6 Roof

6 Roof

Flat Roof. Any roof of less rise than 1′ in 9′ is called a flat roof; and the same methods of finding the lengths and cuts of the rafters may be used as upon a pitch roof.

69. Dormer windows are of many shapes and sizes, and are frequently used as means of decoration, being embellished to a greater or less extent. They frequently form an important element in the architecture of a house.

Fig. 96. — Laying out a Curvilinear Hip Rafter.

Fig. 97. — A Dormer Window.

Their construction is illustrated in Fig. 97.

A "lift" is a form of dormer window, used in places where a gable is either not desired or impracticable. It is also frequently used where economy is an important consideration, though upon the best class of work it has a good architectural character. The construction of a lift is generally similar to that shown in Fig. 98.

The finish of the dormer windows and of the lifts should be in keeping with the rest of the house; but it should be considerably lighter, being only a detail .

Suggestive Exercises

47. What is meant by the pitch of a roof. The run of a roof. The rise of a roof? What are the three pitches in common use? Do the angles of each pitch vary in different-sized houses? Prove it. Does a difference in the rise of a house affect its run? What does it affect?

Fig. 98. — A Lift Window.

Find by the use of formulas the rises of a half, a third, and a quarter pitch house, 26′ wide.

48. Name and show by diagrams the different forms of roofs. What is a curb roof?

49. What shape should always be striven for in laying out a roof? Why is this advisable?

50. From what points is the length of a common rafter measured? Is the length of the rafter affected if the lookout is cut upon the lower end? Demonstrate the use of the formulas in finding the length of a common rafter. Could the dimensions of the roof be used in obtaining the cuts of the rafters? Is it a practical thing to do? What are the standard figures or constants used in laying out the cuts of the different common pitches? Should these figures be used to find the lengths of the rafters? Why? Is there any case in which they may be used for that purpose? Demonstrate the method used in obtaining these constants. Will these figures give correct results if used upon a rafter which is not square with the plate? Which edge of a rafter should generally be placed uppermost? Which part of the square should be used in measuring the run of a roof? In measuring the rise? What figure upon the blade is used in laying out all rafters which are parallel with the plate? Demonstrate by the formula the method of shortening a common rafter to allow for the ridge. Demonstrate the method of laying out the joint at the plate. What is the name of this joint? What is meant by "plumb height" at the plate? What are the sizes of rafters commonly used? How far apart are they usually placed?

51. Demonstrate from the formula the method of finding the length of a lookout.

52. What is the value of a ridge? Is it always used? What governs the length of the ridge of a gable roof. Demonstrate by the use of the formula the method of finding the length of the ridge for a half hip roof. For a full hip roof.

53. What part of a hip rafter is seen in looking at a roof plan? What is its angle with the plate, if the house is square and the pitches are equal? Between what points is the length of a hip rafter measured? What part of a right-angled triangle is the rafter? Demonstrate with a steel square the method of finding the length of the hip rafter. How should the top ends of the rafters of a perfectly square hip roof be fitted?

How much shorter should a hip rafter be cut it a ridge is used? Demonstrate the method of finding the neat length of a hip rafter by means of a steel square. How is the pitch line of Ѕ of the thickness of the ridge found with the steel square? In what respect is this method of finding the length of a hip rafter similar to that of finding the length of a common rafter? What is the relation of the run of a hip rafter to that of a common rafter? Demonstrate the method of finding the constant for the run of a hip rafter. What constants are used for the rises of the hips of a half, a third, and a quarter pitch roof? Demonstrate the method of finding the plumb and seat cuts of a hip rafter by means of a steel square. How are the side or cheek cuts found? Does the pitch of a roof change the horizontal angle at which the hip intersects the ridge? Explain the principle involved in this method of finding the cheek cut. and its application to different angles of intersection. Which end of a hip rafter is usually cut first? From what point on the rafter is the length measured? Demonstrate the graphic method of laying out the bevels of a hip rafter. Describe the methods of backing hip rafters. Upon which edge of the rafter is the backing laid out? How may a roof be framed to make backing unnecessary?

54. Describe the method of finding the length of a valley rafter. How is the cheek cut found if the rafter extends to the ridge? How is the angle found for a valley rafter which fits against a hip rafter?

55. Demonstrate the method of using the steel square in finding the length of a jack rafter. if the common rafter intersects the hip at the apex. If the common rafter does not intersect the hip at its apex. Demonstrate the method of obtaining the length of jack rafters working from the lower end of the hip. What are the constants for cutting the bevels of jack rafters?

56. What is the method of finding the run of a cripple rafter. What allowance should be made in the length of a cripple rafter? Demonstrate the method of laying out the bottom and top plumb cuts of a cripple rafter. What should be the relation of the cripple rafter to the top edge of the valley rafter which it meets? What must be guarded against in nailing cripples and jacks in their places?

57. Demonstrate with the steel square the method of finding the length of collar beams. What is the purpose of a collar beam ?

6 Roof

58. What is the purpose and position of a strut. Is it always square with the rafters? Demonstrate the method of finding the length of a strut with the steel square. How may the formula of a common rafter be used in finding the length of a strut?

59. What are the purpose and position of a purlin? How is its length found? Illustrate a graphic method of finding the length of a purlin. Compare a purlin cut with a hopper cut. Demonstrate the method of using a steel square, to find the cuts of a purlin or a hopper. Describe a simple method of marking a purlin from a partly completed roof.

00. Describe the method of framing an octagonal roof by cutting rafters in pairs. Of framing a hexagonal roof. How can the length of the first pair of rafters be found? Of the second pair? Of the third pair? Describe the method of obtaining the cheek cuts of the third and fourth pairs.

61. Describe the method of finding the cheek cuts of the apex of rafters for a hexagonal roof.

62. Describe the king-post method of framing a polygonal or circular roof. What are its advantages?

63. Demonstrate the methods of finding the backing for a hexagonal or octagonal roof.

64. How can the cheek cuts and the lengths of jack rafters of a polygonal roof be found?

65. How may the seat and plumb cuts of any rafter be found. How may the rise and the run of any rafter be found? How can you find the length of any rafter of any pitch? Is there any difference between the methods of finding the lengths of rafters of a house of uneven pitches, and of one which has the same pitch upon each side? Describe the method of finding the side cuts of hip, jack, and valley rafters of a roof which has different pitches. Compare this principle with that of making the side cut of a jack rafter of a rectangular roof. What is the effect of unequal pitches upon the eaves? How may this be remedied?

66. Describe the methods of framing curb roofs.

67. Describe the method of laying out the hip rafter of a French roof.

68. What is the greatest pitch of a flat roof house?

69. Is a dormer window ever planned for any reason aside from light and ventilation? Describe the construction of a dormer window. What is sometimes used as a substitute for a dormer window? Compare the finish of the dormer windows with that of the rest of the house,


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