Insulation Guide — R-Values for Eastern Washington
Eastern WA Climate Zone
Most of Eastern Washington falls within IECC Climate Zone 5 (some higher elevations are Zone 6). This determines the minimum R-values required by Washington State Energy Code for new construction and major renovations.
Minimum R-Value Requirements (Zone 5)
| Location | Minimum R-Value | Notes |
|---|---|---|
| Attic / Ceiling | R-49 | Most common area of heat loss |
| Exterior Walls (wood frame) | R-20 or R-13+5ci | ci = continuous insulation |
| Floor over unconditioned space | R-30 | Crawlspace or garage below |
| Basement Wall | R-15ci or R-19+5ci | — |
| Crawlspace Wall | R-15ci | Conditioned crawlspace |
| Slab Edge | R-10, 2 ft depth | — |
Types of Insulation
Fiberglass Batts
Most common. Easy to install in standard stud and joist bays. Available in R-11, R-13, R-15, R-19, R-21, R-30, R-38. Best for walls and floors with standard framing spacing.
Blown-In Fiberglass or Cellulose
Ideal for attics. Can achieve high R-values efficiently. Cellulose (recycled paper) has slightly better air-sealing properties. Fiberglass settles less over time.
Rigid Foam Board
Used for continuous insulation on exterior walls, under slabs, and in basements. Three types:
- EPS (Expanded Polystyrene) — R-3.6–4.2 per inch. Most economical.
- XPS (Extruded Polystyrene) — R-5 per inch. Pink or blue boards. Better moisture resistance.
- Polyisocyanurate (Polyiso) — R-6–6.5 per inch. Highest R-value per inch. Best for exterior continuous applications.
Spray Foam
Two types — open cell (R-3.7/in) and closed cell (R-6–7/in). Excellent air barrier. Closed cell also acts as vapor barrier. Best for rim joists, irregular cavities, and areas needing both insulation and air sealing.
The Air Sealing Connection
In Eastern WA’s climate, air sealing is as important as R-value. A well-insulated wall with poor air sealing performs far below its rated R-value. Washington State Energy Code requires blower door testing on new construction. Focus air sealing efforts on: top plates, rim joists, electrical penetrations, recessed lights, and attic hatches.
We stock all major insulation types at our Airway Heights, Colville, and Kettle Falls locations.