McCrary Elementary's 8'x12' Cedar-Framed Greenhouse

Organic gardening programs are thriving in primary school science education curriculums. And why not?  It’s a fun topic to study and even more fun to experience. These hands-on school garden programs help teachers to demonstrate organic garden essentials like seed germination, plant life cycles, effects of seasons, sunlight, temperature and air flow. All up close, and first hand, where the impact and lessons learned are far more meaningful.

The organic garden education program at Asheboro, NC’s Charles W. McCrary Elementary school had been well established, and was already very popular with both students and staff. The school’s garden learning area included many raised beds dedicated to growing edible plant varieties, and pollinator plantings as well.

With these essential pieces in place, what the school needed to expand their organic garden program to the next level was a greenhouse. And after extensive and careful search by school staff - months of scrutinizing greenhouse designs, costs, quality ratings, and reviews - the school’s administrative department contacted us to learn more about our cedar-framed greenhouse designs, which they had already reviewed online.

Through email correspondence and a phone call or two, we methodically addresses and explained every aspect of our cedar-framed greenhouse designs, including the timeline for assembly and installation, options for the greenhouses glazing, type of base and floor, and cost and design options for tiered cedar greenhouse shelving and a child-sized cedar workbench that would make their greenhouse a true garden learning environment.

 

The school’s garden program staff had already measured and selected an excellent site for their greenhouse; a sunny area right in the center of the school’s courtyard, and in the very midst of the sprawling series of edible raised garden beds. This well-chosen greenhouse site was already level, and also in an area protected on two sides by the school building. This site is an excellent example of a microclimate ; an area where nearby buildings, vegetation, fences,  and other features (natural or artificial) contribute to a modification in climate - perhaps warming it several degrees from surrounding area, for example. In this case, the close proximity to the school building shelters the greenhouse from high winds, and also provides passive heat from the brick wall on the right side of the greenhouse, just a few feet away.

The school staff requested an 8’x12’ gable greenhouse for their garden program, and asked that if be installed in their designated site. Timing was also a major factor for this project as they required that the greenhouse be completed during the summer, while school was not in session.

Like all of our gable greenhouses, we built the frame with rough sawn red cedar. This robust gable frame design features 2”x4” rafters spaced 24” apart, and anchored to a 2”x6” red cedar ridge beam. This greenhouse design yields an incredibly strong greenhouse frame that easily withstands high wind, snow, and ice loads - yet, while still allowing maximum sunlight into the structure. 

To ensure a smooth, efficient installation process at the work site, we alway cut and ‘dry fit’ every cedar greenhouse frame at our Charlotte workshop - ensuring that all of the pieces fits together perfectly, before transporting the partially completed frame sections over to the work site for assembly.

McCrary Elementary’s 8’x12’ cedar-framed greenhouse is glazed with 8mm twin-wall, clear, polycarbonate glazing, which is secured to the cedar greenhouse frame with a combination of 2” galvanized roof screws with neoprene washers,  and 1/2”x3” cedar trim. This high-performance greenhouse glazing has excellent light transmission, better insulation value, and is safer to transport, cut, install, clean, replace, and - perhaps most importantly in this example  - work underneath, than single plane glass glazing. 

8mm twin-wall polycarbonate greenhouse glazing is virtually shatterproof, and FAR less likely to be cracked or damaged by falling limbs, rocks, and other debris than glass glazing. And this is an especially important consideration when building a greenhouse for use by school children.

The first step in the installation process of a greenhouse  project like this one is to build, level, and square the cedar base, which must measure exactly 8’x12’ on the outer sides, in order for the frame to fit it correctly. Our greenhouse base design is made with two courses of 4”x4” rough sawn red cedar timbers, joined together with 6”-long structural steel screws.  

With the cedar greenhouse base in place and level, the next step is to place commercial landscape fabric inside, and fill in the floor with about 3” depth of a decorative stone variety, usually selected by the customer.  We recommend darker-colored pebbles as it’s easier to keep the greenhouse floor looking ‘cleaner’ than with lighter-colored pebble varieties. The darker-colored stone also absorbs more heat from the sun during the day, radiating it after sunset, and helping warm the greenhouse at night.

And why do we recommend decorative stone pebbles for a greenhouse floor instead of a concrete slab?  

-Water drains down through a pebble floor anywhere inside the structure ; there’s never a chance of a drain clogging up. 

-A decorative pebble floor is easier to install, costs less, and is more attractive than a concrete slab.

-There’s less chance of slipping and falling on a pebble floor than on a concrete slab ; greenhouses floors made with concrete frequently become slimy and slippery, especially if the slab isn’t poured correctly and the floor doesn’t drain properly.

 

McCrary Elementary School’s  8’x12’ gable greenhouse design includes a total of four automated roof vent windows - two on each side. These 2’x2’ greenhouse vent windows are designed much like a boat hatch - combining a hinged a window that fits tightly over a cedar baffle lip that extends above the surface of the glazing. This proven design helps keep rain water from dripping inside the opening, even if the greenhouse vent window is open.

The school staff liked the single, 36”-wide hinged entry door, and especially the slide bolt that can be secured with a removable padlock - helping to ensure that their cedar-framed greenhouse can be safely secured when not in use. 

And lastly, to bring this hands-on organic garden learning environment to life, we built tiered cedar shelving and a cedar work table with a 32”-tall main work surface  - lower than the standard 36”-tall height, and much easier for elementary school students to gather around and get growing.