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.
Cavity insulation and stud locations can be explored using a calibrated infrared (IR) camera (see IR thermography) to inspect the wall during a period of high differential temperature. Studs will appear as vertical stripes, and substantial insulation gaps should be evident. Knowing ambient and room temperatures plus wind speed, a calculation can be performed to estimate cavity R-value.
Another method to estimate cavity insulation level is to drill a small hole near the top of the stud bay, and inspect it using a borescope. The user should be able to view what type of insulation exists, and what state it is in.
Finally, in some cases, only using a thermal conductivity sensor is reasonable. Be careful where this is placed, to minimize alternate heat transfer paths from affecting the measurement.
Moisture can be inspected using a moisture meter or an IR camera, to get a general sense of where problems may be occurring. Neither of these is a long-term solution. Condensation sensors can be used to sense water condensation at problem areas.
Infiltration of a single wall is seldom of interest. Individual cracks can be inspected during a blower door test using a smoke pen.