This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
The following proportions are given by different authorities for fixing the amount of window surface: (1) One-eighth of the wall surface should be windows. (2) The area of glass should equal at least 1/10 of floor area. (3) One square foot of glass should be allowed to 100 cu. ft. of interior space to be lighted. It is better to have a surplus than a deficiency of light, as if too bright, it can be regulated by blinds or shades.
The height of the window should be twice its width. Architraves should be from 1/6 to 1/7 the width of the window opening, and where pilasters adjoin architraves their width should equal that of the latter. Where consoles are used their length should not be less than 1/3 nor greater than 1/2 the width of the opening. The entablature should be from 1/4 to 1/5 the height of the opening. Where engaged columns flank windows, at least 3/4 of the column should project beyond the face of wall.
To obtain a uniform frieze line around rooms in dwellings, it is well to keep the window and door heads equidistant from the ceiling. Thus, where the walls are 10 or 10 1/2 ft. high, and the doors 8 ft. high, the top of the casing is from 18 to 24 in. from the ceiling. This space may be occupied by frieze and cornice, or a picture mold may extend around the room in line with the upper edge of the door and window casings. Where ceilings are not over 14 ft. high, this same effect can be obtained by introducing transom sash over the doors, filling these with either chipped plate or art glass.
The glass line of windows in dwellings should be about 30 in. from the floor for principal rooms, and about 36 in. for bedrooms. In all cases, the heads of windows should be as near the ceiling as the construction and interior scheme of treatment will permit, to obtain better light and ventilation. The meeting rails of window sash should be placed not less than 5 ft. 9 in. above the floor; otherwise, the rail will be on a level with the eyes, obstructing the view and detracting from the effect of the window. On this account the height of the upper sash is sometimes made only 1/2 that of the lower, or 1/3 the clear height. For buildings of any pretensions, it is a mistake to cut up the sash into small panes. It should be remembered that windows are designed for the purpose of lighting, and all obstructions created by sash bars detract from the desired result. Where the designer prefers to have window sash subdivided, metallic bars of zinc, copper, or lead will be found more durable than wood, and will not take up so much of the daylight area.
Sashes should slide vertically, counterbalanced by means of cord, chain, and weights, or by spring sash balances. Those that are hinged and open inwards cannot be made water-tight, and those opening outwards are likely to be injured by the action of wind, so that for general service the best results are obtained by use of sliding sash. Sash stops should be fastened with screws passing through slotted sockets, thus preventing the sashes from rattling and warping.
In Fig. 21 is shown a view of a window frame with sliding sash, adapted for a frame building. The pulley stile a may be from 1 1/8 to 1 3/8 in. thick. and should be tongued into the blind stop 6 and the plaster cas-ing c, each of which is 7/8 in. thick. These tongues make the stiles rigid, preventing them from deflecting sidewise when the sashes are being operated. An open space of from 2 1/2 in. is left between the back of the pulley stile and the rough stud, thus forming a box for the weights, A movable pocket for the insertion of the weights cut out of the lower portion of each pulley stile on the inside, so that it may be covered by the lower sash. The parting strip d is 1/2 or 5/8 in. thick, and passes into a groove | in. deep in the pulley stile. The outside casing e, 1 1/8 in. thick X 5 in. wide, is firmly nailed through the blind* stop into the pulley stile and to the wall sheathing. The inner face of the window frame is finished with a casing, which may be of any style of finish - in this case, by an architrave, the width being sufficient to cover the plaster joint. The sash stop g, from 1/2 to 5/8 in. thick, is secured with round-headed screws passing through slotted sockets for adjustment. The members g, d, and b should be kept in line, their projection beyond the face of the pulley stile being regulated by the thickness of the sash stop.
The sill h, from 1 1/8 to 1 3/8 in. thick, is tongued into the pulley stiles and well nailed. Sills are sometimes made with a straight inclined surface instead of being worked with two facias, as shown. When water collects on the sill, it is readily drawn under n, the lower rail of the sash, by capillarity, or driven in by wind; by raising the surface under the sash above the level of the outer portion, and running a small rounded groove in the fillet, the effect of the wind is to divert the water outwards. Under h is placed the subsill i, 1 7/8 in. thick, which is attached to the pulley stile, and likewise grooved for the reception of the beveled siding j. For durable work, the window frames should be put together with stiff white-lead paint, particularly adjacent to the sill and subsill. The sashes k are made from 1 5/8 to 1 7/8 in. thick. Strength is added to the upper sash by the elongation of the stile, forming a molded horn, as by this device the tenon of the meeting rail m can be made equal to its thickness. The meeting rails, 1 3/8 to 1 7/8 in. thick, according to width of opening, may be double- or single-beveled, as shown, so that they will come tightly together when closed. The lower rail n may be from 3 to 4 1/2 in. wide, and should be accurately fitted to the sill; the outer edge should be clear about 1/8 in., but the inner portion should be in contact with it, thus preventing the ready passage of water. The inner face should be rebated and beveled to fit the edge of the stool o. This stool should be rebated to form an air-tight joint, and be bedded in white lead. An apron p is fixed to the edge of the sill and to a plaster ground q, and finished with a bed mold as shown. The length of the apron should be equal to the width from out to out of casings, and have the moldings returned on same.
In Fig. 22 is shown a box-frame window, suitable for a stone or brick wall. The general design and construction of the frame and sash are similar to that shown in Fig. 21, the only changes being in parts that require to be adapted to a new condition. In brick walls it is usual to set the window frames during the erection of the walls, thus facilitating the plumbing of the brick jambs, particular care being taken to brace the frames, in order to keep them plumb and level. By keeping the blind-stop casing a 1 in. wider than the back lining 5, the frame can be firmly held in place after the braces have been removed. The sill c, made of 3" plank, is (or should be) bedded in haired lime mortar, or, for first-class work, stiff white-lead paint and white sand. The groove on the bed permits the formation of a mortar tongue, making it practically air-tight; the slightest shrinking and warping of the sill allows the passage of air and water, unless this device to adopted, A 1/2" finished casing d may be attached to the inner frame casing e, after the building is ready for trimming, thus covering its marred condition. The window stool or seat f rests on furring strips, and is tongued into the sill, providing for its expansion and contraction; it is generally finished with a molded apron g. The jamb lining h is tongued into the finished casing, and the opening trimmed with a casing, such as i, nailed to the lining h and the rabbeted plaster ground j.
The hanging stile k in brick-set frames is attached thereto before setting, but where outside blinds are not used, an angle mold may be substituted.
In stone walls, window frames are not usually set until the building is roofed and either prepared for the plastering, or when the plastering has been completed. There are two reasons for this, the principal one being the difficulty experienced in setting jamb stones and lintels while the frame is in position, and the second that, with all due care, the frames are more or less damaged during building operations and are never so true to line, level, and plumb as those set in place after the walls are completed. When set in this latter order, it is necessary to encase the masonry openings with screeds or wooden strips, carefully alined and plumbed, and so arranged to allow for a bed of haired mortar 1/4 in. thick around the jambs and window head. The frames are secured by means of holdfasts or wall plugs. When set in this manner, the casing d is not required, unless it be that the interior trim is of a material different from that of the window frame.