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Field Test Best Practices: A Resource for Practical Residential Building Science

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Envelope

The building envelope surrounds the living space and buffers it from effects of weather. It must provide durability, structural safety, and barriers to heat, water, moisture, and air flow. Testing the performance of portions or the entirety of the envelope in each of these areas is needed to support many research efforts.

Leakage and Infiltration

A cornerstone of energy efficient buildings, in both new and renovated existing homes, is having tight envelopes and effective air distribution systems. Leaky buildings waste energy spent on space conditioning as the conditioned air can escape. However, once you have built a tight building, well-controlled fresh air needs to be brought into the house and distributed uniformly within a home. There are a number of short term tests that are used to quantify the air tightness of a home and duct system and to determine the distribution of outside air. The blower door and duct pressurization tests use similar equipment to pressurize or depressurize the whole house or the duct system, respectively, to measure leakage. The flow rate of air required to maintain a certain pressure can be used to characterize the total leakage area of the house or the duct system. Tracer gas tests provide a more accurate test method, and use the decaying concentration of a harmless gas to calculate ventilation rates.

Building UA

Building UA is the characteristic whole-envelope heat transfer figure of merit. It represents a combined value for the entirety of the envelope, including attic and roof, walls, windows, doors, and foundation.

Walls

In new construction homes, builder partner quality procedures should provide evidence that exterior wall construction is built to the original specifications. Verification is performed by a building UA measurement and an infiltration measurement.

In existing buildings, however, wall state cannot be assumed. Insulation can slump, decay, or not be installed in the first place. Water infiltration can cause degradation over time. Settling can cause cracks to appear. Only destructive exploration will fully expose the actual wall state. However, additional testing can be done to characterize the state of the walls. Performance metrics of interest include R-value of cavity insulation, stud spacing, moisture barrier state, and infiltration level.

Windows

Research on windows in residential buildings typically centers around four types of study: thermal performance, infiltration, lighting impact, and moisture performance.

Foundations

Buildings communicate with the ground by heat and mass transfer through foundations. Measurement of the hygric and thermal performance of foundations is important in some test homes. It should be coupled with modeling where possible. Typical building simulation programs (EnergyPlus and DOE2, for example) have limited capability at present to model residential foundations in a detailed way, so other tools may be appropriate.

Buffer Spaces

Buffer Spaces are comprised of unconditioned spaces that are part of the building system. They include:

  • Attics
  • Crawlspaces
  • Unconditioned basements
  • Garages
  • Mechanical rooms