140 GARDEN DESIGN 



Hollow walls retain heat longer than solid ones, 

 owing to air being a very slow heat conductor, 

 and they are as strong as though solid while using 

 considerably less bricks. Diagrams 51 and 52 

 show two methods of building a hollow 14 in. 

 wall. The second one will be seen to be more 

 economical. 



On the question of expense it is interesting to 

 compare the costs of hollow and solid walls. 



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DIAGRAM 51. 



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W/////////////A DIAGRAM 52. 



Thompson gives the following figures for a wall 

 100 ft. in length and 10 ft. high 



14 in. solid requires about 16,000 bricks. 



14 in. hollow requires about 12,800 bricks. 



9 in. solid, with its piers, about 11,060 bricks. 



Thus it will be seen that where a 9 in. wall will 

 require strengthening by piers, it is almost as 

 cheap to build a 14 in. hollow wall requiring no 

 piers, with far more advantages in the latter, 



