Building Diagnostics Help

Most builders would cringe at the thought of a client calling to report a frozen burst pipe that has just caused extensive water damage to their newly built home. Unfortunately this less than happy scene is played out every winter in an assortment of well built, well insulated homes. As a building consultant that provides infrared heat loss inspections my office gets a call somewhere between the calls to the plumber, insulation contractor, architect and lawyer. Ironically the resulting multi directional finger point is actually quite appropriate. Typically these problems are not the result of poor workmanship by one individual sub, but rather a series of poor building details installed by separate subs that unknowingly compound the problem.

These scenarios include some interesting building dynamics that are a lot less intuitive and a bit more complicated than simply missing insulation or non functional heating systems. Air temperatures measured below 32 degrees can be found well inside the heated envelope in unexpected locations, between heated floors and inside interior partitions. These hidden bays and building assemblies are of course the same locations that serves as chaseways for plumbing and mechanical components.

Fixing a problem in an existing home can be a frustrating and expensive challenge.Fortunately construction details to avoid these scenarios are relatively cheap and easy, if the dynamics that cause the problems are anticipated.

Combining the infrared camera with an infiltration fan helps reveal hidden air leaks and insulation flaws. In the above infrared picture the box soffit above the cabinet is full of cold air.

First don’t assume the building shell is airtight.
Despite all the awareness of housewrap details, beefed up R-values and “too tight house syndrome” the reality is that certain less than obvious building details can expose the thermal shell to exterior air penetrations. These hidden air breaches act as conduits for cold air infiltration. The vast majority of frozen pipes are caused not by missing insulation but by cold air infiltration. Lessoned learned from using an infrared camera and a blower door infiltration fan help explain the way interior building assemblies communicate with the cold outside world. Air moves in and out of a building in a more vigorous manner than is commonly understood. Wind, temperature differences and even mechanical system pressures can result in the equivalent of 100% of the heated air leaving a building every two or three hours. Often a a small number of critical details in the building are responsible for the majority of the air leakage and exchange.

The complex framing details and multiple roof lines so common in present-day construction leaves plenty of opportunities for critical junctions to act as cold air conduits to the outside via, side attics, bay roofs and knee wall eaves. Since the sheathing interface between these unheated areas and the heated space is not continuous or air tight, air movement and infiltration is unfettered. Air communication from adjacent unheated areas such as an attic over a garage, a flat roof line over a one story ell or an poorly planed open soffit vent are typical scenarios. For example, cold air can move horizontally between unheated knee walls space into the adjacent heated floor bays. If the knee wall space happens to be open to a soffit vent the airflow dynamics are increased. The distance between the cold air can easily penetrate deep into the middle of the building.

Air leakage paths are not limited to horizontal movement. Vertical plumbing chases common in wet walls and behind showers can open the interior heated space to the cold attic air above. Another common problem areas is built-in tubs located on exterior walls. Since the tub unit typically is installed to the framing prior to the wallboard being installed there is no effective or continuous air barrier envelope. Since these exterior wall bays are often open to the outside air via adjacent vented eaves and side attics, plumbing under the tub is susceptible.

Relying on batts insulation to stop air flow in any unsheathed wall or open ended building assembly will not work. All insulated wall bays and building assemblies must be detailed air tight before the insulation batts is installed. Alternatively some spray foam insulations provide an air tight barrier when applied in the right location. Which gets to the real issue, Is this an insulation problem, framing problem or design issue? Should the insulation contractor be responsible for an open framing detail? Typical building plans do not detail where the air barrier or thermal envelope is located. This undefined arrangement can be compounded by unblocked soffit vents, creative framing details and the mechanical contractor’s sawzall.

Until these issues are worked out the prudent general contractor may want to take more aggressive steps to stop unchecked air leakage. Since the list of call backs is not limited to frozen pipes but includes comfort complaints, high heat bills and ice dams an eye towards controlling air leakage can have multiple benefits. For builders who use less than air tight insulation this involves taking the steps to seal large leakage paths during the construction process. For example before a tub is built in adjacent to that cantilevered bay roof , an air tight barrier of plywood or rigid insulation can be sealed into place. For irregular framing transitions and other critical junctures a two-part super expanding foam system is a great solution. Being aware of how soffit vents can inadvertently communicate with the heated space can prompt some preemptive blocking that limits the ventilation to the soffit and the attic, not the heated space.

Many builders and insulation contractors scoff at the idea that today’s modern buildings can be excessively drafty. Seeing the evidence through the lens of an infrared camera can be a real eye opener. Seeing the results of water damage from frozen pipe can provide the same lesson in a bit more chilling fashion.