How a house is built
Heat, leaks, and drying
Insulation slows heat. Sealing stops leaks. The wall still has to dry after rain. Marine climate zone 4C.
Arrow keys turn the house. Plus and minus, or the zoom buttons, change the zoom. A horizontal drag turns it after you tap the drawing. Reset view returns to the step camera.
The drawing needs WebGL. The notes on the page still stand.
Heat moves through materials, with leaking air, and by radiation. Insulation slows the first. Sealing slows the second. A shiny surface can slow the third, but only if it faces an air space. Most of the comfort problem in an ordinary wall is the first two.
Moisture rides with leaking air and, more slowly, as vapor. A wall in western Washington gets wet from rain. Winter drying is slow. If the cladding and the weather barrier cannot let that water out, insulation will not save the sheathing. Climate zone 4C is the marine zone used for much of this region. The class of vapor retarder on the inside is chosen for the whole assembly. It is not automatically a polyethylene sheet.