|
Reflective and Batt Insulation used Together in a Wall
Fiberglass insulation does not adequately control air infiltration. Cutting the batts to accommodate electrical boxes, ducts, wiring, plumbing and chimneys creates a free air path through the wall cavity or attic floor. Rigid insulation or reflective insulation attached over the studs instead of in between them provides a tighter air barrier. Sprayed foam insulation also seals and insulates by creating a barrier against air infiltration.
Health and safety issues for installers are a major disadvantage of installing fiberglass insulation. Issues include potential cancer risk from exposure to glass fibers (based on animal studies) and formaldehyde off-gassing from the resin used in the backing and petrochemicals in the resin. Green building practitioners shun fiberglass insulation altogether.
Direct contact with fiberglass and exposure to airborne fiberglass dust can irritate the skin, eyes, nose and throat. In addition to physically protecting your self from fibers during installation with safety gear, installers are advised not to scratch or rub skin or eyes until after thoroughly washing in the shower.
Fiberglass also has the lowest R-value per inch of any insulation on the market - another serious disadvantage. The average resistance of fiberglass insulation to convective air flow is R-3 per inch.
Comparison with other kinds of insulation
Table 2. Average R-values of Insulation Materials
| Insulation type |
R-value per inch of thickness |
| Fiberglass blanket or batt | 2.9 to 3.8 |
| Loose-fill cellulose | 3.4 to 3.7 |
| Expanded polystyrene board | 3.6 to 4 |
| Extruded polystyrene board | 4.5 to 5 |
| Polyisocyanurate board, unfaced | 5.6 to 6.3 |
| Polyisocyanurate board, foil-faced | 7 to 8 |
| Spray polyurethane foam | 5.6 to 6.3 |
| 2 layers of foil -polyethylene bubble core | 4.9 to 14.1 (1/4 inch thick) Details |
| 2 layers of foil -fiberglass core | 7.6 to 10.3 (1/4 inch thick) Details |
| 2 layers of foil -polyethylene foam core | 14.5 (1/4 inch thick) Details |
Don't use Fiberglass Insulation in Basements
Moisture problems in basements have lead experts to recommend against using fiberglass batt or blanket insulation in a basement. The old standard installation of fiberglass batt insulation between framed stud walls on the basement interior with a vapor barrier over the studs is no longer recommended because of excessive problems with mold, mildew, decay and rot.
To maintain its effectiveness, fiberglass must not be exposed to high-moisture conditions such as a damp basement. Moisture will negate the insulation value of fiberglass batts and promote mold and mildew which degrade indoor air quality. Installing a vapor barrier over the interior of the fiberglass will prevent the foundation walls from drying to the interior, a problem with mitigating capillary rise, groundwater leakage and construction moisture. Batts with no vapor barrier will not be effective either as interior humidity will still be a problem.
Current recommendations for basement interior insulation involve placement of a layer of rigid foam or reflective insulation (or both) against the foundation wall. This will keep wood framing and drywall away from the damp masonry wall.
Reflective Insulation
The latest advance in insulation in recent years by far is reflective aluminum insulation used as a radiant barrier. While other types of insulation like fiberglass are made to resist or impede the flow of warm air, reflective insulation reflects back radiant (infra-red) energy from the sun so it does not penetrate the building. It can also reflect back radiant heat inside the house so it does not escape. The concept is simple: each unit of radiant heat energy that is reflected away from your home in summer and each unit reflected back inside during winter means less operation of your air conditioning and heating systems, less wear and tear on your equipment, and less money you pay in utility costs.
Reflective insulation is commonly made of either aluminum foil attached to some sort of backing material or two layers of foil with foam or plastic bubbles in between creating an air space to reduce convective heat transfer also. The aluminum foil component in reflective insulation will reduce radiant heat transfer by as much as 97%. Reflective insulation has the highest R-value per inch of any insulation on the market.
Radiation is the transfer of heat (infra-red radiant energy) from a hot surface to a cold surface through air or a vacuum. Radiation is the dominant method of heat transfer in a building accounting for 65-85 percent of all heat transfer through walls, ceilings, attic and floors. Reflective insulation is an effective barrier against radiant heat transfer because it reflects back almost all of the infrared radiation striking its surface and emits very little of the heat conducted through it. Reflective insulation products also incorporate trapped air spaces as part of the system to retard the convective flow of heated air the way fiberglass insulation does. The total thermal performance of the reflective system varies with the size and number of enclosed reflective spaces within the building cavity.
Click here for a comprehensive article on the Physics of Foil to better understand the principles behind the use of foil as a radiant barrier.
Prodex Reflective Insulation
Advantages of using Reflective Insulation
- Light weight, very strong and easy to install
- Highest R value - up to R14.5
- Can be combined with other kinds of insulation in very cold climates
- Moisture-proof - will not allow moisture to pass through in either direction
- Eliminates condensation within the ceiling and walls when properly installed as a vapor barrier
- Unaffected by humidity with lower moisture transfer and absorption rates than mass insulation - no mildew, mold or fungus growth
- No significant mass to absorb and retain heat
- Very low emittance values "E-values" (typically 0.03 compared to 0.90 for most insulation) which significantly reduces heat transfer by radiation
- No change in thermal performance over time due to compaction, disintegration or moisture absorption - common concerns with fiberglass insulation.
- Easier to install than fiberglass - can be stapled, nailed, glued or sewn
- Safer for workers to install than fiberglass - there are no fibers to breath or cause skin irritation or eye irritation.
- Nontoxic and non-carcinogenic - does not irritate the skin, eyes, or throat and contains no substances which will off-gas.
- Carries a Class A / Class 1 Fire Rating.
- Radon retarder - will limit radon penetration through the floor.
- Not a nesting material for rodents, birds or insects.
- Attractive in areas where the insulation shows such as in a metal building.
- Energy Savings - Research conducted by the Florida Solar Energy Center (FSEC) has shown that the installation of a radiant barrier can have significant economic benefits. Attics account for approximately 22 percent of the heat gain in a typical Florida house. Installing an attic radiant barrier will reduce heat gain through the roof by about 40 percent. This equates to a savings of 8 to 12 percent on the annual electricity costs for air conditioning in a typical Florida home. The summer peak energy use savings was as much as 27%. This study also showed that the average peak reduction from the radiant barrier system was three times a great as that produced by added insulation (a change from R-19 to R-13).
- Basements - Any interior basement insulation must be able to dry to the inside should it become wet as the portion of the wall below grade will not ever be able to dry to the exterior. The insulation system must prevent warm inside air from reaching the cool foundation wall to prevent condensation. Reflective insulation is an effective interior air barrier. In addition, the insulation must be moisture tolerant and should not support mold, mildew or fungus growth or deteriorate when wet.
|
