HOLLOW BEICK WALLS 



35 



In some instances, for example in the case of dairies, the second 

 purpose is the more important, hollow walls being employed chiefly in 

 order to keep the interior of the building in question as cool as possible 

 in summer. 



Hollow walls consist of two separate vertical portions standing 

 parallel to each other, and separated by an air-space or cavity, which 

 varies in width from 2 inches to 4i inches in different walls. The 

 layer of air contained in the cavity is a bad conductor of heat, which 

 phenomenon results in a building that has been provided with hollow 



Fig. 30. 



walls being cooler in summer (and by day) and warmer in winter (and 

 by night) than it would be if it had solid walls of equivalent thickness 

 of brickwork. 



The air space in the wall should have no communication with the 

 outer air, it is therefore shut off from the latter by a covering course 

 of brickwork at the top of the wall. 



As a rule, one of the portions forming a hollow wall is built 4£ inches 

 thick. The other portion, separated from the first by the air-space, may 

 be 9 inches or 14 inches thick, according to the strength required. 



The two portions are bonded or tied together. Various types of ties 



