My 2nd greenhouse, with hardwood windows, all double glazing!!
I have an L- shape 450 m2 garden in an allotment (community garden complex), with my 20 m2 greenhouse, built 2 yrs ago https://www.instructables.com/id/5-x-4-m-greenhouse/ on it, there was also a small old existing greenhouse.
This is a rebuild from scratch.
Costs: ca. E 300.-
Building time: several months on weekends and holidays, finishing always takes more time (garden tasks get priority in tyhe growing season!
Step 1: History
A small, old greenhouse used to be on my lot , but I have never used it: The former occupants, a very nice, very old couple, who used to lease this section of my lot, gave it up 2 years ago. They have worked this lot for 45 years. Their other, remaining lot did not have a greenhouse, so I let them use their old, self built one, for as long as they wanted.
Unfortunately, due to illness, the couple has now terminated their lease contract .
The greenhouse might have lasted another 5+ years, but it is way to low for me. The former, Indonesian builder, is 60 cm (2 ft) less tall than I am. I could have maintained it; make it last some more years.... But: since I sourced lots of quality windows, mostly hardwood, all double glazed(!), the decision was made to take it down and rebuild from scratch....
Step 2: Renovation Project Nearby
The supply (almost infinite amounts) of the highest quality windows , being trashed every day in a nearby renovation project, makes one change building plans!
These are leased apartment buildings. The non profit leasing company does maintenance etc. Due to the financial crisis and its resulting cutbacks, no money for maintenance is available for the next many years, but during the past year they still had a budget.
Their rationale is to replace all window units this year by high quality, highly insulated, plastic units.
No more painting or carpentry, this stuff will last at least 30 + years without anyone looking at it!
(But what a waste! Many bad windows were replaced by new Merbau tropical hardwood units, only last year!).
Every work day 2-4 windows!!! Each hardwood large window weighs ca 35 kg (80 lbs).
Transportation was done on the bike trailer ( https://www.instructables.com/id/Four-wheel-bike-trailer-with-adjustable-length/ , https://www.instructables.com/id/4-wheel-bike-trailer-version-2/ ) , the distance traveled is about 1.5 Km (a mile).
Step 3: Design
-Footprint not much larger than 4 x 3.5 m (building restrictions), 2.5 m+ high (eventual size: 4.15 x 3.70 x 2.75 m)
-Needs to include existing grape vines
-Nice looking and mechanically sound
3 window sizes: 'Large', 'Long' and 'Small'. The first part of the process is fitting the different window sizes into a greenhouse. It means first making an Excel sheet with all possible measurements and combinations of windows, standing and laying.
The drawing was made in Google Sketchup; it makes very nice printouts, for easily getting a permit.
Sketchup pro 8 (Vuze downloads...) includes 'layout', which can calculate measurements.
However..., the smart thing to do is to re-calculate everything manually, as mistakes in the drawing are easily made (elements don't always snap in the proper position)!
I made 4 designs, based on these windows, for fellow gardeners, who proudly built their own greenhouses!
Step 4: Preparation
The foundation of the old greenhouse had to be removed; wrong sizes. It was dug in very deep.
The wood for the frame has been purchased from a demolishing company for E 160.- (Nowadays very few dumpsters with useful building materials)....
Everything for the frame was pre-painted, due to cold December conditions paint had to be diluted with paint thinner (normally I use white spirit in open air; paint thinner gives terrible headaches).
The greenhouse rests on M10 and M12 threads sticking out of concrete pillars on sand beds. No contact between wood and soil.
Just like my other greenhouse, I build it on wooden blocks, and made the foundation afterward. The ground was too wet to do it otherwise anyway...
Sand has been put anywhere near the new foundation elements. Over a sand foundation layer, this creates maximum stability. In winter, one big problem: During freezing, only totally dry sand ca. (3 m^2) could be added. A subsequent storm blew half of it away!!!
Step 5: Building the Standing Frame With Windows
The sketchup drawings are helpful!!! Just have to double check the sizes before cutting the frame components.
I first framed the outer parts.
Putting in one window at each side makes it more or less square.
Even if the sizes are right, and when the studs were straight when painting, it pays to double check when screwing on the windows: temperatures were varying from -4 to + 10 deg C, with huge changes in relative humidity, which tends to twist and turn (warp) the frame. Also, the load changes a lot during building: leaving anything unsupported for a few days warps the frame!
The windows are fastened against the frame by 4-6 sturdy screws. This is much easier and faster than putting them inside the frame!
Step 6: The Roof Frame
Slope no less than 23 degrees ( A shallower angle collects clutter)
Front and side overhang ca. 25 cm, in back ca 40 cm (facing South West , prevailing wind direction when it rains in Holland)
Plastic sheeting is on a roll 2 m wide: roof has to accommodate a single width lengthwise.
On both ends, a 'small' window (which can be opened) + frame
8 trusses support the roof, the trusses with the windows in it, determine the angles, sizes, etc. of the rest ('master trusses').
When the roof is covered, especially with the overhang construction- for styling and wood protection, it can be subjected to huge forces during storms. One 120 mm screw at each joint will not be enough! Screw connections don't become stronger with age! Every connection between the very stable vertical part and the roof will need a bracket. My brackets are from a galvanized steel perforated strip, with special nails to fasten them.
The roof trusses put outward pressure on the vertical sides. Steel strips tightened by M6 turn buckles hold everything in place.
Some wooden braces in the roof construction make everything rigid.
Step 7: Painting
What does painting matter in the instructable? Well, about 1/3 of all construction time was spent painting! Considering the huge amounts of paint used, this greenhouse has a major amount of wooden surfaces. The outside has to be green (mandatory), but the inside is painted 'peach' A nice color for sure, but there is a purpose to it too... The plastic roof cover is greenish. Plants cannot use green light. Blue: OK, red; yes!! By absorbing some of the green light, the peach color balances the spectrum available to the plants (and it looks nice). All outside cracks and joints have been caulked with acrylate (can be painted over).
I got a lot of jokes like:' are you starting a gay bar?' etc., but after the plastic roof is installed it looks more neutral: not pinkish.
A bad problem was the sand drifting around the lower parts of the frame: Better first finish everything, at the end first clean all lower parts (brush all sand off) and then quickly paint all remaining lower parts. Some boards temporary placed against the other side of the base prevented winds blowing through and depositing even more sand!!!
If required, re- sanding and re- painting can be done after a few years, when all drifting sands are incorporated into nice, fertile, moist soil...
When (the very bad) summer took its course, many acrylate joints worked their way out of their gaps, I will have to find another solution for filling the joints between windows...
Of course painting is very important to protect the wood from rain and condensation (occurring every night, and always dripping into the same places) inside. The windows will be OK for 50+ years (hardwood), but the frame is 2nd hand fir! After one year use of the greenhouse, weak spots will have to be addressed... Some pockets will show evidence of moisture accumulation and will rot away if nothing will be done!
2 - 3 coats of primer (or sometimes thinned overcoat paint, and 1-3 coats of finish (and another coat planned after a full year of seasons!).
Using cheap sources for painting materials ('Action stores' etc...), I think total paint costs are ca. E 50.- It visually connects all elements of the building, makes a great design statement and protects the woodwork.
Step 8: Roof Cover
Special greenhouse roof plastic, enforced and UV protected, is available in Holland. The retail price is E3.-/m2, on rolls of 2 m wide. (wider rolls are being produced for the industry as well, but one has to purchase at least a full roll of 100 m. It is guaranteed 5 years, but usually will last for about 10.
Every part the plastic rests on has to be rounded: sharp edges will eventually cause tears. To fix it on the trusses, tiny hardwood or plastic strips could be used, but most of us here use strips of food grade conveyor belt, as our town has a factory making the stuff, with plenty of rejects in the dumpster. A tray of beer makes everybody happy...
The covering job is really a 2 person thing. I did it on my own, with a quite flawed result (self confidence is good, but after all, I'm not an octopus...).
Anyway, after some minor (major) adjustments, the greenhouse is covered.
My other, existing greenhouse had been full of tools and materials. Growing baby plants was not a great idea, as the high humidity caused by watering, spraying and subsequent evaporation makes every piece of steel crumble and decay. Only for this winter, almost the whole place had been paved.
Many things stored in it will find its new place. Tools will find their way home after use. Materials with potential will be sorted out, many useless parts/ materials have been trashed.
Step 9: Gutters and Roof Top
Not easy to find time searching for proper materials! Took another 6 months..
Gutters: leftover galvanized steel 'studs' to hold up drywall (some fire regulations require this for office buildings) from dumpster.
Pre-painted, made to size and closed by means of sheet metal work and lots of silicone caulk.
Outlets: 'washing machine drain' and vacuum cleaner hose attached.
Rain barrels: still have to build blue barrel stands (to get at least some water pressure)...