HFGH 6x8 - observations and tips

10 years ago

Hi everyone, after much hemming and hawing, I built the Harbor Freight greenhouse to house plumeria, and wrote some tips and additions that others might find useful.


Harbor Freight 6'x8' Greenhouse (HFGH SKU 47712): Modifications, tips and cautionary notes.

In July 2010 we undertook a major effort to convert a disused corner of the yard to a greenhouse area. It involved tree removal, foundation building, and greenhouse assembly. I scoured GW and other sites for tips, but found that the actual assembly has different problems than others reported.

Site: a large 4 trunked tree was messy and dropped branches. We chain sawed and chopped the canopy and branches and left the stumps to dry for later removal. The soil is extremely hard beneath 2-3' of topsoil. After many weekends, we completely removed the canopy and created a level area for the GH. A termite infested fence will be replaced later. The neighbor's ash tree provides midday shade in summer.

Foundation: it took a full day to build the pressure treated wood base and floor the interior with pavers. Be obsessive that it is level, square, and properly fits the GH aluminum base.

- Clear and level the area, and remove all roots that might interfere with the floor.

- Assemble the GH base and corner uprights in order to measure the exterior edge: 6'3" x 8'3". This was a different dimension from other postings and different from the manual.

- PTW is not perfectly square, but try to make the foundation accurate and level.

- Line the interior with landscaping fabric after leveling the dirt, and place concrete pavers inside. I filled the excess spaces around the edges with loose stones to collect dirt and debris.

Tools and such for HFGH construction (not in kit)

- Nut screwdriver

- Foam sheets

- Electric drill / screwdriver, extension cord

- Philips screwdriver

- Aluminum tape (in Duct hardware section)

- Carpenters square

- Carpenters level

- Measuring tape

- Scissors

- Silicon grease

- Step stool

- 1 1/2" coated wood screws, approx. 30 to secure the GH frame to the wood foundation

- Remote temperature sensor

Kit: all parts listed were included, however a roller (parts 37, 42, 53) is in the parts list, not included in the kit, but is not used anywhere. Lay out all frame parts on a level surface in numerical order. 95% of the packaging is recyclable.

Important: keep the panels out of the sun! Even 10 minutes in sunlight bakes the protective film, making it extremely difficult to remove.

Assembly: overall, the HFGH instructions are easy to follow and most pieces fit only one way. However, the Door instructions are wrong. Total GH assembly was 10 hours with 2 people, including a half hour to unassemble and reassemble the door sides. The HFGH revised manual is dated 05/03; 12/05

Additional steps and cautions:

- Cut strips of foam as a leak barrier and to shim the GH base. Make sure the base is level and square. Do not attach the base to the foundation until assembly is complete.

- Assemble the entire GH without panels. Do not tighten any bolts until completely finished, and do not drill mounting holes or secure the base to the foundation until the whole frame is put together. If the frame is out of square, parts do not fit - use the carpenter's square to find problems and stretch, bump, lift and jiggle into position. Overall, the frame edges and holes are in the proper locations - if they don't line up, either the part is in the wrong spot or the alignment is off. This is most noticeable when adding the door and roof. Assemble with the nuts on the inside of the GH.

- Many of the steps after building the base and before the window assembly can be done in any order. If only one person is assembling the GH, change the step order to make it easier to build the roof frame. Suggest putting the corner brackets on early, although you will need to take nuts on and off at times.

- Window instructions are minimal - use the diagram on the GH box to visualize them. Install the panel when assembling the windows.

- Door instructions on page 14 have two significant errors. Either the door side pieces are mislabeled or the instructions have the two sides reversed. In our kit, part 28 is actually the door left side, and part 20 is the door right side. We unassembled the door sides and switched them, or the panel clips would not install correctly. In addition, the panels can only be installed during the door assembly. Grease the sliders after installing the door.

- Panels: apply aluminum tape to the panel edges to close the open channels. This helps the insulation, and hopefully keeps out mildew and insects. I used 2 1/2" aluminum tape cut in half - it has a red logo down the length, so apply the tape so the red ink isn't noticeable on installation. With one person taping and the other hanging panels, the installation went quickly.

- We will add more clips to prevent the panels from flying off in the wind - a major concern.

- Depending on the temperatures, may add a blind on the western end to prevent sunburn and excessive late afternoon heat. In winter, may add water jugs as heat sinks in cooler weather.

- Wish list: shelves, solar fan, temperature activated window control


- HFGH 6'x8' kit ~ $225 (sale and coupon)

- Aluminum tape $10

- 30 Cement pavers ~ $50

- 5 8' pressure treated wood 4'x4' (already owned)

- Screws, landscaping cloth $4 and foam from previous wood floor installation

- Remote temperature gauge (La Crosse Technology) ~ $30 from Frys Electronics

- Total: approx $320, not including foundation wood and assuming you already own the tools

Diana =^,,^=

Here is a link that might be useful: HFGH pix

Comments (7)

  • spogarden
    10 years ago
    last modified: 5 years ago

    I love mine, am adding on to it in the fall and changing the door.

  • mudhouse_gw
    10 years ago
    last modified: 5 years ago

    Great pictures! Fortunately, the tree in our way died about a year before we put up our greenhouse (still had to cut it down, though!) We had a furry OSHA inspector too (all extra paws and hands were greatly appreciated.) I love my 10x12 HFGH, enjoying it for my third year. It's totally stuffed with plants, year round.

    "- We will add more clips to prevent the panels from flying off in the wind - a major concern."
    Sounds like you've read the archived threads here about the recurring problem of lost HFGH panels. In addition to extra clips (we did that too) it's pretty easy to add self-tapping screws to the panels, as even more protection against panel loss. The 10x12 is pretty tall and makes an even worse target for wind damage, but there are some scary threads archived here about wind-damaged 6x8 HFGHs as well. Here are some photos showing how we screwed the panels into the aluminum frame (thanks to previous GardenWeb forum members who suggested this improvement.)
    Part Six, Adding the Panels

    "- Depending on the temperatures, may add a blind on the western end to prevent sunburn and excessive late afternoon heat."
    I definately need shadecloth on the roof, west end, and south side (my succulents and cacti cook in there without it.) I also believe that adding shadecloth has helped to increase the lifespan of my HFGH panels in our sunny climate. (I used Aluminet shadecloth.) Some GardenWeb HFGH owners have reported problems with the HFGH panels deteriorating after exposure to sun, but others don't seem to have this problem. My panels have yellowed, but I see no other signs of deterioration (fingers crossed.)

    "In winter, may add water jugs as heat sinks in cooler weather."
    In theory it seems like this would help, but the general consensus seems to be that you'd need very large containers of water to retain enough heat to truly benefit you into the wee hours of a cold morning. Most small greenhouses can't afford to give up the high percentage of space required to make this work, but there's lots of good reading on this topic in this forum (posted by folks who are much smarter than I am.)

    "- Wish list: shelves, solar fan, temperature activated window control"
    Just a warning, the HFGH solar fan is not powerful enough to adequately cool your greenhouse (sounds good, but doesn't quite work.) If you do a search in this forum for HFGH solar fan, there's a thread with a knowledgeable poster sharing his calculations that a 6x8 HFGH would need three of the HFGH solar fans to exchange enough air to drop the temps (if my memory is right.) There are also some posts from folks saying the HFGH vent openers don't last long at all, and it's best to research and purchase other brands that have a better track record.

    Good job, congratulations, and happy greenhousing!

  • slave2thefur
    Original Author
    10 years ago
    last modified: 5 years ago

    Hi Sheri - I did read your blog, and got several helpful hints even tho you built the larger GH.

    Your photos of the self tapping screws made me rethink attaching the panels, particularly near the door. The clips are pushing the door frame out of square, causing a 1/4" gap at the bottom, so I may simply switch to screws. We're also considering using the aluminum tape to seal the panels directly to the frame, particularly for edges that out of direct sun. Has anyone tried this?

    I need to get a feel for the kinds of problems I'll get - tho at this point I may move a lawn chair in there... it's the end of July and tonight it will drop into the 50s !

  • mudhouse_gw
    10 years ago
    last modified: 5 years ago

    Sorry to hear about the clips problem you describe, on the panels near the door, wonder if that's a 6x8 problem? I'm sure there are some minor differences in the kits, and I don't recall bumping into that problem before.

    Although I found the aluminum tape to be wonderfully sticky when new, after about two years it started to peel in some places, and after three years, much of mine is falling off (even on the sides of the greenhouse that don't get bad sun.) I need to replace all of it that I've used to seal my panel ends (I keep putting it off...) So, just a heads-up on the long-term dependability of that stuff, it might bear watching.

    We are finally into our monsoon season here, and enjoying the cloudy afternoons and relief from endless days of full sun and hot temps. But, no 50's temps here yet...!

  • john_geary
    10 years ago
    last modified: 5 years ago

    Hi Sheri

    I ordered my HF 8X10 and have been reading your blog very carefully. I just saw your post about the aluminum tape not lasting. Do you have an alternative in mind?

    John in Mobile

  • mudhouse_gw
    10 years ago
    last modified: 5 years ago

    Howdy John,
    Sorry for my slow reply! I can't figure out how to have GardenWeb email me when there's a reply to a thread I have posted to (sometimes I need a bonk on the head.)

    I haven't tried this product, but Charley's Greenhouse sells a vented polycarbonate tape specifically designed for sealing the ends of poly panels. I would hope it lasts longer than regular inexpensive aluminum tape from the big box stores, due to the higher price, but I really don't know. (Maybe someone else will pop in here with a comment.)
    Charleys Greenhouse polycarbonate tape

    You may be able to find other suppliers of similar products by Googling for polycarbonate tape. Also, plain 'ol aluminum tape might last longer in climates with less severe temp changes than we have here. (I think teens in the winter and over 100 in the summer is kind of harsh for many materials.)

  • DCphotos
    6 years ago
    last modified: 5 years ago

    I put up my 6x8 yesterday. There are a whole lot of parts but it all seemed to go fairly well. I sealed the edges of the panels but that was the only modification, I'm happy with the sliding door. I may look into a stronger attachment than just the metal clips eventually. It's storming today so I will see how well it holds up before I even get my dang plants in it.