contents 1. Purpose of House Wrap 2. Types of House Wrap 3. House Wrap Selection Criteria 4. Benefits of Reflective Insulation as a House Wrap 5. Installation 6. References

The latest advance in house wrap in recent years by far is reflective aluminum insulation used as a radiant barrier. A radiant barrier reflects heat instead of either absorbing it or letting it pass through. 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 and less money you pay in utility costs.

Reflective insulation also performs all of the same functions of traditional house wrap. It is waterproof so it protects against water penetration from the outside which can cause damage to sheathing, framing and insulation. When properly installed, reflective insulation prevents air infiltration through cracks to keep moisture out and heat or air-conditioning inside further reducing utility costs. Reflective insulation comes as a solid aluminum foil sheet or pin-hole perforated to allow moisture in wall cavities to escape.

All new homes are wrapped during the construction process. House wrap is an important element of the building envelope for protecting both the life of your home and the integrity of the building materials behind the exterior siding. There are three main purposes for house wrap.

• Protect the building materials from exterior water penetration
• Reduce exterior air infiltration
• Block radiant heat from penetrating through walls

The primary purpose of house wrap is to protection the building from any exterior water (rain and snow) that penetrates the siding. When properly installed, house wrap will create a drainage plane that allows any water that has penetrated the exterior siding to drain away from the inner wall. Water that passes through to the interior building materials has the potential to cause many problems including wood rot, mold, mildew, fungus growth and insect infestations that will shorten the life of the building.

As many common household activities like cooking, washing and breathing add moisture to the building interior, the house wrap, insulation system, and ventilation system together must allow any water vapor inside the wall cavities evaporate. This is important in humid areas and cold areas where condensation is a consideration. Attaching siding to furring strips mounted on the outside of the house wrap will create an additional airspace for water drainage and evaporation.

House wrap is also an important instrument in reducing outside air infiltration. Reducing air infiltration will keep humidity out and eliminate drafts, helping improve the energy efficiency of the house and increase indoor comfort levels.

Using reflective insulation as house wrap will give you the additional benefit of a radiant barrier. Reflective aluminum foil insulation can reflect up to 97% of the sun’s radiant energy that strikes a house – a big boost to the effectiveness of the house insulation system. Studies have shown that using reflective insulation as a radiant barrier will dramatically cut air conditioning costs in warmer climates making it the energy efficient choice for house wrap.

Reflective insulation

Reflective insulation is commonly made of either 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 can be used by itself or in combination with other types of house insulation.

Reflective insulation has all the benefits of regular house wrap plus a radiant barrier. By using reflective insulation, you can replace typical rigid foam plus house wrap installations with a single product with a higher R-value as reflective insulation has two to three times the R-value of one inch of rigid foam board insulation.

Use a solid reflective insulation like Foil-Foam-Foil where building codes call for a vapor barrier on the exterior of the house. As this is usually in warmer climates, the radiant barrier capability of reflective insulation will be maximized. Use a perforated product like Foil-Foil where a vapor barrier should be place on the interior as in cold climates where condensation inside the walls must be prevented. The perforations will allow moisture in the wall cavities to escape. Using a solid sheet for house wrap in conjunction with a vapor barrier on the interior wall is undesirable as it can create a vapor lock.

Click here for a comprehensive article on the Physics of Foil to better understand the principles behind foil as a radiant barrier.

Other types of housewrap

• Spun-plastic sheet materials are commonly used as house wrap. They are wrapped around a house to protect against moisture penetration during construction. These materials keep water out, and allow moisture to evaporate but do not have any insulating power and do not reflect radiant energy.
• Building paper used as house wrap is a paper sheet or felt material that is either coated or impregnated with asphalt to increase its resistance to water penetration. Like reflective insulation, it can come perforated to let moisture evaporate but like plastic, it provides no insulation or radiant barrier.
• Rigid foam board insulation is naturally resistant to water penetration and can be used as combined insulation and weather-resistive barrier in some wall systems.

• Superior resistance to water penetration
• Moisture vapor transmission where no inner wall vapor barrier is in place.
• Strong and tear resistant for easy installation and prevention of leak and drafts through tears.
• Material should not absorb or retain water.
• Prevents air infiltration through gaps, cracks or holes.
• Surfactant resistant to resist oils and tannins used in cedar or cement siding, bricks and stucco as well as soaps used in power washing.
• Ultraviolet resistant for durability during construction before siding is put on.

• Clean, Lightweight, Flexible & Very Strong
• Easy to install
• Installation requires no special tools or clothing
• Can be stapled, nailed, glued or sewn
• Non-hazardous/Non-toxic/Non-carcinogenic
• Provides up to 19 DB of soundproofing
• Works in temperatures extremes as low as (minus) -20 degrees Celsius and as high as 80 degrees Celsius
• Vapor Barrier, waterproof, non-absorbent - reduces or eliminates condensation when properly installed
• Radiant barrier - reflects 97% of radiant heat
• Does not promote mold, mildew or fungus growth
• Does not provide nesting for birds, rodents or insects
• Provides Class A/Class 1 fire rated protection - meets fire and smoke safety requirements of most federal, state, and local building codes
• UV resistant
• Flexible at low temperatures
• Withstands fluctuations in outdoor temperatures
• Reinforced (Commercial Grade)
• Saves money and energy

Reflective Insulation

If your house exterior will use metal, vinyl, wood, brick or cement plank siding, an exterior house wrap (stucco walls use interior wrap) will be called for. During installation, the house wrap will be integrated into the building envelope along with other wall components including the house insulation, vapor retarder (if separate), flashing and framing members to create a complete weather protection system.

House wrap must be installed with no holes. Significantly more moisture can pass through a hole and into the wall by air infiltration than by diffusion through the material itself. To prevent holes, integrate the house wrap with flashing, windows, doors, floor, and ceiling. House wrap must be folded over the top plate and sealed to the foundation below the bottom plate.

Overlap is important to the proper functioning of house wrap. Roll out the house wrap material along the bottom first. House wrap higher on the wall should overlap the lower layer so that water running down will drain away from the wall. Since water can be driven sideways and also up the wall by wind, the house wrap vertical layers must include an overlap of at least 4 inches. An overlap of at least 8 inches is necessary when you start a new roll to prevent sideways water entry.

Special attention should be given to building corners. Nails should be no closer than 6 inches from the corner and all layers should overlap the corner by 16 inches. This will allow for an 8 to 10 inch overlay of the next roll and still be no closer than 6” from the corner for nailing. Tape all seams tightly.

Taping seams to form a tight weather barrier

Click here for comprehensive installation instructions using reflective insulation.

U.S. Department of Energy,
“Weather-Resistive Barriers, How to Select and Install Housewrap and other Types of Weather-Resistive Barriers”,
June 2000.

Typar Weather Protection System,
“Top Ten Reasons to Use Typar”,
http://www.typar.com.