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