Build an IAQ Healthy Home
Adopted by the MIAQC Board of Directors on November 6, 2003
Copyright 2003 – Maine Indoor Air Quality Council
General Concern for Residential Air Quality in Maine
In Maine, and throughout the country, we are increasingly confronted by the realization that our homes can be harmful to our health. The risk of health effects from indoor environmental pollutants is a serious public health concern, both for the general population, as well as for those populations that spend more time in the residential environment: infants, young children, the elderly, and those with chronic illnesses. Maine residents face exposures to radon, carbon monoxide, lead, asbestos, mercury, tobacco products, chemicals and pesticides, pressed wood products, and biological contaminants. They also may find the air quality in their homes severely compromised by improper design and construction techniques, and/or by their own actions, such as improper renovations and poorly executed energy efficiency design, improper use of humidifiers and un-vented heating devices, and poor cleaning and maintenance practices. Health problems associated with increased levels of irritants and allergens in an indoor environment range from general symptoms of malaise (headaches, fatigue, irritability, nausea, dizziness, diminished ability to concentrate) to problems with asthma, sinusitis and other respiratory diseases. Exposure to toxic substances (such as carbon monoxide, asbestos, radon, lead, and mercury) may produce serious health effects if exposures are not prevented or reduced to acceptable levels.
The purpose of this document is to highlight those practices that need to occur during new residential construction to minimize the likelihood of poor air quality in a residential property. It is in checklist format, and is meant to be used in conjunction with other, more comprehensive building science resources. For every checklist item in this document, there are extensive building science resources that provide detailed “how-to” guidance. The checklist has been sequenced to the actual residential construction process – from site selection and design considerations, to finishing details and building occupant considerations.
Tip: Examples of outside resources include:
- Energy & Environmental Building Association’s Builder’s Guide to Cold Climates. Published with support from the U.S. Department of Energy’s Building America Program. See www.eeba.org.
- U.S. Environmental Protection Agency Indoor Environments Program. See www.epa.gov/iaq
- Standard 62.2, Ventilation and Acceptable Indoor Air Quality In Low-Rise Residential Buildings, published by the American Society of Heating, Refrigeration & Air-Conditioning Engineers. See www.ashrae.org.
This document is designed for new residential construction in Maine.
Guiding Principles of This Document:
There are a number of key guiding principles that apply to indoor environments, including new residential construction.
- There is a well-established link between indoor pollutants and occupant health. (See MIAQC policy statement on the health basis for recommendations)
- The principles for achieving a healthy and productive residential indoor environment are simple. The goal is an environment that is:
- Pollutant and Pest Free
(See MIAQC policy statement on Indoor Air Quality)
- While the methods to achieve these goals may vary, the primary best practice tools are:
- Prevention or Elimination of Pollutants (source control)
- Proper Ventilation
- Thermal and Humidity Control
- Proper operation of the structure by the building owner
- Proper use of the structure by the building occupants
(See MIAQC policy statement on Indoor Air Quality)
- There is a significant relationship between energy efficiency measures and indoor air quality in the residential construction process. (See MIAQC policy statement on energy efficiency and indoor air quality)
- Individual building components and subsystems must be considered collectively in terms of their interaction with each other and their joint IAQ impact on occupants and building performance. Failure to consider these interactions increases the risk for structural issues and systems failures that can result in health and safety concerns for residents. (See MIAQC policy statement on a Whole Building Approach to Indoor Air Quality)
- Building an IAQ healthy home does not necessarily cost more. While the installation of some features may initially be more expensive, they are essential for the health of the residential occupant, and have long-term value for energy efficiency and increased comfort. The recommendations that follow should never be sacrificed due to expense.
- Building an IAQ healthy home requires the equal involvement of the builder (and the builder’s subcontractors), the designer, and the homeowner.
New Construction Guidance – In order of Construction Process:
- A dry or drainable site is necessary to prevent moisture intrusion and subsequent biological contamination in the home.
- There is a link between the quality of the outdoor air and the quality of the indoor air. A site located away from significant sources of outdoor air pollution is preferred. (Examples: high traffic areas, industry, dry cleaners, bus-idling yards, etc.)
The building and site must provide effective drainage measures to control both surface water and sub-grade water and prevent it from entering the building.
- The finish grade on all sides of the building must be sloping away from the building to prevent water intrusion. Guideline: 4 inches of pitch for every 10 feet.
- Water from gutters and downspouts should be directed away from the building either above or below grade
- There should be no disparity between the quality of the home construction and the quality of the foundation on which the home sits. Contractors must understand the importance of the foundation in the quality of the home and its ultimate impact on moisture and IAQ.
- An improperly built foundation can be a primary culprit of air quality problems in homes. The air quality goals when constructing the foundation – no matter which type of foundation the design calls for (basement, slab or crawl space) – are to: prevent moisture (water and vapor) from entering the building through the foundation; let moisture (water and vapor) out if it gets inside; prevent intrusion of soil gases such as radon from entering the building; prevent heat loss in the winter; and prevent pests of all sizes from entering the home. The foundation is part of the “heated envelope” of the building. Designing to control moisture, minimize air leakage and minimize heat loss are just as important in the foundation as in every other part of the building.
- Anytime a sub-grade foundation footing, frost-wall, or basement wall is erected in such a manner as to interfere with the normal sub-grade drainage, a system to remove water must be installed. Where possible, sub-grade perimeter drain pipes should be installed and pitched to daylight. If a sump pump is needed to pump the water from the drain pipes to above ground, install a sealed-type container for the sump pump to prevent air and soil gases from entering the building.
- Always place a layer of coarse aggregate material under a basement floor to create a capillary break and to facilitate sub-slab radon mitigation.
Tip: Crushed rock is widely available in Maine and is economical. Other materials can be used as long as they are coarse and contain no fines.
- No matter the type of foundation being constructed, a barrier must be installed to keep moisture from getting in. Concrete will absorb water like a sponge if not effectively separated from contact with the moist ground. Barriers must be used on and around all foundation concrete footings, floors and walls, as well as exposed earth/ledge areas to provide an effective isolation from moisture in the ground.
- Efforts must be made throughout the construction process to maintain the integrity of this barrier. This includes sealing all penetrations through the walls and floor.
Tip:Options include foam insulation and/or vapor diffusion or waterproof barriers designed to eliminate contact between the concrete and the ground. Damp-proofing with black tar is only minimally effective at preventing concrete from absorbing moisture.
Insulation of the Foundation
- The foundation must be completely insulated: both its walls and floor. The foundation is a part of the “heated envelope” of the house and should be treated in the same manner as all of the living space regarding heat loss.
Tip: Installing rigid insulation (extruded polystyrene foam, minimum 1”) under the floor and inside or outside the walls of the foundation is a cost-effective method to insulate the foundation.
Uncontrolled Air leakage:
- The foundation should be made as airtight as possible. Use waterproof caulking and sealants to prevent air from moving in or out of the foundation.
Design Note: Consider the use of an insulated, monolithic slab.
- Less intrusive – Because it is built completely at or above grade, it takes the home completely away from sub-grade water.
- Lowers cost in a number of ways – easy installation of complete insulation and effective vapor barriers – easy to air-tighten – rarely needs any sub-grade drainage
- Useful for difficult sites, such as those with ledge
Handling & Storage of Building Materials:
Building materials that get wet and stay wet during the construction process are at risk for subsequent mold growth in the home.
- Keep building materials delivered to the site protected from rain and snow.
- Intrinsic moisture from the materials used in the construction process (concrete, joint compound, paint, etc.) must be given a means of drying out. Be careful not to “trap” moisture in the components of the building.
- Complete frame of house before delivery of weather sensitive materials.
- Installing bituthane on full roof surface is an excellent means of protecting home while waiting for roofing completion/installation. (Refer to manufacturer’s specifications to prevent over-exposure of this material.)
- Dry lumber to 15% moisture content or less before covering. If lumber shows signs of mold growth, use a HEPA vacuum and detergent wash, then dry to 15% moisture content. Sand if needed after drying to remove surface mold.
Regardless of the type of framing system used, careful attention to details during the framing stage is necessary to prevent future indoor air quality problems. Framing details most often associated with indoor air quality include: energy efficiency, proper sealing, thermal breaks, accommodating the ventilation system, moisture control, and pest control.
- Seal the sill and band joist area to eliminate potential for air/moisture leakage and pest intrusion.
- Minimize heat loss through the frame of the building by properly sealing and insulating during the framing process. Often, there are pockets or voids in the exterior frame of the house that can only be sealed or insulated during the framing process.
- During the framing process, it is important to think about how continuous air and vapor barriers will be installed. Provisions to accommodate the installation of the air/vapor barrier, particularly at the more difficult junctures behind interior wall partitions and floor systems, should be made during the framing of the home.
Tip: Consider using pieces of foil-faced foam to seal between floor joists, or installing strips of air/vapor barrier behind where interior walls will intersect the exterior walls so that the continuous air/vapor barrier can be attached to the strips at a later date.
- Try to create some kind of a thermal break for the frame of the house. The wood frame of the house is not as good an insulator as the insulation placed within the frame and can conduct heat to the outside.
- Consider using foam sheathing on the interior or exterior of the frame to help reduce heat loss and minimize the risk of cold spots and condensation.
- Consider using a layer of foam insulation between the structural members of window and door headers to help reduce heat loss.
- During the framing process, it is important to think about how the ductwork for the ventilation system will be installed. Keeping the ductwork within the boundaries of the heated envelope will prevent the risk of condensation and subsequent biological contamination, as well as result in a more durable distribution system for the customer.
Design Note: During the design phase, be sure to discuss how best to route the ductwork for your ventilation system throughout the home.
- Don’t put any plumbing in exterior walls. Plumbing should be located in interior walls that are easily accessed for leaks and repair.
Durable Exterior Details:
To maintain good air quality in a home, the home itself must remain dry. Water/vapor intrusion into the walls or ceilings of the home can provide the perfect, hidden environment for mold growth. The primary function of the roofing, cladding, drainage plane, sheathing, flashing, windows, doors, and gutters, is to keep water and water vapor from coming into the home. Other indoor air quality concerns associated with the durable exterior details include the prevention of pests from entering the home.
Guiding principle: construct the home so that water goes down, off, and away from the home.
Design note: During the design phase of the home, consider the positive impact that larger roof overhangs can have on keeping the home dry.
- Prevent water leaks by properly installing the roofing material, flashings, and membranes so that water flows down, off and away from the home.
- When using a ventilated roofing system, ventilate it properly to prevent winter ice dams, leaking, and potential for subsequent mold growth. Please refer to the outside sources noted at the beginning of this guide for detailed guidance and illustrations.
- When using an unventilated roofing system, it is critical to pay close attention to the quality of the air and vapor barriers and the insulation to prevent condensation at leak points. Unventilated roofing systems are not preferred in Maine.
- Use a bituthane membrane on eaves, valleys, roof to wall intersection, and other penetrations such as skylights and stack vents, prior to installing the roofing material.
All cladding will leak, and should not be considered a functioning part of the drainage plane. Cladding is primarily an aesthetic, visual detail.
- A properly installed and sealed drainage plane is essential to prevent water and moisture from leaking into the structure and coming in contact with the frame and insulation of the building. It also serves as the primary means for moisture to flow down, off and away from the building.
- If house wrap is used as a drainage plane, all seams should be properly overlapped and taped or sealed so that it is continuous.
- Penetrations for windows/doors, vent hoods, water spigots, chimneys, and wires must be sealed to the drainage plane.
- All windows and doors must be properly flashed and sealed.
- For wood and fiber cement siding, create a space between siding and drainage plane (a “rain screen”) to allow for drainage of water down and out, and allow moisture to dry from the back of the siding.
- Install insect screen at the base of the rain screen to prevent pests from entering the home.
Tip:Use “cedar breather” when installing cedar shingles. Use 1″ x 3″ vertical strapping when installing clapboards.
Windows & Doors:
The primary indoor air quality principle for windows and doors is energy efficiency. Using energy efficient windows and doors will minimize the amount of cold air that leaks in and reduces the possibility of condensation and resulting mold growth.
- Use low-E glass with argon gas between the panes.
- All windows and doors should be sealed and caulked in place.
- All windows and doors should be properly flashed.
- Select insulated exterior doors with good weather stripping
Tip: Look for windows that have a good ANSI performance rating.
The primary function of insulation is to prevent heat loss in the winter and heat gain in the summer. Insulation helps to keep inside surfaces of walls and ceilings warm during the heating season, and cool during the summer season, thus preventing the possibility of condensation. In order for insulation to work effectively, it must be protected by properly installed air and vapor barriers. (Exception:
rigid insulation and spray in place foam, if properly sealed, usually create their own air and vapor barriers.)
- Insulation must be properly fitted within the wall and ceiling cavities. Gaps will cause cold spots, creating potential for condensation and subsequent mold growth.
Tip: Make sure insulation is properly fitted into the wall cavities around and behind electrical boxes, and behind wiring.
Tip: Installing foam insulation board over the frame of the house creates a thermal break on the frame that reduces the flow of heat and prevents cold spots and subsequent condensation on the frame.
- When using a ventilated roof system, be sure to use baffles to channel air from soffit to attic where it can be ventilated to the outdoors.
- For guidance on selecting appropriate R-value of insulation, refer to state and local codes, (Such as IRC, IECC, NFPA, ASHRAE) and other professional standards. Regional recommendations for the building site climate should also be considered.
Air and Vapor Barriers
- It is critical that both an air and vapor barrier be installed to prevent air and moisture from leaking in or out of the home in an uncontrolled manner. These are generally combined as one product, but can be installed as two separate systems.
Tip: As noted in previous sections of this document, it is important to consider installation of the air and vapor barriers throughout the construction process.
- It is important to consider the wall between the house and an attached garage as an exterior wall. Insulation, air, and vapor barriers should be installed in the same manner as any other exterior wall so that the garage is “thermally separated” and sealed off from the house, greatly reducing the risk of pollutants from the garage entering the house.
Design Note: Consider designing the garage as a separate building to eliminate the risk of pollutants in the garage from entering the home.
Air barriers serve to keep outside air outside and inside air inside, thereby eliminating points where condensation can occur. Air barriers should be:
- Continuous and connected to previously installed portions of the air barrier (see Foundations and Framing sections of this document.)
- Located within building envelope
- Seal all penetrations.
In Maine, vapor barriers serve to prevent moisture from entering the building envelope from the inside. Vapor barriers should be:
- Applied to warm side of insulation (for Maine climate)
- Continuous and connected to previously installed portions of the vapor barrier (see Foundations and Framing sections of this document.)
- Seal all penetrations
Tip: Have sealant tape and expandable foam available for subcontractors to repair any penetrations to either barrier. Explain to them the importance of doing so.
- A controlled ventilation system must be installed in all new residential construction in Maine.
- A fully-ducted heat recovery ventilation system is preferred.
- It removes stale air and pollutants from the entire home.
- It provides fresh air to the entire home.
- It reduces energy costs
- It increases occupant comfort.
Tip: Installation of a fully-ducted heat recovery ventilation system is more expensive up front, but yields long-term energy savings.
- All ductwork must be mechanically fastened and properly sealed (not duct tape)
- All ductwork must be protected from construction debris.
: It is important to accommodate the installation of the heat recovery system during the design phase. Consider use of open web floor trusses.
- It is possible to ventilate a home with an exhaust-only ventilation system comprised of:
- Bathroom fans vented to the outdoors, never to the attic
- Kitchen fans vented to the outdoors.
- A means for allowing fresh, outside air to enter the home
- All gas oven/range appliances must have a range hood direct vented to the outside.
- All clothes dryers should be vented to the outside to prevent high moisture levels in the home
- If burning fossil fuel, a sealed-combustion heating unit (direct vented to outside) is preferred so there is no pathway for carbon monoxide (CO) to enter the home. This includes all wood-burning appliances as well as gas burning appliances used for heating. For non-sealed combustion units, a de-pressurization test should be conducted to determine if make-up air is required and to ensure proper operation of the appliance venting system.
- Combustion appliance outdoor vents have a code-regulated setback from exterior windows, doors, overhangs, etc. to prevent infiltration of combustion by-products from entering the home. Refer to manufacturer’s specifications for setback details.
- If using a ducted forced hot air system – use high efficiency filters and install registers in walls rather than floors to minimize intrusion of dust and particulates into registers and keep the air in the home cleaner.
- Never use unvented gas and kerosene heaters indoors.
Design Note: When using a ducted forced hot air system in well insulated homes, providing conditioned air through registers installed just inside exterior walls is not as important as it was before homes were well insulated. Registers supplying conditioned air at interior walls can save money and enhance occupant comfort.
- Never install plumbing in outside walls
Tip: Consider insulating cold water pipes that may be prone to condensation in summer months.
- Seal all plumbing penetrations passing through the air and vapor barriers.
- Test the plumbing systems before finishing the interior to maintain access to repair leaks and to prevent water damage to porous materials.
Seal all penetrations of electrical wires with caulk and foam
- Install air tight outlet boxes in exterior walls and insulated ceiling
- Insulate behind and air seal electrical panels that are installed on exterior walls
- When a recessed lighting fixture penetrates the vapor barrier, use insulation-contact (IC rated) recessed lighting fixtures.
- Use low or no-VOC paints and finishes
Tip: Delay occupancy by 3-4 weeks to allow for off-gassing of VOC’s (volatile organic compounds) from paints and finishes. If you cannot delay occupancy, keep the heat at 70 degrees Fahrenheit and open windows 1-2 inches to increase ventilation.
- If using particle board cabinetry or furniture, seal exposed edges to prevent off-gassing of VOCs (volatile organic compounds) or consider using or purchasing solid wood cabinetry and furniture.
- Never install carpet in an area likely to get wet
- Damage to the air and vapor barriers must be sealed and repaired before covering.
Landscaping schemes can sometimes contribute to air quality problems in a home. Plants, shrubs and trees placed too close to the building can contribute to moisture problems and provide easy access points for pests to enter the home.
- Foundation plantings should be set away from the dripline of the roof and at a minimum of 24 inches away from the foundation at full maturity.
Tip: Place a two-foot wide strip of pea-stone or non-woody mulch, with landscape cloth underneath, to discourage insect and rodent infestation and prevent vegetation from growing next to the foundation.
- Shade trees should be set far enough away from the home to prevent pest access and eliminate foundation damage from root penetration.
- Exterior vents should be kept free of obstacles
- Finish grade should be no less than 8” away from any wood surfaces