Types of Greenhouses Suitable for Pacific Northwest Growers

The Pacific Northwest (PNW) presents a unique set of challenges and opportunities for greenhouse growers: long wet winters, frequent overcast skies, mild summers, high humidity, and variable coastal winds. Selecting the right type of greenhouse requires balancing light capture, heat retention, humidity control, and durability against wind and snow. This article walks through greenhouse types that work well in the PNW, practical construction and material choices, and concrete guidelines to help hobbyists and commercial growers choose and operate an appropriate structure.

Pacific Northwest climate realities and design priorities

Successful greenhouse design in the PNW starts with understanding regional climate drivers and how they influence structure performance.

• Winter light is limited. Low sun angles and frequent cloud cover reduce solar gain; glazing and orientation matter more than in sunny regions.
• High humidity and persistent moisture increase disease pressure and rot risk; ventilation and drainage are essential.
• Wind and rain are common, and coastal sites may experience salt spray; structural anchors, corrosion-resistant materials, and sealed glazing are practical necessities.
• Snow loads can be intermittent; roofs should shed snow or be engineered for the local code load.

Design priorities for PNW greenhouses therefore emphasize: maximizing diffuse light, retaining heat overnight, managing humidity and condensation, durable weatherproof construction, and effective ventilation that doesn’t compromise heat retention.

Overview of greenhouse types suited to the PNW

This section describes common greenhouse types, how they perform in PNW conditions, and practical pros and cons.

Hoop house / Polytunnel

A hoop house is a lightweight arch structure covered with polyethylene film. It is one of the most widely used greenhouse types for market growers and small farms.

• Advantages: Low first cost, fast build, flexible lengths, good for season extension and row-crop production, roll-up sides available for ventilation.
• Disadvantages: Less durable glazing (film has limited life), poorer R-value than rigid glazing, requires more frequent maintenance and film replacement.
• PNW tips: Use double-layer inflated polyethylene or two layers of film with an air gap for better insulation. Install roll-up or curtain-side ventilation to reduce humidity. Specify UV-stabilized film rated 4 to 6 years and plan replacement cycles.
• Typical sizes: 20 to 30 feet wide, lengths 40 to 300+ feet for commercial use.
• Best for: Market vegetables, cut flowers, high-value row crops, growers who need low-cost, expandable space.

High tunnel (unheated) and gutter-connected houses

High tunnels are similar to hoop houses but often built with stronger frames and sometimes connected in gutter-connected systems to create long, continuous growing bays.

• Advantages: Cost-effective for large production, easier management of microclimate across bays, simple irrigation and benching layouts.
• Disadvantages: Limited winter heating potential unless retrofitted; condensation and humidity control remain concerns.
• PNW tips: For winter production, use double-layer film and consider thermal screens. Gutter-connected systems should include integrated roof drainage to handle heavy rainfall and direct water to storage or infiltration.
• Best for: Market growers focusing on season extension, large-scale propagation, or nurseries.

Freestanding polycarbonate greenhouses (rigid panel)

Rigid twin-wall polycarbonate greenhouses are popular for hobbyists and small-scale commercial growers in the PNW.

• Advantages: Good impact resistance, diffused light, decent insulation (twin-wall or multiwall offers better R-value than single-pane glass), long service life (5-15+ years depending on quality).
• Disadvantages: Higher initial cost than film, panels can yellow over time if low-quality, joints and seals must be well-maintained to prevent leaks.
• PNW tips: Use 6 mm twin-wall as a baseline for hobbyists; 8 mm or thicker for larger structures or colder sites. Choose diffusing panels to spread low winter light more evenly across plants. Seal panel edges and provide thermal breaks to prevent condensation drips.
• Best for: Backyard hobbyists, small nurseries, growers focused on year-round hobby production.

Glass greenhouses (traditional glass or tempered)

Glass greenhouses offer classic aesthetics and very high light transmission.

• Advantages: Excellent light transmission and longevity; easy to clean; traditional look appeals to some markets.
• Disadvantages: Poor insulation unless using insulated glazing, fragile to hail, expensive to build and heat, heavy framing required.
• PNW tips: If choosing glass for a PNW site, prioritize double-glazed units or integrate additional insulation strategies (thermal curtains, insulated north wall). Glass is more practical when used as a lean-to attached to a heated building that provides some thermal mass and backup heat.
• Best for: Botanical displays, high-light requirements, or when budget allows for higher operational heating costs.

Lean-to greenhouse

A lean-to attaches to an existing heated south-facing wall, leveraging the building’s thermal mass and services.

• Advantages: Exceptional passive heating and ease of service (water/electrical access), lower wall costs, reduced heating needs.
• Disadvantages: Limited footprint and less independent airflow; building wall must be structurally suitable.
• PNW tips: Attach to a well-insulated, heat-retaining wall. Use sliding vents and mechanical ventilation to control humidity. Great for overwintering tender perennials and propagation.
• Best for: Backyard growers who want low-energy, high-return space for seedlings and tender plants.

Cold frames and cloches

Cold frames are small, low-profile structures that provide protection and early-season heat retention.

• Advantages: Very low cost, easy to make from recycled windows or polycarbonate, excellent for seed starting and hardening off.
• Disadvantages: Limited space and heat retention; not suitable for large-scale production.
• PNW tips: Use insulated sides, add a thermal mass (water barrels or stones) to moderate nighttime temperatures, provide ventilation on sunny days to prevent overheating.
• Best for: Home gardeners and small-scale propagation.

Geodesic and rigid-framed specialty greenhouses

These include metal-framed or timber greenhouses with higher engineering standards for wind and snow loads.

• Advantages: Very durable, can be optimized for strength in exposed PNW sites, attractive, long-lived.
• Disadvantages: High build cost and complexity.
• PNW tips: Consider for exposed coastal or mountain sites where wind and snow require stronger frames.
• Best for: Long-term commercial installations in demanding sites or growers seeking a permanent, low-maintenance structure.

Glazing and material choices for the PNW

Choosing glazing material is arguably the single most important material decision for PNW growers. Consider light transmission, diffusion, insulation value (R-value), lifespan, and maintenance.

• Polyethylene film: Low cost, good for large hoophouses. Use double-layer with inflation for insulation. Replace every 3 to 7 years depending on quality.
• Twin-wall polycarbonate: Good balance of light diffusion, durability, and insulation. 6 mm twin-wall is a common recommendation for PNW hobby growers; 8 mm for better thermal performance.
• Multiwall polycarbonate (greater thickness): Offers improved insulation and structural rigidity. Useful for commercial structures where energy savings justify cost.
• Glass: Highest visible light transmission but low R-value in single panes. Consider only where aesthetics or specific light-spectrum needs outweigh heating cost.
• Diffusing glazing: Systems that scatter light reduce sunburn on leaves and improve light uniformity, which is valuable in low-angle winter light.

Concrete practical glazing tip: prioritize diffused light and thermal retention over absolute visible transmission in the PNW. A slightly lower peak transmission with better diffusion and R-value will usually outperform a clear single-pane setup.

Ventilation, humidity, and disease control

Humidity management is essential to reduce fungal disease and pest problems common in the PNW.

• Passive ventilation: Roof vents, louvered end walls, and roll-up sides on hoop houses are low-cost solutions. Ensure total openable vent area equals at least 10 to 15 percent of floor area for passive airflow in many designs.
• Mechanical ventilation: Exhaust fans and circulation fans reduce humidity and even temperature. Use thermostats and humidistats for automated control.
• Dehumidification: In severe cases, dehumidifiers sized to greenhouse volume may be needed during fall and winter propagation. Small hobby greenhouses often rely on ventilation and spacing; commercial settings may use mechanical dehumidifiers.
• Air movement: Horizontal airflow fans (HAF) help keep leaves dry and reduce microclimates that promote disease.
• Sanitation: Choose benches and trays that drain well, use clean potting media, and implement a regular sanitation routine to break disease cycles.

Heating and thermal management strategies

Heating needs in the PNW are lower than in continental cold climates, but nights can still drop below freezing. Focus on minimizing heating demand.

• Passive solar design: Orient greenhouse with the long axis east-west so the glazed south face captures low winter sun. Use an insulated north wall or earth berm to reduce heat loss.
• Thermal mass: Water barrels, stone floors, or packed earth store daytime heat and release it overnight. Even modest thermal mass can cut heater runtime significantly.
• Insulation: Insulate the north wall, use thermal curtains or screens to reduce nighttime heat loss, and use double glazing where possible.
• Backup heat: For frost protection only, small infrared heaters or electric heaters sized to maintain a few degrees above freezing may be sufficient. For consistent winter production, gas or wood-fired heaters sized to calculated heat loss may be necessary.
• Compost heating: In smaller setups, buried compost channels can provide localized soil warming.

Concrete heating tip: compute heat loss or consult local HVAC professionals for BTU sizing if you aim for year-round heated production; for frost protection and overwintering, prioritize insulation and thermal mass first.

Foundations, anchoring, wind, and snow considerations

• Anchoring: The PNW’s frequent winds mean secure anchoring is critical. Use concrete footings or ground anchors rated for your local wind speeds.
• Foundations: Raised beds, gravel pads, or concrete slabs are all used depending on permanence. Raised beds within the greenhouse aid drainage and root health.
• Snow: Design roofs with steeper pitches where heavy snow is possible, and build to local snow-load code. For hoop houses, choose frames rated for local snow or plan to shed snow quickly.
• Corrosion resistance: Use galvanized steel, stainless steel fasteners, and salt-tolerant materials near the coast.

Crop selection and layout for PNW greenhouses

Some crops thrive better given PNW light and humidity patterns.

• Winter greens and brassicas: Chard, kale, spinach, and overwintered brassicas do well in protected, cool greenhouses with good airflow.
• High-value herbs and microgreens: Low light requirements and quick turnover make these ideal for PNW winter production.
• Cut flowers: Some varieties (alstroemeria, lisianthus) do well in protected structures; others require higher light and heat.
• Seedlings and plug production: Greenhouses excel at producing seedlings year-round with supplemental heat and light when necessary.

Practical layout tip: design benches to allow 3 to 4 feet of clear aisle between bench runs for good access and airflow; use bench drainage and sloped floors to keep water moving away from plant roots.

Pest management, water, and irrigation

• Slugs and snails: Common in the PNW. Use copper barriers, traps, and nightly sanitation to reduce populations.
• Fungal pathogens: Lower humidity, good circulation, and targeted fungicide treatments (when needed) help control outbreaks.
• Water: Rain is abundant in winter, but greenhouse irrigation should be controlled. Harvest greenhouse roof runoff into barrels or tanks with first-flush diversion and filters to reduce debris.
• Irrigation systems: Drip irrigation and micro-sprinklers deliver water to the root zone and reduce overhead wetting that drives disease. Use pressure regulators and filters to maintain uniform delivery.

Cost, lifespan, and maintenance expectations

• Hoop houses / film: Initial cost low (hundreds to a few thousand dollars for small structures), film life 3 to 7 years.
• Polycarbonate rigid greenhouses: Mid-range cost (a few thousand to tens of thousands depending on size), panels typically last 8 to 15 years or more.
• Glass greenhouses: Highest initial cost and ongoing heating expense; long life if maintained.
• Maintenance: Expect to replace gaskets, check sealants annually, clear gutters, inspect anchors after storms, and replace films or panels per manufacturer guidance.

Decision guide: picking the right type for your goals

If you want a quick recommendation based on common PNW scenarios, consider the following:

• Hobbyist seedling/vegetable grower, limited budget: 8 x 12 to 10 x 20 freestanding polycarbonate greenhouse (6 mm twin-wall) or a modest hoop house with double film. Add thermal mass (water barrels) and passive vents.
• Backyard gardener wanting winter protection and lower energy demand: Lean-to greenhouse on a heated, insulated south-facing wall; polycarbonate panels; thermal curtain for nights.
• Small market grower focused on season extension: Gutter-connected hoop houses or high tunnels with UV-stabilized double film, roll-up sides for ventilation, and modular irrigation. Include space for a small heated propagation house.
• Commercial grower needing year-round production: Rigid multiwall polycarbonate or glass with mechanical ventilation, automated climate controls, dehumidification, and a professionally sized heating system.

Practical takeaways and checklist

• Prioritize diffused light and thermal retention over raw light transmission in winter.
• Use twin-wall or multiwall polycarbonate (6 mm minimum) or double-layer polyethylene with inflation for hoophouses.
• Ensure ventilation equals at least 10 to 15 percent of floor area in openable vents for passive ventilation; add exhaust fans for mechanical control.
• Add thermal mass (water barrels or stone) and insulate north walls and foundations to lower heat requirements.
• Secure structures with proper anchoring and choose corrosion-resistant materials for coastal sites.
• Plan roof drainage and rainwater harvesting; winter rainfall is an asset when managed.
• Anticipate maintenance: replace films/panels, reseal joints, and clean gutters annually.
• Match greenhouse type to production goals: hoop houses for scalable seasonal production, polycarbonate for durable all-season hobby use, lean-to for low-energy protection.

Choosing a greenhouse in the PNW is a balance between light management, humidity control, and weather durability. Take time to match structure type and materials to your site, crops, and budget, and incorporate passive design strategies that reduce ongoing operating costs. With the right choices, PNW growers can reliably extend the season, improve crop quality, and reduce losses from weather and pests.