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A greenhouse roof is not one size fits all, and effective greenhouse roofing can be achieved through a number of different materials. The most common materials used as greenhouse roofs include glass, polyethylene film, double-layered panels of polycarbonate or acrylic, and fiberglass panels or sheeting. Each of these materials has benefits and drawbacks, and one may be more suited to a particular type of greenhouse than another. Each greenhouse roof material has one very important characteristic in common: It is a clear or semi-clear, light-permeable material that will allow the plants inside the greenhouse to receive the light and heat they need to grow.
When choosing which material is best for a greenhouse roof, the builder will want to consider his budget and the type of greenhouse he would like to build. Different materials may be better depending on whether the greenhouse will be small or large, or if it is a permanent or semi-permanent structure. The type of framing materials can also make a difference in the best materials for a greenhouse roof. Having a well-constructed plan is a good first step in determining which roof is best suited to the greenhouse.
The most traditional and permanent solution for a greenhouse roof is glass. It is the clearest, most light-permeable material available, and can be quite long-lasting when installed correctly. Glass is often the best choice for permanent greenhouses, solariums, or sunrooms. Tempered glass, which can be up to five times as thick as regular glass, poses the least risk of cracking or shattering. A greenhouse roof made of tempered glass may be the only roofing material that can hold very heavy, wet snow for long periods without collapsing.
Glass roofing does have its drawbacks, though. It generally requires the highest up front cost, not only due to the cost of the glass, but also because it requires strong, sturdy framing materials to support it. Care must be taken to carefully construct and seal glass greenhouse roofs, as those not sealed properly have a high probability of leaking. Glass also carries a higher risk of breakability than some other materials, and it is not the best insulator.
Fiberglass sheets or panels are a long-lasting, less expensive alternative to glass and may be used in permanent greenhouse structures for 15 years or more. This material is much lighter than glass, so it does not require heavy-duty framing the same way that glass roofing does. Fiberglass is durable enough to withstand many types of weather and other outside elements. Over time, however, the light penetration of this material will be reduced; it does require maintenance in order to maintain the best possible light permeability. Fiberglass is also not as flexible as some other types of greenhouse roofing.
Polyethylene or plastic film is an inexpensive, flexible, readily available and easily applied greenhouse covering. It may be comparable to glass in transparency, lending to excellent light-permeability. Where small, temporary, portable, or seasonal greenhouses are concerned, polyethylene film can be a quick and easy greenhouse roofing solution. It is also easy to apply to greenhouses with curved or arched roofs, and may be used in open-panel or open roof greenhouses when a retractable material is required.
Some types of polyethylene film may be sturdy enough to last up to five years, and some have been treated with additives that help to reflect and radiate heat into the greenhouse. On the downside, film coverings are not as durable as glass or fiberglass, may be more easily damaged than other materials, and require the most frequent replacement. They are unlikely to be a good choice for permanent greenhouses.
Double-layered polycarbonate or acrylic greenhouse roofing, which is generally constructed with equally spaced "webs" between the two layers, retains heat very well. It may be the best roofing material where energy costs or cold temperatures are concerned. It is stronger and more durable than film, and may be flexible enough for use on curved roofs. It is reasonably long-lasting, sometimes up to 10 years.
On the other hand, the double-layer construction does not allow as much light to pass through as glass or single-layer fiberglass. Polycarbonate materials can be susceptible to yellowing, though acrylic is less likely to yellow. This type of material will also not last as long as glass or fiberglass.
How To Put Glass in a Greenhouse Roof
The process of building a greenhouse roof will vary depending on your skill level and the type of roof you’re constructing. Generally speaking, you’ll need to make certain that the glass panes are securely mounted in a frame and that the gaps between the panels are completely filled in order to prevent leaks and retain heat. Framing options include wood, aluminum, and silicone; glazing tape or liquid silicone can be used to seal gaps.
You can purchase a variety of kits that include supplies and instructions for building your own greenhouse, but if you are working with found materials such as old window panes or reused frames it’s a good idea to consult an expert to make sure your materials and design are sturdy and safe. Regardless of your level of building experience, remember to wear eye protection at all times and use other safety gear when necessary.
How To Clean a Greenhouse Roof
The first step in cleaning the inside of a greenhouse roof is to remove as many plants and other items as possible in order to prevent damage and reduce obstacles that limit your movement. Depending on how high your roof is, you’ll need a non-abrasive sponge with a long handle and potentially a stepladder. You'll also need a cleaning solution:
- For a glass roof, you can use either a commercially sold glass cleaner (follow the manufacturer's instructions for dilution and use) or a solution of white vinegar mixed with water. Recipes found online recommend different proportions and some include rubbing alcohol or dish soap. Experiment on an easily accessible portion of the roof or walls to determine which mixture you prefer.
- For fiberglass panels, a vinegar and water solution is recommended. Remember that fiberglass may require more scrubbing than glass or polycarbonate.
- For polycarbonate panels, water mixed with a few drops of mild dish soap is ideal.
To clean the outside of the roof, use a non-abrasive brush or broom to remove leaves and other debris (don’t forget to clear out the gutters as well as the panels). Then use the sponge and cleaning solution to thoroughly clean the surface of the panels. For both the inside and the outside, either use a squeegee on the panels or rinse them with a garden hose to remove any cleaning residue. Clean the roof first, then the walls, and finally the floor to ensure that any dirt loosened from a higher area doesn’t spill onto a surface you've already cleaned.
How To Collect Water From a Greenhouse Roof
If you want to prevent water from pooling on your greenhouse roof a set of gutters will do the job, but adding a rainwater catchment system is a great way to collect water that you can use for your plants. A system can be as simple as a set of gutters with a spout or pipe that empties into a rain barrel, but fancier versions are available.
Depending on your tools, materials, and skill level, you may decide to make your own system. To keep out debris and prevent mosquitoes from breeding in your water collection container, you’ll need to keep it covered. (If children have access to the container it's especially important to have a secure childproof lid.) Many pre-made catchment systems have PVC pipes that run from the end of the gutters and through a fitted hole in the collection container’s lid. A spigot at the bottom of the container will make it easy to collect water for other uses as long as the container is mounted far enough above the ground to accommodate a watering can or bucket.