Weatherization contractors often use a blower-door test to help pinpoint leaks in the building envelope. Once your house is depressurized, you can use your bare hands to feel for air infiltration. The most common places to find air entering basements are around windows and doors and between the concrete foundation and the mudsill. But some air-leakage paths may surprise you: Air can even seep through the crack at the perimeter of your basement slab or through a sump in the basement floor. Here are five places to check for air leaks in your basement and some advice on how best to seal them.

Foundation walls
Walls made of poured concrete or concrete blocks are usually fairly tight. However, if your basement walls have any obvious cracks, fill them with silicone caulk. If the walls are made of stone and mortar, don’t use canned spray foam or caulk to seal cracks. Instead, remove any loose material from these areas, and repair them with mortar and small stones.

Use caulk or canned spray foam to seal leaks near wall penetrations for your electrical service, water service, cable service, or natural-gas service. Your home also may have penetrations for a fuel-oil filler pipe, an oil-tank vent, or a clothes-dryer vent. If basement access is awkward, some cracks may be easier to seal from the exterior.

In a tight basement Atmospherically vented appliances—for example, water heaters, furnaces, or boilers attached to old fashioned brick or metal chimneys—depend on air leaking through cracks in your walls to supply combustion air. If your basement is very tight, atmospherically vented appliances could be starved for air, and exhaust gases may struggle to exit through the chimney. That’s why the best appliances for tight homes are sealed combustion appliances equipped with ducts that supply outdoor air directly to the burners.

Because flue gases sometimes include carbon monoxide, it’s always important to be sure that your combustion appliances have adequate combustion air and that your chimneys draw well. If you plan to seal cracks in your basement, arrange for a combustion-safety test of any atmospherically vented appliances once air-sealing work is complete. Contact your gas utility or a home performance contractor certified by RESNET or BPI for more information on combustion-safety testing.

Rim joists
Air can leak through the crack between the top of the foundation wall and the mudsill, the crack between the mudsill and the rim joist, and the crack between the rim joist and the subfloor. The best way to seal leaks in the rim-joist area is with a high-quality caulk.

Once these cracks are caulked, you may want to reduce air leaks further by installing a layer of closed-cell spray foam at the rim-joist area using a two-component spray-foam kit.

Although spray foam is effective, it is expensive and sometimes messy. If you would rather not use it, you can insulate rim joists with rectangles of 2-in.-thick rigid foam (polyisocyanurate or extruded polystyrene). Seal the perimeter of each foam rectangle with caulk or canned spray foam. Don’t use fiberglass batts; they do nothing to slow airflow.

Two ways to air-seal and insulate a rim joist Rim joists are a common source of air leakage in basements and are often left uninsulated. The first step toward an energy-smart rim joist is to caulk gaps between the foundation wall and the mudsill, the mudsill and the rim joist, and the rim joist and the subfloor. As seen in the details shown here, you then can use rigid foam or spray foam to add another layer of air-sealing and to insulate the area.

Rigid foam You can cut the pieces of rigid foam roughly and somewhat undersize because the perimeter of each rectangle should be sealed in place with canned spray foam. With the rim joist air-sealed and covered with rigid foam, you can now add cavity insulation like fiberglass batts or, better yet, a second layer of rigid foam.

Spray foam Extend spray foam from the top of the foundation wall to the underside of the subfloor above. In addition to sealing leaks, 2 in. of cured foam will insulate to R-13. Most building codes, including the International Residential Code, allow spray foam installed at rim joists to remain exposed—without protection from a thermal barrier like drywall—as long as the foam is no thicker than 3-1⁄4 in.

Windows and doors
If your basement has old single-pane windows, they may need new glazing compound and weatherstripping. If the windows are in bad shape, consider replacing them with new double-glazed units.

If you rarely open your basement windows, consider sealing them shut with screws and caulk, or even covering them with rigid foam. (Of course, this advice applies only to small basement windows, not to any egress windows in a basement bedroom.) Don’t forget to caulk between the window frame and the concrete.

Every bulkhead entry needs a tight, weatherstripped exterior door at the base of the stairs. Be sure to caulk or to foam the gap between the door jamb and the foundation. If the door is warped or difficult to weatherstrip, it’s time to replace it. Most lumberyards can order a custom insulated entry door to fit any size opening. If you’re framing the rough opening, use pressure-treated lumber, and seal the frame to the concrete with canned spray foam.

Basement floors
After a new foundation is backfilled, the fill often shrinks away from the foundation, leaving a gap next to the basement wall that allows outdoor air to reach the footings. That’s one way for outdoor air to enter a home through cracks in the basement floor or sump pit. Even if a home has no shrink-age gap, air can still reach the footings, especially in areas with porous soil.

If there’s a crack at the perimeter of your basement slab, clean the crack with compressed air or a vacuum cleaner, and then fill it with caulk. If you have a sump pit without a tight lid, replace it with a new airtight lid. Sumps that have airtight lids are available from Jackel.

Basement ceilings
Chases and chimneys that extend from the basement to the attic should certainly be capped at the top, but the bottom of these chases should be sealed as well. After all, once air gets into a chase, it can move sideways into joist bays and partition walls until it finds an exit crack. This belt-and-suspenders approach is the best way to prevent the stack effect from stealing your home’s heat.

Cover large ceiling holes with plywood, drywall, or rigid foam, and seal the edges with caulk, spray foam, or housewrap tape. While you’re at it, check for holes under first-floor bathtubs or showers. Plumbers typically cut out a big piece of the subfloor to accommodate drain lines and traps; these air pathways should be sealed.Radon is a colorless, odorless, naturally occurring gas that can seep through soil into your basement. High radon levels can damage human health. While most homes have relatively low radon levels, some have dangerously high levels.

Sealing cracks in your basement can affect radon levels in your home, either for better or worse, depending on several factors. If necessary, a radonremediation contractor can install plastic pipes under your basement slab to lower the radonto safe levels.

The best way to determine whether your home needs radon-remediation work is to test the air in your home. For more information on radon testing and remediation, visit epa.gov/radon.

For details on radon mitigation, see GreenBuildingAdvisor.com/radon.

by Martin Holladay
Drawings: Steve Baczek, Architect
From Fine Homebuilding 225, pp. 82-83 January 19, 2012

Amy Fenwick Frank
Division of Codes and Standards
PO Box 802
Trenton, NJ 08625-0802
Fax Number: (609) 633-6729
Email: AFrank@dca.state.nj.us

Following are some of the proposed actions:

Adding a sentence to the current amendment to 210.8(A)(5). The current amendments reverts 210.8(A) (2) and (5) back to the National Electrical Code 2005 text. This proposed amendment will correlate with the existing amendment to 210.8(A)(2), which clarifies receptacles installed under the exceptions to 210.8(A)(5) do not meet the requirements of 210.52(G).”

Section 210.12(B) Branch Circuit Extensions or Modifications Dwelling Units will be deleted, because it is regulated by the Rehabilitation Subcode.

The current amendment to NEC 334.10(1), which permits the use of Type NM cable in accessory buildings or structures of dwellings will be deleted, because the text is now included in the 2011 NEC.

The amendment to 300.4(A)(1) will be retained. This amendment references the building subcode for the placement of cable- or raceway-type wiring methods installed through bored holes in joists, rafters, or other wood members.

The amendment to 334.12(A)(2) will be retained. This amendment deletes this item and permits exposed Type NM cable in dropped or suspended ceilings in other than one- and two-family and multifamily dwellings.

The amendments to the support requirements in 342.30(C) Intermediate Metal Conduit, 344.30.(C) Rigid Metal Conduit, 352.30(C) Rigid Polyvinyl Chloride Conduit, 355.30(C) Metallic Tubing Reinforced Thermosetting Resin Conduit and 358.30(C) Electrical Metallic Tubing, will be deleted, because the 2011 deleted these requirements.

Section 406.4(D)(4), which requires arc-fault circuit-interrupter (AFCI) receptacles to be installed when receptacles are being replaced in a dwelling unit will be deleted, because additions, alterations and modifications are regulated by the Rehabilitation Subcode.

All current amendments to Chapter 5 Special Occupancies will be retained.

The amendment to 645.17, Power Distribution Units will be deleted, because the text is contained in the 2011NEC.

Section 680.42(B) will be deleted and replaced with the text from Tentative Interim Amendment (TIA) issued by the NFPA. This section addresses the bonding requirements for spas and hot tubs. The amendments will not require equipotential bonding of perimeter surfaces for listed self-contained spas or hot tubs that meet certain conditions.

The current amendment to 800.156 will be retained. This amendment deletes the requirement for a communications outlet in dwelling units.

“The new International Green Construction Code will help reduce energy use and greenhouse gases through mandatory green building design.”

Protecting the Environment
Unlike other building codes, which are intended to protect the public’s health, safety, and welfare; this complementary green code is intended to help reduce a building’s negative effect on the environment by setting minimum mandatory requirements. For example, in the code’s current version, mandatory requirements include energy performance that is 30-percent better than the 2006 International Energy Construction Code and fixture and flow fitting rates that are a 20-percent improvement over the 2006 International Plumbing Code.

It is important to note that the IGCC will not supersede or take precedent over established sustainability rating systems, such as the U.S. Green Building Council Leadership in Energy and Environmental Design (LEED®) and American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standards. Rather, the new code will serve as an overlay to the existing International Building Codes and complement those existing standards or systems. The IGCC public comment version contains provisions for:

• Site development and land use
• Material resource conservation and efficiency
• Energy conservation and earth atmospheric quality
• Water resource conservation and efficiency
• Indoor environmental quality and comfort
• Commissioning, operation, and maintenance

Local Jurisdictions Determine Code Application
Both the IGCC and LEED rating program produce the same results and share similar categories, such as site, water, energy, materials, and indoor air quality. However, unlike LEED, which is voluntary and determined by the owner’s level of commitment, the IGCC is intended to be part of the building code enforced by those local jurisdictions that adopt it, integrating with existing international building codes to create a new regulatory baseline for green construction.

A key feature is a section devoted to “jurisdictional electives” that will allow customization of the code – beyond its baseline provisions – to address local priorities and conditions. For instance, if local area has water problems, then a jurisdiction may elect for more strict water conservation measures. Project electives within the IGCC will be determined by the jurisdiction and range from 0 to 14, depending on the level of sustainability the jurisdiction is trying to achieve.

Who will be affected?
The IGCC applies to all occupancies, but does distinguish that residential occupancies shall comply with ICC 700 National Green Building Standard and that equipment and systems primarily used for industrial or manufacturing processes shall not comply with the code. Other than those two exceptions, the IGCC applies to the design, construction, addition, alteration, change of occupancy, movement, enlargement, replacement, and repair of buildings and structures and the site on which the building is located. Like all other I-codes, the code official has the authority to render the interpretation of the code and to adopt any policies and provisions in order to clarify the code.

Schedule
The IGCC is scheduled for final publication in early 2012. Currently, public version 2.0 was released on November 3, 2010, with the following key milestones:

• Public version no. 2: November 2010
• IGCC Code change submittal deadline: January 2011
• IGCC Development hearing: May 2011
• IGCC Final action hearing: November 2011
• Final Release: Early 2012

Be Informed
The IGCC is part of the International Building Code family and is being supported and developed by:

• American Institute of Architects
• ASTM International
• American Society of Heating, Refrigerating and Air-Conditioning Engineers
• U.S. Green Building Council
• Illuminating Engineering Society

 Betzwood Associates completes a residential addition & renovation project in Gladwyne, PA.

Frank Mariani, Inc.

Joanne Bateman Interior Designs, LLC

Peter / Kubilus

A 1⁄8-in. crack doesn’t seem like much to worry about, but a 1⁄8-in. crack that runs the length of your house amounts to a square hole 8 in. on a side—a big-enough hole to toss a cat through. Because it is a crack, you can seal it with caulk, but not all holes in the building envelope are cracks that can be sealed with a tube of caulk. Some of them really are big enough to toss a cat through, and they need to be sealed with sheet goods such as drywall, rigid foam, or plywood.

Some common gaps and holes are listed in the Energy Star thermal-bypass checklist. Among the most common holes found in poorly sealed houses are holes near soffits, chases, and bathtubs. Green Building Advisor has a collection of 56 detail drawings that pertain to the Energy Star checklist. These drawings come from that collection.

Chases and soffits are raceways for air leaks
Older houses often have several big holes in the attic floor. Many are around open chases for ducts, electrical cables, or flues, often running unimpeded from the basement to the attic. When installing plumbing chases in new houses, install air-barrier sheathing first, and seal the gaps between intersecting walls with caulk. As the framing shrinks, these gaps become large. The top of an open plumbing chase in an existing house can be sealed with a variety of sheathing materials as long as seams and edges are sealed with caulk or tape.

If any chases for plumbing pipes, ducts, or flues originate in the basement, be sure to seal the chases at the bottom with the same techniques you used to seal the chases in the attic.

While you’re in the attic, check for any unsealed kitchen soffits. Such soffits are often built above a row of wall cabinets. In new construction, the ceiling drywall should be installed and taped before the soffit is framed. The first clue to a leaky soffit is often a piece of discolored fiberglass insulation. The discoloration is caused by escaping air that has carried dust upward, often for years.

In many existing houses, the sides and top of kitchen soffits are open to the framing cavities. In this case, you can install the neces-sary pieces of air-barrier sheathing from above. Don’t forget to seal the perimeter of the sheathing and any seams with durable tape, caulk, or spray foam. Once the soffit is airtight, don’t forget to replace the insulation.

Tubs hide big holes in floors and walls
 Tub installation When you’re installing a fiberglass tub/shower unit against an exterior wall, it’s essential to insulate and air-seal the wall before installing the tub. On new-construction jobs, remember to install a durable air-barrier material (for example, Thermo-ply sheathing) to cover the insulation.

In an existing house where builders omitted the insulation and the air barrier behind the tub, repairs are difficult. One solution (not the cheapest) is to remove some of the siding and sheathing so that spray-foam insulation can be installed from the outside. A better bang for the buck may be to address the problem as part of a larger bathroom remodel. If you’re contemplating a bathroom upgrade, it may be cheaper to demolish the tub/shower unit and seal the wall properly from the interior.

If your house has an unconditioned basement—in other words, if the basement ceiling is insulated—be sure to pull that insulation aside and check for air leaks under any first-floor bathtubs or showers. Plumbers typically cut out a big piece of the subfloor to accommodate drain lines and traps, but rarely repair the ruptured air barrier. If these cutouts are not sealed, your floor has a huge hole.

Keep fireplace heat inside
Prefab fireplace niche Prefabricated metal fireplaces, whether wood-burning or gasburning, are usually installed in a niche framed into an exterior wall. Unfortunately, many of these fireplace niches are poorly sealed against air leaks.

The best opportunity to prevent such leaks is before the fireplace is installed. After the niche is carefully insulated, the insulation should be covered with a durable, rigid air-barrier material, such as Thermo-ply sheathing, drywall, sheet metal, or OSB. All gaps and seams should be sealed with caulk, spray foam, or contractors’ tape. Where the chimney penetrates the niche ceiling, seal gaps with metal flashing and high-temperature silicone caulk.

To repair air-barrier defects behind an existing metal fireplace, it may be necessary to remove sections of siding and sheathing to provide access for the installation of spray polyurethane foam.

Fine Homebuilding222, pp. 90-91

Center Ice currently offers two NHL size rinks for everything from public skating and hockey to youth and adult leagues. In addition they also offer lessons for Learn to Skate and Learn to Play Hockey. Check them out at Oakscenterice.com.

Betwood Associates PC, along with their design partners N.E. Fisher & Associates and Engineering One PC, was hired to provide architectural and structural professional services to design a 25,000SF addition to the existing twin ice skating facility owned by C.D. Professional Sports, LP.  The new addition will offer a 3rd NHL size rink at the Oaks, PA facility. N.E. Fisher & Associates, Boyertown, PA is the Project Mechanical Engineer, and Engineering One PC, Phoenixville, PA is the Project Electrical Engineer. In addition to the NHL size rink, new Player and Referee Locker Rooms, a “Warm-up Room”, and mechanical space for the rink’s ice making equipment will be provided.

InLand Design, LLC of Exton, PA provided the civil and land development design engineering for the project, which will include improved access to and parking at the facility.

The General Contractor for the project is Dylan Enterprises of Boyertown, PA. Schlosser Steel Buildings, Inc. of Hatfield, PA is providing a Star Building Systems “pre-engineered” building to seamlessly match the exterior of the existing facility. The “cold slab”, ice making and rink equipment is being provided by B K Mechanicals, Inc. of West Chester.

The building design was recently completed, and is currently being reviewed by Upper Providence Township to issue a building permit to the Owner. C.D. Professional Sports, LP anticipates construction to start in the near future, with completion scheduled in the 3rd Quarter of this year.

Use of the new rink by area hockey teams and skaters is anticipated to begin by year’s end.

Understand when to vent your roof, when not to,
and how to execute each approach successfully

So much information has been devoted to the subject of roof venting that it’s easy to become confused and to lose focus. So I’ll start by saying something that might sound controversial, but really isn’t: A vented attic, where insulation is placed on an air-sealed attic floor, is one of the most underappreciated building assemblies that we have in the history of building science. It’s hard to screw up this approach. A vented attic works in hot climates, mixed climates, and cold climates. It works in the Arctic and in the Amazon. It works absolutely everywhere—when executed properly.

Unfortunately, we manage to screw it up again and again, and a poorly constructed attic or roof assembly can lead to excessive energy losses, ice dams, mold, rot, and lots of unnecessary homeowner angst.

Here, I’ll explain how to construct a vented attic properly. I’ll also explain when it makes sense to move the thermal, moisture, and air-control layers to the roof plane, and how to detail vented and unvented roofs correctly.

Theory behind venting
The intent of roof venting varies depending on climate, but it is the same if you’re venting the entire attic or if you’re venting only the roof deck.

In a cold climate, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent any moisture that moves from the conditioned living space to the attic.

In a hot climate, the primary purpose of ventilation is to expel solar-heated hot air from the attic or roof to reduce the building’s cooling load and to relieve the strain on air-conditioning systems. In mixed climates, ventilation serves either role, depending on the season.

Vent the attic
A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. Because the roof isn’t in play here, it doesn’t matter how  many hips, valleys, dormers, or gables there are. It’s also easier and often less expensive to pile on fiberglass or cellulose insulation at the attic floor to hit target R-values than it is  to achieve a comparable R-value in the roof plane.

The success of this approach hinges on the ceiling of the top-level of the house being absolutely airtight before any insulation is installed. It’s also important to ensure that there isn’t anything in the attic except lots of  insulation and air—not the Christmas decorations, not the tuxedo you wore on your wedding day, nothing. Attic space can be used for storage, but only if you build an elevated platform above  the insulation. Otherwise, the insulation gets compressed or kicked around, which diminishes its R-value. Also, attic-access hatches are notoriously leaky. You can build an airtight entry  attic, but you should know that the more it is used, the leakier it gets.

How do people get this simple approach wrong? They don’t follow the rules. They punch a bunch of holes in the ceiling, they fill the holes with recessed lights that leak air, and they stuff mechanical systems with air handlers and a serpentine array of ductwork in the attic. The air leakage from these holes and systems is a major cause of ice dams in cold climates and a major cause of humidity problems in hot climates. It’s also an unbelievable energy waste no matter where you live.

Don’t think you can get away with putting ductwork in an unconditioned attic just because you sealed and insulated it. Ductsealing is faith-based work. You can only hope you’re doing a good-enough job. Even when you’re really diligent about air-sealing, you can take a system with 20% leakage and bring it down to maybe 5% leakage, and that’s still not good enough. With regard to recessed lights and other ceiling penetrations, it would be great if we could rely on the builder to air-seal all these areas. Unfortunately, we can’t be sure the builder will air-seal well or even air-seal at all. So we have to take some of the responsibility out of the builder’s hands and think of other options.

In a situation where mechanical systems or ductwork has to be in the attic space or when there are lots of penetrations in the ceiling below the attic, it’s best to bring the entire attic area inside the thermal envelope. This way, it’s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated.

Vent the roof deck
If the attic space is going to be conditioned, either for living or mechanical purposes, or if a home design calls for a vaulted ceiling, provision R806.3 in the International Residential Code calls for the roof deck above the space to be vented continuously from the eave to the ridge. This is easy to accomplish in simply constructed roofs and difficult, if not impossible, to accomplish in roofs that have hips, valleys, dormers, or  skylights that interrupt the rafter bays.

If you choose to vent the roof deck, then be serious about it and really vent it. The code calls for a minimum of 1 in. of airspace between the top of the insulation and the back of the roof sheathing. That’s not enough. For best performance, the airspace in the vent chute should be a minimum of 2 in. deep. Unless you’re bulk-filling rafter bays between 2×10 or 2×8 rafters with closed-cell spray foam, this approach will likely require you to fur out the rafters to accommodate additional insulation to achieve desired R-values. That can be a pain, but you won’t run into the problems associated with having too little air circulating under the roof. To be sure your roof is getting enough ventilation, there are simple calculations that you can follow.

Beyond the decreased capacity for insulation when venting the roof deck, venting the roof deck or the attic has some other drawbacks worth considering. In cold climates, snow can enter the soffit and ridge vents, melt, and potentially cause rot. Similarly, in coastal environments or in regions with lots of rain and wind, moisture can be forced into the vents and into the roof assembly. In hurricane-prone zones with frequent high-wind events, vented-soffit collapse can pressurize a building, which can cause windows to blow out and the roof to be blown off. Finally, in wildfire zones, floating embers can enter the vents and cause roof fires. If any of these issues are of concern, there is another option.

Create an unvented roof
Through provision R806.4, the IRC also allows you to build an unvented roof assembly. Unvented assemblies work particularly well on complex roofs that would be difficult or impossible to vent properly or on roofs where it would be difficult to insulate properly if the roof were vented.

It should be noted, however, that in high-snow-load areas, you still need a vented over-roof to deal with ice damming. In essence, you’re creating a hybrid vented/unvented roof system.The goal in an unvented roof is to keep the roof deck—the principal condensing surface in roof assemblies-sufficiently warm through the year to prevent condensation from occurring. In most climates, builders have to insulate the roof sheathing to prevent condensation from occurring within the assembly. The exception is hot-dry climates such as in Phoenix, where condensation isn’t as big an issue.

Condensation control is most often accomplished by installing rigid foam above the roof deck or by installing air-impermeable spray-foam insulation directly against the underside of the roof deck. The code also allows for air-permeable insulation, such as fiberglass or cellulose, to be used under the roof deck as long as rigid foam is used above the roof sheathing. Flash-and batt (or flash-fill) assemblies are also allowed. Any of these approaches can adequately prevent condensation from occurring within the roof when the rigid foam or spray foam is installed at the appropriate thickness.

If you’re spraying foam on the underside of the roof deck, be sure you’re using the right product. Closed-cell spray foam works in all climates, but especially well in climate zones 5 through 8, where high R-values are desired and where airimpermeable insulation also must be a vapor retarder. Lowdensity, open-cell foam is permissible, but in climate zones 5 and above, it has to be covered with a vapor-retarder coating, like rigid foam or painted drywall.

Also pay attention to roofing materials. Asphalt shingles require special attention when installed on unvented roof assemblies in hot-humid, mixed humid, and marine climates due to inward vapor drive. To keep moisture out of the roof assembly, a roofing underlayment with 1 perm or less (class-II vapor retarder) must be installed under the shingles. Also, check to be sure that you are in compliance with the manufacturer warranties when installing shingles over an unvented roof in all climates. Some manufacturers don’t warranty or offer only a limited warranty when their products are used over an unvented roof assembly.

Shingles that are installed on unvented roof assemblies operate at slightly higher temperatures, roughly 2°F to 3°F warmer than shingles on vented assemblies. This can reduce their service life by roughly 10%. You can vent the roof cladding, which will increase its  longevity, but the expense of fastening battens over the roof sheathing, then adding another layer of plywood over the battens as a nail base for the shingles, may not be worth the expense. After all, the shingle color and the roof orientation are much more significant concerns when it comes to shingle life.

Unvented roofs
Unvented roofs aren’t nearly as common as vented assemblies, and builders may not be familiar with detailing them correctly. While there are certainly a variety of ways to build an unvented roof assembly that performs well, here are three examples worth considering

The success of a vented attic or roof deck relies on its airtightness. The space above the top plate of exterior walls-at the bottom of each rafter bay-is especially important. Baffles placed in this area channel intake air into either the attic space or vent chutes, and also prevent insulation from falling into the soffit and blocking airflow.

Prevent condensation with the right amount of insulation
An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. The map at right, which is based on table R806.4 of the IRC, lists the minimum R-values required to prevent condensation in unvented assemblies in various climate zones. The thickness of the insulation will vary depending on the type. These R-value requirements are intended only to prevent condensation and don’t supersede the code-required R-values for energy efficiency, which are also listed.

Site-built or prefab baffles?
The success of a vented attic or roof deck relies on its airtightness. The space above the top plate of exterior walls at the bottom of each rafter bay is especially important. Baffles placed in this area channel intake air into either the attic space or vent chutes, and also prevent insulation from falling into the soffit and blocking airflow.

Site-built: 2-in. chutes and baffles Cut 1-in.-thick rigid polyiso insulation into 2-in.- wide spacer strips, and glue them to the inside face of each rafter with a spray-foam adhesive like Pur Stick (www.todol.com). Cut the polyiso insulation to fit snugly in each rafter bay, and foam it in place against the spacer to create a 2-in. chute or baffle.

Size: Custom-cut polyiso foam
Cost: $23 per sheet
Source: Dow

Prefab: fast and functional The AccuVent soffit insulation baffle is made of rigid recycled plastic. It’s more durable than other foam-based products and installs quickly with staples. These baffles should still be air-sealed with spray foam, but they’re a good option if you’re looking for a stock product.

Size: 41 in. by 22 in.
Cost: $1.68 each
Source: Berger Building Products

Fine Homebuilding 212, pp. 68-72
by Joseph Lstiburek

Green building means building houses that are energy efficient, durable, and won’t make people sick after they move in.

It also means using less materials and making better use of the ones you buy.

We can do this by designing and building houses…

• Efficiently
• To last a long time
• To use less water and energy
• That are healthy to live in

In short, we can build green by building even better houses than we’ve been building
— we take the next step in quality.

Green building is an approach to construction that can be applied to public and commercial buildings as well as the houses we live in. It guides every step of design and construction, from choosing a building site to installing a heating system. Green building is alternately described as “sustainable” building, and ultimately this may be a more accurate way of looking at it.

Green buildings are as varied as the people who live in them. There is no single template for a green house. But even though green houses may look different from the outside, their designs are based on three broad principles:

Energy efficiency. The house uses as little energy as possible. Whenever feasible, renewable forms of energy should replace fossil fuels, which by definition are not renewable.

Conservation of natural resources. This broad objective recognizes that resources are finite. There is only so much timber, ore and water to go around, and what resources are available to us should be used thoughtfully. Seen through this lens, durability, low environmental impact and low maintenance all become important attributes for a house.

High indoor air quality. Green houses are designed to be healthy houses. Moisture, mold, and radon don’t plauge a green home. Building materials, furnishings, paints and finishes should not contribute toxins and irritants to indoor air. Even with clean air though, houses need mechanical ventilation that assures a steady flow of fresh air.

When we see an Energy Star label on a new refrigerator or washing machine, we recognize it as a good thing. Green isn’t that simple. But understanding the principles behind sustainable building helps us make appropriate decisions about the houses we build.