Get Your House Right: Lintels
Openings in masonry walls may be spanned in two manners:
lintels or arches. Lintels, depending on the material, are most economically
used for shorter spans. Arches, because they are in compression and not
subject to bending or shear stresses, can span further. The visual expectation
for the size of the lintel is based on what was traditionally possible in
masonry construction, without hidden structure.
In Figure 1, the thin lintel is disturbing because, logically, it could
not support the weight of the wall above; and, although not structurally
flawed, the overhang is excessive. The lintel in Figure 2 is both thicker
than necessary for the span and does not have any overhang or bearing. Were
it not for hidden support, this lintel would slide into the void below like
Figure 3 shows a reasonable lintel. The height, to the nearest brick course,
is approximately 1/6 the width of the opening. This can also be calculated
by doubling the span in feet, and converting it to inches, i.e. a 3-inch
span would have a 6-inch lintel, (but for practical purposes, this would
probably be increased to 8 inches to align with the next brick course).
The overhang of the lintel in the wall is a minimum of 4 inches, or 1/2
the height of the lintel, whichever is greater.
Bad: Lintel not thick enough to visually support
the load above.
Bad: Lintels that do not overlap the span.
Good: The height of the lintel should be at least
1/6th the length of the span and overhang 1/2 the lintel height.
Marianne Cusato and Richard Sammons are architects
with Fairfax & Sammons Architects in New York. They are co-authoring
"Get Your House Right, A Builders Guide to Avoiding Common Mistakes
in Traditional Architecture" with Léon Krier, which will
include a compilation of drawings addressing many of the typical mistakes
made when designing, detailing and building traditional architecture.