Ebook Building construction handbook (Sixth edition): Part 2

5 SUPERSTRUCTURE

CHOICE OF MATERIALS
BRICK AND BLOCK WALLS
GAS RESISTANT MEMBRANES
ARCHES AND OPENINGS
WINDOWS, GLASS AND GLAZING
DOMESTIC AND INDUSTRIAL DOORS
TIMBER FRAME CONSTRUCTION
REINFORCED CONCRETE FRAMED STRUCTURES
FORMWORK
PRECAST CONCRETE FRAMES
STRUCTURAL STEELWORK
COMPOSITE TIMBER BEAMS
TIMBER PITCHED AND FLAT ROOFS
TIMBER DECAY AND TREATMENT
LONG SPAN ROOFS
SHELL ROOF CONSTRUCTION
RAINSCREEN CLADDING
PANEL WALLS AND CURTAIN WALLING
CONCRETE CLADDINGS
PRESTRESSED CONCRETE
THERMAL INSULATION
THERMAL BRIDGING
ACCESS FOR THE DISABLED

295


External Envelope—Choice of Materials
STAGE 1

Consideration to be given to the following :~
1. Building type and usage.
2. Building owner's requirements and preferences.
3. Local planning restrictions.
4. Legal restrictions and requirements.
5. Site restrictions.
6. Capital resources.
7. Future policy in terms of maintenance and adaptation.

296


Solid Brick Walls
Bricks ~ these are walling units within a length of 337Á 5 mm, a
width of 225 mm and a height of 112Á 5 mm. The usual size of bricks
in common use is length 215 mm, width 102Á 5 mm and height 65 mm
and like blocks they must be laid in a definite pattern or bond if
they are to form a structural wall. Bricks are usually made from
clay (BS 3921, BS EN 772-3 and BS EN 772-7) or from sand and
lime (BS 187) and are available in a wide variety of strengths,
types, textures, colours and special shaped bricks to BS 4729.

297


Brick Bonding—Principles
Typical Details ~
Bonding ~ an arrangement of bricks in a wall, column or pier laid
to a set pattern to maintain an adequate lap.
Purposes of Brick Bonding ~

1. Obtain

maximum

strength

whilst

distributing

the

loads

to

be

carried throughout the wall, column or pier.
2. Ensure lateral stability and resistance to side thrusts.
3. Create an acceptable appearance.

Simple Bonding Rules ~
1. Bond is set out along length of wall working from each end to
ensure

that

no

vertical

joints

are

above

one

another

in

consecutive courses.

2. Walls which are not in exact bond length can be set out thus …

3. Transverse
continue
width

of

or

cross

unbroken
wall

298

across

unless

by a face stretcher.

joints
the

stopped


Brick Bonding—English Bond
English Bond ~ formed by laying alternate courses of stretchers
and headers it is one of the strongest bonds but it will require
more facing bricks than other bonds (89 facing bricks per m2)
Typical Example ~

299


Brick Bonding—Flemish Bond
Flemish

Bond

~

formed

by

laying

headers

and

stretchers

alternately in each course. Not as strong as English bond but is
considered to be aesthetically superior uses less facing bricks. (79
facing bricks per m2)
Typical Example

300


Brick Bonding—Special Bonds

301


Brick Bonding—Stack Bond
Stack Bonding … the quickest, easiest and most economical bond
to lay, as there is no need to cut bricks or to provide special
sizes. Visually the wall appears unbonded as continuity of vertical

joints is structurally unsound, unless wire bed-joint reinforcement
is placed in every horizontal course, or alternate courses where
loading is moderate. In cavity walls, wall ties should be closer than
normal at 600 mm max. spacing horizontally and 225 mm max.
spacing vertically and staggered.

Horizontal stack bond

Vertical stack bond

Application … this distinctive uniform pattern is popular as nonstructural

infill

panelling

to

framed

buildings

and

for

non-load

bearing exposed brickwork partitions.
cavity wall ties at 600 mm max.

horizontal spacing and 3 courses
max. vertically
bed joints reinforced with
high tensile mesh woven
stainless steel wire in 25
or 75 m standard rolls

Reinforced stack bond

302


Brick Bonding—Attached Piers
Attached Piers ~ the main function of an attached pier is to give
lateral support to the wall of which it forms part from the base
to

the

top

of

the

wall.

It

also

has

the

subsidiary

function

of

dividing a wall into distinct lengths whereby each length can be
considered as a wall. Generally walls must be tied at end to an
attached pier, buttressing or return wall.
Typical Examples ~

Requirements for the external wall of a small single storey nonresidential building or annex exceeding 2.5 m in length or height
and of floor area not exceeding 36 m2 ~


Minimum thickness, 90 mm, i.e. 102.5 mm brick or 100 mm block.



Built

solid

of

bonded

brick

or

block

masonry

and

bedded

in

cement mortar.


Surface mass of masonry, minimum 130 kg/m2 where floor area
exceeds 10 m2 .



No lateral loading permitted excepting wind loads.



Maximum length or width not greater than 9 m.



Maximum height as shown on page 305.



Lateral

restraint

provided

by

direct

bearing

of

roof

and

as

shown on page 468.


Maximum of two major openings in one wall of the building.

Height maximum 2.1 m, width maximum 5 m (if 2 openings, total
width maximum 5 m).



Other small openings permitted, as shown on next page.



Bonded or connected to piers of minimum size 390Â 190 mm at
maximum 3 m centres for the full wall height as shown above.
Pier connections are with pairs of wall ties of 20Â 3 mm flat
stainless steel type at 300 mm vertical spacing.

303


Attached Piers
Attached piers as applied to 1/2 brick (90 mm min.) thick walls ~



Major

openings

A

and

B

are

permitted

in

one

wall

only.

Aggregate width is 5 m maximum. Height not greater than 2.1 m.
No other openings within 2 m.


Other walls not containing a major opening can have smaller
openings of maximum aggregate area 2.4 m2 .



Maximum of only one opening between piers.



Distance from external corner of a wall to an opening at least
390 mm unless the corner contains a pier.



The minimum pier dimension of 390Â 190 mm can be varied to
327Â 215 mm to suit brick sizes.

304


Small Non-Residential Buildings or Annexes
Construction of half-brick and 100 mm thick solid concrete block
walls (90 mm min.) with attached piers, has height limitations to
maintain stability. The height of these buildings will vary depending
on the roof profile; it should not exceed the lesser value in the
following examples ~

Note: All dimensions are maximum.
Height is measured from top of foundation to top of wall except
where shown at an intermediate position. Where the underside of
the

floor

slab

provides

an

effective

lateral

restraint,

measurements may be taken from here.

305


Brickwork—Jointing and Pointing
The appearance of a building can be significantly influenced by the
mortar finishing treatment to masonry. Finishing may be achieved
by jointing or pointing.
Jointing

…

the

finish

applied

to

mortar

joints

as

the

work

proceeds.
Pointing … the process of removing semi-set mortar to a depth of
about

20 mm

and

replacing

it

with

fresh

mortar.

Pointing

may

contain a colouring pigment to further enhance the masonry.
Finish profiles, typical examples shown pointed …

approx. 20 mm

Flush or bag rubbed

Keyed or bucket handle

Recessed

Weathered or struck
applied finish
of cement and
sand render

Overhung struck

Raked

Examples of pointing to masonry

Note:

Recessed

exposed

and

situations,

overhung

as

finishes

rainwater

can

should
be

not

detained.

be

encourage damage by frost action and growth of lichens.

306

used

This

in

could

Special Bricks
Specials … these are required for feature work and application to
various bonds, as shown on the preceding pages. Bonding is not
solely for aesthetic enhancement. In many applications, e.g. English
bonded manhole walls, the disposition of bricks is to maximise wall
strength and integrity. In a masonry wall the amount of overlap
should not be less than one quarter of a brick length. Specials
may be machine or hand cut from standard bricks, or they may be
purchased
relatively

as

purpose-made.

expensive

as

These

they

are

purpose-made

individually

bricks

are

manufactured

in

hardwood moulds.
1

cross joint

2

brick

1 brick

225 mm

112.5 mm

(215 mm)

(102.5 mm)
75 mm
(65 mm)

perpend

Pressed brick

Format size
arris

(actual size)

bed joint

frog or
indent

perforations

King closer
Extruded brick
1

stretcher

header face

2

face

1
4

brick

brick

Queen closer
Bevelled closer

1
4

1

brick

4

brick

1
2

3
4

bat or snap
header

bat

3
4

1

brick

2

brick

Standard bricks and cut specials
Ref.

BS

4729:

Specification

for

dimensions

of

bricks

of

special

shapes and sizes.

307


Purpose-Made Special Bricks
Brickwork

can

be

repetitive

and

monotonous,

but

with

a

little

imagination and skilled application it can be a highly decorative
art

form.

Artistic

potential

is

made

possible

by

the

variety

of

naturally occurring brick colours, textures and finishes, the latter
often

applied

as

a

sanding

to

soft

clay

prior

to

baking.

Furthermore, the range of pointing techniques, mortar colourings,
brick

shapes

and

profiles

can

combine

to

create

countless

possibilities for architectural expression.
Bricks are manufactured from baked clay, autoclaved sand/lime or
concrete. Clay is ideally suited to hand making special shapes in
hardwood

moulds.

Some

popular

formats

are

shown

below,

but

there is no limit to creative possibilities.

plinth header

plinth stretcher
102.5 mm wide

plinth wide-bed

plinth external

215 mm long

158 mm long

return

squint angle

angle brick

dog-leg brick

birdsmouth

cant

double cant

single bullnose

double bullnose

bullnose on end

bullnose mitre

single bullnose

double-headed

header

bullnose

(cow nose)

Purpose-made and special shape bricks

308


Special Bricks—Plinths
Plinths … used as a projecting feature to enhance external wall
appearance at its base. The exposed projection determines that
only frost-proof quality bricks are suitable and that recessed or
raked out joints which could retain water must be avoided.
Typical external wall base …

plinth

102.5

wide-bed

102.5
112.5

42

dpc
plinth

wide-bed

stretcher

stretcher

144.5

215

Alternatives
56
102.5

Corbel

…

a

projecting

verge

feature at higher levels of

a

building.

created
bricks

This

by
laid

may

be

using

plinth

upside

down

plinth

eaves

stretcher
plinth

with header and stretcher

header

formats maintaining bond.
For

structural

integrity,

the amount of projection
(P)

must

third

of

not
the

exceed
overall

one
wall

P

thickness (T). Some other

P<

types of corbel are shown
on the next page.

T
3

T

Corbel feature at junction of
eaves and verge

309


Special Bricks—Corbels, Dentils and Dog Toothing
Corbel
of

…

a

inverted

plinth,

generally

located

the

levels

higher

building

to

of

a

create

A

typical

is

quarter

detail

below

cut brick
projecting
courses

a

example

headers

window board

brick on edge

at

feature.
bonded

window sill

type

as

a

window

openings.

cavity wall

Corbelled sill
Dentil

Coursing

…

a

variation

on

continuous

corbelling

where

alternative headers project. This is sometimes referred to as table
corbelling.

alternate header

dentil course

Section

dentil
course

P<
P

T

T
3

Dentil course

Dog Toothing … a variation on a dentil course created by setting
the feature bricks at 45 .
toothed
course
set at 45°

cavity wall

Dog toothing
Note: Cavity insulated as required.

310

Solid Block Walls
Blocks

~

height

the

these

are

walling

dimensions

units

specified

exceeding

for

bricks

in
in

length,
BS

width

3921.

or

Precast

concrete blocks should comply with the recommendations set out
in BS 6073-1 and BS EN 772-2. Blocks suitable for external solid
walls

are

classified

as

loadbearing

and

are

required

to

have

a

minimum average crushing strength of 2Á 8 N/mm2.
Typical Details ~

Refs. BS 6073-1: Precast concrete masonry units.
BS EN 772-2: Methods of test for masonry units.

311


Cavity Walls
Cavity Walls ~ these consist of an outer brick or block leaf or skin
separated from an inner brick or block leaf or skin by an air space
called a cavity. These walls have better thermal insulation and
weather resistance properties than a comparable solid brick or block
wall and therefore are in general use for the enclosing walls of
domestic buildings. The two leaves of a cavity wall are tied together
with wall ties at not less than the spacings given in Table 5 in Approved
Document A … Building Regulations (see below).
The width of the cavity should be between 50 and 75 mm unless
vertical twist type ties are used at not more than the centres
given in Table 5 when the cavity width can be between 75 and
300 mm. Cavities are not normally ventilated and should be sealed
at eaves level.

* Note: Stainless steel or non-ferrous ties are now preferred.

312


Cavity Walls

313


Parapet Walls
Parapet ~ a low wall projecting above the level of a roof, bridge
or balcony forming a guard or barrier at the edge. Parapets are
exposed to the elements on three faces namely front, rear and top
and will therefore need careful design and construction if they are
to be durable and reliable.
Typical Details ~

314


Masonry Fin Walls
Historically, finned or buttressed walls have been used to provide
lateral
as

support

churches

principle

and

and

to

tall

single

cathedrals.

include

storey

Modern

theatres,

masonry

structures

applications

gymnasiums,

are

such

similar

warehouses,

in

etc.

Where space permits, they are an economic alternative to masonry
cladding of steel or reinforced concrete framed buildings. The fin
or pier is preferably brick bonded to the main wall. It may also be
connected with horizontally bedded wall ties, sufficient to resist
vertical shear stresses between fin and wall.
external cavity wall

alternate
courses
bonded

wall ties at
appropriate
intervals
to resist shear
forces (max.
every 4th course)

fin

BONDED FIN WALL

fin

TIED FIN WALL

Structurally, the fins are deep piers which reinforce solid or cavity
masonry walls. For design purposes the wall may be considered as
a series of `T' sections composed of a flange and a pier. If the wall
is

of

cavity

construction,

the

inner

leaf

is

not

considered

for

bending moment calculations, although it does provide stiffening
to the outer leaf or flange.
wall ties at
standard spacing

flange

'T' section
fin or
pier
flange width
= fin spacing
spacing of fins

depth
of fin

width of
fin

FIN WALL AS A STRUCTURAL 'T' SECTION

315


Masonry Diaphragm Walls
Masonry diaphragm walls are an alternative means of constructing

tall, single storey buildings such as warehouses, sports centres,
churches, assembly halls, etc. They can also be used as retaining
and boundary walls with planting potential within the voids. These
voids may also be steel reinforced and concrete filled to resist the
lateral stresses in high retaining walls.

'I ' section

box section

cavity or
void

Plan

masonry cross rib

A diaphragm wall is effectively a cavity wall where the two leaves
of masonry are bonded together with cross ribs and not wall ties.
It

is

stronger

than

a

conventionally

tied

cavity

wall

and

for

structural purposes may be considered as a series of bonded `I'
sections

or

box

sections.

The

voids

may

be

useful

for

housing

services, but any access holes in the construction must not disturb
the

integrity

of

the

wall.

The

voids

may

also

be

filled

with

insulation to reduce heat energy losses from the building, and to

prevent air circulatory heat losses within the voids. Where thermal
insulation standards apply, this type of wall will have limitations
as the cross ribs will provide a route for cold bridging. U values
will increase by about 10% compared with conventional cavity wall
construction of the same materials.

Ref. BS 5628-1:

Code of practice for use of masonry. Structural
use of unreinforced masonry.

BS 5628-3: Code of practice for use of masonry. Materials
and components, design and workmanship.

316


Damp-proof Courses and Membranes
Function ~ the primary function of any damp-proof course (dpc) or
damp-proof membrane (dpm) is to provide an impermeable barrier
to

the

passage

of

moisture.

The

three

basic

ways

in

which

damp-proof courses are used is to:1. Resist moisture penetration from below (rising damp).
2. Resist moisture penetration from above.
3. Resist moisture penetration from horizontal entry.
Typical Examples ~

317


Materials for Damp-Proof Courses (1)
Building Regulations, Approved Document C2, Section 5:
A

wall

may

be

built

with

material, engineering bricks

a

`damp-proof

or

course

of

bituminous

slates in cement mortar, or

any

other material that will prevent the passage of moisture.'
Material
Lead

Remarks
BS EN 12588

Code 4 (1Á 8 mm)

May corrode in the
presence of mortar.
Both surfaces to be
coated with bituminous
paint. Workable for
application

to

cavity

trays, etc.
Copper

BS EN 1172

0Á 25 mm

Can cause staining to
adjacent masonry.
Resistant to corrosion.

Bitumen

Hessian or fibre may

BS 6398

decay with age, but this

in various

will not affect efficiency.

bases:
Hessian

3Á 8 kg/m2

Tearable if not

Fibre

3Á 3 .. ..

protected. Lead bases

Asbestos

3Á 8 .. ..

are suited where there

Hessian & lead

4Á 4 .. ..

may be a high degree of

Fibre & lead

4Á 4 .. ..

movement in the wall.

LDPE

BS 6515

0Á 46 mm

(polyethylene)

No deterioration likely,
but

maybe

difficult

to

bond, hence the profiled
surface finish. Not
suited under light loads.
Absorbs movement well.

Bitumen polymer
and pitch polymer

1Á 10 mm

Joints and angles
made with product
manufacturer's adhesive
tape.

Polypropylene BS 5319

Preformed dpc for

1.5 to 2.0 mm

cavity trays, cloaks,
direction changes and
over lintels.

Note: All the above dpcs to be lapped at least 100 mm at joints
and adhesive sealed. Dpcs should be continuous with any dpm in
the floor.

318


Materials for Damp-Proof Courses (2)
Material

Remarks

Mastic

12 kg/m2

BS 6925

Does not deteriorate.

asphalt

Requires surface
treatment with sand or
scoring to effect a
mortar key.

Engineering

BS 3921

bricks

<4Á 5%

Min. 2 courses laid

absorption

breaking joint in
cement mortar 1:3.
No deterioration, but

may not blend with
adjacent facings.

Slate

BS EN 12326-1

4 mm

Min. 2 courses laid as
above. Will not
deteriorate, but brittle
so may fracture if
building settles.

Refs:
BS 743: Specification for materials for damp-proof courses.
BS 5628: Code of practice for use of masonry.
BS 5628-3: Materials and components, design and workmanship.
BS 8215: Code of practice for design and installation of dampproof courses in masonry construction.
BRE Digest 380: Damp-proof courses.

Note:

It

was

not

until

the

Public

Health

Act

of

1875,

that

it

became mandatory to instal damp-proof courses in new buildings.
Structures

constructed

before

that

time,

and

those

since,

which have suffered dpc failure due to deterioration or incorrect
installation,

will

require

remedial

treatment.

This

could

involve

cutting out the mortar bed joint two brick courses above ground
level in stages of about 1 m in length. A new dpc can then be
inserted

with

mortar

packing,

before

proceeding

to

the

next

length. No two adjacent sections should be worked consecutively.
This

process

is

very

time

consuming

and

may

lead

to

some

structural settlement. Therefore, the measures explained on the
following two pages are usually preferred.

319