b'not, however, a licensed professional as defined by the building code. The advisor recommended converting the homes air and vapour barrier system from drywall and sheet polyethylene toEVEN SMALL INCREASES IN ROOF a medium-density polyurethane spray foam. Even the attic could be converted to interior usable space by applyingTEMPERATURE CAN HAVE A SUBSTANTIAL the foam to the underside of the roof (Photo 2) and providing high-efficiencyIMPACT ON VAPOUR PRESSURES.HVAC above the ceiling. Substantial improvements in air-tightness were the goal of that recommendation.In forming their recommendation regarding the roof, the advisor specifi-cally referenced Albertas new vari-ance to the NBC-2019AE permitting unvented roofing. Further analysis byUse An RCABC Membera professional was not mandatory; the advisor had the generic engineeringIts Chaos Without Usreport1 and a statement of equivalency from the province. The spray foam installation conformed with the strin-gent requirements of the report, and this was documented by the builder.Roughly four months after conversion, in the first summer post-renovation, problems with the shingles began to appear. The shingles were buckling, and to a degree that the ridges were clearly visible from the ground (Photo 1). After a brief and relatively simple investigation, it was determined that the shingle failure was the result of wrinkles forming in the self-adhered membrane (Photo 3). Summer heating of the dark coloured roof increased temperatures on the roof, and the spray foam insulation locked moisture and heat in the outer layers of the roof. Even small increases in roof temperature can have a substantial impact on vapour pressures. It is clear that vapour pressure spikes below the adhered underlay caused the blistering and visible ridges. The ridges subsided with colder weather but will be back next summer. The long-term effect of this natural seesaw brought on by unvented roofing is difficult to predict. Worse than the shingle buckling, the conversion also seems to have voided the roof warranty early in the life of the assembly. In preparing for this article, I spoke with one major shingle manufacturer who sells in the Alberta604-882-9734 1 rcabc.org RDH Building Science Laboratories M-25608.000ACC - Alberta Unvented Roofs Evaluation Report. March 4, 2022.SPRING/SUMMER 2025 15'