Tigard summers are mild on paper and warm in practice. About three miles from the city center, NOAA’s Beaverton 2 SSW station averages 82.3°F highs in July and August and records about 15 days a year at 90°F or higher. A glass cellar wall in a west-facing great room meets those afternoons head on, so displays here are sized for peak sun and room heat, not for the monthly mean.
The other half of the year is wet. Nature Park–Beaverton normals show roughly 39 inches of precipitation annually, with each month from November to January above 5.5 inches, and regional dew points then track close to air temperature. How to handle moisture in the cellar wall is disputed. Joseph Lstiburek of Building Science Corporation notes that vapor flow through a cellar wall reverses with the seasons, objects to vapor barriers on both sides of such a wall and prefers semi-vapor-impermeable layers such as rigid XPS or spray foam; cooling manufacturers such as WhisperKOOL instead require plastic sheeting on the warm side. The equipment maker’s installation terms and the wall design are settled together.