ARC 252.
2 Building Construction I
B. Arch II / II
CHAPTER SIX: WALLS AND PARTITIONS
CAVITY WALLS
A cavity wall is a construction made from two leaves or skins of the wall, with a space or a
cavity in between them. The wall is generally constructed from bricks or building blocks with
a 50mm gap in between. The choice of the material especially above DPC will be dependent
on durability, strength and appearance.
Purpose of Cavity
The main advantage of this wall is to prevent the penetration of moisture to the internal
surface and thereby possibly protect the internal (main / load bearing wall) from weathering
effects and to improve the insulation values.
Stability of Cavity Walls
Although, the cavity is not bridged in anyway, non corrosive metal ties are used to connect
the two skins of walls. As there is no definite bonding between wall thicknesses, the height of
the wall is restricted. Metal ties are embedded in the horizontal mortar joints. With the wall
ties, the cavity is nearly as stable as a solid wall of the same thickness.
Drying the Cavity
Airbricks can be used for ventilation purpose of the cavity, i.e. to allow moisture trapped in
the cavity to escape. Rain water in the cavity can also be drained off by narrow outlets or
weep holes below DPC placed at each third / fourth vertical joint between stretchers. This
practice should be applied only in very wet climate / environment conditions since there is
possibility of lowering up of thermal and sound insulation values of the wall.
Solid Filling of Cavity below Ground
The cavity wall below DPC or GL is usually filled with weak mix of concrete thus creating a
solid wall. This practice is more often followed to overcome the pressure of soil on two sides
which create a tendency for the wall to move closer towards each other. To achieve additional
strength, a 1 B wall can be used with cavity above.
Extent of the Cavity
Cavities usually start at about 150mm below DPC level and end up at the eaves level in case
of sloping roof or under copings in case of parapet walls. While at openings, cavities are
discontinued.
Cavity Wall Ties
Wall ties are used for the stability of the cavity wall and they must be of non-corrosive metal
protected from corrosion effects. There are mainly three types if wall ties which are:
galvanized iron twisted ties
fish tail end gives good bond to mortar and the twisted portion in the middle
prevents water to run to the inner wall / leaf
double triangle tie
laid with bend hanging down on cavity so that water will drip off
galvanized wire butterfly tie
laid with ends of wire in mortar
this wall tie may have tendency to allow mortar droppings in the cavity
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Spacing of wall ties
Intervals usually are
B. Arch II / II
900mm horizontally
450mm vertically
300mm vertically at openings
Constructional Precautions
bricks / blocks used to comply with requirements and properly bonded and solidly set
in mortar
the leaves must be tied width approved ties at approved spacing
the cavity should be greater than 50mm and less than 75mm in width at any level
the leaves are to be greater than 100mm in thickness at any level
mortar usually 1:4 / 1:6 (cement / sand)
the roof load partly supported by outer leaf
overall thickness - 225mm for any length and height up to 3.6m
cavity should be free from any droppings and no contact between leaves be there
except for wall ties or except at lintels / sills / slabs / roofs
masonry wall in stretcher bond for non-load bearing type
separate DPC is laid for the two wall leaves
Prevention of dampness in cavity Walls
Building regulation requires cavity to be carried 150mm below DPC and any bridging other
than wall ties is to be provided with suitable damp proof membrane to prevent passage of
moisture. At opening jambs, vertical jambs DPC treatment is advisable, unless other suitable
measures are taken.
Building regulation also requires DPC to be at least 150mm above highest adjoining GL or
paving to prevent moisture rising into building.
Advantages of Cavity Wall Construction
able to withstand driving rain from penetrating inner wall surface
gives good thermal insulation
no need of external rendering
enables use of cheaper and alternative materials for inner wall construction
a nominal 225mm cavity wall has a higher sound insulation value than a standard one
brick thick wall.
Disadvantages of Cavity Wall Construction
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B. Arch II / II
requires a high standard of design and workmanship and good supervision during
construction
the need to include vertical DPC to all openings
slightly expensive in cost than standard one brick thick wall
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MASONRY
Masonry may be defined as the construction of building units bonded together with mortar.
The building units may be stones, bricks or pre-cast blocks of concrete. When stones are used
as the building units, we have stone masonry. Similarly in brick masonry, bricks are used. A
composite masonry is a construction in more than one building units.
Masonry is used for construction of foundations, walls, columns and other similar
components of buildings. It performs functions such as:
supporting loads
subdividing spaces
providing thermal and acoustic insulation
affording fire and weather protection, etc.
Types of masonry
1. Stone masonry
2. Brick masonry
3. Hollow concrete block masonry
4. Reinforced brick masonry
5. composite masonry
Definition of terms used in masonry
1. Course:
horizontal layer of masonry units
thickness of units in single course is equal, also thickness of mortar joint is equal
2. Header:
bricks / stones so laid that the length of units is perpendicular to the face of the wall
3. Stretcher:
bricks / stones so laid that length of units is parallel to face of the wall
4. Header course:
course of brick / stonework showing only header
5. Stretcher course:
course of brick / stonework showing only stretcher
6. Bed:
lower surface of brick / stone in each course
7. Bond:
overlapping of brick / stones in alternative course so that no continuous vertical joints
are formed and individual units are fixed together
8. Quoins:
exterior angle / corner of wall
brick / stone facing quoins are brick or stone quoins
9. Face:
surface of wall exposed to weather
10. Back:
inner surface of wall
11. Hearting:
inner portion of wall between facing and backing
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12. Side:
surface of units in direction transverse to face and bed
13. Joint:
junction of adjacent units (bed joints, vertical joints, etc.)
14. Closer:
portion of brick cut in such manner that one long face remains uncut
closer is header of small units
15. Queen closer:
portion of brick obtained by cutting a brick length wise into two portions
16. King closer:
brick cut in such manner that the triangular piece between the center of one end and
the center of the other (long) side is taken out
17. Frog:
depression created on the top face of brick to prevent displacement
18. Toothing:
bricks left projecting in alternative courses
19. Lap:
horizontal distance between the vertical joints of the successive courses
20. Arris:
edge of brick
21. Racking back:
termination of the wall in stepped way
STONE MASONRY
Material used for stone masonry:
stone
mortar (lime, cement, mud, etc.)
Stones
igneous rock (granite)
sedimentary rock (sandstone, limestone)
metamorphic rock (marble, slate)
Classification of stone masonry
Depending upon the arrangements of stones, degree of refinement of used in shaping of
stones and finishing adopted, stone masonry can be classified as follows:
1. Rubble Masonry
2. Ashlar Masonry
1. Rubble Masonry
stone blocks are used either undressed or roughly dressed
has wide joints
Types of Rubble Masonry
a) Random Rubble (uncoursed)
roughest stone masonry
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b)
c)
d)
e)
f)
g)
h)
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stones are not uniform in size and shape and greater care is need while using them
it is required that the stone units adequately distribute the pressure over the maximum
area
long continuous vertical joints are avoided
liberal use of header for the proper transverse bonds
Random Rubble (built to course)
the method of construction is same as Random Rubble ( uncoursed), but the work is
roughly leveled up to form the courses
courses vary from 30 to 45cm in thickness
Square Rubble (uncoursed)
use of stones having straight beds and sides
stones usually squared
dressing of stones using hammer
use of riser stone large stone generally thorough
use of leveller thinner stones
use of snecks
Square Rubble (built to course)
units leveled up to courses
height of courses may vary
use of quoins, thoroughers
small stones in between quoins up to height of larger stones to complete course
Square Rubble (regular course)
height of stone in any course is always same
Polygonal Rubble Masonry
stones are finished on face, to an irregular polygonal shapes
face joints run irregularly in all directions
both rough picked and closed picked
Flint Rubble Masonry
masonry of flints or cobble stones
cobbles vary in width and thickness from7.5 to 15 cm
length from 15 to 30 cm
cobbles hard but brittle
masonry either coursed or uncoursed
strength increased by using lacing courses either of long stones or bricks at vertical
interval of 1 to 1.2 m
Dry Rubble Masonry
mortar is not used in joints between stones
requires more skill in construction
for non-load bearing walls, temporary compound walls and sheds, etc.
2. Ashlar Masonry
consists of stone blocks accurately dressed with extremely fine bed and end joints
blocks may either be square or rectangular
height of the stone blocks vary from 25 to 30 cm
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B. Arch II / II
height of the blocks in each course is equal but it is not necessary to keep all courses
of same height
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BRICK MASONRY
made of brick units bonded together with mortar, use of bricks and mortar
mortar may be lime mortar, cement mortar, mud mortar, etc.
use of factory made bricks
strength of brick work depends upon quality of brick, quality of mortar and methods
of bonding
Brick masonry is preferred over other types of masonry for following reasons:
1. All the bricks are of uniform size and shape, can be laid in definite pattern.
2. Brick units are light in weight, smaller in size and hence can be easily handled by the
bricklayers by hand.
3. Bricks need no dressing.
4. Even unskilled / semi-skilled masons can do brick work.
5. Easily available at all sites.
6. Light partition walls and filler walls can easily be constructed with brick work.
7. Easy ornamentation work with brick work.
Types of Bricks
1. Traditional Bricks
in Nepal, bricks like Ma Appa, Dachhi Appa (wedged shaped brick), etc.
bricks used in traditional buildings
also ornamental bricks with various motifs
2. Modular Bricks
standardized bricks
Nepalese modern bricks, Chinese fair faced bricks
Classes of Bricks
1. First Class Bricks
2. Second Class Bricks
3. Third Class Bricks
First Class Bricks
strictly confirm to standard sizes of modular bricks
manufactured from good quality plastic earth
have good uniform color
well burnt, hard ringing sound is emitted when two bricks are struck together
have straight edges and even surfaces
free from cracks, chips, flaws, etc.
when immersed in water for one hour, they do not absorb water more than 1/6
of their weight
no sign of efflorescence
Second Class Bricks
also confirm to standard size
slightly irregular in shape and color
also fully burnt, gives ringing sound
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when immersed in water for one hour, they do not absorb water more than of their
weight
Third Class Bricks
quite irregular in shape and size and finish
not fully burnt due to which they are reddish-yellow in color
low crushing strength
not used in quality B/W (brickwork)
Bonds in B/W
interlacement of bricks when they are laid
method of arrangement of bricks in courses so that individual units are tied together
and vertical joints of the successive courses do not lie in same vertical line
various bonds seen distinguish in elevation
unbonded wall has little strength and stability
helps in concentrating load over large area
Rules for Bonding
For proper bonding of B/W, it requires:
bricks of uniform size
length of brick be twice the width plus one mortar joint
amount of lap min. B along length of wall
min. B along the thickness of wall
less or no use of brick bats except in special cases
center line of header coincided with center line of stretcher in alternative courses
vertical joints along the same line in alternative courses
Types of Bonds
Following is the commonly used and popular types of brick bonds.
1. Stretcher Bond
2. Header Bond
3. English Bond
4. Flemish Bond
Stretcher Bond
all the bricks are laid as stretchers on the face of wall
length of bricks are along the direction of wall
used for B walls
used in partition walls
Header Bond
bricks are laid as headers on the face of wall
length of brick along the thickness of wall
overlap kept equal to width of brick
use of bats in alt. courses
used for 1 B thk. walls
no strength to transmit pressure in direction of length of wall
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B. Arch II / II
not suitable for load bearing wall
useful for curved B/W
used in construction of footing
English bond
most common, used for all thicknesses
alt. courses of headers and stretchers
queen closer to break vertical joints in successive courses in header course
strength in B/W
Flemish Bond
each course consist of alternative headers and stretchers
alt. course starts with header at corner
use of queen closer to develop lapping
every header supported centrally over the stretcher below
of two types:
o Double Flemish Bond
o Single Flemish Bond
Double Flemish Bond
each course has same appearance in both front and back face
alt. header and stretcher laid in each course
better appearance than English Bond
use of queen closer
use of and bats
Single Flemish Bond
consist of Double Flemish Band facing and English Bond backing
use strength of English Bond and appearance of Flemish bond
used for 11/2 B or thicker walls
COMPOSITE MASONRY
constructed out of two or more types of building units
used for improved appearance and economic use of material
common types of composite masonry:
o stone composite masonry
o brick-stone composite masonry
Stone Composite Masonry
combination of ashlar and rubble masonry
rubble as backing and ashlar giving pleasing appearance
should be made monolithic
should use thorough stones
both backing and facing should be constructed simultaneously
use of metal cramps to tie if necessary
Brick-stone Composite Masonry
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1. Brick backed ashlar masonry
ht. of ashlar twice the thickness of brick
alt. course ashlar header, stretcher
2. Brick backed stone slab facing
use of stone slab, tiles like marble stone
use of big panels
use of metal cramps
3. Rubble backed brick masonry
brick facing with rubble at the back
in case if stone is adequately available
HOLLOW CONCRETE BLCOK MASONRY
regular shaped and sized blocks
load transferred to foundation is reduced, because of less solid volume
great saving in material
blocks structurally stronger than bricks
no. of joints reduced saving mortar
hollow space results in better insulation against sound, heat and dampness
do not require plaster
thinner wall construction
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PARTITION WALLS
Partition walls are thin internal walls constructed to divide the spaces. They are usually thin
and light in construction and used to divide buildings into rooms, corridors, cubicles, etc. the
main function of any partition wall is:
division of space
insulation of heat and sound
privacy
fire protection
Partition walls can be both load bearing and non-load bearing but they are non-load bearing
in most of the cases.
Load Bearing Partitions
constructed of bricks, blocks or stones
requires foundation to transmit superimposed load
considered to be permanently positioned
Non-load Bearing Partitions
no need to have foundation for transmitting structural loading
constructed to carry out only their own weight
Requirements of good partition
should be thin as to utilize max. floor area
provide adequate privacy (sight/sound)
constructed of light, sound and strong and durable material
should be simple, easy and economical to construct
have fire heat ans damp resisting qualities dn be proof against insects/fungus attacks
should be strong enough to carry its own load, to resist impact
Timber Partitions
For any timber partition, the basic principle is to construct a simple grid of timber to which
dry lining such as plywood, plasterboards, etc can be attached. They are lighter than brick /
block partitions but less efficient as sound and thermal insulators. They are easy to construct
with proper fixing of members.
Construction
The vertical members called studs (quarters) are secured by two horizontal length of timbers
i. e. head and sole plates.
studs: 75 x 40, 90 x 45, 100 x 75, spaced at 350 600 C/C
ends of studs are housed 12mm deep into the head and sill
studs are stiffened by noggin pieces at vertical intervals of 900 to 1200 mm
noggings (100 or 75 x 50 or 38) fitted horizontally and tightly between studs to which
they are nailed
head is secured with nails to ceiling joists
sill is fixed to floor
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if necessary, provision of door openings are formed by forming a head between two
studs and fixing a door frame into the opening in stud partitions
Brick / block Partitions
built directly off the floor up to ceiling
usual wall thickness is 110mm
plastered on both sides
openings inserted in the walls
Other Partitions
glass block partitions
plaster boards
metal lath partitions
G. I. sheet partitions
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