My attached solar greenhouse

[Doug Kalmer]

My attached greenhouse is 8'x18', and attached to the south side
of my solar heated home. I built both in the mid 80`s, for little
money. The greenhouse initially cost me about $300 to build, but it
was single glazed then. I started out by pouring a footer, and laying
up 6" blocks, which I then externally covered with 2" of foam board,
topping it off with an 8" treated sill plate. I had found some
46"x76" sliding glass door replacement tempered glass for $15 each,
so I framed walls with 2x4`s to fit them. I initially used corrugated
fiberglass for the roof, it lasted about 10 years, then I replaced it
with twinwall polycarbonate, which is much better. I have a pea
gravel floor over the soil, a scrounged brick pathway, and four 55
gallons drums of water for thermal mass. The drums support benches,
and are along the house wall. I put in a planting bed and shelving for
plants, and my wife found out she liked growing plants so much it
started her out in a greenhouse business. The attached greenhouse
serves to start plants in January, then in February we transfer them
to the 22'x48' freestanding greenhouse. The attached also is an
airlock in the winter, as it covers an entrance door, which we open
in sunny cold weather to help heat the house. It is a handy place for
firewood, and the dogs stay there on winter nights. I also installed an
exhaust fan thru the adjoining wall , which I wired to an AC
thermostat, so it can come on at about 85*F greenhouse temp to blow
warm air into the house, useful when we are not home. The adjoining
wall also has a window with a lower vent space below it, when we are
not going to be home during sunny cold weather, I removed the
insulated cover to the vent, so air can be returned to the greenhouse
from the house, it has a 4 mil flap on the greenhouse side to prevent
reverse flow. I have large screened vents in both east and west ends
for warm weather ventilation, and in summer I cover the roof with 60%
shade cloth. The greenhouse provides heat, acts as an airlock,
provides a place to grow food and house plants, it helps us earn a
living by providing a place to start plants to sell, it is a great
place to hang out in sunny cold weather, all in all, we really like
it.

[Eric Lewis]

I am also building an attached passive solar room but with a slightly different approach. I call it a sun space rather than a green house because it is intended to be a year-round room for both people and plants. The first order of business of course was to orient it toward the south; mine is less than ten degrees east of south. The next issue was thermal mass, something you can't have too much of. I decided to go with a concrete slab because as a living space there were complications of chair legs and cleanliness associated with gravel. The slab is tinted dark gray and is insulated around the edges with 1-1/2" of blue board. We will be adding at least eight 55-gallon drums of water in a few weeks to further modify the temperatures. Because half of the adjoining wall is a garage door we can place four of the drums just inside the big building to store heat in there, and the other four in the sun room; all will be hit by direct sun in the winter. Roof glazing is tricky in this climate if you want to avoid overheating three out of four seasons and I have taken care to manage it. I have installed 5'x16' of twin wall (insulated) 8 mm polycarbonate skylight. Above it is 5' of solid roof/ceiling and below it is a 20" overhang of solid roofing. I have purchased four foil-backed 1" styrofoam panels to make sliding shutters that will cover the skylights from below during the hot season and on winter nights. We also will have an 80% sun screen over the top in the summer attached with bungee cords. The overhang will block the summer sun from hitting the vertical glass in the summer, yet allow the winter sun to shine under it to half-way up the north wall. Overheating will also be avoided by virtue of the fact that the south glass is all casement windows, thus turning the sun space into a screened-in porch. (The windows were salvaged from a house down the street scheduled for demolition). There will also be a thermostatically-controlled fan mounted up high on the east wall. Excess heat in the winter from the sunspace can be used to heat the two-story building it is attached to either by opening the garage door to the shop or opening vents at the top of the north wall connected to floor grills in the adjoining upstairs living space. My sun space is decidedly more expensive to build than Doug's but I believe it will be worth the $5,000 I intend to spend on it. About 80% of it will be built with salvaged materials.

[Doug Kalmer]

People use the terms- "Greenhouses, sunrooms, sunspaces" interchangeably, and it is difficult to differentiate by use, or design, as lines blur. Typically, a greenhouse is a space designed for keeping plants alive year round, so it should not allow temps to fall below 40*F in winter. It needs thermal mass to keep it from freezing in winter. It should also have a floor that can easily deal with lots of water being sprayed around. If you intend to water a lot of plants in your sunspace, consider that slabs will pool water, requiring drains, which need somewhere to drain to without clogging. I find the dry laid brick pathway surrounded with gravel is a good floor, as it provides thermal mass, as well as good drainage, and was cheap and easy to install. Our brick path can support chairs.
My experience with tinting concrete was that colors were faded looking, it reduces the strength of the concrete, is expensive, and why tint the concrete below the surface anyway? Concrete surface stains have better color rendition, soak into the surface, so they don`t show wear, and are cheaper without weakening the mix. I hope you are taking precautions to keep termites out of the exterior insulation.
I suggest black plastic drums, I have had steel ones rust out.
I wonder if 80% sunscreen will allow for healthy plant growth, I believe ours is 50%, and I can see the difference it makes in the plants.
If you want stable sunroom temps year round, day and night, then I agree that you can`t have too much thermal mass (TM). However, if you want the attached sunroom to help heat the home, then thermal mass should be inside the home, not the sunroom. Consider that the insulation in the sunroom will not be as effective as the insulation in the home, so it will hold onto the gained winter heat better. Also, the more TM in the sunspace, the less heat will be available for the living space. It`s all a compromise, but if you design for the intended use, you will be more satisfied with the end product.
I look forward to seeing the finished product. Doug