Tips for Building a Solar Room or Greenhouse
A do-it-yourselfer can design and build a solar room for a relatively low cost, with relatively low risk. You don't need electrical wiring or plumbing, and you don't need to obey all the building code requirements that are unavoidable inside of a house.
Before you get into the details of design, you should make some decisions about where you want the room and what kind of environment you want to create. Always build your sunroom on a southern front (although eastern sunrooms are popular as well for breakfast niches). Put the absorbers and thermal mass on the north side, at the back of the room. If you can't, your room will still work but not to maximum advantage.
The best location in your house is adjacent to the kitchen for attached greenhouses and adjacent to the living room or family room for sunrooms. These locations afford not only the most efficient use but also the most use in general.
Try to use as much of your home's existing walls as possible, preferably on both the east and west end of the sunroom. These walls are already insulated, and they match the house.
An easy and straightforward candidate for solar rooms are existing porches and decks that already have the basic support structures and flooring in place. All you need to do is build up and around.
As much as a well-designed solar room can enhance your house's aesthetics, a poorly designed one can make your house look awkward and uninviting. Make very good drawings done to scale before you begin building (use graph paper and let 1 inch of graph paper represent 1 foot). Consider all the angles, and if you can, draw some different perspectives (from the street, for example). The more thought you give to the appearance before you start, the better the odds that your solar room will increase the value of your home.
As you draw your design and try to figure out what materials you want to use for your glazing, remember these tips:
Sloped glazing allows for more sunlight entry, but it also gets much dirtier and is leakier and harder to install.
Avoid horizontal glass because it can be dangerous if it breaks and therefore takes special engineering techniques to ensure integrity.
In cold climates, use between 0.65 and 1.5 square feet of double-pane glass for each square foot of building floor area. In temperate climates, use between 0.3 and 0.9 square feet for each square foot of building floor area.
In practical terms, don't worry if you can't achieve these ratios. Anything will work to your advantage. Solar rooms are usually compromises between the best physics and the best aesthetics and cost. In general, aesthetics should win for sunrooms, functionality should win for greenhouses.
Glass shops often do retrofits of entire houses; they remove the old windows and install new ones. You can buy the old windows for next to nothing (they're usually single pane, but if they're almost free, you can't complain). Reusing such glass may lend a discontinuous visual effect, so be prepared to add some paint or other finishes.
A lot of new plastic materials are very effective at glazing. These materials are unsuitable in your house, but they're okay in a solar room. If you're building a strictly functional greenhouse, you can use corrugated plastic roofing panels on both the roof and sides.
If possible, use the same roofing and siding and window materials that your house is made of for better aesthetics.