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How to Minimize Air Leaks on a Building InspectAPedia®  -     Keeping it Tight: how production builders keep air infiltration to a minimum with careful planning and plenty of caulk Guide to preventing building air leaks & air infiltration Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

This article discusses how builders minimize air leaks during construction, planning, layout, and use of caulk sealants. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Readers interested in building tight homes, sealing air leaks, and stopping un-wanted heat loss and heat gain should see AIR SEALING STRATEGIES, also see AIR BYPASS LEAKS, see AIR LEAK DETECTION TOOLS and see Convective Loops & Thermal Bypass Leaks . Contactus to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Solar Age Article on minimizing air leaks in buildings by proper design and layout as well as judicious use of sealants

"Keeping it Tight: production builders are keeping air infiltration to a minimum with careful planning and plenty of caulk" - links to the original article in PDF form immediately below are followed by an expanded/updated online version of this article.

• Keeping it tight - PDF form, how to minimize air leaks in buildings, part 1 - use your browser's back button to return to this page
• Keeping it tight - PDF form, part 2 - use your browser's back button to return to this page

Cutting the air exchange rate in a building from 0.50 to 0.25 air changes per hour will typically produce the same range of savings as doubling wall R-values from R-20 to R-40 and can be done for much less money. Dollars put towards caulking and sealing is money well spent. Builders, snooping around with smoke pencils and infrared cameras using thermography (thermal images showing areas of unwanted heat loss or gain) have identified a number of trouble spots in new construction - some obvious and some not.

This article focuses on proper air sealing in new building construction. For a detailed article on weatherization retrofit procedures to find and stop un-wanted heat loss or gain in existing buildings see HEAT LOSS DETECTION TOOLS.

Making an Air-Tight Building Shell

Energy conscious builders establish their first line of defense while roughing the building shell.

First floor framing sealing against air leaks

Begin at the beginning with an inexpensive fiberglass or foam sill sealer, compressed between the sill plate and the foundation wall (illustration at left). This is a tricky area to caulk later, so get it right the first time, doubling the sill sealer where necessary to fill larger gaps between the sill plate and the top of the foundation wall.

As the band joists (rim joists) are laid up, add a bead of caulk between the band joist and the sill plate.

Follow with a bead of caulk between the subfloor and the rim joist and sill.

Continue with caulk between the subfloor and the band joist, and between the subfloor and the bottom plates of the outside walls.

This glued-up assembly will help prevent air from flowing under the exterior walls or between basement and outdoors. If insulating sheathing is used, butt and seal rigid wall insulation to exterior foundation insulation where they meet at the sill. If possible, keep wall and foundation insulation flush on the building exterior so that the siding can be carried right over the joint with no flashing. This makes for tight, neat, and easy exterior detailing.

Second floor sealing against air leaks

In a two-story structure, caulk around the second floor band joist the same as at the first floor. Caulk the upper top plate to the band joist, band joist to subfloor, and subfloor to the bottom plate of the second story wall.

Sealing at building corners

Building corners tend to be leaky and un-insulated. They deserve special attention. As in other exterior joints that coincide with breaks in the interior finish, caulking is helpful here. Seal either sheathing to sheathing, or sheathing to framing. If insulating sheathing is used, run a length of tape up the corner. See FRAMING DETAILS for BETTER INSULATION for details of building corner framing techniques to improve insulation and sealing.

If a permeable sheathing is used, the entire building, from sill to top plate, may be wrapped and taped with an air and water barrier that "breathes" such as Dupont's Tyvek® or Parsec's Airtight White™. If these materials are fully taped at seams and door and window openings, they could eliminate the need for much of the exterior caulking. See HOUSEWRAP AIR & VAPOR BARRIERS for details on selection and use of these products.

Sealing Air Leaks at Interior Building Framing

Builders have been surprised to discover how much air leakage occurs through cracks and holes in interior building partitions. Convective heat loops also occur in uninsulated building interior partition walls, even if the walls are sealed at top and bottom. (See Convective Loops & Thermal Bypass Leaks).

Stop these leaks at the source by isolating interior stud cavities from basement, attic, and outside walls. Holes and notches for plumbing and wiring are the main culprits. But interruptions in the interior vapor barrier, where partitions meet outside walls and ceilings are also potential leaks. To prevent breaks in the interior air/vapor barrier, secure a piece of polyethylene on the ceiling or outside wall before erecting the interior partition. This piece can then be overlapped to join the full poly vapor barrier when later installed. Make these and all laps in the poly barrier over a framing member (many prefer two) so that the sheets will be compressed together by the drywall.

Holes drilled later through the top or bottom plates into unconditioned spaces should be sealed with a shot of foam or, if smaller, a glob of caulk.

Sealing Air Leaks at Doors & Windows

The standard approach to caulking doors and windows - between exterior casing and siding rarely does an adequate job. These notorious heat thieves merit a double dose of protection. So seal them from both outside and inside.

Aluminum and vinyl-clad windows generally install by nailing through an exterior flange. A bead of caulk gunned under the flange seals these units with minimal effort. Similarly, a bead of caulk under the exterior casing on all-wood units may do the trick. but in these a little more care is needed at joints and miters in the exterior trim.

On the inside, aim for an airtight seal between the jamb and rough opening. Some builders choose to foam this gap. This is best done with a small bead shot deep into the gap where the window unit can resist the forces of the expanding foam. (Windows have actually cracked!). As extra protection, a tight fitting length of wood can be tapped into the window jamb to hold it true while the foam sets up. The remainder of the space can then be stuffed with fiberglass.

If the poly barrier is sealed intact to the window jamb, then fiberglass alone should suffice in the rough opening. To achieve a good seal here, run the vapor barrier right across the window opening and make diagonal cuts from window corner to window corner. Insert these flaps between the window jamb and the interior casing. Trim the excess with a sharp knife. A low infiltration window, sealed thus, should leave you and your smoke stick draft free.

Interior Finish Sealing Details Against Air Leaks

Airflows seem to ignore baseboards, drywall joints, and miscellaneous interior trim, so seal your vapor barrier well to subfloors and lap it at corners between walls and between wall and ceiling.

At this point, things are looking pretty good except those messy cuts around pipes and electrical boxes. these necessary evils to a well-sealed home can be dealt with in several ways. Strapping out the drywall 3/4-inch off the studs and vapor barrier adds both an insulating air space and a convenient conduit for plumbing feeds and wiring. Shallow boxes can be installed here without puncturing the vapor barrier.

WARNING: wiring and copper piping in locations exposed to damage from future nails and screws that may be driven through drywall to hang a picture, say, must be protected by steel plates, or routed deeper into the wall cavity. One of our -DJF- friends called to say that on moving into his new home he drove a picture nail through drywall, only to hear a hissing sound. His mistake was to pull the nail, converting a small water supply leak from a punctured copper pipe into a large one before he turned off the water.

Some builders have had good luck with slitting a tight X in the vapor barrier and taping the flaps to the inside of the box with polyethylene tape. Use a plastic box (without all the holes) and caulk where the wire enters the box. WARNING-DJF: Be careful: adding any combustible material inside of an electrical box or panel may violate electrical codes and could add to a future fire risk.

The Vapor Box™, a shallow plastic pan, designed to fit around and seal off electrical boxes, is manufactured in Canada.

Electrical boxes should be sealed on inside walls as well, but without a vapor barrier, different strategies apply. Caulking or foaming plastic boxes to the drywall should do the trick. WARNING-DJF: if you're using foam to seal around electrical boxes, take not not to squirt foam inside of the box itself. The foam gaskets work ok if electrical box and drywall are lined-up just right. On ceilings, try to keep wiring and shallow electrical boxes on the warm side of the vapor barrier by strapping over the poly. WARNING: see our note above about protecting wiring from damage - a lower risk at ceilings.

Seal off plumbing where it crosses from unconditioned to conditioned spaces. Plumbing in outside walls will prove harder to seal and exposes pipes to possible freezing. One or two strategically placed plumbing chases make it easier to recognize and seal these leaks - but don't forget to take a look at Convective Loops & Thermal Bypass Leaks when using this approach.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Blower Door Test Results on New Construction

Trying to take some of the guesswork out of the battle against air leaks, solar designer Terry Brennan of Red Wing in upstate New York, puts his homes, half completed, to a blower door test and routinely finds the equivalent of a 1- to 2-square foot gaping hole in leftover cracks - even after a conscientious sealing job has been done on the building shell. Brennan prefers to run the test with exterior walls insulated and drywalled, and interior partitions open. Subfloors are still exposed and the attic is uninsulated to allow access to ceiling and partition leaks.

In new construction after building sealing, these air leaks appear at junctions of floors, walls, ceilings, and around chimneys and electrical fixtures. He has found interior partitions as leaky as exterior walls - due primarily to unsealed holes in top plates. On more than one occasion, he has found wide open recessed light fixtures (required to be left open by code) installed contrary to specifications. So much for specifications!

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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INSULATION & VENTILATION INSPECTION & IMPROVEMENT
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK MINIMIZATION
AIR SEALING STRATEGIES
ASBESTOS IDENTIFICATION IN BUILDINGS
ATTIC LEAKS, CONDENSATION & ATTIC MOLD
BATHROOM VENTILATION
BASEMENT LEAKS Moisture or Mold
BASEMENT HEAT LOSS
BLOWER DOORS & AIR INFILTRATION
BRICK LINED WALLS
BUCKLED FOUNDATIONS due to INSULATION?
CATHEDRAL CEILING INSULATION
CRAWL SPACES
  Crawl Space Dryout Procedures
  Crawl Space Safety Advice
  Crawlspace Mold Advice
  Media Blasting for Mold Removal
  Mold on Dirt Floors
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
ENERGY SAVINGS in BUILDINGS
ENERGY SAVINGS PRIORITIES
ENERGY SAVINGS RETROFIT CASE STUDY
ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE
ENERGY SAVINGS RETROFIT OPTIONS
ENVIRONMENTAL HAZARDS
FIBERGLASS INSULATION
FIBERGLASS HAZARDS
FIBERGLASS MOLD
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FREEZE-PROOF A BUILDING
HEAT LOSS CALCULATIONS
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
  BASEMENT HEAT LOSS
HEAT LOSS R U & K VALUE CALCULATION
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSEWRAP - TYVEK INSTALLATION DETAILS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INSULATION & VENTILATION INSPECTION & IMPROVEMENT
INSULATION CHOICES
INSULATION FACT SHEET- DOE
INSULATION IDENTIFICATION GUIDE
  Asbestos Identification in Buildings
  Asbestos-Free Insulation Materials
  Balsam Wool Batt Insulation
  Cotton Insulating Batts
  Cellulose loose fill insulation
  Concrete insulation, light-weight
  Fiberglass Insulation
  Foam Board Insulation
  Foam Insulation Types - Visual Id
  Homasote & Other Insulating Board
  Icynene Foam Spray Insulation
    Icynene Spray Foam
    R-values of Icynene® vs. Polyurethane Foam
    Mold Resistance of Foam Insulation
    Open-celled vs. Closed-cell Foam Insulation
  Insects & Foam Insulation
  Mineral Wool - Rock Wool Insulation
  Mold in Fiberglass Insulation
  Mold in Foam Insulation
  Paper Duct Insulation
  Perlite Insulation
  POLYISOCYANURATE FOAM INSULATION
  POLYSTYRENE FOAM INSULATION
  RADIANT BARRIERS
  RIGID FOAM USE INDOORS
  Urea Formaldehyde Foam Insulation UFFI
  URETHANE FOAM Deterioration, Outgassing
  Vermiculite Insulation
INSULATION MOLD
INSULATION LOCATION for BASEMENTS
INSULATION LOCATION for CAPES, CRAWLSPACES
INSULATION for GREENHOUSE or SOLARIUM
INSULATION MATERIAL IDENTIFICATION GUIDE
INSULATION R-Values & Properties
Insulation Values of Log Home Walls
INTERIORS of BUILDINGS
MOISTURE CONTROL in BUILDINGS
Mold Growth Resistance of Foam Insulation
MVOCs & MOLDY MUSTY ODORS
ODORS & SMELLS DIAGNOSIS & CURE
RADIANT BARRIERS
ROT, FUNGUS, TERMITES
  TERMITE SHIELDS vs TERMITICIDE
ROT, TIMBER FRAME
SOLAR ENERGY SYSTEMS
SOUND CONTROL in BUILDINGS
STAIN DIAGNOSIS
THERMAL MASS in BUILDINGS
THERMAL MASS in UPSTAIRS
THERMAL TRACKING & HEAT LOSS
  Ceiling Thermal Tracking Marks
  Wall Thermal Tracking Stains
  Floor Carpet Thermal Tracking Stains
  Air Bypass Leaks Marks on Insulation
  Thermal Tracking to Diagnose IAQ
  Stains HVAC Supply Registers
  Pet Stains on Floors
  Pet Stains on Walls
  Human Occupant Stains on Walls
  Stains from Candles, Woodstoves, Fireplaces
  Other Stains on Indoor Walls & Ceilings
  What to Do About Thermal Tracking
VAPOR BARRIERS & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
VENTILATION in BUILDINGS
WATER ENTRY in BUILDINGS
WINDOWS & DOORS
  SKYLIGHT LEAK DIAGNOSIS & REPAIR
  SITE BUILT DOUBLE GLAZED WINDOWS
  SLOPED GLAZING DETAILS
  VERTICAL GLAZING DETAILS
  WINDOW / DOOR ENERGY EFFICIENT, DOE
  WINDOW LEAKS INTO BASEMENT
WINTERIZE A BUILDING

• Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
  
• Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
  Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in BUILDINGS, and other topics.
• The Vapor Box™, NGR Saver Distributors, Box 50, Gro8up 32 RR B, Winnipeg, Manitoba R3 C4A3 Canada 204-338-5960.
• "Active Solar Heating Systems", U.S. Department of Energy, including
• "Radiant Heating Systems" U.S. DOE
• "Absorption Heat Pumps & Coolers", U.S. DOE
• "Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
• "Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.

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