46 GREENHOUSES 



by reflection of between 2 and 3 per cent, on- 

 ly. Roofs of this pitch are not difficult to 

 build, and do not present so large a radi- 

 ating surface for the area covered as do roofs 

 having a pitch of 65 degrees. Roofs having 

 a pitch of less than 26 degrees are seldom 

 satisfactory because the snow does not clear 

 from them well and they are likely to leak. 

 The water of condensation which forms on 

 the inside of the roof is also likely to drip up- 

 on the plants when the pitch is less than 

 about 26 degrees. When the pitch is greater, 

 the water will usually follow down the glass 

 to the edge of the house. In even-span houses 

 (see Chapter IV) the pitch of the roof varies 

 from 26 to 35 degrees, 26 and 32 being the 

 most popular. In some specially constructed 

 houses it is as great as 45 degrees. Most 

 builders equip houses up to 25 feet in width 

 with roofs having a pitch of 32 degrees, and 

 above 25 feet with roofs having a pitch of 26 

 degrees. 



Measuring the Pitch. The degree of pitch 

 of any even-span roof may be determined tri- 

 gonometrically when the width of the house 

 and the height of the ridge is known or can 

 be measured. If the house illustrated in 



