A variation of solid brick construction is the so-called hollow
or vaulted wall in which the face and common brick are separated
by a two-inch air space and bonded together by metal ties laid in
the mortar joints at proper intervals. This type of wall has been
extensively used for many years, especially in the East.
[Illustration: Fig. 30. Hollow or Vaulted Brick Wall]
[Sidenote: For and Against]
Its friends claim that it is stiffer than a solid wall of the same
amount of brick; that it offers a better insulation, by reason of
the air space, against cold and dampness; and that therefore it
saves the necessity of furring and fire stops on the interior wall
surface. On the other hand, admitting the value of the air space
and the consequent saving of furring, objection is made that the
air space is apt to get filled with mortar and brick chips during
construction; that the metal ties, unless heavily galvanized or
dipped in asphaltum, rust out in a comparatively short time; and
that it is not as strong a bearing wall as the solid wall of the
same brick content. Mr. Arthur W. Joslin, a contractor and builder
of Boston, whose extensive practice gives his judgment weight,
says in summing up the pros and cons: "The 10-inch vaulted wall
is strong enough for ordinary dwellings, even though the ties do
rust out, unless it is built out of the poorest kind of brick with
very poor mortar. In my opinion, a vaulted wall, if properly built,
the vault not filled up with droppings, and provisions made for
ventilating from the inside, is an ideal wall for dwelling house
construction, but I would not recommend it for buildings for other
purposes where there would be more or less of a dead load coming on
the floors." On the matter of comparative costs, Mr. Joslin adds:
"It is cheaper to build an 8-inch solid than a 10-inch vaulted
wall, and slightly cheaper to build a 10-inch vaulted than a
12-inch solid wall."
The accompanying drawing shows a cross section of this type of
brick wall. Except in a few particulars, its construction does not
differ essentially from that of the solid brick wall as already
described.
A 12-inch brick foundation is wide enough for the 10-inch wall and
a 16-inch foundation for the 14-inch wall. The metal ties, heavily
galvanized or coated with asphaltum, should be placed about 18
inches apart at every fifth or sixth course and extend at least 2
inches into the mortar joints.
Fire stops are not needed, nor is furring, as the plaster may be
laid directly on the brick. In order to preserve the chief merit
of this type of brick wall, great care should be taken, during
construction, that the 2-inch air space be not allowed to fill up
with mortar and brick chips.