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Contents

Introduction

Section 1 Walls

Section 2 Floors

Section 3 Roofs

Section 4 Flat Roofs

Section 5 Windows and Doors

Section 6 Stairs

Section 7 Fire Prevention

Section 8 'U' Value Requirements


 

Description: This unit introduces the elements of the superstructure for a domestic building.

Author:  Gates MacBain Associates


Introduction

This unit looks at the construction of the superstructure of a dwelling.  The unit introduces you to the elements which go to make up the building.   

This unit can be approached by looking at each of the parts as separate elements or by looking at the way they all fit together.   

Guidance and links are provided under each of the headings below and you should ensure that you understand each of these. 


Section 1 Walls




Aims and Objectives

At the end of this section you should be able to:
  • State the requirements of a wall
  • Differentiate between solid and cavity walls


The purpose of a wall is to:   
  • Enclose space and provide shelter, security and privacy
  • Provide support for the upper floor and roof
  • Strength and stability – it must be able to withstand all loads applied to it with the structure or loads such as wind.
  • Provide resistance to the elements in that it should not be adversely affected by rain, snow, wind or sun and to be able to keep these from entering the building
  • Be aesthetically pleasing – it must be acceptable to the occupants and conform to local planning requirements
  • Be durable – it must be able to function for an acceptable measure of time without the need for excessive maintenance
  • Provide thermal insulation by keeping the occupants comfortable and be able to meet the requirements laid down by the Building Regulations
  • Sound insulation – resist the passage of sound within the structure
  • Fire resistance – maintain the integrity of the building for a sufficient length of time to allow the occupants to escape to a place of safety in the event of a fire

Types of Walls  

Walls fall into a number of types though the only ones we are going to look at in this unit are: 
  • Masonry - which can be:
    • Solid
    • Cavity                  
  • Frame  - you should be familiar with the method of construction of a timber frame.                                   
Other factors you should be aware of are: 
  • Bonds – the way bricks or blocks are laid so that the joints are staggered to improve strength and structural integrity.
  • Damp Proof Course membranes – used to prevent the ingress of moisture into the building.

Materials  

The material used for walls will be determined by: 
  • Structural type of building – if the wall is to be load bearing or non load bearing.
  • The requirements of the wall - the wall of a recording studio will need special emphasis on sound insulation; a building in an exposed position will need emphasis on weather exclusion and durability.
  • Availability - a shortage or long delivery date for certain materials may exclude their use if the building is required quickly.
  • Speed of erection - wet trades normally take longer to construct a building than dry construction.
  • Cost - this must not only consider the cost of the materials but also the cost of labour to construct the building.

Options 
  • Stone 
  • Brick
  • Block
  • Concrete
  • Timber
  • Glass
  • Metal,
  • Plastic. 



Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 5)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 5)



Self-Assessment Task


  • With the aid of drawings explain the difference between a solid and cavity wall and state their requirements in order to meet the Building Regulations.




Section 2 Floors




Aims and Objectives

At the end of this section you should be able to:
  • Show a construction detail for solid, pre-cast and timber floors.


You should now be able to find your way around the publications listed so see what you can find out about floors.  You will have the choice of the following pages to select from:
  • Timber
  • Ground bearing slabs
  • Pre-cast concrete
The books below provide good guidance with regard to the types of floor and the way they are constructed.



Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 6)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 4)




Self-Assessment Task

With the aid of drawings explain:  
  • Solid and pre-cast ground floors, how they are constructed and the measures taken to ensure that no moisture can gain entry to the building.
  • The design features of a timber suspended upper floor.





Section 3 Roofs




Aims and Objectives


At the end of this section you should be able to:
  • Explain the purpose and requirements of a roof and to produce an annotated drawing of a pitched roof.


This is the part of the building which spans the external walls at their highest point; as it is part of the external envelope it must be able to achieve certain performance requirements.                                                                     
Performance Requirements            
  • Weather exclusion.    The roof covering must be able to resist the effects of wind, rain, snow, sun etc. in order to protect the occupants of a building, their possessions, and the building itself.
  • Structural strength and stability. The means of supporting the roof covering must be strong enough to carry the weight of the covering and any imposed loads such as rain and snow; any workmen who may have to use the roof for maintenance, any storage vessels situated on the roof, and the effect of wind which can cause positive or negative pressures. 
  • Drainage.  All rain falling on the roof must be removed in the most direct way so as to prevent the building from becoming excessively wet.
  • Durability.   As the roof is the most inconvenient to gain access to, the coverings should not be affected by moisture, frost, atmospheric pollution, and other harmful agents which would cause a failure of the weather-exclusion properties or lead to heavy maintenance costs. Design must cater for the effects of thermal and moisture movement.
  • Thermal insulation.  Warm air being less dense than cold air, rises, therefore in a heated building the greatest amount of heat loss occurs through the roof, unless suitable precautions are taken.  The Building Regulations lay down a maximum coefficient of thermal transmittance for domestic roof construction so that the energy used for heating is not wasted.
  • Lighting and ventilation.  In large industrial buildings special measures may have to be taken to allow lighting and ventilation through the roof.
  • Fire resistance.  The roof must prevent the spread of fire from structure to another and maintain its integrity for sufficient period to allow the escape of the occupants.
  • Appearance.  This must harmonise with the surroundings in order to meet the requirements of the local planning authority. The Planning Authority will consider the shape of the roof, type and colour of covering.
  
Although there are a number of types of roofs which can be classified by shape, span or structural design we are only going to look at two in this unit: 
  • Pitched
  • Flat 
Pitched 

This is when the slope in any plane exceeds 10° to the horizontal. There are a number of types of pitched roof and these can be seen in the two books below.    

The make up of the roof is governed by the load and span, while the pitch may be determined by the type of covering that is to be placed over the timber carcass. 

The timber carcass may be formed in the traditional way or by trussed rafter and you should be aware of both of these types of construction, these can be seen in the books listed below.  You should also be aware of the terms used in roofing shown in the table below.  


Terms found in roofs  

 Eaves  lowest edge of a roof which overhangs the wall. Provides protection  and a surface to fix the rain-water gutter.
 Gable triangular part of the end wall of a building with a sloping roof.
 Pitch  slope of the roof given in degrees.
 Span  horizontal distance from the outsides of the wall plates.
 Ridge  the spine of the roof.
 Wall plate a bearing and fixing for the roof members, distributes the load over the supporting walls.
 Common Rafter main load bearing member which spans between the wall plate and ridge.
 Jack rafter functions as common rafter but span between wall plate and hip rafter, or ridge and valley member.
 Hip rafter  accepts the load from jack rafters and provides external angle for roof.
 Valley rafter as for hip rafter but for internal angle.
 Ceiling joist prevents the rafters from spreading and provides a fixing for the ceiling.
 Purlin  provides intermediate  support to rafters.
 Struts compression members, transferring loads from the purlin.
 Hangers and Binders provides support for the ceiling joists.
 Collar provides additional support and restraint. 

Coverings 

Pitched roofs can be covered with a number of materials these include slates, tiles,  corrugated sheets and thatch.     


Slates   

Slates are usually made from natural slate and cover many older buildings. They are a dense material which splits into thin sheets. There are a number of types which include:  
  • Welsh slate
  • Westmorland
  • Cornish
The slates are secured to the timber battens using nails for each slate. The nails are made of galvanised iron, zinc or copper. The length of the nail will depend on the thickness of the slate.   

The minimum pitch on which slates can be fixed is 25o. Slates are laid Double Lap.     


Double Lap Roofing   

Double lap roofing means that at any point of the roof there will always be two thicknesses of slate or tile covering that point. It will also be bonded so that no vertical joint is immediately above a vertical joint of the course above or below. In order to ensure that this requirement is maintained special tiles are required at verge, eaves, hip and valleys etc. Abutments are made water tight by means of flashings, and by the use of soakers fitted under the tiles. The lap will depend on the pitch of the roof and the exposure.   

Tiles are now a more economical type of covering and are widely used. There are two main types:   
  • Clay tiles. These are either hand or machine made. They can be plain, or interlocking, and come in a variety of profiles and colours.   
  • Concrete tiles.  Similar to clay tiles only made from concrete.       

Plain Tiling   

Plain tiles are laid double lapped as for slates. They should have a minimum pitch of either 45o for hand made tiles or 35o for machine made. Concrete tiles are cheaper than clay though are heavier which can mean larger roof members. 

The tiles have a slight camber to prevent water entering by capillary action. A variety of special tiles are available for hip, ridge and valleys. The tiles have a slight camber to prevent water entering by capillary action. 

A variety of special tiles are available for hip, ridge and valleys.     


Single Lap Roofing  

This consists of the tiles overlapping at head, base and side. The side lap is determined by the pattern of the tile, though the head lap should not be less than 75mm.  These can be used on pitches above 15°, with different types of patterns being used on different pitches.  
Tiles are nailed at eaves, hips and ridge and every 4th or 5th row up the slope of the roof.  




Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 5)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 6)




Self-Assessment Task

  • Produce annotated drawings to illustrate the construction of a pitched  roof.
  • Describe the installation of two possible types of covering that can be used for this type of roof.




Section 4 Flat Roofs




Aims and Objectives

At the end of this section you should be able to:
  • Produce an annotated drawing of a flat roof.


Flat roofs are the simplest and the cheapest form of roof which can be used on a dwelling, though they do require more maintenance over the years than  pitched roofs. 

Flat roofs consist of a standard base secured to the walls with a weatherproof covering.  


Decking 

This is the structural base which supports the waterproof covering. It can be either timber or reinforced concrete.  
  • Timber.  This is composed of decking supported by a system of beams. The system can be softwood joists, plywood or boxed beams, or latticed beams in metal or timber for larger spans. The size of the beam depends on the span. Firring pieces are fitted in order to give the decking the required fall. The decking can then be fitted to the beams, it can be softwood boarding, plywood sheets, wood-wool slabs, compressed straw or ribbed metal sheets.
  • Reinforced Concrete.   This is a concrete slab reinforced with mild steel the size and spacing of which depends on the span. The thickness is also proportional to the span. Precast concrete beams can also be used to form a base for a screed of 25 - 50mm which provides the top surface and fall.

Covering 

A number of options are available to provide a cover for flat roofs and you should check the resources listed in this section to determine the options and their requirements.
 

Other Factors 

You should be aware of the following, all of which are described in the books listed.
  • Terms & Materials
  • Felt & Batten
  • Slate
  • Plain Tiles
  • Single Lap Tiles
  • Flashings
  • Ventilation
  • Resources




Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 5)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 6)




Self-Assessment Task

  • Produce annotated drawings to illustrate the construction of a  flat roof.
  • Describe the installation of two possible types of covering that can be used for this type of roof.




Section 5  Windows and Doors




Aims and Objectives

At the end of this section you should be able to:
  • Explain and illustrate the different types of windows.


The purpose of a door is to allow people and objects to move in and out of the various parts of the building, whereas a window is to allow light into the building, provide a means of ventilation, and to allow the occupants visual contact with the outside world. 

The Building Regulations lay down certain requirements with regard to windows and ventilation. 


Types of Windows 

Windows consist of a frame of timber, metal, or uPVC which holds the glass unit in place. Windows may open to provide ventilation or they may be for light purposes only. 

There are a number of different types of windows and we will look at the following two: 
  • Casement 
  • Sash 
The weathering of windows is intended to prevent rain, sleet and snow entry; to stop water driven or drawn inwards by air pressure, or  capillary action, and to prevent draughts. The way this is achieved is to slope or rebate the surfaces, or to project the surface to carry the water clear.  

Drip grooving prevents the water from running back by surface friction and getting into the casement joints or from soaking the wall under the window. Check grooving prevents capillary action.   


Casement Windows 

These are hung by one edge which hinges to a solid frame. They can be hinged from the top, bottom or either side, and they may open inwards or outwards. It is easier to ensure weather proofing of windows which open outwards than inwards. 

Casements can also be horizontally centre or pivot hung which is useful for high rise buildings.   

A variety of fittings are available according to the type of window and its location.    


Sash Windows 

These may be spring balanced type, which have slim. cylindrical balance springs housed in grooves in the back edge of the sash stiles. 

Leaf spring type, which balance by friction against the pulley stiles.  

Weight balanced type, the frame of which is hollow at either side to enclose a metal balance weight. This type is the most common form in traditional construction.     

Consult the specified resources to ensure you understand the types and design features related to doors and windows.  




Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 5)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 7 & 8)




Self-Assessment Task

  • Produce an annotated drawing of a sash and casement window and explain the methods used to prevent the ingress of water into a building at this construction component detail.





Section 6  Stairs




Aims and Objectives

At the end of this section you should be able to:
  • Explain the requirements relating to stairways as specified in the Building Regulations.


The purpose of stairs is to provide access from one floor level to another and to provide a means of escape in the event of fire. 

They can be designed to go in a straight line or they can turn corners either by the use of tapered steps or by the use of landings.  


Terminology
 
Stairs - the means of moving from one floor to another
Stairwell - the space in which the stairs and landing are housed.
Tread - the upper surface of a step on which the foot is placed
Riser - vertical member between two consecutive treads
Step - riser plus tread
Nosing - the exposed edge of a tread
Going - horizontal distance between two consecutive risers
Rise - vertical height between two consecutive treads
Flight - series of steps without a landing
Newel - post forming the junction of flights of stairs with landings or carrying the lower end of strings
Strings - members receiving the ends of steps which are generally housed to the string and secured by wedges
Handrail - provide protection and run parallel to the string either attached to the wall or spanning between newels
Baluster - vertical infill members between a string and handrail
Balustrade - Consists of vertical balusters and handrail for protection to prevent falling from stairs or landing
Pitch line - a line connecting the nosings of all treads in any one flight  


These requirements apply if the stairway: 
  • is part of the means of escape from the building.
  • has a rise of more than 600mm.
  • has a drop at the side of more than 600mm.

You should consult the Building Regulations with regard to the requirements specified for the headings below. This can be done by visiting the specified website.  


Steepness of Stairs (Pitch)  

This is controlled by the rises and the goings, though limits of pitch are laid down, for
  • Private Stairs (Stairs used by only one dwelling)
  • Common Stairs (Stairs used by two or more dwellings)

Rise and Going 

In a flight of stairs, all steps should all have the same rise and the same going. You should visit the Building Regulations document on the website listed blow to obtain the current requirements.  


Headroom 

All stairways should have a clear headroom over the length and width of the stairway.   


Construction   

All treads should be level.   

If the stair has open risers the treads should overlap by at least 15mm and be constructed so that a 100mm sphere cannot pass through the open risers.     


Widths  minimum  unobstructed   

You should ascertain the requirements for:  
  • Private stairways to one room only (excluding kitchen or living room).
  • In all other cases.
  • Common stairways.

Length of Flights  
  • After every 16 risers there must be a landing.
  • After every 36 risers there must be a change of direction of at least 30o.
    
Handrails    

A stairway should have a handrail on at least one side if its width  is less than 1m, but on both sides if the width is over 1m. There is no need to have a handrail beside the bottom two steps.   

Handrails should be set at a specified height, measured from the pitch line or from the floor of the landing. They must be secure.   


Landings 

These should be provided at the top and bottom of every flight. The width and depth should be at least as great as the minimum width of the stairway. 

Parts of a floor can count as a landing. A door can swing across a landing at the bottom of a flight only if it leaves a minimum distance across the full width of the flight.   


Guarding 

Flights and landings must be guarded at the sides if there is a drop of more than 600mm. The means of guarding can be a wall, screen, railing or balustrade.                           




Websites




Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 6)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 9)




Self-Assessment Task

  • Explain the actual requirements for a stairway according to the Building Regulations.





Section 7  Fire Prevention




Aims and Objectives

At the end of this section you should:
  • Be able to describe the ways that fire can spread within a building and how the risk of this is reduced.


The design and construction of all building must consider its’ vulnerability in a fire. The purpose of the Building Regulations regarding fire is to prevent injury and loss of life to the occupants of a building and to the public generally, and not to safe guard property. Fire must be restricted from spreading to or from buildings and within the building for sufficient time to allow the escape of any persons in the building.  A number of factors must be considered in the prevention of the spread of fire as well as providing occupants with a means of escape should one occur.  


Internal Fire Spread  

The spread of fire within a building can be restricted if the elements of the structure have a specified minimum period of fire resistance. This includes the requirements to resist: 
  • collapse
  • fire penetration
  • transfer excessive heat
The Building Regulations lay down minimum periods of fire resistance, for a house up to four storeys the structural elements must have a minimum resistance of  half hour, though this is to be 1 hour for separating walls.  


Surfaces 

In order to prevent the spread of fire within a building, surfaces should have adequate resistance to the spread of fire and, when ignited, exhibit a rate of heat release reasonable to the circumstances.  


Structure 

A building shall be constructed so that in the event of fire, its stability is maintained for a reasonable period, sufficient to allow the escape of all occupants. 

The regulations advice the division of a building into compartments. 

Concealed spaces shall be sealed and divided, where necessary to prevent the unseen spread of fire or the passage of smoke. 

Walls common to two or more buildings must have adequate resistance to fire and smoke.  


Compartmentation

Fire hazard increases as the floor area/cubic capacity increases, since a larger area is capable of becoming engulfed with flames.  

If a building is divided into compartments, fire spread can be restricted by the use of fire resistant materials to form the walls, floor and ceiling of the compartment.      


External Fire Spread 

The external walls of a building and the roof shall provide adequate resistance to the spread of fire over the surface and from one building to another, having regard to its use and the siting of the building.  


Requirements 

The Regulations cover a number of purpose groups of buildings and each has its own requirements as to the minimum period of fire resistance. The groups are covered in different sections and a table is given in each section as to these periods.  

Section 1 deals with dwelling houses and table 1.1 on page 7 gives the minimum period of fire resistance for the elements of the structure.     


External Walls   

These must be constructed of materials of limited combustibility if over 3 storeys and/or less than 1m from the boundary, or over 15m high regardless of distance from the boundary.   

Certain restrictions are made on the use of external cladding, insulating material and internal surface materials, but these may be used if they are not relied upon to form part of the fire resistance.     


Separating Walls   

These are walls which are common to two or more buildings. They must have the same resistance as loadbearing walls with a minimum of 1 hour.       


Building Regulations   

The Building Regulations which relate to fire can be seen by visiting the Building Regulations website shown below.  



Websites




Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann (Part 5)
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell (Chapter 6)




Self-Assessment Task

  • Explain how the building regulations deal with the risk to a building with regard the spread of fire.




Section 8  'U' Value Requirements




Aims and Objectives

At the end of this section you should be able to:

  • Explain the requirements of the Building Regulations with regard to heat loss from buildings.


Thermal insulation standards are set in the Building Regulations, for all walls, floors and roofs which enclose a dwelling. It does not apply to sheds, stores and other exempt structures. 

The purpose of this part of the Regulations is to conserve energy. 

Heat is lost from a building either by the movement of air or through the material of the structure by way of conduction. 

Conduction will only occur in solids, as heat is conducted through the material by molecules of the material vibrating, the hotter the material the more the molecules will vibrate, causing other molecules to vibrate through the material. 

The amount of conductivity will depend on the material, as some materials are better conductors of heat than others, metals are good conductors, whereas timber is not. 

The density of the material also determines the conductivity, as air trapped in the material (air does not conduct heat well) will provide good insulating characteristics. 

Thermal Conductivity is expressed as the heat flow in watts per square metre of surface area of material, for a temperature difference of 1°C per metre thickness.   

The factors which effect the rate of heat loss from a building are:  
  • Type of material
  • Thickness of material
  • Temperature difference
  • Air movement over surface
Air will also form a film on the surface of the material which tends to insulate the wall surface from the warmer air, this is if the surface is smooth, as on internal surfaces. On the rougher external surface the wind causes eddy currents, whereby causing heat to be transferred at a higher rate. This form of heat transfer is by convection and is dependent on the velocity of the air passing over the surface, and on the roughness of the material. 

To prevent the loss of heat, materials which do not conduct the heat so easily ( less dense ) should be used, or additional insulation should be provided by the use of fibre glass, rockwool or other similar insulators.  

Air spaces in the form of a cavity between two skins of wall will also give the building a degree of insulation. 

The amount of heat in watts which is transmitted through one square metre of structure when the temperature difference at each side of the structure differs by 1°C, is  stated in W/m2 °C and is known as the thermal transmittance coefficient.  The thermal transmittance coefficient  for specific parts of the building is specified in the Building Regulations. The elements can have a lower value but must not have a higher one.  The lower the value the better the insulator. 




Websites




Publications

  • Chudley, R. and  Greeno, R. (2006) Building Construction Handbook, 6th edn. Oxford: Butterworth-Heinemann.
  • Emmitt, S & Gorse, C (2005) Introduction to Construction of Buildings, Oxford, Blackwell




Self-Assessment Task

  • List and explain the factors which affect the heat loss from a building.
  • List the current u-values for the main parts of the building structure.





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