Thermal II - Insulation & the Thermal Envelope

Course competency

On completing this course you can specify an insulation material for a given assembly and climate, calculate whole-wall R-value including framing effects, trace a continuous thermal boundary through every junction and penetration of a building, detail out thermal bridges, design foundation and slab insulation against the frost line, specify an air barrier and verify it with a blower door, decide the drying direction of an assembly and whether it needs vapour control at all, and specify and install windows that perform as their labels claim.

Why this course exists

Course 5 taught the building how to collect heat. This course teaches it how to keep it.

The two are not equally forgiving. A passive solar design that is 10% off still works. An envelope that is 10% off leaks that 10% every hour of every winter for the life of the building, and - unlike orientation - most of its failures are invisible. A missing R-value shows on a bill. A thermal bridge shows as mold behind a cabinet in year four. An unsealed penetration shows as a cold bedroom nobody can explain.

The envelope is where regenerative buildings are won and lost, and it is won in the details rather than in the decisions.

Getting the envelope right is not only an energy question. It is a durability question, a health question and a resilience question. Moisture management in particular is arguably more critical than thermal performance for long-term durability and occupant health.

The organizing principle

The Perfect Wall

Structural support and thermal mass on the inside. Continuous insulation on the outside. Water, air and vapour control layers properly integrated between them.

The term is building scientist Joseph Lstiburek's, and the principle is the foundation of everything in this course.

Why that order and no other:

• The mass is always warm. It never sees a freeze-thaw cycle, never accumulates condensation, and is always available to absorb and release heat into the living space
• The structure is protected from both exterior climate and moisture-driven deterioration
• Continuous exterior insulation eliminates thermal bridging through studs, joists and every other structural element

For a Biotecture tire wall this is implemented directly: the rammed-earth tire wall is both structure and thermal mass, with rigid foam exterior insulation and a protective render coat. The result is thermally massive, well insulated, and durable over centuries with minimal maintenance.

Every lesson in this course is a consequence of that diagram.

The correction carried from Course 5

Buildings account for roughly 30% of global final energy consumption and more than 55% of global electricity consumption (IEA). Operationally they produce about 28% of energy-related CO₂ emissions; including construction, just under 40%.

Both the textbook and the live site state "approximately 48% of all electricity generated globally." That is a garbled US figure and it is wrong. It appears in at least two places on the live site - chapter 1 and the chapter 11 conclusion of the thermal course - and both need correcting.

Course structure