BUILDING CONSTRUCTION

1. S.S.A.S.I.T, SURAT GTU

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3. Cavity wall
• A cavity wall or hollow wall consists of two
separate walls, called leaves or skins, with a cavity
or a gap of 5 to 10 cm between them. Two leaves
of a cavity wall may be of equal thickness or
unequal thickness.
• In case of non load bearing walls the two leaves
of cavity are made of equal thickness. In case of
load bearing walls the internal leaf may be made
thicker than the external leaf to meet the
structural requirements.

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7. • The outer wall known as outer leaf , consist of
10 cm. thick and the inner wall is more thick and
strong to carry the impact load safely.
• The two walls or leafs are tied together with
metallic cotta ties to obtain structural stability.
• They are spaced at 90cm. Apart horizontally
and 30 cm to 45 cm. apart vertically staggered
position.
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8. Advantages of cavity wall
1. The direct moisture cannot travel inside the
building, as there is no direct contact between the
inner and outer leaves.
2. The cavity between the two leaves is full of air
which is bad conductor of heat. Hence
transmission of heat from external face to the
inside the room is very much reduced. Cavity walls
have about 25% greater heat insulating value than
the solid walls.
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9. 3. They have good sound insulation property.
4.They are economical.
5. The nuisance of efflorescence is very much
reduced.
6. Loads on foundations are reduced because of
lesser solid thickness.
7. As the walls are having cavity inside the loads on
the foundation are reduced.
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10. Brick cavity walls
• The cavity walls for flat and inclined roofs. In
case of brick cavity wall, each leaf is half brick
thick. This type of walls are capable of taking
load of two storied residential buildings. The
cavity between two leafs are tide may very from
40 mm to 100mm in width.
• The inner and outer leafs are tide together
with metallic wall ties , spaced at 90 cm. apart
horizontally and 30to 45cm apart vertically in
staggered position. 10

11. • The cavity should start near the ground level
and ends near the eaves level in case of
sloping roof or near the coping in case of flat
roof with parapet wall.
• The cavity should start 15 cm. Blow the damp-
proof course level so that the condensed
moisture below the level of DPC can be drained
out.
• The bottom of cavity should be at least 15 cm.
above the outside ground level, so that entry of
moisture can be prevent. 11

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13. POSITION OF CAVITY AT FOUNDATION
LEVEL
 At foundation level, the various alternatives are
adopted in the provision of cavity. In fig. A the cavity
extends up to the base of the footing, of the footing,
with damp proof course introduced just below the floor
level. This is the more common arrangement.
 However, if the brick work below G.L. is not carefully
constructed, water will enter through the joints, collect
in cavity and travel through inner leaf, causing
dampness in the flooring.
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15.  In such case The portion of the cavity between top of
the foundation concrete and the G.L. be filled with 1:2:4
concrete at least 150 mm below D.P.C (fig.B).
 Alternatively the cavity may be provided up to ground
level 150 mm below DPC (fig.C). In both cases Separate
D.P.C. is provided for both the leaves.
 Rain water gaining access to the cavity through the
outer leaf, and collecting in the cavity may be drained
off by the provision of narrow outlets or weep holes.
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18. POSITION OF CAVITY AT PARAPET
LEVEL
 In the case of flat roofs, with a parapet, the cavity may
extend either up to the bottom of coping or up to a
level slightly above the flat roof.
 When the cavity extends up to the bottom of coping,
D.P.C. course is provided between the bottom of coping
and top of cavity, so that rain water does not enter the
cavity.
 In case of sloping roof ,the cavity is extended up to or
near the eaves level.
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20. POSITION OF CAVITY AT OPENINGS
• At the door or window openings, the
constructional treatment given to the cavity
wall requires special considerations.
• At the sill level, it is always advantage to keep
the back of the sill flush with the back face of
the external wall.
• At the top of openings of doors and windows,
stone or brick arch or concrete lintel is provided
to carry the loads from the structure above the
opening.

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22.  Wall ties are mostly mild steel thoroughly galvanised or
dipped in hot tar and sanded to protect from rust.
Stainless steel is used now used.
 These are various patterns; the washer shown is to hold
insulation boards in position against the inner leaf.
 These ties must be placed at distances not exceeding 900
mm horizontally and 450 mm vertically, and should be
staggered.
 Ties must be placed at 300 mm vertical intervals at all
angles and door and window jambs to increase stability.
Wall Ties
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24. Wall Ties
There are a large variety
of different types of wall
ties, but they all have two
basic requirements of:-
(a) Tieing the outer and inner
leaf of the cavity wall
together.
(b) Prevent moisture passing
from the outer to the
inner skin of brickwork.
Most wall ties are currently
made from stainless-steel or
nylon.
Stainless-steel wire
wall tie with plastic
disc to hold sheet
insulation in place.

25. Spacing of wall ties
Mortar droppings must not be allowed to accumulate on wall ties because this
would form a bridge for water to pass from the outer to inner leaf.

26. Precautions during cavity wall
construction
1.The contact between the inner leaf and the
outer leaf should be the least.
2. The half brick thick leaf of cavity wall should be
constructed with stretcher bond.
3. The D.P.C. should be laid separately for both
leaves.
4. The bottom most horizontal D.P.C. should be
laid at least 150 mm above the bottom of the26

27. 5. Wall ties should be strong and rust proof.
6. The bottom of cavity should be well-ventilated
by use of air bricks or ducts.
7. To prevent the entry of moisture, the bottom of
cavity should be kept 150 mm above the
outside ground level.
8.The cavity wall should be properly drained by
providing weep holes immediately below the
main horizontal D.P.C.
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9. Wall should be constructed with greater care so
that mortar droppings or brick rubbish etc. do not fall
inside the cavity.
10. Special attention should be put to see that the
rats, vermin's or mosquitoes do not find access to the
cavity.
11. The doors or window jambs should be build solid
by means of headers which should be either of
precast concrete slab or brick headers. The lintel
should cover full width of the wall and the bearing of
lintel should be sufficiently strong and solid.

29. 12. The top of cavity may be built of at least two solid
courses of bricks.
13. Two leaves of the wall should be raised
simultaneously and uniformly. The position of wall
ties should be predetermined so as have uniform
spacing, preferably in centers.
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