Keeping the Heat In

Previous | Table of Contents | Next

Chapter 3: Comprehensive Air-Leakage Control

Introduction

Air-leakage control is the single most important retrofit activity, and it should be considered first in any retrofit strategy. Blocking air leaks brings many benefits: increased comfort, reduced heat loss, protection of the building structure and reduction of the amount of noise and dust that enters from outdoors.

Comprehensive air-leakage control is the systematic identification and sealing of as many air-leakage paths as possible. The ventilation system also should be considered. Many of the leaks are obvious breaks in the air-barrier system, such as through and around windows, doors and electrical outlets. Other air leaks are more difficult to identify, such as bypasses around chimneys and plumbing stacks that can channel air directly from the basement to the attic.

Comprehensive air-leakage control can result from a systematic effort of weatherstripping, caulking and applying gaskets and tapes. Air-leakage control is also an essential part of every insulating job. Every time you insulate, you must also install or upgrade the air-barrier system. This will help you to get the most from your insulation job and help ensure that moisture does not enter into the insulation or building envelope.

Warning: Furnaces, fireplaces, woodstoves and any other fuel-burning appliances also require air for combustion and for diluting and exhausting the products of combustion out of the house. If there is not enough air, it is possible that the chimney or flue could backdraft or spill dangerous gases into the house. Refer to the section entitled “Combustion Air” on page 121 for further information. Also, if you suspect that you have a problem, you should speak to your heating contractor.

House as a System

Remember that the house works as a system in which each component is related to other components. Changing one thing can affect other aspects of the house.

This is especially true with air sealing, which can affect the house moisture flows, and combustion and ventilation air supply. As the envelope is tightened, household humidity levels rise. This can cause condensation and moisture problems. Less air is available for combustion appliances and less fresh air circulates throughout the house. Therefore, an important part of comprehensive air-leakage control is attention to whole-house ventilation and combustion-air supply.

Each house will respond to comprehensive air sealing in its own unique way. This has to be monitored in each case. Older houses may require remedial measures before comprehensive air sealing; moisture that has crept into the walls over time can result in mould buildup, and the house’s wind and air barriers may need repair or replacement. The best way to avoid problems is to understand how they occur and to take steps to control humidity and ventilation.

Humidity, ventilation and combustion air are discussed in more detail in Chapter 8.

Part I: Finding Leakage Areas

How to Locate Air Leaks

The first step is to identify where the leaks occur. Air leaks where there is a hole in the building envelope and a pressure difference. In winter, the house tends to operate like a big, fat chimney. This means that air tends to enter the house at lower levels and exit at the upper levels and ceiling.

Identifying the specific leakage areas can sometimes require a little detective work. You can hire a contractor who has the right equipment to do a test for you. Or you can do your own detective work by making a “draft detector” and using the checklist of leakage areas and perhaps your own “pressure test” to locate those places where air is leaking.

Leak Detector

There is an easy way to locate air leaks: make yourself a “leak detector.” All you need are incense sticks. Hold two or three together for more smoke and easier detection. Powerful leaks will cause the smoke to dissipate and the tips of the incense to glow. Slower leaks will cause the smoke to trail away or move toward the leak.

On a cold day, check for drafts in all suspected areas. It is easier to locate air leaks on windy days. You’ll be surprised to discover how many spots need to be sealed with caulking or weatherstripping. You should also check for possible leaks on the interior walls and features of your house. There may be a direct route through partition walls or along floor joists to the outside that should be sealed.

Pressure Test

Professional air-sealing companies often use a depressurizing fan test to identify and measure the air leaks in a house. A powerful fan is inserted in a doorway, and all intentional openings – windows, doors, chimneys and vents – are closed or sealed. The fan depressurizes the house and leaks are easily identified where air rushes into the house. A professional fan test can also determine the total leakage area in the house, the extent of the work required, the effectiveness of the work as indicated in a post-retrofit test, and indications of backdrafting and spillage problems.

You can perform your own rudimentary fan test by closing all windows and doors and turning on all the exhaust appliances in the house, i.e., bathroom and kitchen fans, clothes dryers (on cool cycle) and any portable fan placed in a window (if you can seal around it). Be careful during the test. Turn off the furnace and water heater (if fuel-fired) to prevent backdrafting caused by other exhausting devices.

You can now go around the house with your leak detector and identify and mark the air-leakage locations that should be sealed.

The rest of the chapter looks at caulking and installing air and vapour barriers. See Chapter 7 for a discussion on weatherstripping windows and doors.

Checklist of Leakage Areas

A few areas of the house deserve special attention, but don’t limit your detective work to just these places.

Checklist

Inside the main living areas, check the following:

• window-glass panes for tightness, and around both the window sash and the window casing;
• around the door, including the threshold and around the door frame;
• electrical outlets, including ones on interior walls;
• exhaust fans and vents (these should vent to the outside and close properly when not in use);
• corners where two walls meet with an imperfect seal;
• light fixtures in the ceiling;
• interior trim and baseboards;
• cracks in the wall finish or ceiling;
• the joint where a wood frame wall joins a masonry wall or chimney;
• doors and hatches into unheated attics;
• fireplace dampers and fireplace bricks;
• behind bathtubs and under sinks;
• above sliding pocket doors; and
• around plumbing pipes and ductwork.

Inside the attic, check the following (you may have to move aside existing insulation):

• around the plumbing stack and any other pipes entering the attic;
• around wires or ceiling light fixtures that penetrate the attic floor;
• around ducting that enters the attic from inside the house;
• at the junction of the ceiling with interior wall partitions;
• attic access doors;
• around chimneys;
• along any shared walls; and
• the ceiling area over bathrooms and stairwells.

Inside the basement, check the following:

• where the wood-frame wall (sill plate) meets the masonry (concrete or stone) foundation or where joists penetrate the masonry wall;
• any holes or gaps where the electrical lines, gas lines or oil fill pipes go through the wall (be careful!);
• holes for wiring and plumbing going into external walls;
• leaky ducting or poorly fitted hot-air registers or cold-air intakes;
• around window and door framing;
• cracks in the foundation wall and slab; and
• floor drains.

Part II: Caulking and Other Air-Sealing Materials

Caulking

Air seal any cracks and penetrations on the inside surface of exterior walls, ceilings or floors. Interior sealing will prevent air from escaping into hidden cavities in the walls and roof. The sealing will be protected from the elements on the inside, and it will be easier to periodically check its condition. Any moisture that does reach that wall space, however, should be allowed to escape to the outside; otherwise, moisture problems might result.

It is not advisable to seal the outside surface of an exterior wall (i.e., the cold side). Caulk only those cracks that will allow water entry. If you are painting the house, try not to plug the joints in the siding and use a permeable (latex) paint or stain. The outside of the walls must be left alone to breathe and dispel moisture.

Caulking Basics

Use tubes of caulking compound and a caulking gun for most sealing jobs. Try the grip with a tube in the gun before buying. Some guns may have a trigger spread that may be too large for your hand. The gun should have a shut-off. A thumb release on the gun is convenient since it permits one-hand operation.

If you are doing a complete job, you will need many tubes of caulking – one standard size tube will make a bead 6 mm (1/4 in.) wide and 7.6 m (25 ft.) long.

There are several types of caulking compounds available. People often have a bad experience when they first try caulking because they purchase an inexpensive or inappropriate caulking compound. Cheap compounds are difficult to apply and lack durability. Be sure to choose a material well suited to the task. See pages 33 to 35 for a guide to the different types of caulking and their application.

How to Caulk – Step by Step

1. Identify the areas to be caulked (as outlined earlier in this chapter).
2. Do not try to caulk in an area where the temperature is below 5°C (41°F); the compound will become stiff and difficult to work with. Read labels carefully for storage and application temperatures.
3. Make sure the area to be caulked is clean and free of dirt, loose paint and old caulking. Replace deteriorated wood and re-nail loose boards. If there are particularly large cracks – greater than 6 mm (1/4 in.) – use a special filler such as oakum or a foam backer rod before caulking. Push this material into the crack to a depth equal to half of the crack width.
4. Cut the nozzle of the tube to a size that will allow the bead of caulk to overlap both sides of the crack. Make the cut square and then break the seal with a wire or long nail pushed down the nozzle.
5. Push the caulking gun along at right angles to the crack or joint. The caulk is then forced into the crack to fill the gap completely. Make sure the caulk adheres to both sides of the crack and that there is sufficient caulk to allow for movement or shrinkage.
6. The seal should also be neat. Effective caulking takes practice, so go slowly at first, following instructions on the tube. “Tooling,” or finishing the bead, can usually be done with a wetted sponge or finger before the caulk sets, but do not use your mouth to wet your finger!
7. Latex and silicone caulk can be cleaned off with water before they set. For other caulks, you can try a standard solvent (e.g., toluene, varsol or brush-cleaning solvent) or check the manufacturer’s literature. Be sure to release the pressure lever on the gun to prevent caulk from dripping as you move from place to place.

Other Sealing Materials and Applications

A number of other materials are used to provide an air barrier at different locations in the house. These include specialty gaskets and tapes, as well as sheet materials such as polyethylene, spun-bonded olefin, rigid insulation, drywall, plywood and sheet metal. Installation techniques are critical when using sheet materials as an air barrier. All edges, seams and penetrations in the sheets must be sealed. Further details are provided in other chapters.

Air and Vapour Barriers

It is often possible to install a new air and vapour barrier using sealed drywall as the air barrier and layers of paint or sheet polyethylene as the vapour barrier. Alternatively, sealed sheet polyethylene can be installed on the warm side of the insulation to provide both an air barrier and a vapour barrier. Proper installation is critical (see illustration above).

• Use wide sheets to minimize seams.
• All seams and edges should overlap over a solid backing, such as a stud.
• Run a bead of non-hardening acoustical sealant between the overlapped sheets over the support.
• Staple through the sheets and the bead of sealant. All other staples should be avoided or minimized.
• The finish (e.g., drywall) acts as an anchor, securing the seam. If the polyethylene is recessed in the wall, a batten can be nailed over the seam to provide mechanical support.
• Seal all penetrations. Where possible, they should penetrate at a solid backing such as plywood and be caulked.

Tips on Sealing Some of the Leakiest Areas

Electrical Outlets

If you notice a draft through an outside wall electrical outlet, it must be sealed. (Some inside wall outlets can also provide leakage paths, so do check them.) Turn off the power to the outlet by turning off the circuit breaker or removing the fuse. Check to make sure the power is disconnected by turning on a lamp. There are special foam pads, approved by CSA International, that fit between the cover plate and receptacles. You will obtain a better seal if you caulk the gasket before installation. Place child safety plugs in seldom-used outlets. Some foam pads come with a gasket that fits on the safety plug.

If you are installing an electrical outlet during a renovation, get a good seal by placing it in a special plastic box that is available from many hardware or electrical supply stores. Caulk the penetration for the wire, and seal the new air and vapour barrier to the edge of the box.

Trim Areas (Baseboards, Mouldings and Window and Door Casings)

Seal areas of air leakage around all trim. In some cases, this can be done easily by sealing all the joints with a flexible caulk that is clear, paintable or of a matching colour. A more effective solution for leaky or poorly fitted trim is to carefully remove the trim and seal behind it. Insulate wide cracks with a foam backer rod and seal them with caulking, polyurethane foam or other suitable material.

If baseboards are removed, you might also be able to caulk between the wall finish and the bottom wall plates and between the plates and the floor.

Glass Panes

The seal between glass and its wood frame should be tight. Check the glazing carefully and be certain that all the seals are intact, with no cracks or missing sections. If not, repair them with putty or glazing compound. Putty usually costs less, but tends to dry out and crack faster, unless you put linseed oil on the wood first. A glazing compound, on the other hand, lasts longer and stays semi-soft and usable longer. Remove the old putty and apply the new materials with a putty knife. Be sure to press it firmly into the space for a good seal.

Fireplaces

A crackling fire makes a room cosy, but what happens when the fireplace is not in use? If the damper is left open, warm air from the room shoots up the chimney. When the fireplace is not in use, close the damper. Take a flashlight and make sure the damper fits tightly. If it doesn’t, fix it yourself or have it repaired.

Even with the damper closed, a great deal of heat still escapes up the chimney. Commercially available glass doors for fireplaces are usually not very tight or effective. Ideally, you should also install an outside combustion air duct to the fireplace to improve operation, efficiency and safety. Ask at your local building-supply outlet or wood-burning appliance dealer if a kit is available.

You can also seal off an unused fireplace. Close it up by putting an airtight plug of some sort in the chimney or across the fireplace opening. This can be made from board material that is cloth-covered and provides a good seal at the edges (see diagram above left).

Check for any air leaks where the chimney meets the wall (remove the trim if necessary). Caulk this joint with a flexible caulk.

Chimney

There may be a large gap where a masonry chimney rises through the attic. This space can be partially sealed by stuffing it tightly with pieces of mineral wool batt. Do not use any material that is, or may become, flammable. For greater effectiveness, cut pieces of sheet metal to fit around the chimney. Seal all the joints with a flexible, heat-resistant sealant (see diagram above right).

If you have a factory-built metal chimney rising through the attic, do not insulate closer than 50 mm (2 in.) as this can create hot spots in the chimney lining and can present a fire hazard. Instead, install a collar of metal or other fire-resistant material around the chimney and caulk to prevent air leakage into the attic.

Attic Hatch

Seal the attic hatch exactly as you would seal a door to the outside. Caulk around the frame and between the casing and the ceiling plaster board. Apply weatherstripping along the edges of either the casing or the access panel itself.

Finally, install hooks with eye bolts or some sort of latch mechanism to hold the hatch firmly against the weatherstripping. The hatch itself should be insulated.

Windows That Are Never Opened

If you don’t need a window for ventilation or as a possible emergency escape route, seal it by caulking rather than weatherstripping. Caulking is likely to be quicker, cheaper and more effective. Install a special strippable caulk that can be removed when you want to operate the window again.

Mail and Milk Chutes

Seal the chute if it is no longer in use. If you use it regularly, seal around the frame and replace the weatherstripping. If the chute cover is on a spring, make sure it closes properly. A drop of oil can sometimes work wonders or, if necessary, replace the spring. Alternatively, you can buy a new cover. Consider closing your mail chute permanently and replacing it with an outside mailbox.

Contracting the Work

Homeowners can usually do an effective air-sealing job if they have the time and patience and are conscientious about air sealing in areas that can be difficult and uncomfortable to work in (e.g., the attic). However, professional air sealers can usually do a much better job because of their experience in locating and sealing leaks. Contractors may be experienced in using a depressurizing fan door (sometimes called a “blower door”) with smoke pencils and with specialty caulking and sealants.

Another service that many air-sealing companies can offer is testing and assessment of ventilation and combustion air requirements, including backdrafting testing.

Typically, professional whole-house air sealing can cost from $500 to $2,000 depending on the size and complexity of the house and work required. The contract should specify each area to be sealed and the materials to be used.

Previous | Table of Contents | Next