Framing a DIY Greenhouse Roof
The roof of a greenhouse is what makes a DIY greenhouse what it is. It should provide sufficient light, retain heat inside, prevent cold from entering the greenhouse and provide protection from snow, excessive rain, hail, strong wind and falling debris. Building a strong roof of high quality material will make your greenhouse a perfect environment for growing seedlings, tropical plants, or fruits and vegetables for your family year around.
Most people build their DIY greenhouses by taking advantage of the numerous and often affordable types of greenhouse kits. Kits contain most parts necessary for a fully functioning greenhouse, including the roof. They are fairly easy to assemble following the included instructions and often videos. Assembling greenhouse kits still require a certain amount of building skills, a few tools and the help from one or two friends.
If you are determined to build your own greenhouse, you probably have enough experience building various structures and have all the necessary tools. Materials you need depend on the type of greenhouse you plan on building. Most DIY greenhouses are made of wood, which is easy to work with, or of combination of wood and PVC pipes.
Framing a Roof for a Quonset Greenhouse
There are many types of greenhouses, but majority of DIY greenhouses are the Quonset type, made of PVC pipes and covered with
polyethylene sheets. Although you can make your Quonset greenhouse using only PVC pipes of different size, using wood for the foundation and sidewalls would make your greenhouse much stronger and more stable.
Building a roof for the Quonset type greenhouse is actually the same as building the greenhouse itself.
A wooden foundation is secured to the ground with earth anchors or it is fastened to cement posts below the frost line. Two sidewalls are connected with a top ridge, and the PVC pipes are bent over the top ridge and fastened to the foundation with pieces of rebar. Space your PVC ribs at two feet intervals. Hoops are nailed to the top beam for added strength. Your greenhouse roof is now ready to be covered with sheets of polyethylene film. Poly glazing can be single and double layered and it provides excellent light distribution and heat retention. One of the disadvantages of Quonset type greenhouses is that the walls are curved, cutting on the workable space.
A-Frame Greenhouse Roof Framing
An A-frame greenhouse is another DIY greenhouse type that is fairly easy to frame. You require 2”x4” for the rafters, cross-rafters and the top ridge. Place rafters at 2’ intervals. Use pressure treated pine or hardwoods like redwood or cypress, but pre-treat all pieces before installing them to increase durability. Wood is prone to decay in humid greenhouse environments if not treated with a preservative. Use galvanized nails or screws to attach the roof to the foundation. Place cross-rafters one third of the distance from the top ridge to facilitate fastening of the poly sheet.
Placing your A-frame on a knee-wall, which will increase its height and the usable working space.
The two vertical walls can accommodate a door and vents, or you can simply leave excess poly sheet to cover the entrance. This is suitable only if you are using your greenhouse as a cold frame and do not plan to heat it.
Gable Style Roof
A gable style greenhouse has the roof placed on vertical walls, which are attached to the foundation. Rafters and studs should be placed at two feet intervals and blocking should be nailed every 24-36 inches between both rafters and studs.
This type of frame can be made to support rigid glazing panels, such as polycarbonate or fiberglass. If using fiberglass or polycarbonate, make sure that all seams are well sealed.
Be honest with yourself about your building skills and experience, to avoid costly mistakes or worse; a failing DIY greenhouse that is not performing as it is meant to.