Infiltration - the Stealthy Suspect in Condominium Heat Loss
Bob Burns, P.E., R.S.
Cold air belongs outdoors. Hardly a new concept. But the logic is becoming more compelling as the cost of energy to heat our buildings climbs skyward. Providing the BTU's to heat infiltrating cold air can amount to as much as 30% of the total cost of maintaining wintertime comfort levels in residential buildings. Now that's a significant factor. And cold air infiltration has many choices in its attack on our heating dollar. The very nature of building construction provides the opportunities. An arctic blast on the windward side of a building will clearly drive cold air in through the gaps around loose windows and doors. But the same wind will cause a negative pull on the leeward face of the building as it cascades over it. This will draw in cold air through construction that we assumed were pretty much airtight. Just one example is the space out beyond knee walls on second floors - a fairly common construction seen in condominium style buildings. The pathway for the building's structural ventilation from soffit vents to ridge vents leads right through this space. Doors to these spaces are rarely airtight so cold air can slip in around the door frames. Now on a windy day, you would probably feel the draft effect but under conditions that are more static the cold air would just quietly become part of the heat loss package. Other locations for cold air entry are the bottom plate of the exterior wall framing where it sits on the sub-flooring. The surfaces of plate and sub-flooring are rarely perfectly level resulting in gaps that welcome cold air entry. But the primary suspect for cold air infiltration is invariably the windows because there are many of them and because the techniques for installing them can leave numerous pathways for cold air. Tightening up your windows by adjustment and caulking around the exterior frames is a simple step that can return significant dividends.
