Transcript Walls File - NPTC Moodle

External Walls
Carl James
Here we look at the external walls of a typical modern
dwelling – often known as a ‘domestic construction’. While
this form of construction is very traditional, modern
materials are now widely used to improve the performance
of the wall.
In particular, there has been a vast improvement in the
insulation incorporated into new buildings.
Functions of an external wall
Structural In most domestic construction, cellular techniques
are used – your own home is likely to be of this type. (see
next Slide)
Here the walls act structurally to transfer loads to the
foundations from the floors and the roof, as well as the
superimposed loads from the users of the building. The
diagram below shows how loads are distributed through a
building down to the foundations.
Weather protection
A major function of
the external wall is
to provide
protection from
wind, rain and snow.
This is achieved in
three ways:
Thermal insulation
The Building Regulations require all buildings to be well insulated: for
example, external walls should have a U-Value of 0.35 W/m²/°C.
This is normally achieved by fitting insulation into the wall cavity, either as a
partial fill (where an air space is maintained) or a full fill (where the entire
cavity is filled with insulation). An alternative, or additional, method is to use
insulation blocks.
These have insulating properties, through the use of a lightweight aggregate,
aeration (where air bubbles are introduced into the concrete) or by the
inclusion of insulation such as polystyrene or fibreglass.
Sound insulation
The wall must prevent excessive transfer of
sound from the outside of the building,
e.g. traffic noise from a busy road.
The most effective way do to this is by
using dense materials, such as concrete
blocks.
Security
The external walls
of a building
provide security
against burglary
and unwanted
intruders.
Lighting
Most walls in traditional
construction do not allow the
transfer of light.
However, in modern construction,
glazing systems and curtain walling
mean that, in some buildings, the
external wall can have the function
of providing natural light.
Superimposed loads – the load applied to a
structure: for example, the weight of furniture
or items stored in the building, or the load
imposed by snow on the roof
Curtain walling Job – a glazed cladding system
used on some high rise structures
Openings in external walls
Head
The head is the part of the opening, such as a door or window, that has the
task of supporting the load of brickwork above it.
As well as carrying the load, the head has to transmit the load to the jambs at
the sides. Lintels or beams are used for the construction of such heads.
Different types of material are used depending on the type of opening
involved.
Jamb
This is the vertical part of the wall opening. On a single door or
window opening, one side is known as the hanging jamb, and
the other is the closing or shutting jamb.
There are several different types of jamb treatment, depending
on the type of wall. On a solid wall, the jambs are bonded to
give them their shape and strength; in cavity walls, the area
where the opening is can be closed by a timber frame,
incorporating a damp-proof course (DPC) (PTO)
as required by the Building Regulations. The detailing of the
vertical DPC, cavity closure and insulation is particularly
important. If this is not done correctly, ‘cold bridges’ could
be created, and moisture or damp could penetrate.
On the next slide are some examples of what jamb
treatments to openings might look like.
Arches
An arch is made from special types of brick called voussoirs.
These bricks are wedge-shaped, designed to support each other and
carry a load over an opening. However arches can also be constructed
from standard bricks where the radius of the curvature is quite loose.
When an arch is being constructed, it is important that the arch is
given a temporary support until the mortar is set and arch is able to
carry its own weight.
Sills
Look at any window or door, and you will see that
it has a piece of material below it – plastic,
concrete or timber. This material is shaped to
allow rainwater to run off, away from the opening.
This is called a sill or threshold. It does not have to
carry any load, but is simply there to get rid of the
rainwater that runs down the surface of the door
or window.