lintel design and detailing
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Unlike arches, which carry
loads in compre s s i o n ,
beams and lintels act as
flexural members spanning
horizontally between supports.
Beams are primary supporting
members in a structure, but lintels
usually are smaller members span-
ning and carrying only the loads
immediately above window and
door openings. Whether they’re
made of steel, reinforced masonry,
stone, concrete, or wood, lintels
must resist compressive, bending,
and shear stresses.
Arching actionMasonry laid in running bond
c reates a natural corbeled arc h
( F i g u re 1). In fact, before tru e
masonry arches were invented, cor-
beled arches, vaults, and domes
w e re used to span openings too
l a rge for a single block of stone or
length of timber.
Lintels must be designed to carry
their own weight, plus the weight
of the masonry inside the triangle
formed by the line of arc h i n g
action. This triangular area has
sides at 45-d e g ree angles to the lin-
tel; there f o re, its height is one-h a l f
the span length (Figure 2). Outside
this area, the weight of the masonry
and any uniform loads from the
floor or roof above are assumed to
be carried to the supporting abut-
ments by natural arching. For this
assumption to be true, however, the
a rching action must be stabilized by
8 to 16 inches of masonry above the
top of the triangle.
If arching action cannot be
assumed to occur because of inade-
quate height above the load trian-
gle, or because the masonry is not
laid in running bond, the lintel
must be sized to carry the full
weight of the wall above it, includ-
ing that occurring outside the trian-
gle. When arching action is
assumed, the lintel re q u i res tempo-
rary support until the mortar has
c u red enough to allow the masonry
to bear its share of the load.
A rching action produces a hori-
zontal thrust at each abutment
Lintel design and detailingBase lintel design on loading and aesthetics, butalways detail to prevent cracks and leaks
By Christine Beall
Figure 1. Corbeled arch created by naturalarching action of running bond masonry.
Figure 2. Arching action above a lintel determines area of load. Figure 3. Concentrated load distribution.
( F i g u re 2). The abutments, there-
f o re, must have enough mass to
resist this force. If the opening is
near a corner or another opening,
or if a movement joint occurs at the
side of the opening, it also may be
necessary to size the lintel to carry
all of the loads above it, without
assuming any arching action in the
m a s o n r y.
Whether above or below the top
of the arching load triangle, c o n-
centrated loads are distributed as
uniform loads along the base of a
triangle whose sides are at
6 0-d e g ree angles to the lintel
( F i g u re 3).
Once the total load on the lintel is
known, it can be sized to resist the
calculated stresses. Deflection
should be limited to 1/600 of the
span to avoid cracking the masonry.
Lintel typesS t ructural steel shapes are com-
monly used to span openings in
brick masonry. Steel angles are the
simplest shapes and are suitable for
openings up to 8 feet wide, where
superimposed loads are no more
than 5,000 pounds per lineal foot.
For wider openings or heavier
loads, steel beams with suspended
plates can be used (Figure 4). Steel
angles should be a minimum of 1⁄4
inch thick. The horizontal leg
should be at least 1⁄2 inches wide to
support a nominal 4-inch wythe of
masonry adequately. The bearing
length at each end of the lintel
should be at least 4 inches.
Openings in concrete masonry
walls are spanned more commonly
with U-shaped lintel blocks, re i n-
f o rced with deformed steel bars
and grouted. Standard brick also
may be used to construct re i n f o rc e d
masonry lintels, even though they
do not have continuous channels
for horizontal steel. Reinforc e m e n t
can be added in bed joints or in a
widened and grouted collar joint
c reated by using half units (Fig. 5).
R e i n f o rced masonry lintels
should be the same width as the
wall they support, and should
have a minimum bearing
length of one half the unit
length. Design aids have been
developed and published in
technical notes by both the
Brick Institute of A m e r i c a
(BIA) (Refs. 1 and 2) and the
National Concrete Masonry
Association (NCMA) (Refs. 3,
4, and 5). These can be used to
select the appropriate amount
of re i n f o rcing steel for brick or
block lintels (see also “How to
Design Reinforced Masonry
L i n t e l s , ” Masonry Construction,
M a rch 1991).
Steel and timber industry design
manuals can be used to size lintels
of these materials. BIA Tech Note
31B (Ref. 6) also contains design
tables for the most common steel
lintel sizes. Design tables also may
be used for concrete, precast con-
c rete, natural stone, and cast stone
lintels. Of course, simple engineer-
ing analysis can be used in design-
ing lintels of any material. Some
p roprietary support systems also
p rovide flexural strength for
masonry lintels (see M a s o n r yC o n s t r u c t i o n, December 1991).
Steel lintels should be hot-d i p
galvanized for corrosion re s i s t a n c e .
Field cuts and welds should be
coated with a zinc-rich “galvaniz-
ing” primer. Exposed surfaces also
may be painted but will then
re q u i re periodic maintenance.
Accommodating movementBuilding movement must be con-
s i d e red in any type of constru c t i o n ,
and exterior walls are particularly
subject to diff e rential thermal,
m o i s t u re, and structural move-
ments. Walls built of homogeneous
materials generally experience less
d i ff e rential movement than those
combining dissimilar materials.
Interior walls also experience less
movement than exterior walls
exposed to diff e rent thermal and
m o i s t u re environments on opposite
s i d e s .
C o n t rol joints in concrete mason-
ry and expansion joints in clay
masonry usually are re c o m m e n d e d
adjacent to windows and doors
because walls are weakest at open-
ings and there f o re most vulnerable
to cracking from thermal and mois-
Figure 5. Reinforced brick lintels.
Figure 4. Steel lintels.
t u re movements. To be most eff e c-
tive, movement joints should sepa-
rate the masonry carried by the lin-
tel from that in the adjacent wall.
This ordinarily means locating
them at the end of the lintel.
In multistory buildings, sills and
lintels must be the same length in
o rder for the joints to align vertical-
l y. If sills and lintels are of unequal
lengths, some alternative detailing
is needed to align movement joints
with the opening and avoid an off-
s e t .
A piece of flashing placed under
the lintel bearing area pre v e n t s
bond between the steel and the
masonry and allows slippage to
occur without cracking. A b a c k e r
rod or bond-b reaker tape and
sealant should be used in the joint
at the front edge of the lintel
because mortar at this location will
crack and spall.
A l t e r n a t i v e l y, re i n f o rced masonry
lintels can be designed as continu-
ous bond beams across several
openings, allowing greater flexibili-
ty in the location of movement
joints away from the windows and
doors. Even in 4-inch veneer walls
carried on steel angle lintels,
installing joint re i n f o rcement in the
courses just above and below the
opening can strengthen the wall
section against movement cracks;
this way, control and expansion
joints can be placed in less notice-
able locations.
Thermal and moistureprotection
Since any opening in a wall is an
opportunity for a leak, moisture
p rotection at lintels is critical. In
walls constructed of single-wythe
c o n c rete block or thro u g h-wall hol-
low brick, only a thin face shell and
a correspondingly thin mortar joint
separate the interior of the wall
f rom rain and wind. Moisture that
penetrates the exterior face flows
down through the open
c o res of the units and
must be re d i rected back to
the outside just as it is in
cavity walls.
Flashing should be
located above re i n f o rc e d
masonry lintels as well as
steel lintels. In single-
wythe walls, there are sev-
eral ways to install flash-
ing. With standard units,
metal throughwall flash-
ing can be installed as
shown in Figure 6A. The
back leg of the flashing is
turned up to pre v e n t
water from flowing
t o w a rd the inside, and
weep holes or cotton
wicks can be used to drain
m o i s t u re. If the first
course of units above the
lintel is laid with face-s h e l l
bedding, the cotton wicks
should be spaced at 16
inches on center, extend-
ing upward through every other
c o re .
A m o re complicated but better
detail is shown in Figure 6B. Here ,
the flashing course is constru c t e d
with two 4-inch units so that the
flashing can be turned up between
them and then folded back to the
opposite face shell. The back edge
of the flashing should be folded to
Figure 6. Lintel flashing details for single-wythe masonry.
Figure 7. Lintel flashing details for masonryveneer walls.
p revent moisture from flowing
t o w a rd the inside.
F i g u re 6C shows the Flashing
Block1™ design developed by
N C M A re s e a rchers, with integral
weep hole slots and a reglet for the
back leg of the flashing. (Because
this is a new design, check avail-
ability before specifying Flashing
Block™.) Single-wythe clay mason-
ry walls can be similarly detailed,
as can walls with one-piece pre c a s t
c o n c rete or stone lintels. Unless
solidly grouted, single-wythe walls
generally are more suitable in drier
c l i m a t e s .
S i n g l e-wythe walls insulated only
with loose-fill perlite or vermiculite
will have a thermal bridge at the
flashing and lintel courses, where
the thermal resistance is lower than
the rest of the wall. In climates
w h e re high thermal resistance is
re q u i red, or where condensation of
m o i s t u re vapor may be a pro b l e m ,
higher performance is achieved
with continuous insulation located
at the inside face of the wall. When
re q u i red, vapor re t a rders should be
located on the warm side of the
wall. Air barriers also may be
re q u i red in some instances to mini-
mize condensation.
Masonry cavity and veneer walls
re q u i re that flashing at lintels
extend from the exterior face of the
masonry across the cavity and into
the backing wall. Where masonry
forms the backing wythe, the flash-
ing should be turned up and insert-
ed into a mortar joint (Figure 7A). If
the window or door frame bridges
the cavity, soft joints should allow
for any potential diff e rential deflec-
tion or shortening of the two
wythes. Air and vapor movement
also should be controlled care f u l l y
to prevent heat loss or condensa-
tion. Insulation in the
wall cavity should continue
below as well as above the flashing
to reduce thermal bridging.
W h e re masonry veneers are con-
s t ructed with wood or metal stud
backing walls, the back leg of the
lintel flashing should extend behind
the sheathing or be lapped under-
neath the building paper so that its
top edge is not exposed (Figure 7B).
Air and vapor movement also
should be controlled, but the exact
location and installation of air barri-
ers and vapor re t a rders may vary
slightly depending on enviro n m e n-
tal conditions and type of constru c-
tion. Generally, however,
f o i l-backed gypsum board is not
adequate because the joints cannot
be sealed.
Flashing should be turned up at
the end of lintels to form an end
dam, and all joints should be
lapped and sealed. If stainless steel
or copper flashing is used with gal-
vanized steel lintels, the
two metals must be isolated to
p revent galvanic corrosion. A p i e c e
of 15-pound, asphalt-i m p re g n a t e d
roofing felt provides the re q u i re d
separation.
References1. “Reinforced Brick Masonry, FlexuralDesign,” BIA Technical Notes on BrickConstruction, Number 1 7A, BrickInstitute of America, 11490 CommercePark Dr., Reston, VA 22091.2. “Reinforced Brick and Tile Lintels,” BIATechnical Notes on Brick Construction,Number 17H, BIA.3. “Concrete Masonry Lintels,”NCMA-TEK 25, National ConcreteMasonry Association, P.O. Box 781,Herndon, VA 22070.4. “Concrete Masonry Lintels,”NCMA-TEK 25A, NCMA.5. “Lintels for Concrete Masonry,” NCMA-TEK 81, NCMA.6. “Structural Steel Lintels,” BIA TechnicalNotes on Brick Construction, Number31B, BIA.Christine Beall is an architect and consul-tant in Austin, Texas, and a regular con-tributor to this magazine.
PUBLICATION #M930106Copyright 1993, The Aberdeen GroupAll rights reserved
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