Chapter 6:                      Walls

This chapter discusses air sealing and insulation for walls in existing buildings. Air sealing begins by inspecting the disconti­nuities in walls, such as the following.

•       Inside and outside corners of walls.

•       Openings for windows and doors.

•       Protrusions and indentations in walls.

Insulation begins by evaluating the existing wall insulation and deciding on the feasibility and cost-effectiveness of installing additional wall insulation. Other wall-insulation issues may include the following.

•       Whether you can install wall insulation at all, such as in walls already partially insulated.

•       Whether to insulate from interior or exterior of the home.

•       How to open a wall cavity and restore it after insulating the wall cavity.

•       How to install insulation to the wall’s surface.

6.1   Air Sealing Walls

Most wall air leakage involves the wall’s discontinuities, joints, and irregularities.

See “Material and Sealant Specs” on page 112.

6.1.1   Multifamily Firewalls

Firewalls are structural walls between buildings or dwelling units that prevent the spread of fire from one unit to another. If a firewall isn’t monolithic on all sides because of balloon fram­ing, open-cavity CMU, open chases, attic bypasses, or other dis­continuity, restore the firewall to code-compliance. Access attic-and floor penetrations, basement penetrations, and the vertical-edge penetrations throughout the firewall assembly and seal them.

✓     When air-sealing, preserve existing fire ratings of materi­als and assemblies along with existing-material compati­bility and comparable durability.

✓     Verify that non-monolithic fire walls, such as balloon-framed walls, are airtight assemblies both to air flowing horizontally and vertically.

✓     Seal air channels, created by furring strips or wall framing, against a monolithic firewall. At a minimum seal the top and bottom of each channel, and/or densepack the chan­nels with fibrous insulation.

✓     Seal gaps and cracks with air-sealing materials and back­ing materials that are compatible with and similar to exist­ing materials with fire-containment functionality.

See “Air Sealing and Fire Containment” on page 111. See “Balloon Framed Walls” on page 193. See “Fire Testing and Rating” on page 577. See “Fire Safety” on page 23.

6.1.2   Built-In Cabinets/Shelves

Built-in cabinets and shelves are a feature of older homes and present challenges for air sealing. Sealing these areas from inside the cabinet requires care and attention to appearances.

✓     If possible, establish both an air barrier and insulation behind the cabinet, out of sight of the occupants.

✓     Install drywall or wood wherever the cabinet is open to a wall cavity after insulating the cavity.

✓     Use caulking that is compatible with the colors of the sur­rounding wood if you seal its interior-facing side.

6.1.3   Wall Framing Around Fireplaces and Chimneys

Leaks around fireplace chimneys are often severe air leaks. Use this procedure to seal air leaks through the chimney chase.

✓     Cut sheet metal to fit the gap that borders the chimney with overlaps connecting to nearby framing lumber.

✓     Bed the sheet metal air seal in sealant (ASTM E136), and then fasten the sheet metal to the framing with staples, nails, or screws.

✓     Seal the metal patch to chimney or flue with an ASTM 136 compliant, non-combustible sealant.

✓     For large chimney chases, cover the chase opening with structural material such as plywood. Maintain clearances between the structural seal and the metal or masonry chimney as listed in “Clearances to Combustibles for Com­mon Chimneys” on page 340.

6.1.4   Pocket Door Cavities

When located on the second floor, cap the top of the entire wall cavity in the attic with rigid board, caulked and mechanically fastened.

Pocket doors connected to the exterior walls present difficult air sealing and insulating challenges. You many need to address these framing situations from the exterior in order to install a durable and efficient repair that provides a good air seal and allows you to install insulation into the exterior wall cavity

6.1.5   Cooling Appliances Installed through Walls or Windows

•       Remove window units in the fall and re-install in the spring.

•       If the client doesn’t want to remove the unit seasonally, cover the unit with a room-air-conditioner cover as shown here.

•       Units installed through walls should have a sheet-metal sleeve that seals well to the surrounding framing and finish. This metal sleeve provides a smooth surface to seal to the room air conditioner or heat pump.

•       Seal the unit’s perimeter with one-part foam or caulking, depending on the width of the joint.

6.1.6   Balloon Framed Walls

Balloon framed two-story walls are common in older homes. Some modern homes have balloon framed gable walls, where the studs rise above the level of the ceiling joists and are cut at an angle to frame the gable. Even when these balloon framed gable walls are full of insulation, air can convect through the insula­tion. On occasion, windstorms have blown the insulation out of the wall cavity into the attic.

✓     Dense-pack insulation into the wall cavities to reduce air leakage and convection.

✓     Dense-pack insulation into an air-permeable bag inserted with the fill tube into the balloon-wall floor cavity.

✓     Seal stud cavities from the attic, basement, or crawl space with an insulation plug, covered with a 2-part-foam air seal.

✓     Or seal the tops and bottoms of cavities with a rigid bar­rier, such as drywall or plywood, sealed and bonded to surrounding materials with 2-part foam.

See also "Wall Insulation" on page 198.

6.2   Air-Sealing Small Openings

Minor air sealing includes sealing small openings with such materials as caulk or weather stripping. See “Material and Seal­ant Specs” on page 112.

6.2.1   Window and Door Frames

Sealing from the exterior serves to keep bulk water out and pro­tect the building. If the crack is deeper than ⁵/₁₆-inch, it should be backed with a material such as backer rod and then sealed with caulk. Any existing loose or brittle material should be removed before the crack is re-caulked. See also "Windows and Doors" on page 245.

6.2.2   Rim Joist Area

The rim joist area is composed of several joints. They can be sealed from the basement or crawl space with caulk or foam. Remove dust before applying sealant. See also "Rim-Joist Insula­tion and Air-Sealing" on page 227.

6.2.3   Masonry Surfaces

Brick and various types of masonry block aren’t air barriers. Seal masonry surfaces with a masonry-patching compound, mortar mix, or polyurethane caulking. For cement-based patches, buy a mix designed for patching. Prime the damaged areas with a masonry primer/adhesive. Liquid water resistive barriers (WRB) are often excellent air barriers.

6.2.4   Interior Wall Top Plates

Workers install drywall after they build interior walls. Thus the top plates of interior walls are open to the attic. Top plates shrink, opening cracks that run the entire length of the interior wall. Move insulation and seal the cracks with caulking or two-part foam.

6.3   Wall Insulation

Install wall-cavity insulation with a uniform coverage and den­sity. Wall cavities encourage airflow like chimneys. Convection currents or air leakage can significantly reduce wall insulation’s thermal performance if channels remain for air to migrate or convect.

Important: Provide the client with an insulation receipt or cer­tificate, with the insulation type and number of bags installed, installed thickness, coverage area, and insulation R-value. See “Insulation Receipt or Certificate” on page 120.

Blown Wall-Insulation Types

Cellulose, fiberglass, and open-cell polyurethane foam are the leading insulation products for retrofit-installation into walls.

6.3.1   Wall Insulation: Preparation and Follow-up

Inspect and repair walls thoroughly to avoid damaging the walls, blowing insulation into unwanted areas, or causing a dust hazard.

Preparing for Wall Insulation

Before starting to blow insulation into walls, take the following preparatory steps.

✓     Calculate how many bags of insulation are needed to achieve the R-value specified on the bag’s label.

✓     Inspect walls for evidence of moisture damage. If an inspection of the siding, sheathing, or interior wall finish shows a moisture problem, don’t install sidewall insulation until the moisture problem is identified and solved.

✓     Inspect indoor surfaces of exterior walls to assure that they are strong enough to withstand the force of insulation blowing. Reinforce interior sheeting as necessary.

✓     Inspect for interior openings or cavities through which insulation may escape. Examples include balloon-framing openings in the attic or crawl space, pocket doors, unbacked cabinets, interior soffits, and openings around pipes under sinks and closets. Seal these openings with airtight, rigid, blocking material to prevent insulation from escaping the wall cavity.

✓     Verify that exterior wall cavities aren’t used as return or supply ducts. Either avoid insulating these cavities, or re-move the ducts and reinstall them somewhere else.

✓     Verify that electrical circuits inside the walls aren’t over­loaded. Maximum ampacity for 14-gauge copper wire is 15 amps and for 12-gauge copper wire is 20 amps.

✓     Perform a voltage-drop test to evaluate the size and condi­tion of hidden wiring on older homes. Use a “Sure Test Branch Circuit Analyzer”, or similar device that measures the voltage drop at full load (15 amps). Voltage drop may not exceed 5%.

✓     Install S-type fuses to prevent circuit overloading if neces­sary.

✓     Don’t insulate cavities containing unshielded high-tem­perature devices — chimneys, flues, vents, wall heaters — unless they are zero clearance devices or unless you can maintain the required clearance.

✓     Don’t insulate cavities containing knob-and-tube wiring. See “Electrical Safety” on page 51.

Patching and Finish after Insulating

The insulators, the home owner, and others should agree about the patching method and the final appearance of the wall finish. The insulators are usually responsible for patching holes and returning the interior or exterior finish to its previous condition or some pre-agreed level of finish.

✓     Patch the exterior wall sheathing with wood plugs, plastic plugs, or spray foam insulation.

✓     Use caulk or putty and primer to dress exposed exterior plugs.

✓     Seal gaps in external window trim and other areas that may admit rain water into the wall.

✓     Patch interior finish with standard plastering methods or a chair rail trim board.

✓     Install drywall with joint compound to open cavities to comply with IRC fire codes.

Wall Insulation Quality Control

Retrofit wall insulation has more risk of incomplete application than insulation that you can visually inspect. Consider these quality control options to verify the proper coverage and density of retrofit wall insulation.

•       Viewing the wall through an infrared camera.

•       Looking through an electrical outlet or other access hole for insulation.

•       Calculation of installed weight of installed insulation com­pared to wall-cavity volume and required density.

Drilling Exterior Sheathing: Insulation Retrofit

Avoid drilling through siding. Where possible, carefully remove siding and drill through sheathing. This procedure avoids the potential lead-paint hazard of drilling the siding. Drilling through only the sheathing also makes it easier to insert flexible fill tubes since the holes pass through only one layer of material.

If you can’t remove the siding, consider drilling the walls from inside the home. Obtain the owner’s permission before drilling indoors, and practice lead-safe weatherization procedures. See “Lead-Safe Procedures” on page 48.

Consider these possible methods of removing siding.

•       Cut completely through the paint on wood-siding joints with a sharp utility knife before carefully prying the siding off.

•       Remove asbestos shingles by pulling the nails holding the shingles to the sheathing, or else cut off the nail heads. Dampen the asbestos tiles to reduce dust. Wear a respirator and coveralls when working with asbestos siding.

•       Use a zip tool to remove metal or vinyl siding.

•       Insulate homes with brick veneer or blind-nailed asbestos siding from the indoors.

•       Use a decorative chair rail to cover holes drilled indoors.

Restore holes drilled for insulation to an appearance as close to original as possible, or in a manner that is satisfactory to the customer.

6.3.2   Retrofit Closed-Cavity Wall Insulation

This section describes two ways of installing wall insulation.

1.      Blowing walls with fibrous insulation using a fill tube from indoors or outdoors.

2.      Injecting liquid foam into a closed wall cavity.

Blowing Walls with a Fill-Tube

Install dense-pack wall insulation using a blower equipped with separate controls for air and material feed. Mark the fill tube in one-foot intervals to help you verify when the tube reaches the top of the wall cavity.

Select insulation that has a flame spread and smoke develop­ment index of 25/450 or less.

To prevent settling, blow dry cellulose insulation to 100% cover­age and at least 3.5 pounds per cubic foot (pcf) density. Fiber­glass dense-pack must be 2.2 pcf and the fiberglass material must be designed for dense-pack installation.

Insulate walls using this procedure.

1.      Drill 2-to-3-inch diameter holes to access the stud cav­ity.

2.      Probe all wall cavities through holes, before you fill them with the fill tube, to identify fire blocking, diago­nal bracing, and other obstacles.

3.      Start with several full-height, unobstructed wall cavities so you can measure the insulation density and calibrate the blower. An 8-foot cavity (2-by-4 on 16-inch centers) should consume a minimum of 10 pounds of cellulose or 6 pounds of fiberglass.

4.      Insert the hose all the way to the top of the cavity. Start the machine, and back the hose out slowly as the cavity fills.

5.      Then fill the bottom of the cavity in the same way.

6.      After probing and filling, drill whatever additional holes are necessary for complete coverage. For example: above windows, missed areas with fire blocking.

7.      Use the blower’s remote control to achieve a dense pack near the hole while limiting spillage.

8.      Seal and plug the holes, repair the weather barrier, and replace the siding.

Insulating the Wall-Floor Junction of Two-Story Walls

When insulating the perimeter of walls between the first and second floors, blow an insulation plug into the perimeter floor cavities for both thermal resistance and airflow resistance.

This method is effective for both balloon-framed and platform-framed walls. With platform-framed walls, the wall insulation is discontinuous at the floor cavity unless you drill and blow through the rim joist there. With balloon-framed walls, there is a gaping hole at the second floor and no rim joist

This insulation plug prevents the second-floor cavity from being a thermal bridge and an air-leakage conduit. Using a fill tube, blow the insulation into a air-permeable bag that expands inside the cavity. The bag limits the amount of insulation necessary to insulate the joist cavities at the floor perimeter.

Injecting Liquid Foam

Select insulation that has a flame spread and smoke develop­ment index of 75/450 or less.

Injecting liquid foam is more expensive than blowing fibrous insulation, but liquid foam provides better performance when existing walls are partially filled by batts. The batts are often 1-to-2 inches thick and are usually flush with the interior or exte­rior wall surface. Try injecting the foam from outdoors to fill the cavity and compress the batt slightly. From indoors, the foam may just stretch the batt facing and fail to create a fully insulated wall cavity.

Open-cell polyurethane foam, formulated to expand less than the sprayed variety, is the leading wall-retrofit foam. Techni­cians install the foam through holes (<1 inch) spaced about two feet apart using a simple nozzle that barely enters the cavity. Technicians use drinking straws or other indicators to judge the level that the foam has filled during installation. Technicians don’t normally use fill tubes to inject open-cell foam because the tube would be too difficult to clean.

See “Special Safety Precautions for Spray Foam” on page 128.

6.3.3   Open-Cavity Wall Insulation

Fiberglass batts are the most common open-cavity wall insula­tion, but rock wool may have a quality advantage over fiberglass. Batts achieve their rated R-value only when installed carefully.

A variety of sprayed insulation products may out-perform batts with expert installation. However, these products are more expensive and have their own installation challenges.

This section describes ways of installing wall insulation.

1.      Installing batts in an open wall cavity.

2.      Spraying wet-spray fiberglass or cellulose into an open wall cavity.

3.      Spray open-cell or closed-cell foam into an open wall cavity.

4.      Blowing fibrous insulation behind netting.

Open-Cavity Batts

✓     Use unfaced friction-fit batt insulation where possible. Fluff the batts during installation to fill the depth of the wall cavity.

✓     Choose medium- or high-density fiberglass batts: R-13 or R-15 rather than R-11, and R-21 rather than R-19. Or, con­sider rock-wool batts.

✓     Seal all significant cracks and gaps in the wall structure before you install the insulation.

✓     Insulate behind and around obstacles with scrap pieces of batt before installing batts.

✓     Staple faced insulation to outside face of studs on the warm side of the cavity. Don’t staple the facing to the side of the studs because this method leaves an air space that allows convection currents.

✓     Cut batt insulation to the exact length of the cavity. A too-short batt creates air spaces above and beneath the batt, allowing convection. A too-long batt bunches and folds, creating air pockets.

✓     Split batt around wiring, rather than letting the wiring compress the batt to one side of the cavity.

✓     Fiberglass insulation, exposed to the interior living space, must be covered with a thermal barrier or at least half-inch drywall or other material with a flame-spread rating of 25 or less.

✓     Fiberglass batts exposed to unoccupied spaces like attics must be covered with an air barrier such as house wrap or foam sheeting to prevent R-value degradation by convec­tion and human exposure to fibers.

See “Fiberglass Batts and Blankets” on page 121.

Sprayed Open-Cavity Wall Insulation

Both fibrous and foam insulation can be sprayed into open wall cavities. Varieties include the following.

•       Fiberglass or cellulose mixed with water and glue at a spe­cial nozzle sprayed into the open wall cavity with the excess shaved off (fibrous damp-spray insulation)

•       Open-cell or closed-cell polyurethane foam sprayed into an open wall cavity. Installers either spray the foam short of filling the whole cavity or shave off the excess foam after it cures.

•       Select insulation that has a flame-spread /smoke-developed index of 75/450 or less.

Blowing Open Wall Cavities behind Netting or Fabric

Blowing dry fibrous insulation behind netting or fabric is a common way of insulating open walls before drywall applica­tion, especially with cellulose. However, you must install the insulation to a sufficient density to resist settling.

✓     Select insulation that has a flame spread and smoke devel­opment index of 75/450 or less.

✓     Select a restrainer netting or fabric that supports the above densities without bulging excessively.

✓     Fasten the netting or fabric with power-driven staples, 1.5 inches apart.

✓     Verify density of at least 3.5 pcf for cellulose or 2.2 pcf for fiberglass.

✓     Roll bulging insulation with a roller to facilitate drywall installation.

6.3.4   Insulated Wall Sheathing

Insulated sheathing is an excellent retrofit, when you replace the siding and windows. Insulated wall sheathing covers an interior or exterior wall surface with insulation, reducing thermal bridg­ing through structural framing.

Always fill the wall cavity with insulation before installing insu­lated sheathing. Insulating wall sheathing is usually foam board, such as polystyrene or polyisocyanurate. Comply with these specifications.

1.      Seal all holes, gaps, and penetrations in existing sheath­ing.

2.      Some multifamily siding-replacement jobs require a “thermal barrier” like drywall as exterior sheathing for fire containment.

3.      Verify that the existing exterior wall has a functional water-resistive barrier (WRB). House wrap, perforated tar paper, or the foam insulation itself may function as the WRB. However, consult with your building depart­ment to verify.

4.      Fasteners should penetrate wood structure at least 1.5 inches.

5.      Seal all insulation seams, joints and connections in each foamboard layer with compatible sealant — caulk, tape, or mastic, for example.

See also "Foundation Wall Insulation" on page 234.

Fasteners for Insulated Sheathing

Fastening the insulating sheathing requires one of the following to secure the insulation to the wood sheathing or masonry under it.

•       A batten board

•       An embedded strip

•       A broad staple

•       A long wood or masonry screw with a large washer

•       A special adhesive (masonry)

Use appropriate fasteners for bonding foam to wood or masonry materials. Wood battens or embedded strips allow attachment of a variety of siding materials. The embedded strips work best with steel, aluminum, or vinyl sidings, which are lightweight and which drain rain water through weep holes in every piece of siding.

If you plan to use a heavy siding, such as fiber cement or tradi­tional stucco, consult a structural engineer to verify that the fas­teners can adequately support the heavy siding.

6.3.5   Wall Insulation in a Retrofitted Frame Wall

Retrofitters, seeking superior energy performance, sometimes build a wood-frame wall attached to the interior or exterior of the existing wall. Common insulation choices include all the wall-insulation choices discussed previously.

Select insulation that has a flame spread and smoke develop­ment index of 75/450 or less.

Workers must install vapor retarders, and air barriers into the new wall assembly as appropriate for the climate and existing wall characteristics. The exterior side of a retrofitted insulated frame should have sheathing and a water resistive barrier like house wrap.

6.3.6   Insulating Unreinforced Brick Walls

Unreinforced means that the builders used no steel or other metal reinforcement. There are three types of unreinforced brick walls.

1.      Traditional brick walls with header bricks that hold two layers of stretcher bricks together. Larger buildings may have three or more brick layers instead of two.

2.      Various types of cavity brick walls with usually one layer of brick on either side of a cavity.

3.      Wood-frame brick veneer walls with a single layer of brick veneer that attaches to a typical wood frame wall with a cavity between the brick and the wood-frame wall up to 2 inches.

All three of these brick assemblies may have structural problems depending on the condition of the bricks and mortar joints. Mortar can turn to dust over many decades; cavity brick walls can be frighteningly fragile; and small movements can topple 100-year-old brick veneer. Consult a structural engineer before making any modification to an unreinforced brick building.

See also "Basement Wall Insulation" on page 237.

6.4   SWS Alignment