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VIII. — Description of Hollow Brick Roofs, as constructed on the 
Estate of Earl Grey, at Hoicick, Sj-c., and as purtlij illustrated 
in the accompamjing Sketches. By Robert Dunx. 
A ROOF of tliis kind is formed hy simply throwing an arch of 
holh)\v bricks over the building ta bo covered. Such roofs have 
been used for ordinary farm buiUlin<>^s for the sake of their 
economy and durability. An arch of ordinary bricks or of stone 
would of course equally answer to cover a building of moderate 
width, but would be so heavy that, much expense would have to 
be incurred in building the side walls strong enough to support 
the weight, and resist the outward thrust. Common walls built 
of common materials are strong enough to support the weight of 
a hollow brick arch, and its outward thrust can be effectually 
resisted by iron tie-rods, costing very little. 
In the accompanying sketch, the tie-rods will be seen secured 
to both stone and cast-iron springers ; the one or the other may 
be used, according to circumstances. The iron springers are 
cast of the form shown in the drawing ; they are merely a cast- 
iron box, about 4 inches deep, with a web or network formed 
inside (as shown bv the drawing). The web inside the box, and 
the outer edges, all stand the same height from the bottom ; and 
the whole, bottom and all included, are thin cast iron, varying 
from l-4th to 3-8ths of an inch in thickness, and are so contrived 
that each springer shall not weigh more than fifty-six pounds. It 
will be seen that the portion of the web against which the nut 
of the tie-rod acts is made a little stronger, and upon the prin- 
ciple of the arch, in order to secure strength with lightness. 
The principle of the construction of the iron springer is such, 
that it would be impossible to injure it but by a power sufficient 
to break it to atoms ; while its dovetail or tapering outline gives 
it a position on the walls exceedingly difficult to change. The 
inside or hollow portion of the springer, alter the tie has been 
secured, is carefully packed with masonry, and its position on 
the walls depends very much upon the care with which it is 
packed outside with the materials of which the wall is formed. 
Where stone springers are employed, they are formed, as 
regards outline of plan, similar to the cast iron, only (should 
stones of sufficient size be available) they may be made the full 
thickness of the wall, as shown by the section of stone springing. 
There are various modes of securing the ends of the tie-rods 
to the springers. When the springers are of stone, an eye is 
made on each end of the rods, passing over a bolt cut deep into 
the stonework, and secured from rising with a small pin ; the 
opening made in the top of the stone, into which the tie and 
