Ways To Insulate A Greenhouse Ready For Winter

Last Updated on June 12, 2023 by Real Men Sow

Although it’s obvious that a property with greenhouses looks better than one without them, the main reason someone would want a greenhouse is to protect the plants from the harsh elements of every season. We need to insulate a greenhouse because we want to keep as much energy as possible. What are the basics of greenhouse insulation?

The Importance Of Knowing About How To Insulate a Greenhouse

The main benefits of good greenhouse insulation are that it saves money on heating costs and makes the greenhouse more efficient. This is especially important if you have to maintain a higher temperature in order to combat cold weather.

A few factors can affect how you insulate a greenhouse kit. Make sure to check the seals and quality of the polycarbonate before you buy one. Also, think about the purpose of the foundation. There are ways to insulate an existing greenhouse if it does not have good insulation.

Does The Foundation Affect How You Insulate a Greenhouse?

Sometimes, greenhouse foundations are overlooked when talking about insulation. Keep in mind that the ground foundation will allow frosty temperatures to enter your greenhouse if the ground freezes. The ground can heat up to 15%. This heat loss is more important for greenhouses that have crops grown in the ground or raised beds because they need to protect their roots.

You don’t have to put foundation insulation in, but you can prevent heat loss by choosing the right foundation type. Gravel, dirt, and peat rock are all good options. You should not set up your greenhouse with cement/concrete, or wood as it will provide poor insulation.

Advanced Steps To Insulate A Greenhouse Foundation

Ground insulation can be installed around your greenhouse’s perimeter by simply adding a layer of soil insulation. Because of geothermal energy, the soil below the frost line has a constant year-round heat. It is a thermal mass that stores heat and slowly releases it later.

Styrofoam boards (about 2in thick), or foam can be used to insulate the greenhouse’s outdoor borders. The foundation should be placed vertically and extend to at least one foot. You may need to dig deeper foundations if you live in Zone 4 and lower. The board should be placed against the greenhouse foundation.

What Is Considered Good When You Insulate a Greenhouse?

Insulation is what gives your plants the right temperature and humidity. No matter what design you choose, insulation will save precious plants and significantly reduce your energy consumption. Let’s take a closer inspection of every part of the greenhouse that has good insulation.


Polycarbonate sheets are well-respected. It offers many benefits, particularly in greenhouse insulation. It is light, UV-resistant and flexible. Polycarbonate retains its excellent qualities at temperatures as low as -40F and as high up as 284F.

Heat loss is most often caused by poorly insulated roofs and sidewalls. It is therefore important to choose the right glazing for greenhouse insulation.

Polycarbonate panels are made with hollow multi-wall hollows to create air pockets. The panels have a higher insulation value because of the air in them. For greenhouse thermal insulation, twin-walled panels are often used. Triple-walled sheets are better for insulation. You can also find thin-walled panels that offer durability, light diffusion, and decent insulation values. However, if insulation is a concern, you should always choose the twin- or triple wall.

Measuring Insulation Capability

The R-value is used to determine the panel quality of polycarbonate. To measure insulation capability, the R-value is used. A higher value means greater insulation benefit. Thermal conductivity, also known as the K-Value, is the material’s ability to heat conduct. The material that provides greater insulation has a lower K-Value. It is the measurement of the heat (or the BTUs) that are transmitted per hour within a square foot of insulation one-inch thick.

10mm twin-wall polycarbonate1.894.55
Polycarbonate 8mm twin-wall1.604.76
6mm twin-wall polycarbonate1.545
Polycarbonate with twin-wall 4mm1.435.27

Insulation Seals 

You can keep the heat that has built up during the day inside the greenhouse overnight. The seals between the panels and frame come in handy. To prevent heat loss, some greenhouses use silicone sealant or rubber seals. Tape is sometimes used by DIY gardeners to cover holes, but this is not a permanent solution for drafts.

A silicone sealant is the best permanent solution to drafts. It fills in cracks at the corners of the frame. To make vents, windows and doors close tightly, you will need to use rubber seals or glazing strips. Drafts must be blocked, as they can cause irreparable damage to plants.

You should also ensure that your greenhouse seals are maintained. Repair any cracks, gaps, or panes once or twice per year. To ensure heat does not escape, make sure the vents and doors are sealed.

Ideas To Insulate A Greenhouse

Before insulation, blocking drafts is a must. This means that vents, doors, and gaps within the frame should be securely fitted. All broken panes must also be replaced. Also, ensure that your groundcover is neatly tucked on all sides of your greenhouse. You might end up spending more on heating or weeding than you saved by covering the edges.

Double Glazing & The Good Old Bubble Wrap

Plastering the entire greenhouse with plastic is an inexpensive and effective way to create a double glazing effect. This will decrease heat escape and seal any air gaps. Double glazing can be added to a greenhouse during construction. This can be a costly project but it is well worth it.

Bubble wrap is a great insulation material to double-glaze. It’s inexpensive and easy to use. Because it allows for more light access, choose bubble wraps that have larger bubbles. While bubble wrap that is wrapped in plastic may work, the best bubble wraps for greenhouse insulation are those made specifically for horticulture.

If the greenhouse frame is made from wood, you can attach the bubble wrap using either a staple gun (or drawing pins). To attach the bubble wrap onto an aluminum frame, you will need greenhouse clips. The roof also requires bubble wrap insulation.

Reflective Insulation

Reflective insulation’s main purpose is to reduce radiant heat transfer across those spaces. This is a major contributor to both heat loss and heat growth in the summer. They are cost-effective and affordable ways to maintain BTUs. It is resistant to mold, mildew and bugs.

Thermal Insulation Foil For The North Side Of The Greenhouse

The north side of your greenhouse can be used as thermal insulation foil to reflect heat and light back into it. This is due to the thermal insulation foil design that has two layers of silver foil wrapped around bubble plastic material. The thermal foil placed inside the greenhouse roof makes it possible to retain heat for longer periods.

Night-Time Insulation

Many materials can capture heat during the day and make the greenhouse cozy at night. Thermal blinds and screens are designed to capture heat during the day. They can be costly options.

You can easily cover the plants with layers of fabric to insulate them overnight. You can layer the fabric twice, or even three times over the plants. This can be done with thicker materials, such as blankets. Then to prevent them from flattening plants, make sure you suspend heavy fabrics on canes and hoops.


There is one drawback to using thick blankets or other heavy materials to cover plants overnight. It can be difficult to remove them during the day. This is done to let light in during the day. The use of expensive thermal screens or blinds will prevent this problem. 

They are made from transparent material, which allows the sun to shine through during the day. This solution may not be possible, and it depends on how large the greenhouse is. If you live in colder regions or have large greenhouses with a small surface area, a greenhouse heater may be necessary. 

Cloches and Cold Frames

Cloches and cold frames will provide extra protection for your plants. You can recycle empty plastic bottles to make mini cloches for your plants. Simply cut off the plastic bottle’s bottom and place them on top of your plants.

Bubble wrap and plastic containers can also be used to protect individual plants. To avoid overheating your plants, make sure to remove cold frames and cloches on warm days. They can also be put back in the morning to provide a warm and cozy environment.

Real Men Sow
Real Men Sow

Hello, I’m Pete and I’m currently based in the west of Scotland, in a small place called Rosneath, where I’m exploring my garden adventures. I personally started gardening around 6 years ago and initially, I started out by growing my favorite fruits and berries, such as strawberries, Raspberries & Gooseberries. Since then I’ve added a lot of vegetables and working closely with my neighbor, it’s been a lot of fun.