UN 1.0—Introduction
Existing Homes underfloor weatherization measures include adding insulation, sealing floor penetrations, adding ventilation, installing a ground cover and adding water pipe insulation. Insulation shall be installed to reduce heat loss between conditioned space and unconditioned spaces, or to the outside of the house. Basements containing HVAC ducts or which have a direct access to the interior conditioned space of a home shall be considered conditioned space. Insulation installed between a conditioned basement and conditioned space of the home is not eligible for Energy Trust incentives.
All accessible underfloor areas, regardless of eligibility for incentives, must meet the applicable requirements to be considered a complete measure, unless a requirement is waived by Existing Homes or physical barriers exist (see section IN 1.5). Areas where existing insulation is greater than R-11 are not eligible for incentives. However, areas where existing insulation is greater than R-11 must meet all applicable specifications so that areas where existing insulation is less than R-11 may qualify for an incentive.
Insulation that is not in continuous contact with the bottom of the subfloor is not acceptable.
To qualify for an Existing Homes incentive, existing condition must be R-11 or less, and underfloor insulation must meet the following conditions:
- Compression of insulation is allowed to maintain continuous contact with the bottom of the floor.
- Insulation levels between R-21 and R-30 are allowed if insulation is in continuous contact with the floor and fills the entire cavity depth, from the bottom of the subfloor to the bottom of the joist or beam.
If standing water is found in the crawlspace, it shall be drained before the floor can be insulated. A sump pump may be needed for some situations. Draining the water is the responsibility of the homeowner.
Insulation shall be installed so that there is no air space between the insulation and the floor.
Before installing insulation in contact with active knob and tube wiring, electrical system shall be inspected and receive written approval by a licensed electrician. Insulating floors with active knob and tube wiring shall be at the discretion of the contractor and homeowner, and adhere to state and local code.
UN 1.1—Underfloor Preparation and Debris
Degradable and absorbent scrap materials, especially wood and cardboard, shall be removed from the crawlspace. The underfloor shall be checked for water leaks and wood decay before and after work occurs. The homeowner shall be notified and corrective measures taken, when necessary.
UN 1.2—Ventilation
Crawlspaces shall be ventilated by openings in exterior foundation walls. Such openings shall have a net area of not less than one square foot for each 150 sq. ft. of underfloor area. Where moisture due to climate and ground water conditions is not considered excessive, Existing Homes may allow operable louvers and the required net area of vent opening to be reduced to 1/300 or less (minimum 1/1500), provided the underfloor ground surface area is covered with an approved ground cover.
Openings shall be located as close to corners as practical and shall provide cross ventilation. The required area of such openings shall be equally distributed along the length of at least two opposite sides. Vents shall be covered with corrosion-resistant wire mesh with mesh openings not to exceed 1/4" in dimension. Existing vent openings covered with wire mesh need not be modified.
Where venting cannot be reasonably added except by breaching a foundation, ventilation requirements shall be waived.
UN 1.3—Ground Covers
All crawlspaces require a ground cover. All ground covers shall be a minimum of 6-mil black polyethylene. (Non-transparent ground covers may be used, if approved by Existing Homes). If an existing ground cover does not meet Existing Homes specifications, it shall be repaired or a new ground cover shall be installed. All seams shall be lapped at least 12". The cover shall be continuous with no rips, tears or gaps. Exposed soil or earth in a basement must comply.
UN 1.4—Sealing Floor Penetrations
To prevent transmission of water vapor and to support the effective R-value of the underfloor insulation, all floor penetrations are required to be sealed, including plumbing, wiring and duct penetrations, and similar openings in the air barrier of the underfloor. Caulk, foam or other compatible sealants shall be used.
Bathtub/shower drain accesses shall be sealed. If the drain trap is above the level of the floor, provisions to maintain accessibility for maintenance shall occur.
Illustration UN 1.4
UN 2.0—Basic Installation Procedures
Floor insulation shall be in contact with the floor. Compression of fiberglass batt-type insulation is permitted in order to assure continuous contact between the insulation and the subfloor. Use of un-faced batt-type insulation is acceptable. There shall only be one vapor retarder in the assembly and it shall be in direct contact with the subfloor and face the conditioned space of the home.
Kraft facing (commonly attached to batt-type insulation) is a vapor retarder. If kraft facing is attached, it must be in contact with the heated floor of the home.
Illustration UN 2.0A
Insulation shall be pulled free from any temporary stapling. Insulation shall be cut to fit without gaps or overlaps. There shall be no gaps at the perimeter of the foundation.
Illustration UN 2.0B
Insulation shall be supported so that it does not block or restrict crawl space ventilation. Insulation may be compressed, if necessary, to meet this requirement.
Spray foam and rigid foam insulation that meet the requirements of the specifications defined in this manual are acceptable for insulating underfloor areas–provided the installation complies with thermal and ignition barrier requirements for foam plastics, as detailed by the jurisdictional building code.
When installing foam insulation products, manufacturer's name, product identification and information to determine the end-use shall be left with the homeowner and presented to an Existing Homes representative for review during the QC process.
UN 2.1—Floor Insulation Support
Materials
Use one of the following materials
to support floor insulation:
Wood lath—Wood lath shall be a minimum of 1/4 x 1 inch.
Twine—Twine shall be non-stretching polypropylene or polyester.
Wire—Wire shall be stainless steel, copper or an equivalent material of similar corrosion resistance, with a minimum diameter of 0.040 inch (size 18 AWG). Self-supporting wire hangers are not acceptable.
Hand stapling is not a durable fastening technique and will not qualify a project for an Energy Trust incentive.
Fasteners for lath, twine or wire may be either hot-dipped galvanized nails, screws or corrosion-resistant staples that are at least 18-gauge and long enough to penetrate wood at least 5/8 inch.
Illustration UN 2.1
UN 2.2—Spacing Requirements for Support Systems
Staples shall be driven with a power-actuated stapler to achieve at least 5/8 inch penetration. The maximum spacing for support systems is as follows:
Table UN 2.2
Spans |
Maximum Spacing |
24 inches or less |
18 inches apart |
48 inches |
12 inches apart |
60 inches |
8 inches apart |
72 inches |
6 inches apart |
Wood lath shall not be used for spans greater than 48 inches. Splicing is not allowed to meet this requirement. Wood of thicker dimension may be used for wider spans.
Support systems for spans of over 72" or support systems not secured to the bottom of the joists require prior approval by Existing Homes.
Batt-type insulation shall be supported no more than 3 inches from the ends. This support shall be parallel to the end of the batt. Small pieces of insulation shall be supported.
Illustration UN 2.2
Insulation shall be supported so that it is in direct contact with the bottom of the subfloor sheathing.
Support systems shall be fastened to the underside of floor joists. Joists may be skipped; however, the maximum spacing shall not exceed 12". The maximum span of skipped joists shall not exceed 48".
UN 2.3—Water Pipe Insulation
All hot and cold water pipes not enclosed within the floor insulation shall be insulated to a minimum of R-3. Leaking water pipes shall be repaired before insulating them.
All water pipe insulation shall be secured with twine, corrosion-resistant wire or plastic compression ties. Tape is not allowed to secure water pipe insulation. Do not cover the handles and spigots of safety drain valves with insulation.
Fiberglass insulation shall have a minimum finished thickness of 1", be in continuous contact with the water pipe, and be secured every 12". Insulation shall be secured to the beam at a minimum of every 12" when water pipes run next to a beam or joist.
Pre-formed insulation shall be properly sized. Corners shall be mitered to fit tightly. The inside diameter of the pre-formed insulation shall match the outside diameter of the water pipes. Pre-formed insulation shall be supported every 24", and within 3" of the ends. If connections and corners are larger than piping, exposed joints shall be insulated with fiberglass or pre-formed insulation equal to the outside diameter of the connection and corners.
UN 2.4—Inside Access Doors for Underfloors
All operable accesses between unconditioned and conditioned spaces shall be insulated to R-25 for floor hatches, and R-15 for doors in walls. Insulation shall be securely fastened to access doors using staples and twine or a similar method that ensures the effectiveness and durability of the insulation. Inside access doors shall be weatherstripped.
Illustration UN 2.4
Alternatively, R-5 or greater rigid insulation installed between the access cover and a rigid protective material (OSB, plywood or other durable rigid material) under the entire insulation area is allowed. Insulation must be sealed around the perimeter to the access cover using caulk, adhesive or spray foam. The rigid protective material must be mechanically attached to the access cover to securely hold insulation in place. Access cover assembly must be tightly sealed using weather stripping around the entire perimeter.
UN 2.5—Outside Access Doors for Underfloors
Any outside access shall have a door that is easily opened to permit inspection, and shall be weather- and vermin-resistant. Vertical accesses may be screened when it is part of the crawl space ventilation system. Horizontal hatch covers shall shed water. Wood in contact with soil or concrete shall be pressure-treated.
Existing covers are acceptable, provided that they are in good condition, weather-resistant and vermin-resistant.
UN 2.6—Dryer Exhaust
Dryer exhaust ducts shall be vented to the exterior of the structure, sealed to prevent exhaust air from entering the building, shall have a back-draft damper, and shall terminate in a code-approved vent cap. New dryer ducts shall be rigid metal and shall be securely connected with mechanical fasteners and permanently supported. Exhaust systems shall comply with local code and manufacturer specifications, be as straight as practical and shall not exceed 25 feet. To prevent blockage with lint, dryer vent ducts shall not be connected with screws. A metal clamp or UL-rated foil tape may be used to secure dryer duct connections.
UN 2.7—Downdraft Exhaust Ducts
Downdraft exhaust ducts may have a 90-degree turn, shall exit through the foundation or exterior wall, be sealed (with no visible gaps) to prevent exhaust air from entering back into the building, and shall end in a code-approved vent cap.
UN 2.8—Miscellaneous Underfloor Specifications
Underfloor areas that allow easy human access must comply with the requirements defined in IN 1.7 Human Contact Areas, to protect occupants from encountering fibrous insulation in areas where routine storage or maintenance occurs.
When installing batt-type insulation with a vapor retarder, the vapor retarder shall face the heated area of the building. Do not install new insulation with a vapor retarder under pre-existing insulation.
Uninsulated walls between conditioned and unconditioned spaces in the underfloor area shall be sealed for air leakage, insulated to a minimum of R-15 and create a continuous thermal envelope. The floor cavities between joists that connect adjacent conditioned space to unconditioned space shall be sealed with a rigid air barrier. When no wall exists, one that extends to the bottom of the subfloor shall be constructed, and an effective air and thermal barrier shall be installed.
Exhaust systems for household appliances—dryers, ranges and miscellaneous exhaust fans—shall be vented to the exterior of the structure, and sealed with no gaps to prevent exhaust air from entering back inside the building. Exhaust devices with ducts in a crawlspace shall meet the same specifications as exhaust devices venting though attics (sections AT 1.7, 1.8, 1.9).
An air barrier or skirting shall protect underfloor insulation that is exposed to the wind, including unskirted crawl spaces and cantilever floors.
Unconditioned, unvented basements with concrete floors and walls do not require a ground cover, foundation vents or water pipe insulation, except for pipes located on exterior walls. Unconditioned vented basements with concrete floors and walls do not require a ground cover, but water pipes must be insulated according to UN 2.3. Basements with exposed soil or earth shall have a ground cover installed on exposed areas.
UN 2.9—Rim Joist Insulation (optional measure)
When underfloor insulation is not installed above a basement, insulation installed in direct contact with the wooden perimeter band or rim joist may qualify for the wall insulation incentive. Each joist bay shall be sealed for air leaks prior to installation of insulation. Batt-type or foam insulation used in this application shall be tightly installed, securely fastened, be at least R-15 and comply with state and local codes. A human contact barrier shall be installed over batt-type insulation. Incentives will not be paid for rim joist insulation installed in crawl spaces; underfloor insulation shall be installed in homes with crawl spaces.
UN 2.10—Installing Foam Insulation
Spray foam insulation may be used for insulating and air sealing an underfloor area either on its own or in combination with other insulation types (flash and batt). This assembly must meet the requirements for R-value, be in contact with the heated surface, and comply with the thermal and ignition barrier requirements for foam plastics as defined by the prevailing jurisdictional building code. There shall be no gaps or voids in the insulation assembly and all other applicable underfloor specifications shall be met.
Spray foam is exempt from support requirements. When used in combination with other insulation types, spray foam shall be installed in contact with the heated surface of the home.
Customers should be notified if spray foam insulation will limit access to electrical services, HVAC systems, or plumbing.