottom to allow for good cross-ventilation. Talk with a contractor about which types of vents would be best for your attic.
As you add insulation, it’s important to not block any combustion air supply source or any ventilation openings, especially in the eaves. Ventilation chutes should be installed during the insulation job to prevent vents from being blocked off. Also, keep insulation three inches away from recessed light fixtures, chimneys, fan motors and flues to reduce fire danger. Do this by surrounding the objects with a sheet metal barrier. Also, extend the barrier four inches above the finished insulation level. While it may be rare, if you have a water heater, furnace or knob and tube wiring in your attic, consult a professional for information on insulating around these obstacles.
Whatever insulation type you choose, follow the manufacturer’s directions carefully and don’t unwrap the insulation until you get it up in the attic. Also, since you’ll be spending time in a dusty space, wear a respirator dust mask, work gloves and protective clothing. It’s a dirty job, but well worth the doing!