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Question-- I want to add an attached greenhouse (sunspace), but I am on a limited budget. I want to use it for living space, heating my house and growing plants. How can I build an inexpensive do-it-yourself one?

---P.Z.Answer-- Using inexpensive materials, you should be able to build a simple 8-foot-by-10-foot greenhouse yourself for several hundred dollars. As your budget allows, you can gradually make efficiency improvements and add features.

You can also purchase inexpensive do-it-yourself sunspace kits. These often use bolt-together aluminum frames and doors. You can order the kits with the glass and screening included or you can often find it cheaper locally. If you plan to use your greenhouse primarily as a sunspace for living area, a vertical front wall design is best for more headroom. It is easy to install front and roof shades for overheating control with this design.

For predominantly gardening use and solar heating of your house, a slanted front wall is acceptable and it requires less material. This design sometimes tends to overheat in mid summer, so you'll need several vents.

The south side of your house is the best greenhouse location. For effective heating, your house wall should face within 30 degrees of true south. Note the types of trees nearby. Fast growing varieties can shade it quickly.

You can make the frame with 2 x 4 or 2 x 6 lumber. Try to size the framing so you can use standard-size patio door replacement panels. Make removable frames so you can replace them with screens in the summer.

With your tight budget, start out with flexible plastic sheets or heavy plastic film. If you choose a plastic material, check with the salesperson to make sure it is ultraviolet (UV) light-stabilized.

To control the temperature and improve the efficiency, you need some type of thermal storage mass. Brick flooring or water-filled drums is effective. Use heavy bricks or concrete blocks to support tables or planting trays.

Operable vents in the roof and movable insulating shades also help. As your budget allows, you can purchase thermostatically-controlled fans to circulate the heated air into your house and sun-sensor automatic vents.

A simple greenhouse should be able to produce about 40 pounds of tomatoes, 25 pounds of cucumbers, 75 heads of lettuce, and some other salad vegetables. This can reduce your annual grocery/salad budget by $150 and pay back the material cost of the greenhouse in several years.

Write for Utility Bills Update No. 735 showing do-it-yourself instructions and diagrams for building an inexpensive attached-sunspace and a list of nine manufacturers of ready-to-assemble sunspace kits. Please include $2 handling fee, cash or check.

Question-- We have a free-standing wood burning fireplace in our family room and the wall behind it needs paint. What type of paint should we use or is there a better wall coating to use? -----F. J.

Answer---A light-colored, even a shiny, surface behind your fireplace will reduce the heat loss through the wall. More of the heat will be reflected out into your room. You should be able to feel the additional radiant heat.

If the stove is the approved distance from the wall, most paints should withstand the heat. Ceramic-filled paint is particularly reflective to heat. Brushed or shiny aluminum sheet squares are very effective. Ordinary mirror tiles, while they look reflective, do not reflect much heat.