1) Owners report premature deterioration of the polycarbonate clear plastic panels in hot/sunny climates such as Zone 9a where I live. Harbor Freight claims the panels have UV protection but many owners have questioned this assertion based on rapid discoloration, brittleness and pitting of the panels.
2) The aluminum frame pieces are thin and the unit is flimsy and unstable during construction making it very difficult to assemble by just one person. Even when finished, the unit is somewhat flexible and susceptible to damage in light and moderate wind or rain. The manufacturer even stipulates the unit should be erected only in areas “sheltered from the wind”.
3) The 6x8 unit has minimal headroom inside (approximately 6' at the peak) and the doorway is just 5'4" tall making it difficult or uncomfortable to enter and exit.
4) The unit comes with a sliding door rather than a hinged door. Owners complain the slide mechanism often jambs and that the door can be blown off the tracks in light to moderate winds.
This Instructable demonstrates how these problems can be reduced or eliminated by:
1) Covering the questionable polycarbonate panels with high quality UV protected 6 mil plastic film. (Cost approximately $60)
2) Building a rigid 2x4 framework of benches and shelving which doubles as a solid interior structure for anchoring the aluminum framework during construction and for providing ongoing stability. (No additional cost assuming benches and shelves are already planned.)
3) “Raising the Roof” of the HF unit nearly a foot by using 2x12's set on edge for the greenhouse’s base. (Little or no additional cost compared with alternative “foundation” systems described in the construction manual.)
4) Reconfiguring the stock door so that it is solidly hinged to the framework rather than operated as a flimsy slider. (Cost approximately $20 for hinges, latches and weatherstripping.)
The tools and materials needed for these improvements will be identified in the individual steps which follow. One cautionary note, the assembly instructions which come with the HF greenhouse are notoriously difficult to follow. The good news is there are a number of owners on the web who have documented their builds and provided helpful tips for deciphering the directions. With just a bit of searching around you will be able to locate these references and eliminate a lot of frustration during the assembly.
One other consideration to keep in mind. In addition to the additional $80-$90 in cost for upgrading your HF unit, these improvements are somewhat time consuming, particularly the application of UV resistant film to each polycarbonate panel. I would estimate that at least 16 to 20 additional hours are needed to build the unit as described below versus erecting the unit in stock fashion. For some people it may be worth it to step up to a more expensive greenhouse kit that includes panels with established UV protection.