Greenhouse Glazing Options - This is a long post! - BC Greenhouse Builders

Greenhouse Glazing Options – This is a long post!

Posted on June 25, 2020 | Categories: Uncategorized

What is the best glazing choice for your greenhouse?

There is one thing we know for sure.  All gardeners are different and like to experiment with  staging, crops and climate control to maximize their output.  Because of that, we offer many glazing options including single tempered glass, tempered insulated double glass, twinwall polycarbonate, and fivewall polycarbonate. For those customers wanting even more specific climate control, we also offer tinted, high performance low E and laminated glass.   It’s important to know that you can intermix glazing to achieve the best result!

Your Location:

When considering your location, we like to know if you experience four seasons, stormy weather, hail, high winds or extreme heat.

Your Lowest Nighttime Temperatures:

We like to know what the lowest nighttime temperature is to ensure that our heating recommendation in combination with the glazing will never cause a cold shock to your plants.  It’s always a good idea to give yourself a buffer with the heating BTU’s especially given that the greenhouse comes with a lifetime warranty and most of our greenhouses are in use for decades before they are passed along to family members.

How Many Seasons do you want to Grow?

If you are in a winter climate and wish to grow in four seasons, we will offer guidance on how to best achieve your goals.  There are many ways to passively heat a greenhouse enough to winter over plants provided you have good solar gain during the day or are willing to add supplemental heating.

Do you have natural shade nearby?

Greenhouses are designed to capture the heat and you want to make sure your plants do not get scorched.  A single glass greenhouse without natural shade nearby will require some sort of shading whether that is shade cloth, whitewash or drapery.

Using the Greenhouse for Living and Growing Space:

If you would like to use the greenhouse for living space, consideration must be given to additional ventilation and how best to achieve that.  An exhaust fan system is the fastest way to exchange hot air but not often the quietest.  An evaporative cooler, additional side vents or louvres or motorized ridge vents might be a good option too.

What would you like to grow?

Deciding whether you would like a cool, warm or hot greenhouse will help us to make recommendations with glazing, heating and cooling, too.  Hothouse veggies like tomatoes, peppers and cucumbers require minimum heat to flower and produce.  Tropical plants like orchids, foxgloves and bromeliads are tender plants that need heat to thrive.  Check out these scenarios for tips that might help you decide!

Three Different Customers with Three Different Climates:

A Cool House:

Our customer Jennifer lives in mild climate and wants
to winter over. Jen chose a greenhouse with single glass sidewalls and
a twinwall polycarbonate roof. She maintains a night temperature of
40 – 45 Fahrenheit (5 – 7 Celsius) to protect her fuchsias, begonias
and the polycarbonate roof adds extra protection for her tomatoes and
peppers in the summer. The best of both worlds!

A Warm House:


Tom lives in a colder climate that sees a significant
amount of snow but he wanted to grow citrus trees, orchids and foxgloves.
A Cape Cod fivewall polycarbonate was the perfect fit and with
very little additional heat, Tom could maintain the night temperature of
55 Fahrenheit (13 Celsius). The fivewall polycarbonate glazing allowed
for the best combination of light transmission and heat retention. The
steep pitch of the roof causes the snow to simply slide off!


A Hot House:

Henry wanted to create more living and growing space.
He liked the idea of the home attached Pacific double glass and then
was sold on its energy efficiency and was amazed at how easy is was to
maintain a night temperature of 65 Fahrenheit (18 Celsius). He now has a three season
sitting and growing room for his tropical and rare houseplants.

Technical Details on Glazing Choices:


Single-GlassSingle glass makes for a nice show piece in your yard. Our single glass is tempered safety glass to minimize any possibility of breakage or injury. Glass appeals to gardeners who want full light transmission to control the amount of sun in the greenhouse.

Single Glass 3MM, Insulating R-Value .96 Approximately 95% light transmission.

IMPORTANT NOTE:  Unless you have natural shade in your yard, a full single tempered glass greenhouse will require some type of shading.  Greenhouses are designed to capture heat and you do not want to scorch your plants.


Double-GlassInsulated double glass maintains superb heat insulation for all types of growing. Our double glass is tempered safety glass to minimize any possibility of breakage or injury.

Double Glass 16MM, Insulating R Value 2.1 Approximately 90% light transmission

Optional high performance Low E glass (R Value) Heat Gain = 3.45. Approximately 70% light transmission

IMPORTANT NOTE:  Double glass will provide a conservatory look and feel and as such, is higher cost than our other glazing.  The double paned windows in your home will give you some insight to the very custom greenhouse that is manufactured with full double glass bays.


TwinwallOur 6mm twinwall polycarbonate is the most economical. It is a practical choice for a working greenhouse as it offers 50% more insulation than single pane glass and diffuses harmful sunlight in the summer. It is essentially unbreakable, making it very safe in a family environment. The insulation will prevent the temperature in the greenhouse from changing drastically and results in the best possible growing environment.

Twin Wall 6MM, Insulating R-Value 1.62. Approximately 82% light transmission.

IMPORTANT NOTE:  You can not see through polycarbonate.  You can see shapes and shadows but it is not transparent.


FivewallOur 16mm fivewall polycarbonate is the most energy efficient glazing available on the market today. It offers 50% more insulation than double glass and 80% more insulation than twinwall polycarbonate. Fivewall is ideal for colder climates and gardeners who grow specialty plants, or for those who wish to reduce long term heating costs.

Fivewall 16MM, Insulating R Value 3.0. Approximately 62% light transmission.

IMPORTANT NOTE:  Fivewall is the most insulating glazing product on the market today but with a 62% light transmission you will have a harvest delay of 2 to 3 weeks due to diffused sun exposure.