Building a Polycarbonate Cross Country Greenhouse

Polycarbonate Greenhouse


Polycarbonate Greenhouse


During the early months of summer in 2012 we had the good fortune of starting a great polycarbonate greenhouse project. It encompassed building a large 27 x 51 polycarbonate greenhouse by Cross Country. In the beginning we had a good idea of what we needed to do first. How to build a large aluminum framed Greenhouse by Cross Country Greenhouse can be a good challenge even for the most experienced tradesman who have built greenhouse structures before.

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Cross Country Polycarbonate Greenhouse

We first had to layout the footprint on the ground before any excavation took place. As you may know a large aluminum framed polycarbonate greenhouse does require a foundation. Regardless of permitting requirements, you should always have a firm foundation.

An engineered foundation,greenhouse kit pricing, greenhouse kits, cross country greenhouse kit, polycarbonate kits, lean to greenhouse kit as required in most areas, such as ours, or a foundation, that utilizes the same specifications. The main concern was doing it right the first time, as this always is a wise choice and in the long run much cheaper than taking short cuts.

Mapping out the footprint with string and markers allows us to perfectly square the foundation footprint. Once that was established we then began to excavate, carefully digging along the marked outline so as to keep the foundation trench as square as possible. Keeping in mind, while digging the trench, it must be wide enough to allow for form work. There’s nothing more frustrating and time consuming than having to deal with tight trench locations when setting up forms and working with steel.



Once the form work was completed which took about 2 days with 6 form workers we then began the pour. A formed stem wall trench this size took about 16 yards of concrete. There was no spread footer required, just a 30-36″ below grade stem wall. The next day the forms were stripped to allow the concrete to cure for a couple of days thereafter.

The result was perfection plus, we were able to keep the forms square within a ¼ of an inch not bad over a 51 ft run. Top of wall was level and now we were ready to build. Now that the foundation was ready, the initial set-up required us to install a 2 x 10 sill plate along with custom aluminum flashing. This provides for an overhang on the outside perimeter of the concrete with a drip edge to divert moisture.

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Once that was done we then proceeded to assemble the gable wall members, from there we then assembled the side wall members. Then the heavy weight bearing trusses were assembled and installed into place. This then led to installing all of the cross members to tie the trusses and gable walls together. This task took 2 persons about 8-9 working days. Once the frame was up and secure, we always check to see that our structure is still true to square and plum. If you don’t do this step it becomes difficult to install all of the precut polycarbonate panels, since they are precut, there is little room for error. The installation of the polycarbonate panels was another 10 -12 day task since all of the polycarbonate panels have to be taped and sealed on each end.

We also had to assemble, build and caulk all of the polycarbonate ridge vents, 12 in total and all of the solar operated windows, 6 in total, sounds easy, but very time consuming. Overall to build this project to completion took about 4 weeks plus…

Is polycarbonate good for greenhouses or is glass better

You may be wondering about this, so let’s discuss. For this project we used 16mm which equals 5/8 overall thickness, 5 wall clear polycarbonate roofing sheets as well as for the side walls. This particular product is very suitable for light which allows for 67% light transmission and it’s a tough rigid panel with 5 air spaces sandwiched in between which also allows for greater heat retention during the colder months, much more effective than double pane glass.

Furthermore glass greenhouses get very hot due to intense sunlight transmission which then will require shading tarps if you’re in a region with intense sunlight.
Polycarbonate manufactures warranties offer a 10 year time frame against any breakage due to hail, it is said that hail will bounce off these panels before it penetrates and if it does penetrate then the warranty becomes effective. Bear in mind the installation and shipping of any replacement panels due to any warranty issues is always determined by the dealer or company that installed your greenhouse. Some may provide free installation and free delivery during the warranty period and others may charge. Every scenario is different. The one thing for sure is that the warranted polycarbonate panels are free of charge if it is determined that breakage was caused by hail within the warranty period. Overhead tempered or laminated glass generally does not carry any warranties and it’s a bit more expensive.

Polycarbonate Greenhouse Ventilation

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as you can see, this is the most critical detail for any greenhouse, overhead ridge vents, cross ventilation by way of operable windows, and a forced air fan along with auto air intake louvers to circulate air whenever needed.

Overhead polycarbonate framed ridge vents are extremely important since hot air rises, there must be a way for hot air to escape. This can be accomplished with auto operated actuators or solar powered vent openers.

In this particular project the solar powered option was the way to go… highly effective, very long lasting operation, way less expensive than power and relatively simple maintenance.





Caulking your Cross Country Greenhouse

always remember this, polycarbonate greenhouses are not fish tanks so it’s important to caulk wherever you think moisture may infiltrate. Areas such as ridge vent edges, eave connections, sill plate connections, perimeter fan applications, intake louver applications, entry doors and window edges, these are areas where moisture can penetrate. So when you’re done assembling and even while your assembling, take the time to caulk with the correct caulking. Silicone clear caulk is the preferred product since silicone does have flexible qualities that won’t dry and cake up long after the assembly is done.


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Grow your veggies and herbs the right way

Now that we’ve accomplished what we set out to do, you can begin to propagate your polycarbonate greenhouse.

The many greenhouses that we build generally are left with dirt floors, this way you can use the ground for growing and / or design in-ground planting beds with 2 x10 wood border frames or better yet decorative stone block or plain cement block walls to compartmentalize your growing sections.

Whats nice about growing in the ground, the dirt retains moisture much better than raised beds, easy to maintain, easy to add and top off with new enriched dirt with every changing season, easy watering and you don’t have to worry about drainage. With raised beds, the dirt dries out very quickly and you do have to change most of the dirt way more often than what you may think. I’ve seen dried up dirt become pulverized dust within one season with no growing value whatsoever not to mention lots of unnecessary hard work and more expensive to build.

Been there, done that! Ultimately it’s your choice. A polycarbonate Cross Country Greenhouse is by far the best residential backyard Greenhouse money can buy.