Bring Nature Inside With an Indoor Greenhouse

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PHOTO: FOTOLIA/JACQUES PALUT
An add-on indoor greenhouse can provide a great place to grow plants, furnish heat to your home, and supply extra living space.

Do you have high energy costs? Dreary surroundings? You
can solve both of these problems with the indoor greenhouse solution.

It’s no news to most people that heating or cooling a
mobile home can be a very expensive proposition. It may
come as a surprise, however, to learn that with only a
moderate outlay of money and time, these energy costs can
be noticeably reduced by installing an indoor greenhouse. In addition, you can gain a place to
grow fresh foods, sturdy seedlings for transplanting to
outside beds or containers, and a year-round supply of
beautiful flowers to grace the dining table and brighten
the home.

I’m speaking, of course, of the benefits you get when you
build an attached greenhouse. Mine, a 7 foot by 24 foot structure,
does all of the above very well; furthermore, its design is
simple, its materials are standard, and it can be easily
duplicated or adapted by anyone with basic carpentry skills
and equipment.

BEGINNING AT THE END

My Albuquerque mobile home is large (24 feet by 52 feet), but the
construction principles I followed would be the same for
any size home. The greenhouse was attached to the south (in
my case, 24 feet) end of the home. My son did the designing,
wiring, and insulating . . . a hired carpenter did the
foundation and framing . . . and I did most of the glazing
and finish work. First we removed one window from the
adjoining office (originally a bedroom) and replaced it
with a door to provide access to the interior of the house.
We then poured a 6 inch by 12 inch concrete footing and topped it
with 6 inch by 8 inch by 16 inch masonry blocks to form the foundation.
One foot of pumice was used for ground insulation, while
inch-thick sheets of plastic foam were used to insulate the
foundation.

Next we constructed the greenhouse framework–out of 2 by 4s–at the proper angle to catch the sun’s rays in
winter. Authors Rick Fisher and Bill Yanda state in The
Food and Heat Producing Solar Greenhouse
(John Muir
Publications, Inc.) that “a formula . . . for establishing
the tilt of the south face is the latitude plus 35
degrees.” However, this optimum angle can be varied
somewhat without losing much light transmittance.

I used greenhouse-grade fiberglass on the outside of the
structure and Monsanto 602 UV resistant plastic
on the inside, creating double walls with a dead air space
in between. And by applying sealants at every crack and
juncture, I’ve been able to minimize heat loss.

The Indoor Greenhouse Solution: The Inside Story

Ten 55-gallon oil drums were cleaned, painted black, laid
side by side on a framework, and filled with water to
collect and store the sun’s heat for later dissipation at
night. We piled river rock on the floor area behind the
drums to hold additional warmth. A workbench was
constructed over the barrels and a deck laid over the
rocks; both platforms were built of 2 by 4s nailed 1/2 inches
apart to provide slots for drainage. The entire interior of
the greenhouse can be easily hosed down to remove dust and
dirt and to increase the humidity. White paint on the
walls, supports, deck, and benches reflects sunlight to all
sides of the plants, helping them to grow evenly; as a
fringe benefit, it also makes the interior of the structure
appear larger and airier than it actually is.

Here in New Mexico the intensity of the sun dictates a
solid roof on any dwelling, be it for people, pets, or
plants. So I put corrugated metal roofing backed with 6 inch
fiberglass insulation batts above the ceiling in the
greenhouse. Since summer sunlight was still too hot and
bright for many plants, I set removable panels of
inch-thick plastic foam between the 2 by 4s on the outside.
In the interior, I installed ordinary window shades upside
down along the outer edge of the workbench. I centered a
screw eye in the bottom rod of each shade and another screw
eye set in the greenhouse framework just above it. Nylon
cord was run through the paired screw eyes and knotted,
enabling each shade to be raised to the exact height
desired for optimum shading of the bench and interior.

Other features include an old kitchen sink–purchased
at a junkyard for $10–which was connected to plastic
pipe that brings in water from an outside faucet. We also
used plastic pipe to make a straight, trapless drain that
carries wastewater to a plant bed outside. Clay pots,
plastic pots, and 20-gallon plastic garbage pails
containing various potting materials are all stored under a
bench along the north wall. I place plants needing diffused
light and less heat on this bench or hang them from hooks
above it.

To make good use of the heat generated in the greenhouse,
we installed an exhaust fan and a duct near the ceiling to
funnel hot air into the rest of the mobile home, but most
of the time the warmth circulates freely without the use of
the fan. Outside ventilation is provided by a set of vents
and a window on the east end. A used evaporative cooler
takes care of most of the structure’s air-conditioning
needs. Purchased for $25, it was installed on the vent at
the east end and often supplies enough cool air for the
entire home. [EDITOR’S NOTE: Swamp coolers, as these
units are sometimes called, are most effective where the
outside humidity is very low, as in the southwestern United
States.]
I now use the home’s main air-conditioning
unit only on extremely hot summer days.

A Breakdown Version: The Portable Greenhouse

Mobile home owners who would prefer a portable
greenhouse will find that one similar to mine can be
constructed from panels: 8 feet by 8 feet is a good, workable size.
The two ends of the greenhouse, one side, and the roof can
all be held together with slip pins inserted in regular
hinges. Barrels can be placed against the mobile home wall
or at other strategic places. Freestanding benches can be
used for potted plants, or plants can be grown directly in
the ground, as in a cold frame. The entire portable unit
should be anchored to a foundation of some kind, however,
such as concrete blocks or railroad ties.

Indoor Greenhouses: The Bottom Line

My greenhouse was built from new materials in 1977. At that
time, the total cost–including labor–was $980. A
pproximately $500 of that sum was for materials. Today the
cost would be higher, of course, but you could save a
considerable amount if you built with good used lumber.

And is the whole thing worth it? Absolutely, I say! My
greenhouse cut my fuel consumption in half the
very first year; meanwhile, my house has been beautified
season after season with blossoming geraniums, petunias,
begonias, and gloriously fragrant freesias. I feel my
initial investment started paying off right at the start,
and has kept on doing so, year after year.