DE-79-03-3 -- The Use of Low-Moisture-Permeability Insulation as an Exterior Retrofit System-A Condensation Study

Laboratory and field studies were carried out to determine whether. the use of low-moisturepermeability insulation as an exterior retrofit system increases winter moisture accumulation within the existing wood siding, sheathing, and cavity insulation. A full-scale insulated test wall was sandwiched between a hot and cold box apparatus in the laboratory. The exterior surface of one half of this test wall was fitted with a low-permeability insulation retrofit system. The exterior surface of the test wall was subsequently exposed to two consecutive steady-state winter conditions, while the interior surface was exposed to a typical indoor condition for a residence. The moisture accumulations within various components of the two halves of the test wall were compared. The moisture-transfer processes which occurred in the test wall were modeled with an ASHRAE diffusion model modified with a term to account for air leakage from the hot to the cold box. A limited field survey of several wall constructions was carried out to compare field observations of moisture conditions with laboratory results. In addition, the effect of accumulated moisture of wall heat transmission was examined.