Building Envelope Quick Reference
This cheat sheet covers envelope design principles heavily tested on the ARE 5.0 PDD exam. See the Building Envelope topic guide for detailed study.
Wall Assembly Layers (Outside to Inside)
- Cladding/finish: Brick, stone, metal panel, stucco, siding
- Air space/drainage cavity: Typically 1" minimum for rainscreen
- Water-resistive barrier (WRB): Building wrap (Tyvek, etc.) or fluid-applied
- Sheathing: Plywood, OSB, gypsum, or continuous insulation board
- Continuous insulation (ci): Outboard of structure to reduce thermal bridging
- Structure: Studs, CMU, concrete
- Cavity insulation: Batt or blown-in between studs
- Vapor retarder: Placement varies by climate zone
- Interior finish: Gypsum board, paint
Vapor Retarder Placement by Climate
| Climate | IECC Zones | Vapor Retarder Location | Rationale |
|---|
| Cold/very cold | 5, 6, 7, 8 | Interior side (warm-in-winter) | Prevent interior moisture from condensing in wall |
| Mixed | 4 | Interior side or use smart retarder | Moisture drives vary seasonally |
| Hot-humid | 1, 2, 3 | Exterior side (warm-in-summer) or omit | Prevent exterior moisture from condensing on cooled interior |
| Marine | 4C | Interior side | Heating-dominant climate |
Rule of thumb: Place vapor retarder on the warm side of the wall assembly. Never sandwich vapor retarders on both sides (traps moisture).
Air Barrier vs Vapor Retarder
| Property | Air Barrier | Vapor Retarder |
|---|
| Controls | Air leakage (convection) | Moisture diffusion (vapor drive) |
| Continuity | Must be continuous and sealed at all joints | Can have small gaps at seams |
| Location | Anywhere in assembly (typically outboard) | Warm side of assembly |
| Permeance | No specific perm rating requirement | Class I: ≤0.1 perm; Class II: 0.1–1.0 perm; Class III: 1.0–10 perm |
| Material examples | Sealed sheathing, fluid-applied membranes | Polyethylene sheet, foil-faced insulation, kraft paper |
| Required by code | Yes (IECC all zones) | Zones 5+ (Class I or II on interior) |
Common R-Values
| Material | R-Value per Inch |
|---|
| Fiberglass batt | R-3.2 to R-3.8 |
| Cellulose (blown) | R-3.5 to R-3.8 |
| Mineral wool batt | R-3.0 to R-3.3 |
| XPS (extruded polystyrene) | R-5.0 |
| EPS (expanded polystyrene) | R-3.8 to R-4.4 |
| Polyisocyanurate | R-5.6 to R-6.5 |
| Spray foam (closed-cell) | R-6.0 to R-7.0 |
| Spray foam (open-cell) | R-3.5 to R-3.7 |
| Concrete (solid) | R-0.08 |
| Brick (common) | R-0.2 |
| Gypsum board (1/2") | R-0.45 |
| Air space (3/4"–4") | R-0.97 (non-reflective) |
| Interior air film | R-0.68 |
| Exterior air film | R-0.17 |
Flashing Types and Locations
| Location | Purpose | Material |
|---|
| Window head | Divert water over window | Metal, self-adhered membrane |
| Window sill (pan flashing) | Catch water that penetrates jambs | Metal or membrane with end dams |
| Base of wall | Redirect cavity water to exterior via weep holes | Through-wall metal or membrane |
| Roof-to-wall intersection | Prevent water entry at transition | Step flashing + counterflashing |
| Shelf angle | Support masonry veneer at floor lines | Metal angle with flashing above |
| Parapet cap | Protect top of parapet wall | Sheet metal coping |
Drainage Plane Principles
- Rainscreen: Pressure-equalized cavity behind cladding; drainage path for water that penetrates cladding
- Barrier wall: Single waterproof surface (no drainage cavity)-e.g., single-wythe precast
- Mass wall: Thick wall absorbs and slowly releases moisture (e.g., stone, CMU)
- Weep holes: Open head joints at base of masonry every 24"–33" o.c.
- Through-wall flashing: Must extend from interior face to exterior face with drip edge
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