Chapter 21: Air Sealing

1. Introduction

Air leakage can account for over 50% of a home's heating and cooling costs, and contribute to problems with moisture, noise, dust, and entry of pollutants, insects, and rodents. Commonly used sheet materials, such as drywall, sheathing, and decking, are effective at stopping air leakage. The key is to seal all holes and seams between sheet materials to create a continuous air barrier. Airsealing must be done throughout the construction process: during framing, prior to insulating and installation of interior finish materials, after installation of fixtures, and as a part of the final punch-out. Volunteers will have numerous opportunities to assist in creating a properly air sealed Habitat home.

2. Safety Issues

Foam insulation can be harmful if inhaled or when it comes into contact with a person's skin. When handling foam insulation wear gloves, goggles and a face mask. Do not allow anyone to work without a face mask.

If foam insulation gets on your skin, follow the directions on the can for proper treatment.

3. Prior tasks to have been completed before starting

• All rough-ins (electrical, plumbing, security, and HVAC) complete and inspected.
• All drywall nailers and blocking installed.
• All doors and windows installed

4. Recommended Staff/Crew Assignments

Air sealing is completed in multiple stages throughout the build. Most jobs surrounding air sealing will require one or two crews of 3-4 volunteers.

6. Tools/Equipment list

Tools & Equipment Needed at Each Site:

• Extension Ladder (16')
• Step Ladders (8')
• Step Ladders (6')
• Caulking gun

Tools Each Crew Member Will Need:

• Retractable Utility Knife with Extra Blades
• Measuring Tape (16' Min.)
• Safety Glasses
• Work Gloves
• Face Mask

7. Material List

• Caulk
• Insulation Foam
• Duct Sealing Mastic

8. Quality Checkpoints

____ All sheet material holes filled
____ All ductwork seams properly filled
____ All plumbing and electrical penetrations properly sealed
____ Attic hatch properly insulated and sealed

9. Construction Drawings and Text

NOTE: The following drawings, diagrams, and text are to be used on the job site when a question arises as to methods and procedures associated with the task. The notes on the drawings have been geared toward use as a quick reference. If a more in-depth explanation is needed, please read the text description. But most importantly, consult your Habitat Site Supervisor and Construction Manager for advice as needed.

1. Air Sealing:

During earlier construction phases, the installation of various sheet goods (drywall, sheathing, etc.) by volunteers can result in the creation of large gaps between pieces of material. These gaps are often hidden from view like under the bath tub. Avoiding these gaps is inexpensive during construction. The key is to identify problem areas in the design process, assign the responsibility for sealing the holes, then checking to ensure the air sealing was done effectively.

The first priority to air sealing should be no large holes in the sheet materials that form the air barrier. In addition, air sealing must be done throughout the construction process: during framing, prior to insulating and installation of interior finish materials, after installation of fixtures, and as a part of the final punch-out. The materials that form the air barrier must be designed to provide a seal that will last the life of the home or be easily re-applied by the home owner.

The air sealing tasks will be divided into those tasks that should be done prior to installing drywall and those tasks that should be done after the drywall is installed.

Air Sealing-Before Drywall
Seal the bottom plate of exterior walls with caulk by sealing the inside edge after the walls are raised.

 For bath tubs on outside walls, insulate the exterior wall and air seal behind the tub with sheet goods before the tub is installed. After the drain is installed, seal the tub drain penetration with rigid foam insulation and spray foam.

Seal windows and exterior doors with backer rod and caulk or spray foam. Be careful when using spray foam as it can expand and pinch jambs and may void some window warranties.

Seal all electrical wire, plumbing, and HVAC penetrations between any conditioned and unconditioned spaces.

 Air Sealing-After Drywall
Seal all electrical switch and outlet boxes to drywall with caulk.

Seal all light fixture boxes to drywall with caulk.

Seal bath and kitchen ventilation fans to drywall with caulk.

Seal all duct boots to the floor or drywall with caulk or mastic.

Seal any plumbing penetration through drywall with caulk.

If not done before drywall installation, seal the tub drain penetration (from the basement) with plywood or rigid board insulation and caulk or backer rod.

 For the attic access hatch, insulate the top of the hatch board with at least two inches of rigid foam insulation or fiberglass batt; seal the hatch opening with weather stripping.

Sealing Ductwork

One of the biggest energy wastes in a new home can be found in leaks in the ductwork of forced-air heating and cooling systems. Leaky ductwork often accounts for 10 to 30 percent of the total heating and cooling costs in a home. If the duct leakage is 20% of the total air flow in a home, the efficiency of the cooling system can drop by 50%. Heating efficiency is similarly affected. Duct leakage also lowers the heating and cooling capacity, and can lessen equipment life.

First, the leaks in the ductwork must be located. Begin with a visual inspection of the system. All joints in the ductwork should be sealed. The joints are properly sealed with a duct sealing mastic. Starting at the furnace, a crew assigned to duct sealing should begin inspecting and sealing each joint in the ductwork. Particular attention should be made to the elbow joints at the register boots. Seal the joints in the boots and seal the boots to sheet goods (drywall, subfloor) with mastic. In addition, seal both joints at the elbow to ensure a completely sealed joint. Continue sealing the ductwork throughout the entire home in this manner.

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  Page last updated Saturday, May 3, 2008 at 6:40:07 PM