Glass or Polycarbonate: The Short Answer

Glass or Polycarbonate: The Short Answer

If you want the most light and a traditional look, choose glass. If you want better insulation, no risk of shattering and a lower price, choose twin wall polycarbonate. Almost everything else follows from those two priorities.

Neither material is superior in every respect, which is why both remain on sale after decades. The decision comes down to what you grow, where the greenhouse stands, who uses the garden, and how long you expect the structure to last.

You can compare both ranges directly: glass greenhouses and polycarbonate greenhouses.

Side by Side

Light Transmission

Glass transmits more light than polycarbonate, and in a British winter that difference is worth having. Between November and February daylight is short and weak, and every percentage point of transmission matters for anything still growing.

The light also behaves differently. Glass transmits it directly, so the interior has bright patches and sharp shadows that move through the day. Polycarbonate scatters light through the cell structure, spreading it more evenly across the house.

Diffused light is not simply a weaker version of direct light. It reaches lower leaves and the shaded sides of plants that direct light misses, and it reduces the risk of scorching foliage pressed against the panel. For seed raising and leafy crops, many growers prefer it. For fruiting crops in midwinter, the extra transmission of glass wins.

Heat Retention

This is where polycarbonate has a clear advantage. Twin wall sheet holds a layer of still air between two skins, and that trapped air is what insulates. A single pane of glass has no equivalent.

In practice a polycarbonate house holds a higher minimum temperature overnight than a glass house of the same size, and it takes less heating to keep it above frost. Over a winter of running an electric greenhouse heater, that difference shows up on the electricity bill.

Triple wall polycarbonate insulates better again, at further cost to light transmission. It suits overwintering rather than year round growing.

If you have glass and want the insulation, lining the inside with bubble sheet from the protection range closes much of the gap for a fraction of the cost of reglazing.

Safety and Breakage

Horticultural glass breaks into sharp shards. In a garden used by children, beside a path, or on a site where a football is a realistic hazard, that is a genuine consideration rather than a theoretical one.

Toughened safety glass is heat treated so it breaks into small blunt fragments instead. It costs more and weighs the same, and it is the sensible specification for low level panes and anywhere people pass within arm's reach.

Polycarbonate removes the question entirely. It does not shatter under impact, which is why it is used across the Nordgro range and why it is common on allotment sites and exposed ground.

Durability and Lifespan

Glass is effectively permanent. A pane that is not broken by impact will transmit the same light in thirty years as it did on the first day. It does not yellow, does not degrade in sunlight and does not scratch in normal use.

Polycarbonate has a working life rather than an indefinite one. UV exposure gradually clouds the sheet, and most panels are usable for ten to fifteen years before transmission drops noticeably. Quality sheet carries a protective coating on the outer face to slow this.

Fitting a panel the wrong way round is a common assembly error and shortens its life considerably, because the coated face has to be outward. Check the printed film before you fit.

Polycarbonate also scratches. Abrasive pads and solvents mark it permanently, so cleaning needs a soft brush and a horticultural cleaner rather than anything aggressive. The cleaning range covers products suitable for both materials.

Weight and Wind

Glass is heavy, and that weight works in two directions. It stiffens the structure and helps hold the frame down, but it also means the frame must be square and properly seated or panes will crack under load.

Polycarbonate is light, which makes assembly easier for one person and reduces the load on the frame. It also means the whole structure has less mass resisting the wind. Panels can lift out of their channels in a gale if the clips are not sound.

Either way, anchoring is what keeps a greenhouse in place. An anchor kit matched to your base should be fitted during assembly rather than afterwards.

Cost

Horticultural glass is the cheapest glazing per panel. Twin wall polycarbonate sits in the middle. Toughened safety glass is the most expensive.

Whole house prices do not always follow that order, because a polycarbonate model may use a lighter frame and a glass model a heavier one. Compare complete structures rather than glazing alone.

Running costs go the other way. A polycarbonate house costs less to heat through winter, so over ten years the cheaper glazing to buy can be the more expensive to own if you heat it.

Which Should You Choose

Choose glass if

• You grow through winter and need maximum light in the darkest months.
• You want a structure that will still be glazed in thirty years.
• Appearance matters, and you want a traditional glasshouse look.
• The site is sheltered and not used by young children.

Browse the glass greenhouse range.

Choose polycarbonate if

• You want to hold frost off with the least heating.
• Children play in the garden, or the greenhouse is close to a path.
• The site is exposed, or on an allotment where breakage is a risk.
• You want a lower purchase price and easier assembly.

Browse the polycarbonate greenhouse range.

Consider toughened glass if

• You want the light of glass without the sharp breakage.
• The house is large, where panel size makes safety more relevant.
• Low level panes sit beside a route people walk.

You Can Mix Them

Nothing requires a single material throughout. A common approach is toughened or standard glass in the roof, where light matters most and impact is least likely, with polycarbonate in the lower side panels where people and equipment pass.

The same applies to repairs. If a pane breaks, replacing it with polycarbonate is entirely workable provided the thickness suits the channel. It will look different from the panels around it, which is the only real objection. Standard sizes in both materials are stocked in the replacement glazing range, along with glazing clips.

Common Questions

Does polycarbonate grow plants as well as glass?

Yes, for most crops. The reduced transmission is offset by better light distribution and higher overnight temperatures. The exception is growing that depends on maximum light in midwinter, where glass performs better.

How long does greenhouse polycarbonate last?

Ten to fifteen years is typical before transmission drops noticeably. UV coated sheet fitted the correct way round lasts longest.

Is toughened glass worth the extra cost?

It depends on the site. Where children use the garden or panes sit beside a path, the way it breaks is worth paying for. On a sheltered adult garden, standard horticultural glass is adequate.

Can I replace glass panes with polycarbonate?

Usually yes, provided the sheet thickness suits the glazing channel. Check the channel depth before ordering and expect a visual difference between the materials.

Which is better for a small greenhouse?

Polycarbonate more often. A small enclosed volume loses heat quickly overnight, and the insulation matters proportionally more than in a large house. See the small greenhouse range.

Next Steps

Once the glazing is settled, size is the other decision that shapes everything else. The size guide sets out what each floor area allows, and the material overview covers frame options alongside glazing.

If you already know roughly what you want, the full greenhouse range can be filtered by size, shape and material.