There are other features of economy in design which should be observed. The simpler and more straightforward the design, the cheaper it is and the more beautiful it can be made in the hands of the good artist. Simplicity is the highest art, as it is also the most economical thing. Likewise the cost of a house can be reduced by shaping as nearly to a square as possible, and reducing the outside walls to the minimum. The semi-detached house in the group plan accomplishes this in the best manner, and gives to the whole structure that low, long skyline that is so very pleasing. This also makes one soil-line and one chimney do for both houses, a great point in economy. Some architects believe these group houses are the only economical solution of the problem of the small house. III ESSENTIAL STANDARDS OF QUALITY IN BUILDING MATERIALS _Materials Used_ It will be remembered that the commonest types of small houses are the wooden frame house and the masonry-and-wood house. Now it is essential that certain definite qualities be required of all materials of construction which enter into the building of these houses, and although there are many facts covering the standard qualities and methods of manufacture, yet one cannot expect to remember all of them. It is sufficient if one knows those qualities which mean satisfactory building and durability when applied to the structure. Of the large number of materials which enter into the construction of a house, the following are the most important and should be maintained at a high standard: wood, clay products, cementing materials, metals, glass, and paint. WOODS It is possible to enter into a long discussion of the classes, qualities, methods of conversion, defects of wood and similar subjects, but these are not pertinent to the main idea, namely, the essential qualities of woods which are used in the construction of the small house. There is a prevalent impression abroad that the supply of wood is becoming so depleted that it will in the future be used only for special ornamental features. This is wrong, for we still have enough virgin forests left to supply the country for several generations, and with the growth of forestry we will maintain a certain source of supply. [Illustration: Waney edges Knots Star and ring shakes Common timber defects] We have two classes of woods on the market which are used in different parts of the structure, according to their special qualities. These are commercially known as hard and soft woods, although this is not a very scientific distinction, since some of the soft woods are harder than some of the hard woods, and vice versa. Scientists have more accurate names than these, but as the above are so well established, there is no doubt as to what is meant.