Designs That Work
Cold Climate
Best Practices
High performance Building America homes in cold climates
must cope with substantial moisture drive from the building interior and
into the building enclosure during the heating season as well as ground
water and moisture issues given that full basement and crawlspace
basements dominate within this climate zone. Many if not most high
performance production homes within this climate zone are being equipped
with central forced air conditioning systems, introducing yet another
moisture stress that requires control in the design and outfitting of the
envelope and HVAC system.
The following Best Practices have been compiled primarily
from two BSC resources: the Building America Performance Targets
and the three Cold Climate Building Profiles, the “Denver,” the “Chicago,”
and the “Minneapolis.” All climate-specific Best Practices are
identified with a bolded and bracketed [C].
1. Process – Building Design, Systems Engineering, and
Commissioning
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Design for Energy Performance - Energy performance
40% better than the 1995 Model Energy Code base case house (i.e. equal to
10% better than Energy Star performance requirements).
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Systems Engineering
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Commissioning – Performance Testing
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Air leakage (determined by blower door depressurization
testing) should be less than 2.5 square inches/100 square feet surface
area leakage ratio (CGSB, calculated at a 10 Pa pressure differential); or
1.25 square inches/100 square feet leakage ratio (ASTM, calculated at a 4
Pa pressure differential); or 0.25 CFM/square foot of building enclosure
surface area at a 50 Pa air pressure differential. If the house is divided
into multiple conditioned zones, such as a conditioned attic or
conditioned crawl space, the blower door requirement must be met with the
access to the space open, connecting the zones.
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Ductwork leakage to the exterior for ducts distributing
conditioned air should be limited to 5.0% of the total air handling system
rated air flow at high speed (nominal 400 CFM per ton) determined by
pressurization testing at 25 Pa. Two acceptable compliance mechanisms are
(1) test duct leakage to outside at finish stage, or (2) test total duct
leakage at duct rough-in stage.
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Forced air systems that distribute air for heating and
cooling should be designed to supply airflow to all conditioned spaces and
zones (bedrooms, hallways, basements) as well as to provide a return path
from all conditioned spaces or zones. Interzonal air pressure differences,
when doors are closed, should be limited to 3 Pa. This is typically
achieved by installing properly sized transfer grilles or jump ducts (see
Transfer
Grille Detail
and the
Transfer Grille Sizing Table).
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Mechanical ventilation system airflow should be tested
during commissioning of the building.
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Testing of the house should be completed as part of the
commissioning process. The
SNAPSHOT Form is available for download as a
convenient way to record the testing information ().
Instructions
for completing the form are also available. Unique or custom house plans should each be tested. In a production
setting, each model type (i.e., floor plan) should be tested until two
consecutive houses of this model type meet testing requirements. At this
point, testing on this model type can be reduced to a sampling rate of 1
in 7 (i.e., 1 test, with 6 "referenced" houses). Small additions to a
floor plan (e.g., bay window, conversion of den to bedroom) should be
considered the same model type; major changes (e.g., bonus room over the
garage, conversion of garage into a hobby room, etc) should be considered
a separate model type.
2. Site – Drainage, Pest Control, and Landscaping
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Drainage – Grading and landscaping shall be planned
for movement of building run-off away from the home and its foundation,
with roof drainage directed at least 3 feet beyond the building, and a
surface grade of at least 5% maintained for at least 10 feet around and
away from the entire structure.
-
Pest Control – Based on local code and Termite
Infestation Probability (TIP) maps, use environmentally-appropriate
termite treatments, bait systems, and treated building materials that are
near or have ground contact (See
http://www.uky.edu/Agriculture/Entomology/entfacts.htm). [C]
-
Landscaping – Plantings should be held back as much
as 3 feet and no less than 18 inches from the finished structure, with any
supporting irrigation directed away from the finished structure.
Decorative ground cover—mulch or pea stone, for example—should be thinned
to no more than 2 inches for the first 18 inches from the finished
structure (See Building Profiles). [C]
3. Foundation – Moisture Control and Energy Performance
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Moisture Control - The building foundation shall be
designed and constructed to prevent the entry of moisture and other soil
gases. (See Building Profiles). [C]
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Semi-permeable rigid insulation should be used as both a
thermal layer and vapor control beneath the slab—a 6-ml poly vapor barrier
is required if rigid insulation is not used here. Use either rigid
insulation or poly, not both. [C]
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Sub-slab drainage shall consist of a granular capillary
break directly beneath the slab vapor barrier.
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Perimeter drainage should be used per the Building
Profiles – Cold Climates. [C]
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Use radon resistant construction practices as referenced
in the ASTM Standard "Radon Resistant Design and Construction of New Low
Rise Residential Buildings”.
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Energy Performance – A basement insulation system
(type of insulation, location, thermal/air sealing/vapor permeability
properties/fire rating) that controls the flow of heat and moisture is
required for this climate. A number of different approaches will work; a
number will not (see Building Profiles and
Basement Insulation Systems).
[C]
4. Envelope - Moisture Control and Energy Performance
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Moisture Control
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Water management - Roof and wall assemblies must contain
elements that provide drainage in a continuous manner over the entire
surface area of the building enclosure, including lapped flashing systems
at all penetrations. See the Building Profilesor the EEBA Water
Management Guide for specific details for various wall assemblies. [C]
-
Vapor management – Roof and wall assemblies must contain
elements that, individually and in combination, permit drying of
interstitial spaces. In this climate, control of the first condensing
surface by boosting the thermal resistance of exterior sheathing is an
important element of high performance construction. See
Building Profiles.
[C]
-
Energy Performance
-
Air leakage - Exterior air flow retarder—foam sheathing;
interior air flow retarder—gypsum board is sealed to the slab and frame
walls (Airtight Drywall Approach). For details of the ADA for interior air
flow retarder, see the
Building Profiles. [C]
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Windows - Recommend one of two approaches:
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U-factor 0.35 or lower and SHGC (solar heat gain
coefficient) 0.35 or less, regardless of climate.
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Climate-specific glazing properties if passive solar
orientation and design can be employed by the builder and occupants employ
proper window treatments and their use. [C]
5. Mechanicals/Electrical/Plumbing – Systems Engineering,
Energy Performance, Occupant Health and Safety, and Envelope/Mechanicals
Management
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Systems Engineering
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Energy Performance
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Occupant Health and Safety
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Base rate ventilation: controlled mechanical ventilation
at a minimum base rate of 15 CFM per master bedroom and 7.5 CFM for each
additional bedroom should be provided when the building is occupied.
-
Spot ventilation: Intermittent spot ventilation of 100 CFM
should be provided for each kitchen; all kitchen range hoods must be
vented to the outside (no recirculating hoods). Intermittent spot
ventilation of 50 CFM or continuous ventilation of 20 CFM when the
building is occupied should be provided for each washroom/bathroom.
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All combustion appliances in the conditioned space must be
sealed combustion or power vented. Specifically, any furnace inside
conditioned space should be a sealed-combustion 90%+ unit. Any water
heater inside conditioned space should be power vented or power-direct
vented. Designs that incorporate passive combustion air supply openings or
outdoor supply air ducts not directly connected to the appliance should be
avoided.
-
Provide filtration systems for forced air systems that
provide a minimum atmospheric dust spot efficiency of 30% or MERV of 10 or
higher.
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Indoor humidity should be maintained in the range of 25 to
60% by controlled mechanical ventilation, mechanical cooling, or
dehumidification. See
Relative
Humidity.
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Carbon monoxide detectors (hard-wired units) shall be
installed (at one per every approximate 1000 square feet) in any house
containing combustion appliances and/or an attached garage.
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Information relating to the safe, healthy, comfortable
operation and maintenance of the building and systems that provide control
over space conditioning, hot water, or lighting energy use shall be
provided to occupants.
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Envelope/Mechanicals Management
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Plumbing - No plumbing in exterior walls. Air seal around
plumbing penetrations in pressure boundary (air barrier) such as rim
(band) joist or ceiling.
-
Electrical - Seal around wires penetrating air barrier or
pressure boundary.
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