What sizes of passive solar greenhouse does Swell Farms build?

Swell builds two standard sizes: a 9×12 ft backyard kit (108 sq ft, permit-exempt in most BC jurisdictions) and a 14×20 ft production unit (280 sq ft, climate battery optional). Custom sizing available on request. Book a site visit for a quote.

Can I grow year-round in Campbell River in a passive solar greenhouse?

Yes. Cold-hardy crops -- kale, spinach, lettuce, carrots, herbs -- grow year-round in a well-designed passive solar greenhouse on Vancouver Island. Frost-sensitive crops get 6–8 extra weeks each end of the season. Key requirements: 8mm twin-wall polycarbonate glazing and adequate thermal mass (water barrels).

What glazing do you recommend for a BC greenhouse?

We build with 8mm twin-wall polycarbonate as our standard spec. It diffuses light better than glass -- important on Vancouver Island's overcast days -- handles hail and snow without cracking, and keeps cost down. For year-round no-freeze builds, upgrading to 16mm or 25mm polycarbonate adds insulation value. We don't use single glass as primary glazing.

What's the best roof pitch for a greenhouse on Vancouver Island?

Roof pitch is determined by local snow load, not solar angle. Polycarbonate diffuses light so well that any angle between 45 and 70 degrees captures within 5% of the theoretical optimum. The real job of the roof pitch is shedding snow reliably. For larger greenhouses on Vancouver Island, typical pitches run 6:12 to 8:12. Smaller builds can go steeper since overall height stays manageable.

Do I need a permit for a greenhouse in BC?

Structures over 10 m² (about 107 sq ft) generally require a building permit. Our 9×12 backyard kit (108 sq ft / 10 m²) is permit-exempt in most BC jurisdictions. The 14×20 production unit (280 sq ft) typically needs a permit. We handle permit research as part of the quoting process.

Passive Solar Greenhouse Planner

Greenhouse Planner

Size Selector

Two standard sizes with proven cut lists. Dimensions are internal. Glazing pitch is set by your local snow load requirements.

Backyard Kit

9 × 12 ft

108 sqft / 10 m²

Glazing area: 5.2 m² south face
Peak height: 10 ft (3.0 m)
Knee wall: 3 ft
Rafter length: 14.5 ft
Aspect ratio: 1.3:1
Thermal mass: 520 L (3 barrels)
Vent count: 1 roof vent
Permit-exempt in most BC jurisdictions
For: 1–2 people, herbs + greens

Production Unit

14 × 20 ft

280 sqft / 26 m²

Glazing area: 12.9 m² south face
Peak height: 12 ft (3.7 m)
Knee wall: 4 ft
Rafter length: 18.2 ft
Aspect ratio: 1.4:1
Thermal mass: 1,290 L (7 barrels)
Vent count: 3 roof vents
Climate battery available as add-on
For: Family of 4, year-round production

Swell passive solar greenhouse -- shed roof, polycarbonate south wall, insulated north wall, Vancouver Island setting

Select a size above to see full calculated specs. All sizes can be quoted with custom dimensions -- contact us for custom sizing.

Solar Gain Calculator

Compare monthly solar gain against heat loss to find which months need supplemental heat. All calculations use real Vancouver Island solar data and the Rob Avis passive solar formulas.

Location

Glazing type

Glazing area (m²)

Auto-filled from Size Selector. Backyard 9×12: 5.2 m² | Production 14×20: 12.9 m²

Target inside temp (°C)

Mode 1 (no freeze): 15°C. Mode 2 (season extension): 10°C. Drives heat loss calculation.

Monthly solar gain vs. heat loss (kWh/day)

Month	Sun hrs/day	Avg low °C	Solar gain kWh/day	Heat loss kWh/day	Net balance kWh/day

Glazing Comparison

All five glazing types compared side by side. Data from Rob Avis / Verge Permaculture and 2025 Vancouver Island pricing. Swell Farms builds with 8mm twin-wall polycarbonate as standard. 16mm and 25mm options available for year-round no-freeze builds.

Property	8mm Twin-wall Poly Budget	16mm Triple-wall Poly Recommended	25mm Five-cell Poly Preferred	Double Low-E Glass	Single Glass Not Recommended	PE Film Double Inflated
R-value	R-1.8	R-2.6	R-3.2	R-4.0	R-1.0	R-2.0
U-value (W/m²K)	3.6	2.5	2.1	1.8	5.8	3.5
SHGC	0.58	0.48	0.45	0.40	0.86	0.70
Light transmission	90%	72%	79%	72%	90%	84%
Light quality	Diffused	Diffused (better for plants)	Diffused (better for plants)	Clear + low-E coating	Direct -- hot spots	Diffused
Lifespan	15 yr (warranty)	15–20 yr	20–25 yr	25–40 yr	20–30 yr (with maintenance)	3–5 yr (film only)
Hail resistance	Good	Excellent	Excellent	Good (tempered)	Poor -- shatters	Good (film, repairable)
Snow load performance	Good -- 25 lbs/sqft rated	Excellent -- sheds well	Excellent -- sheds well	Good	Risk of cracking under load	Good (flexible)
Condensation drip	Moderate (channels to edge)	Minimal (channels to perimeter)	Minimal (channels to perimeter)	Moderate	High -- drips on plants	Low (anti-drip coating available)
Best for	Budget Mode 2 -- mild coastal VI	Mode 2 standard -- most VI builds	Mode 1 preferred -- year-round	Premium permanent builds	Do not use as primary glazing	Temporary or production hoophouse

Local VI supplier: 8mm twin-wall polycarbonate is available from GreenhousePlastics.ca with free delivery Victoria to Nanaimo. This is the most affordable polycarbonate option on Vancouver Island -- good for Mode 2 / 3-season builds. For year-round (Mode 1), upgrade to 16mm or 25mm for the higher R-value.

Why polycarbonate outperforms glass on Vancouver Island: Our coast is overcast 60–70% of winter days. Polycarbonate diffuses light, spreading it evenly across all leaf surfaces -- critical for photosynthesis in low-light conditions. Glass creates direct-beam hot spots and cold gaps. Polycarbonate also withstands hail and snow impact without shattering, handles thermal expansion across large panels, and weighs significantly less, reducing rafter loads.

Minimum transmissivity rule: Do not use any glazing below 70% light transmission as primary greenhouse glazing. Below this threshold, plants become leggy, photosynthesis slows, and yields drop significantly. Both 16mm and 25mm polycarbonate meet this threshold. Single glass at 90% transmits too much direct heat in summer, causing overheating and blossom end rot.

Season Extension Calendar

Select your location and crops to see a colour-coded 12-month growing calendar. Mode 1 gives year-round production for cold-hardy crops. Mode 2 adds approximately 6 weeks each end of the outdoor season.

Location

Select crops to display

Prime growing (outdoor + greenhouse)

Greenhouse only (extended season)

Marginal / cold frame

Not growing

Passive Solar Greenhouse Planner

Start here -- what's your goal?

Greenhouse Planner

Size Selector

Calculated specifications

Solar Gain Calculator

Monthly solar gain vs. heat loss (kWh/day)

Glazing Comparison

Season Extension Calendar

Want a real quote on your build?