184 EXTERIOR HOUSE DESIGN HOUSE BUILDING MATERIALS Wood is a popular material because workmen understand it; it is relatively cheap, looks well, and gives good insulation. It is possible to buy chemically treated wood, which is practically termite-proof and much more durable than ordinary wood. Good- looking, durable plywood panels are now used for exterior walls, as well as interior. They are particularly valuable in prefabrica- tion and in other rapid construction. Brick provides good insulation, has a pleasing variety of color, does not require painting, and is fire-resistant and vermin-proof. A brick house is worth the extra cost, if the budget permits. Stucco \$ an exterior surfacing made of Portland cement, sand, water, and sometimes lime and mineral coloring matter. Stucco is weatherproof, rot-proof, and fire-resistant. However, ordinary stucco may crack and termites may infest the wood underneath. Concrete is a weight-bearing material made from proper propor- tions of cement, sand, gravel or crushed rock, and water. It can be poured between forms, making solid walls on the job, or can be bought as blocks containing large hollow spaces which are valuable for insulation. These blocks should be used more than they are, for they are relatively cheap and are available anywhere. Concrete is fireproof and termite-proof, and its surface can be painted or stuccoed. It should not be used in damp locations. Hollow clay tiles are a valuable weight-bearing material which also should be used more for houses. The tiles are harder than bricks and can be stuccoed or painted with special paints. Glass sheets are used for walls in Modern homes where the ele- ments of light and space are stressed. Glass blocks admit light and sunshine while excluding sight, sound, heat, and cold. Composition panels of many types for exteriors are now on the market. Some of the best, which are fireproof and waterproof, are made of cement and asbestos. Various vegetable fibers, plaster, and plastics, among other materials, are also used. The panels, which are often one story high and of different widths, lend them- selves to rapid construction and mass production, Steel framing is more desirable but more costly than wood fram- ing. Steel panels are practical and are particularly good in pre- fabricated houses.