Civil Engineering Reference
In-Depth Information
as strong as dense stone. With steel inside it, it will do
amazing things, like span a ceiling as beams or become
the hull of a boat.
Lay stone in mortar on the slab, just as you did on
your foundation footings. Build up solidly to floor
height or leave ducts for fresh air or an ash dump.
You may have built a pier to support the floor joist
sleeper end already (if any), or you may want to build
the whole fireplace first to floor level. I lay the slab,
then go up almost to floor level first, incorporating the
sleeper pier if any, with flashing separating it from the
masonry. Then I finish the fireplace after the house is
up and pretty well settled. Or I do the whole thing at
a later date.
Extend the slab well into the room for hearth foot-
ing. It can be less massive here, because it doesn't sup-
port the chimney. The hearth must extend at least 20
inches into the room, beyond the stone face of the fire-
place. I bring up stone, through a hole left in the floor,
to hearth level, then lay flagstones here for the hearth
into the fireplace, at which point I switch to firebrick.
The Firebox
If you don't plan to squeeze extra heat from a metal
heat box, build entirely of masonry. Bring the back of
the fireplace cavity up and forward with firebrick in a
slope or a curve to reflect heat outward. This back
should stop only about 10 inches from the front stone
wall, which is the lintel stone, and several inches (9 or
10 inches) above its lower edge. Here is where a
Cutaway side view of the fireplace. The smoke shelf is extremely
important to eliminate smoking. Flue tile is a building code require-
ment. The log wall above the mantel must be separated from the
flue opening with eight inches of masonry. The bottom edge of the
lintel must be at least nine inches below the damper.
This is the reinforced concrete footing slab to support the fireplace
and chimney. It should be at least one inch thick and twice the area
of the chimney it is to support.
