176 FARM ARITHMETIC. 



Shingles are 16 inches long and average usually 4 inches 

 wide. When laid 4^ inches to the weather, -each average 

 shingle will cover 4 x 4^ or 18 square inches. Eight 

 average shingles will, therefore, cover 1 square foot and 

 800 shingles will cover a square. On account of waste, it 

 is better in making an estimate to allow 900 or 1,000 

 shingles per square. The pitch of the roof should never 

 be less than one-third ; that is, in a building 60 feet wide, 

 the comb or peak of the roof should be at least one-third 

 of 30 feet or 10 feet higher than the plates on which the 

 rafters rest. A pitch of one-half gives a much better pro- 

 tection from rain and melting snow and makes a more 

 durable roof. 



622. Allowing 800 shingles per square, how many 

 thousand would be required for the roof of a house 35 

 feet long, the length of the rafters on each side of the roof 

 being 14 feet? 



623. How many average shingles are required per 

 square if laid 4 inches to the weather ? 3 inches ? 



624. Allowing 900 shingles per square, how many 

 thousand are required for a house 40 feet long, if the 

 rafters are 16 feet long? 



Length of rafters. If the width of a building and 

 the pitch of the roof be known, the length of the rafters 

 may be calculated by the following rule : 



Square each of the two legs of the right-angled triangle 

 of which the rafter is the hypothenuse, add these squares 

 and extract the square root of the sum. The result is the 

 length of the rafter. These lengths may include the over- 

 hang, as in the following problem. 



625. How long are the rafters of a barn 30 feet wide, 

 when the pitch is three-fifths and the overhang is 1 foot? 



