Dear Jim: I want to add a greenhouse on my house for the children’s recreation room and to grow some plants. I cannot afford a fancy kit, so I plan to build it from scratch. What is the best way to design an efficient one?

– Ron M.

Dear Ron: You should be able to build a nice greenhouse yourself at a reasonable cost using scrap materials. It sounds as though you are interested more in what is called a “sunroom” as living space than a true greenhouse.

A friend of mine in my neighborhood built a beautiful sunroom (he also uses it for plants) using scrap materials. He contacted local replacement window companies. He was able to get scrap replaced old windows for free. He designed and built the sunroom around the sizes of these free windows.

Depending on how tight your budget is, you may be able to buy a do-it-yourself sunroom kit at a reasonable price. Many of them are modular with lightweight aluminum frames and clear plastic windows and screens. As your budget allows, you can gradually add on sections to enlarge it.

If you are lucky enough to have a wall on your house facing solar south (different than compass south), you may be able to use the sunroom to help heat your house. This requires specific design concepts and details. At the worst, a south-facing sunroom can be built that requires little additional heat to stay comfortable and allow plants to survive through the winter.

When building a sunroom from scratch, a wood frame is much easier to work with than aluminum. Since you are planning to have plants in it, the indoor humidity level will be fairly high. This also will create some condensation at night. Using pressure treated lumber for the main framing would be wise.

A key design question is whether to have a vertical or slanted front? A slanted front reduces the roof area and overall material costs. It is fine for plants, but it reduces the headroom near the front of the structure. During the summer, a slanted front tends to overheat since it faces the sun.

A modified design with a several-foot-high vertical knee wall and a slanted front above it is another option. This provides more headroom and room for low plants against the knee wall. A brick or stone knee wall provides additional thermal mass to improve year-round comfort and efficiency.

Cover a portion of the roof, or all of it on a slanted front design, with plywood and shingles. This minimizes overheating during the summer.

Write for (or download at www.dulley.com) Update Bulletin No. 769 – do-it-yourself instructions and diagrams to build a sunroom/greenhouse. Include $3 and a business-size SASE, and send to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.