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Air-Leakage Control
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 noise and dust 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, wood stoves 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, the chimney or flue could backdraft or spill dangerous gases into the house. If you suspect that you have a problem, you should speak to your heating contractor.
House as a System
Before beginning any retrofit work, it's a good idea to review what's involved and to understand how your work might affect other aspects of the house. If you think things through and plan carefully in the early stages of work, the work will meet your expectations and you will have fewer unpleasant surprises.
It's important to remember that the house operates as a system. All the elements of a house – the environment, envelope, mechanical systems and occupant activities – affect each other, and the result affects the performance of the house as a whole. Understanding these relationships is the secret to avoiding problems.
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.
The lesson here is that a change to one component of the house can have an immediate effect on another component. The combined effect of many small changes over time can also affect the balance of the system.
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.
More information on humidity, ventilation and combustion air