What Is the Best Orientation for a Washington Greenhouse?

Choosing the best orientation for a greenhouse in Washington State is one of the most important design decisions you will make. Orientation determines how much sunlight the structure receives, how heat builds up and is lost, how wind and storms affect it, and which crops will thrive inside. Because Washington includes very different climates — the maritime, cloudy west and the sunnier, drier east — the best orientation depends on site-specific factors. This article gives practical, location-specific guidance and checklists you can use to orient and configure a greenhouse that performs well year-round.

Climate and solar basics for Washington

Washington spans roughly 46 to 49 degrees north latitude. That produces large seasonal shifts in solar altitude and day length:

At solar noon near the winter solstice, the sun in Washington often sits around 20 to 25 degrees above the horizon.
At solar noon near the summer solstice, the sun climbs to roughly 65 to 70 degrees above the horizon.

These numbers matter because winter solar gain is critical for passive heating, and winter light comes very low from the southern sky. Summer sun is high and can easily overheat a greenhouse if you do not provide shade or ventilation.
Western Washington (Seattle, Olympic Peninsula, coastal areas) is maritime and receives frequent cloud cover and rain in winter. Eastern Washington (Columbia Basin, Spokane) is more continental and receives more clear-sky sun year-round but colder nights in winter. Both regions benefit from maximizing direct southern exposure in winter, but they differ in wind patterns, shade risk, and how much passive solar gain you can count on.

General orientation principles

Maximize unobstructed southern sky exposure. In winter the sun tracks low across the southern horizon; objects to the south that will block low-angle sun (buildings, trees, fences) will cost you most of your winter heat and light.
Place the primary glazed surface to face true south (not magnetic south). Small deviations (a few degrees east or west) are usually unimportant, but try to be within 10 degrees of true south.
Insulate or minimize glazing on the north side. The north wall receives little direct sun and is the greatest source of overnight heat loss.
For a freestanding rectangular greenhouse, orient the long axis east-west so the long glazed side faces south. That configuration captures winter sun along the length of the benching area and provides the most uniform light in winter months.
For hoop houses or quonset-style tunnels, consider a north-south ridge orientation only if you prioritize even morning/afternoon light and summer ventilation; otherwise favor a south-facing long side for winter solar gain.

Orientation options and trade-offs

Long axis east-west (south-facing glazed wall)

This is the classic passive-solar greenhouse orientation: the long side of the greenhouse faces true south, and the ridge runs east-west. Advantages:

Maximum low-angle winter sunlight is captured along the length of the growing benches.
Solar gain is more consistent through the day in winter; more useful heat and light for overwintering crops.
Easier to position thermal mass (water barrels, rock beds) along the north side to collect and slowly release heat.

Trade-offs:

In summer the greenhouse can overheat unless you use shade cloth, ventilation, and evaporative cooling.
The east and west ends receive low-angle light early and late in the day, which can create glare and hot spots unless benches are arranged carefully.

Best for: Most small and medium-size freestanding greenhouses in Washington, especially where winter light is the limiting factor (Western WA and long-winter crops).

Ridge north-south (glazing on both east and west sides)

Orienting the ridge north-south so both long sides get even morning and afternoon sun can be useful for some hoop houses and for crops that benefit from even light distribution across the day. Advantages:

More even temperature and light distribution during the growing season.
Less intense afternoon overheating on a single south-facing wall.

Trade-offs:

Loses some winter efficiency: low-angle southern winter sun hits only one side briefly rather than bathing the entire long side.
Reduced passive solar heating makes supplemental heat or thermal mass more necessary during cloudy winters.

Best for: Single-season hoop houses, nurseries that value even shade and airflow, or when the site is constrained so that a south-facing side is impossible.

Site-specific considerations for Washington

Western Washington (Seattle area, Olympic Peninsula)

Prioritize unobstructed southern exposure. Even modest overhang or tree shadow from the south can dramatically reduce useful winter light.
Expect cloudy winter days. Rely on orientation, doubled glazing, thermal mass, and good insulation of the north and end walls to preserve heat earned on sunny days.
Position a lean-to greenhouse against a well-insulated south-facing wall whenever possible; the wall acts as a heat sink and reduces glazing area and heat loss.
Prevailing winter storms often come from the southwest; locate windbreaks to the west or northwest and orient doors to the leeward (east or north) side to reduce cold air infiltration.
Use double-polycarbonate glazing or double polyethylene to improve R-value; consider a thermal curtain for nights.

Eastern Washington (Spokane, Tri-Cities, Columbia Basin)

You get more clear-sky sun but also colder nights and stronger continental winds. South-facing orientation remains ideal.
In areas with strong winter winds from the northeast, place your long axis so you reduce wind loading on the greenhouse face; provide windbreaks on windward sides.
Snow loads can be an issue in some locations; a steeper roof pitch helps shed snow and allows higher winter sun capture on the greenhouse face.
Thermal mass is particularly effective here: daytime solar gain with heavy nighttime losses benefits from water barrels, masonry, or insulated soil beds.

Practical design details that depend on orientation

Roof pitch and glazing angle: Because winter sun is low, the glazed face should be pitched to better intercept low-angle rays. A roof or glazing surface tilted between 10 degrees below and up to 15 degrees above your latitude will increase winter solar gain. For Washington latitudes (around 47 degrees), consider adjustments toward a steeper south-facing roof if you are trying to maximize winter heat.
North wall: Make the north wall as insulated and non-glazed as possible. Use masonry, insulated framing, or reflective insulation. Keep doors and access on the north side when practical to reduce heat loss through openings.
Thermal mass and placement: Place mass (water barrels, masonry) along the north side and center of the greenhouse where it will absorb southern sun and re-radiate at night without blocking light to plants.
Ventilation and shading: On south-facing greenhouses, place vents at or near the ridge and on the east/west ends. Use automatic roof vent openers and removable shade cloth for summer.
Headhouse and work areas: Put potting benches, storage, and heat systems on the north side or in an attached headhouse to buffer the growing area from cold north winds.

A simple orientation checklist

Find true south on your site (use a compass corrected for magnetic declination or a smartphone sun-path app).
Check for obstacles that block low-angle southern sun from November through February. Remove or avoid south-facing obstructions if possible.
Orient the long glazed wall to face true south for best year-round performance in most cases.
Insulate the north wall heavily; minimize glazing to the north.
Plan doors on the north or east side where practical to limit heat loss and cold drafts.
Add thermal mass along the north side or center and plan for night-time insulation (thermal curtains).
Size vents for summer and place them high (ridge vents) and low (side vents) to create effective cross flow.
Design or select glazing and roofing pitch to improve low-angle winter capture and to shed snow in colder eastern locations.

Final recommendations and practical takeaways

For most Washington sites — both western maritime and eastern continental — the best single rule is to face the primary glazed surface true south. This captures the most useful winter sun when temperatures and light levels are lowest.
Orient the long axis east-west so the greenhouse faces south. This provides uniform winter light and makes placement of thermal mass and benches straightforward.
For hoop houses or single-season tunnels you may consider a north-south ridge to even out daily light during the growing season, but accept that winter passive heating will be reduced.
Insulate and minimize glazing on the north side, use thermal mass on the north or central interior, locate doors away from the sun-facing side, and provide adequate ridge ventilation and summer shading.
Tailor details to your local microclimate: in Western Washington prioritize shading from tree or building shadows and use better glazing R-values; in Eastern Washington prioritize wind protection, snow-shedding roof geometry, and increased thermal mass for nighttime protection.

With these principles in hand you can choose an orientation that balances year-round light, heat retention, and ventilation for your crops and site. Spend time on site analysis — true-south alignment, shading patterns through the winter, and prevailing wind direction — and you will significantly improve greenhouse performance with relatively simple layout and orientation choices.