It is a very poor strategy to rely on building leakage to supply your home with “fresh” air. Active ventilation (see below) is an important component of airtightness strategies.
Airtightness should be planned — Accurate energy modeling of your building will require a target for airtightness as a key variable. It is very informative to adjust the rate of air leakage in your energy model and witness the effect on energy performance. Lowering the rate of leakage can, in some circumstances, have a greater effect on efficiency than raising insulation quantities. Choosing a target for airtightness is central to planning for energy efficiency.
Airtightness should be tested — Planning a target for airtightness is important, but it’s worthless unless you ensure the target is reached in construction. Airtightness testing using a blower door should be carried out as soon as the air control layer is complete (and accessible) so you can fix any problems before the layer is covered by finish materials.
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Airtightness requires active, balanced ventilation — Healthy and efficient building assemblies require airtightness, while your home requires the exhaust of excess moisture, and the occupants require fresh air from a properly designed and installed ventilation system. System components will vary depending on climate conditions, but an appropriate strategy must be chosen and implemented.
Active ventilation is often derided as an “iron lung” for the building, but if you are willing to have active systems for heating, cooling, refrigeration, hot water, laundry, and other services, then an active ventilation system — often consisting of a fan or two in a box — should not be viewed as contrary to your building objectives.
“I’ll just open a window” is often used as an excuse for not designing an active ventilation system. This can be part of a ventilation strategy, but it doesn’t work well on still days, on days when interior and exterior temperatures are similar, or in rooms with a single window and a closed door. It’s also extremely inefficient when the temperature differences between inside and out are high and does not work at all when not operated due to comfort or neglect.
Air leakage rates — The flow of air through the building assembly is most commonly expressed in residences as ACH50 — the number of times the volume of air in the building will change per hour when there is a 50 pascal air temperature drops, the air gets denser, and the relative humidity increases, even though no additional vapor has been introduced into the system. pressure difference between the interior and the exterior. A leaky older home may be 8-10 ACH50, while current code requirements are between 2-5 ACH50. Extremely efficient homes are less than 1 ACH50