PPT on Lintels in cavity walls

1. Cavity Walls
Lintels

2. Tutor Copy

3. Openings in brickwork
When openings are required in brick walls,
the brickwork above the opening will be
require some form of support.
Even though the brickwork may be bonded
correctly, the area immediately above the
opening will more than likely collapse
because of the loadings imposed from
above.

4. Openings in brickwork
If we consider an opening of any given size,
the area that is likely to collapse is roughly
in the shape of a 45˚ triangle directly above
the opening. However, if the opening is
inserted at a later date, the area that may
collapse can be encompassed within a 60˚
triangle directly above the opening.

5. Note:
The darkest bricks are the only ones that are likely to fall before a
lintel is installed into a wall previously constructed because of the
self corbelling effect of the bricks above. In theory the lintel
supports the weight of materials within a 60˚ triangle, plus any
superimposed floor or roof loadings.

6. Lintels
The constructional member inserted into a wall to
support a load above an opening is called a lintel.
A lintel may be a horizontal steel, concrete or stone
beam which spans over openings in walls and
supports the structure above it.
In early buildings a large timber beam or a large block
of stone would be used to support any imposed loads.

7. Modern lintels are made from either reinforced
concrete or galvanised steel or a combination of
both. These types of lintel are extremely strong and
can support masonry over considerable spans,
enabling large windows or door openings to be
installed without additional support.
The design of the lintel will determine the method of
construction required at lintel level.

8. Stresses imposed by loads
When loads are imposed upon a lintel, the
lintel will have a tendency to sag or bend at
its weakest point. Because the lower part of
the lintel is being stretched it will be in
‘tension’ while the top part is being
squeezed, and will be in ‘compression’.
In addition the lintel will be subjected at the
points of support (the side walls) where the
vertical loads are trying to sever the beam.

9. The imposed loads create stresses upon or
within any lintel, in particular at the top and
at the bottom, which may cause cracking
and failure. The size, shape and design of a
lintel must be such that it can overcome
these imposed stresses and loads.

10. Choosing a lintel
The function of a lintel is to bridge the gap above wall
openings and to carry the load of the brickwork or masonry
over the opening. The lintel will transfer the imposed loads
to the jambs of the opening.
To enable the lintel to fulfil its role correctly, it should not
bend or deflect under the imposed loading therefore it
should be constructed of a material with sufficient strength
to support the loads that are likely to be imposed.
The type of lintel used will depend upon the size of the
opening and the loads that it may be required to support.

11. The materials used for lintels can be:
• Stone.
• Brick (often supported on steel
or built as an arch).
• Concrete.
• Steel.

12. Stone lintels unfortunately, are not strong in
tension and can only be used for short spans, for
them to be used for greater spans, the size of the
lintel has to be increased making them very heavy
and costly. In older houses, stone lintels do not
support the full width of wall and timber lintels are
inserted behind them.
However, stone
lintels can be used
as a decorative
feature but they are
usually supported
on the inside by a
galvanised steel
lintel.

13. Brick lintels are used to make an integrated feature over
external openings, but they are not particularly strong and
are classed as non-loadbearing.
The most common form is a soldier arch which is a course
of bricks set on edge and has a flat soffit. Usually this type
of lintel is supported on a proprietary steel lintel of a design
and type that will support the brickwork above.
Alternatively the bricks can be supported on a strip of flat
or angled steel bar. The strength of a brick lintel can be
greatly improved by shaping it and building it in the form of
a curved arch.

14. Concrete lintels
When concrete is used as a lintel it can cope with the
compressive stresses but it CANNOT cope with the tensional
stresses. Concrete is strong in compression but weak in
tension.
The lintel designer will include steel reinforcement bars to
counteract these tensile stresses.
The steel reinforcement should be positioned 25mm from the
bottom of the lintel.
This will provide maximum resistance to the stresses but also
protect the steel from corrosion and possible damage by fire

15. Steel lintels
Galvanised pressed steel lintels are widely used for
internal and external openings.
There are various versions available: some are used
for brick and blocks while others can be used for
timber-framed construction. The version used for
cavity walls includes a tray that channels moisture to
the outer brickwork.
These lintels are light in weight, and some are
perforated to provide a key for a plaster finish. They
are also available in standard sections and lengths.
Heavyweight rolled steel joists, often referred to as
RSJs, are mainly used to span large openings, in
particular when large rooms are required or when
converting two rooms into one.

16. Steel lintels
Note:
A lintel must be of a suitable size and shape for
the job it has to do. The size should be derived
from calculations based upon the weight of the
materials used in the construction of the
building.

17. Calculations for specifying a lintel are
usually a job for a structural engineer.
However, there are tables relating to the
weight of materials used that are available
to establish the figures.
Local Building Control Officers can insist on
proper calculations submitted with a
planning application for building approval.