Sources and References

Primary texts — Straube, J. F. and Burnett, E. F. P. Building Science for Building Enclosures. Building Science Press, 2005. Hutcheon, N. B. and Handegord, G. O. P. Building Science for a Cold Climate. National Research Council of Canada, 1995.

Supplementary texts — Allen, E. and Iano, J. Fundamentals of Building Construction: Materials and Methods, 7th ed. Wiley, 2019. ASHRAE Handbook of Fundamentals (current edition). Lstiburek, J. Builder’s Guide to Cold Climates. Building Science Press, 2006.

Online resources — Building Science Corporation research reports and insights archive (buildingscience.com); ASHRAE open-access standards (90.1, 160, 62); National Research Council Canada building science publications; Passive House Institute (PHI) technical documentation; Oak Ridge National Laboratory envelope research reports.

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Chapter 1: Functions of the Building Enclosure

The building enclosure is the physical separator between the conditioned interior and the exterior environment. Its function is not one function but many, and those functions often conflict. A well-designed enclosure must simultaneously control rain, air, vapour, heat, sound, fire, light, and structural loads, while being buildable within the cost, schedule, and skill of the construction market. The design task is one of reconciling these demands through a system of layered materials.

1.1 The Four Control Layers

Building scientists organize enclosure design around four control layers, listed in priority order:

1. Water (rain) control. The single most important function; most enclosure failures are moisture failures. The water control layer is usually a drainage plane behind the cladding or a face-sealed waterproof membrane.
2. Air control. The air barrier limits infiltration and exfiltration, which drive energy loss, moisture movement, and comfort problems.
3. Vapour control. The vapour retarder (or the strategic absence of one) manages diffusion of water vapour through the assembly.
4. Thermal control. The insulation layer resists heat flow.

These four layers do not have to be four different materials. A self-adhered bituminous membrane can function simultaneously as water barrier, air barrier, and vapour retarder. A single layer of closed-cell spray polyurethane foam can serve all four. Economies of integration must be balanced against redundancy and repairability.

1.2 The Perfect Wall

John Straube’s conceptual perfect wall places all four control layers on the exterior of the structure. Thermal insulation sits outboard of the structure, water and air barriers sit immediately outboard of the sheathing, and cladding with a drainage gap covers everything. The structure stays at interior temperature and humidity, avoiding condensation and thermal bridging. The principle scales to roofs (the perfect roof) and slabs (the perfect slab): the four control layers are always outboard of the structural mass.

Chapter 2: Heat, Air, and Moisture Transport

2.1 Heat Transfer Modes

Conduction through the opaque wall is governed by Fourier’s law. The steady-state heat flux through a wall of total thermal resistance \(R\) with inside-outside temperature difference \(\Delta T\) is

\[ q = \frac{\Delta T}{R}. \]

Total \(R\) is the sum of layer resistances \(R_i = t_i/k_i\), with thickness \(t_i\) and conductivity \(k_i\), plus inside and outside surface film resistances. The U-factor is \(U = 1/R\).

Radiation matters at roof assemblies and inside cavities. Convection inside cavities is suppressed by narrow dimensions or by filling with insulation.

2.2 Thermal Bridges

A thermal bridge is a region of higher conductivity that creates a shortcut for heat through the enclosure. Steel studs in a wood-framed wall, cantilevered balconies through an insulated wall, and window frames all bridge heat. Two-dimensional or three-dimensional analysis via software such as THERM or HEAT2 predicts the effective U-factor of assemblies with bridges. An uncorrected stud wall may deliver only 60% of the insulation’s nominal R-value.

2.3 Air Leakage

Air leakage through an enclosure is driven by three pressures: wind, stack effect, and mechanical system imbalance. Stack effect in a heated building pulls outdoor air in near the base and pushes indoor air out near the top, with neutral pressure plane near mid-height. The pressure difference at height \(h\) above neutral is approximately

\[ \Delta p = \rho g h\left(\frac{T_i - T_o}{T_i}\right), \]

where temperatures are absolute. A 10-storey building at 30 °C indoor-outdoor temperature difference generates about 25 Pa pressure difference between top and bottom, enough to move substantial air through any leakage path.

Measured air tightness is expressed as air changes per hour at 50 Pa (ACH\(_{50}\)) or air leakage at 75 Pa per exterior surface area. Passive House requires ACH\(_{50}\) ≤ 0.6; conventional Canadian construction is often 2 to 5 ACH\(_{50}\); leaky old buildings exceed 10.

2.4 Vapour Transport

Vapour diffuses from high to low partial pressure through permeable materials according to

\[ \dot m = \mu A\,\Delta p_w, \]

where \(\mu\) is the permeance (kg/(m²·s·Pa) or imperial perms). Diffusion is usually slower than air leakage; the latter can deliver orders of magnitude more moisture through a single hole. Nevertheless, in heating climates a layer of low permeance (vapour retarder) on the warm side of insulation is often specified to prevent condensation within the assembly. In cooling climates the vapour retarder may need to be on the exterior, or absent entirely.

2.5 Dew Point and Condensation

Condensation occurs where temperature drops to dew point. In a cold-climate wall in winter, the temperature drops across the insulation; if the vapour pressure is not controlled, it will reach saturation somewhere within the insulation. The Glaser method plots partial pressure and saturation pressure through the assembly; any crossover indicates potential condensation. Hygrothermal software (WUFI) extends this to transient analysis with capillary moisture.

Chapter 3: Rain Management

3.1 Rain Penetration Mechanisms

Rain enters enclosures through three mechanisms: gravity (direct flow down the face), kinetic energy (droplets driven by wind), and capillary action (wicking through porous materials). Complete prevention requires addressing all three.

3.2 Approaches

Face-sealed cladding (EIFS, some masonry) relies on perfect exterior waterproofing. Any breach leads directly to interior damage. Long-term performance depends entirely on workmanship and sealant maintenance.

Drained cladding includes a ventilated or drained cavity behind the cladding. Water that bypasses the cladding reaches a drainage plane (building wrap, self-adhered membrane) and sheds down through weep holes. This is robust against imperfect cladding installation.

Rain screen takes drainage further. A pressure-equalized cavity behind a partially open cladding prevents pressure differences from driving droplets inward. Properly executed, rain screens are the highest-performing approach in wet, windy climates.

3.3 Flashings

Flashings divert water around penetrations and transitions: window heads, window sills, parapets, roof-to-wall intersections, through-wall penetrations. A flashing must lap over the drainage plane below and under the drainage plane above, creating shingling that sheds water outward. A failure to shingle correctly is the most common construction error causing enclosure water damage.

Chapter 4: Opaque Wall Assemblies

4.1 Traditional Mass Walls

Solid masonry (brick, stone, adobe) relies on mass to absorb and re-release heat slowly. In hot, dry climates the time lag flattens indoor temperature swings. In cold climates the thermal resistance is too low to meet modern energy codes, requiring added insulation.

4.2 Frame Walls

Wood or steel frame walls fill stud cavities with batt or blown insulation. To reduce thermal bridging, continuous exterior insulation board (rigid foam, mineral wool) is added outboard of the sheathing. A 2x6 stud wall with R-20 cavity insulation and R-10 continuous exterior insulation achieves an effective R-value near R-27, compared to R-14 for a cavity-only wall with steel studs.

4.3 Double-Stud, SIP, and Mass Timber

Extreme-performance assemblies include double-stud walls with deep insulation cavities (R-40 or higher), structural insulated panels with EPS or polyurethane cores, and cross-laminated timber panels with continuous exterior insulation. Each achieves high R-value with different trade-offs in cost, embodied carbon, and vapour behaviour.

Chapter 5: Roofs

5.1 Low-Slope Roofs

Low-slope (flat) roofs fail more often than any other enclosure component. A conventional roof places the membrane on top of the insulation, exposing the membrane to UV and thermal cycling. An inverted (protected membrane) roof places insulation over the membrane, sheltering it at the cost of allowing the insulation to get wet. Proper drainage (at least 1:50 slope, preferably 1:25), reliable penetration flashings, and accessible maintenance define long-life low-slope roofs.

5.2 Steep Roofs

Steep roofs shed water by gravity. Asphalt shingles, metal panels, slate, and clay tiles span climates and cost ranges. Ice damming in cold climates occurs when warm air from the living space melts snow on the upper roof; meltwater refreezes at the cold eave, backing up under shingles. Remedy: cold roof construction (vented attic with deep insulation at ceiling level) or, for cathedral roofs, enough exterior insulation to keep the roof deck below freezing.

Chapter 6: Windows and Glazed Systems

6.1 Thermal Performance

A window has three components contributing to its U-value: centre-of-glass, edge-of-glass, and frame. Double glazing with argon fill and a low-emissivity coating achieves U-values near 1.7 W/(m²·K); triple glazing with two low-e coatings reaches 0.7 W/(m²·K). Frames are usually the weak link; insulating spacers and thermally broken frames matter as much as glass selection.

6.2 Solar Heat Gain

The solar heat gain coefficient (SHGC) is the fraction of incident solar radiation that becomes interior heat. Values range from below 0.2 for heavily tinted glass to above 0.6 for clear glass. Cold-climate windows want high SHGC for winter solar gain; hot-climate windows want low SHGC. Orientation-specific selection and exterior shading improve year-round performance.

6.3 Air and Water at Windows

Window-to-wall interfaces account for a disproportionate share of leakage and water damage. Sill pan flashings, back dams, end dams, and drained-and-sealed installation methods are standard practice. The window must be integrated with the wall’s drainage plane, air barrier, and vapour retarder, each of which requires careful detailing.

Chapter 7: Interaction with Structure and Mechanical Systems

7.1 Structural Accommodation

Buildings move. Concrete shrinks and creeps; steel thermally expands; wood moves with moisture. The enclosure must accommodate these movements through expansion joints, slip connections, and flexible sealants. A rigid enclosure attached to a moving structure will crack, leak, or both.

7.2 Mechanical Interaction

The tighter the enclosure, the more reliant the building becomes on mechanical ventilation. At ACH\(_{50}\) below 1.5, mechanical ventilation is essential to deliver code-required outdoor air and remove moisture, CO\(_2\), and contaminants. Heat recovery ventilators and energy recovery ventilators recover 70 to 90 percent of the energy in exhaust air. Enclosure and mechanical systems must be designed together; optimizing one in isolation usually hurts the other.

Chapter 8: Construction, Quality, and Retrofit

8.1 Construction Process

Enclosure performance is determined at installation. Self-adhered membranes require clean, dry substrates; sealants require proper joint geometry; continuous insulation requires fasteners that do not puncture the air barrier. Mock-ups and field air-leakage testing catch errors before the building is enclosed.

8.2 Commissioning

Enclosure commissioning verifies that the as-built performance matches the design: thermal imaging under pressurization identifies air leakage paths; whole-building blower-door tests measure leakage; fenestration water-spray tests verify window installation. Increasingly, codes require whole-building air tightness testing, which sharpens the contractor’s incentive to build tight.

8.3 Retrofit

Existing buildings account for the large majority of the built stock. Retrofit adds insulation, air tightness, and new control layers to structures never designed for them. Interior retrofit risks creating cold, damp structures; exterior retrofit (overcladding) preserves the original structure but requires new flashings and window reinstallation. Hygrothermal simulation is essential because the modified assembly moves the dew point into new locations, and mistakes manifest slowly as decay or mould years later.