Domestic Construction

Construction Management

Domestic Construction

Introduction

Welcome to this Higher National Unit. The unit is a 1 credit unit at SCQF 6. The unit covers most aspects of house building construction.

The content of this unit includes the following:

  • Timber frame and masonry wall construction and finishes;
  • Performance requirements and materials used to construct Doors, windows, stairs;
  • Types of floor construction and performance requirements; and
  • Types of pitched and flat roof construction and their finishes/coverings.

This unit has 4 outcomes. This learning pack will take you through each outcome in sequence and at the end of each outcome there will be a question and answer section to check your understanding before moving on to the next outcome.

When you have completed the work of all 4 outcomes, you will then be prepared to undertake the formal assessment for the unit.

I hope you enjoy your study of this unit.

Section 1

External Wall Construction

Introduction

External wall construction for houses is split into two categories:

  • Traditional Masonry Construction
  • Timber Frame Construction

Traditional masonry construction uses two masonry walls with a space between them, known as a cavity. Many pre-1940 buildings were constructed using solid masonry walls (no cavity) but modern buildings will have a cavity incorporated.

Traditional masonry cavity walls are built from combinations of brickwork, blockwork and/or stonework, bedded in mortar, with brick/block and block/block the most common forms of construction for domestic housing.

External Wall Construction

External Walls

External Walls

Traditional masonry external walls of cavity construction. Cavity walls were originally designed to provide an airspace that would reduce dampness from the external face to the internal face of the external wall by providing a break in continuity of solid materials to reduce damp penetration across the wall.

This also helped improve the thermal performance of the wall, particularly when lightweight concrete blocks were used as the external leaf.

As insulation standards have improved over the years, it is likely that modern cavity masonry walls will have insulation incorporated within the cavity and use concrete blocks with good thermal properties to achieve the required standard.

External Wall Construction

Masonry Walls

Masonry walls 1
Masonry walls 2

External Wall Construction

Cavity walls

Cavity walls gain structural stability through:

  • Wall ties; and
  • Lateral restraint.

External Wall Construction

Wall ties

Wall ties ensure that the separate leafs of the wall act together in the distribution of loads and prevent the spreading of the walls.

Wall ties should comply with BS 5628-1:2005 & BS 5628-6.1:1996 which describes butterfly, vertical twist and double triangle ties shown below:

Wall ties

There are many variations of wall ties shapes and styles, including those used for supporting rigid board insulation within the cavity. Materials used include galvanised steel, aluminium, nylon and pvc. Wall ties are also used for timber frame inner leaf cavity walls to tie with the masonry external leaf.

External Wall Construction

Lateral Restraint

Lateral Restraint

Lateral restraint provides stability to the external cavity walls by tying the structural elements together, i.e. the floors and roofs with the external wall as shown in fig.

External Wall Construction

Cavity wall insulation

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External walls require thermal insulation to comply with Building Regulations and to ensure that heat losses are reduced to minimum standards.

The insulation may be located on the exterior face, within the cavity as complete fill or partial fill or alternatively on the inner surface as part of the dry lining system.

It is very common to locate the insulation within the cavity whilst retaining an airspace, this is known as partial cavity fill.

See diagram.

External Wall Construction

Junctions

Junctions

The external wall may constructed from the foundation to ground floor level as a solid wall using trench blocks or as two leaves of the cavity wall. Where two leaves are used, the cavity should be filled with a weak concrete up to ground level.

This will provide increased resistance to ground pressures and prevent the cavity being filled with seeped ground water.

See diagram.

External Wall Construction

Junctions (cont.)

Junctions

The external wall continues from ground floor level to intermediate floor level at which point the upper floor is tied to the inner leaf to provide lateral restraint, as shown in the diagram opposite for joists running parallel with the wall. Joist hangers are built into the wall where joists are at right angle to the wall.

External Wall Construction

Junctions (cont.)

When the wall reaches roof level the cavity will normally be closed at this point and the roof and wall are tied together to provide further lateral restraint.

See diagram.

Eaves

External Wall Construction

Openings

Openings

Openings are required in external walls for doors and windows. It is very important that the opening is supported at the top of the opening by a lintel (or lintels) of sufficient strength to support the load immediately above.

It is also very important that water ingress is prevented around openings by good design and construction.

Click here to see types of openings.

External Wall Construction

Timber Frame

Timber frame construction for external walls of houses commands around 90% of the market share in Scotland. Timber frame construction offers advantages, such as, lightweight construction, improved quality control due to 'off site' fabrication and quicker erection time.

Timber frame construction entails the inner leaf being constructed of timber and the outer leaf constructed of masonry. See diagrams.

The inner leaf of timber frame is the loadbearing leaf and, therefore, it must be of sufficient strength to carry the load from intermediate floors and the roof. The two leaves of the external wall gain increased strength and stability by being secured together using wall ties.

Click on the image on the right to see a range of timber frame diagrams.

External Wall Construction

Timber Frame (cont.)

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The detail below shows a typical timber frame external wall detail (timber studs are more often a nominal thickness of 150mm to accommodate thermal insulation).

External Wall Construction

Wall finishes

The external wall finishes to the masonry external leaves of both traditional and timber frame construction normally consist of:

  • Facing brick
  • Cement Render (smooth, or pebble dashed)
  • Decorative Stone

External Wall Construction

Facing Brick

Facing bricks provide a natural decorative finish to the external wall without the need for render. There is a wide range of facing bricks available in a variety of colours and textures.

Pigment is used within the mortar mix to provide a colour to the mortar that will compliment the facing brick colour.

Timber Frame

External Wall Construction

Render

What is render?

Renders are surface coatings, usually based on a mixture of sand, cement and lime with the addition of either chemicals or aggregate.

In certain cases renders contain additives such as resin or binders. Rendering involves the application of layers of mortar applied to the face of the wall. In most cases this will include the base coat and the finishing coat.

The choice of render will depend upon:

  • the degree of exposure;
  • the appearance required;
  • the presence of any pollutants; and
  • the nature of the backing material.

External Wall Construction

Render (cont.)

Types of the finish

1. Dry dash/Pebble dash

These give a rough finish of exposed pebbles or crushed stone graded from 6 to 13mm and are produced by throwing the aggregate on to the surface of the freshly applied coat of mortar. In some cases the aggregate can be lightly pressed into the mortar to improve bonding.

Dry dash/Pebble dash

2. Roughcast/Wet dash/Harling

This is a rough finish produced by throwing on a wet mix containing coarse aggregates and a cement binder. The aggregate in the finish coat is composed of sand and crushed stone or gravel from about 6 to 13 mm, the proportions of sand and gravel being adjusted according to the effect required. Roughcast finishes are applied on an undercoat with a spattered coat beneath it. Like pebble dash finishes they are satisfactory for use in severe conditions.

Roughcast/Wet dash/Harling

External Wall Construction

Render (cont.)

Smooth floated finishes

Types of the finish

3. Smooth floated finishes

Smooth finishes to render are achieved by using a wood, felt or cork faced float to provide the surface finish.

Coarse sand is recommended for this type of Rendering especially in exposed conditions where rain and frost are likely to be severe.

External Wall Construction

Decorative Stone Finish

Decorative stone may form the entire external leaf of the cavity wall or alternatively, thin stone 'slips' may be adhered to a concrete block or common brick external leaf wall.

External Walls - Openings 1
External Walls - Openings 2

External Wall Construction

Internal Walls

Internal walls within houses may be considered as loadbearing or non-loadbearing. Loadbearing walls carry the load from a wall or floor above, and therefore require additional strength. They are normally constructed of either timber frame or masonry (block or brick).

Timber frames have a nominal section size of 100mm x 50mm and requires a double head plate to accommodate loading.

Masonry units, most often lightweight concrete blocks, of nominal thickness of 100mm are often used for loadbearing walls. Most blocks are suitable for loading in 2 storey domestic buildings.

Non-loadbearing walls are simply self supporting room dividers known as partition walls. There are many options for there construction. Normally, lightweight timber frames of nominal section size of 70mm x 45mm is used rather than masonry units.

Another option for internal wall construction is lightweight steel framed walls, although, at present they have a much smaller presence in the house-building market.

External Wall Construction

Party Walls

Party walls are the walls that separate two dwellings, i.e. the wall between neighbours. The are part of semi-detached and terrace house construction. The main requirements of party walls are fire resistance and sound insulation.

The type of construction of the party wall will normally be dictated by the construction of the external walls, i.e. if the building is constructed of timber frame then it is most likely that the party wall will be constructed of timber frame and similarly for masonry construction.

Most often the party wall is constructed as cavity walling. The leaves of the cavity wall will normally require to be tied together for structural strength, however, the number and cross sectional area of the wall ties should be reduced as far as practicable for improved sound insulation, whist ensuring the structural integrity of the wall remains sufficient.

Masonry walls should continue to the underside of the roof to form a complete barrier against fire spread. Fire-stopping may be required at this location.

Timber frame walls must attain the required fire resistance period for the party wall. This is normally achieved by the use of fire resistant lining boards including gypsum panels. Sound insulation may be achieved by the combination of heavy board materials and sound insulation batts (quilts).

Handout Activity 1

External Wall Construction

Produce a handout that:

  1. State the two categories of external wall types commonly used in UK house-building.
  2. List five performance requirements for external walls.
  3. Describe reasons why timber frame construction is widely used for external walls.
  4. Produce a horizontal cross-section through a window opening in a masonry cavity wall.
  5. Produce a vertical cross-section through a window opening in a masonry cavity wall.
  6. List three finishes used on external walls.
  7. Describe what is meant by 'dry lining' on internal surfaces.

A worksheet has been provided to enable you to complete the activity.

All the answers can be found within the materials in this unit.

Section 2

Doors

Introduction

Doors

The performance requirements of external doors include the exclusion of water ingress, security, access and egress from the building, fire resistance, thermal insulation, sound insulation and privacy.

There is a wide choice of materials used to construct external doors including uPVC, timber and aluminium. The sketch below shows the main components of a traditional timber door.

Doors

Door Types

Door types 1

The most simple form of external door is the ledged and braced door and the modified Framed, ledged and brace door. These styles of doors were verypopular due to their cost, but are mainly used for agricultural and cottage type building now.

Doors

Door Types (cont.)

Door types 2

Wooden doors come in a wide variety of styles. It may be that there is a need for additional light to be provided by the door as shown opposite.

Wooden doors require to be treated by an external waterproof coating such as paint or varnish. As with all openings in external walls, great care should be taken around the opening to avoid water ingress.

The threshold is a very important location where there is potential for water ingress, so good detailing is required.

Doors

Door Types (cont.)

Door types 3

uPVC external doors are very popular due to there very low maintenance.

As with wooden doors the are available in a wide variety of styles, colours and textures. They do not require protective coatings and will not decay or rust.

Doors

Thresholds

Threshold details must ensure that water is excluded. There are a wide variety of configurations designed for this purpose. Thresholds may include weather (water) bars, gaskets, seals and anti-capillary grooves and drips.

Thresholds 1
Thresholds 2

Doors

Internal doors

Internal doors

Most internal doors do not require fire resistance, security or thermal insulation properties and, so, may be constructed of very light materials, such as, pressed hardboard. These doors may be hollow core with additional timber located for the provision of hinges and handles (with latches).

There may be a need for borrowed light and therefore, the door may contain glass. As there are many styles and materials used for internal doors, costs range from very economic to more expensive elaborate hardwood doors.

Doors

Ledged and Lined

Ledged and Lined

This basic type of door consists of lining/match boarding which is held together by ledges.

This type is very seldom used due to the tendency to sag and distort on the side opposite the hinges. In order to overcome this braces are added, the use of braces increases the rigidity.

Doors

Ledged, Lined and Braced

Threshold details must ensure that water is excluded. There are a wide variety of configurations designed for this purpose. Thresholds may include weather (water) bars, gaskets, seals and anti-capillary grooves and drips.

Ledged, Lined and Braced 1
Ledged, Lined and Braced 2

Doors

Framed, Ledged, Lined and Braced

Framed, Ledged, Lined and Braced

This type of door is an improvement on the previous types. They include stiles which are jointed to the top, bottom and middle rails using haunched mortise and tenon joints.

The use of the framework increases the door's strength. Braces are optional on these doors. But their use further increases the doors strength. The top rail

The bottom and middle rail are usually 28 x 145 mm and jointed to the stiles using barefaced tenons.

Doors

Flush Doors

Flush doors are generally manufactured under factory conditions. They normally consist of two outer skins of plywood or hardboard, bonded to a light frame, plus at least one lock block. The better quality door has vertical lipped edges.

Various methods are used to produce flush doors, these include the following:


Solid Core

Formed either with sheets of chipboard or cork, or from laminated timber which has been planed to size, then butt-jointed and glued. This core provides strength together with good sound insulation.


Skeletal Core

Cheaper and lighter in weight than the solid core and comprises an outer timber frame with intermediate horizontal rails. The whole core should contain at least 50timber. The skeleton or timber railed core is similar to the semi-solid core but the intermediate rails should be not more than 125 mm apart, giving an even lighter and cheaper door. Alternatively they can be formed by the creation of a lattice-work of hardboard, paper board, or cardboard strips, or by the use of closely packed spiral timber shavings. The aim of the core is to provide a low-cost low-weight infill which supports the surface finish and does not allow undulation or rippling.

Doors

Flush Doors Construction


Flush Doors Construction

Doors

Fire Resisting Doors

Fire doors are required to close openings within walls. Also, to satisfy the Building Regulations, they are required to offer fire resistance for a minimum period of time. (i.e. ½ hour or 1 hour)

If the fire breaks out within a building, a fire door will have to prevent the passage of:

  1. Smoke
  2. Hot Gases
  3. Flames

All FIRE DOORS must be self-closing.

The fire resistance of a door can be defined by reference to the following criteria:

  • Stability: The resistance to the collapse of the door.
  • Integrity: The resistance to the passage of flames or hot gases to the face of the door away from the fire.
  • Insulation: Resistance to the excessive rise in temperature of the unexposed face.

Fire-resisting doors should be prefixed by their stability & Integrity ratings. A 60/45 Fire Door has a minimum 60 minute Stability rating and a 45 minute Integrity rating.

Doors

Fire Resisting Doors Construction


Fire Resisting Doors Construction 1
Fire Resisting Doors Construction 2

Doors

Fire Resisting Doors Certification

A fire door is carefully, precisely, designed and engineered and tested in accordance with British and European standards to demonstrate proven fire resistance performance.

Fire Resisting Doors Certification

Doors

Common Sections

Depending on their location, frames have either:

  • rebates in the solid sections, with no moulding on the other edges; or
  • square sections, with the rebate formed by nailing a timber door strip (planting) onto the square section, at a position to suit the door size.
Common Sections

Doors

Thresholds (detail)

Thresholds (detail)

Doors

Locks & Latches

Ironmongery is the general term given to all metal fittings used in carpentry and joinery. Typical door ironmongery on internal and external doors include:

  1. mortice lock or latch
  2. mortice dead lock
  3. cylinder lock or latch
  4. the handles that operate locks and latches
  5. covering plates over key holes
  6. letter plates
  7. bolts - barrel, straight, cranked or flush
  8. hinges

It is important when selecting or ordering door ironmongery and furniture that the handing of the door is considered. Some locks and latches are not reversible.

It is also essential to ensure that the width of the door stiles is sufficient to accomodate the locks and latches.

Doors

Mortice Locks

There are two types:


1. Mortice lock and latch - this is a combination of a spring bolt that is operated with a handle.


Mortice Lock 1

2. Mortice dead lock - this only operates with the use of a key to turn the dead bolt.


Mortice Lock 2

Both types have levers to secure the lock. A 5-lever lock provides better security than a 3-lever lock.

Doors

Mortice Latches

These are generally used to keep internal doors in place when closed. In some types, the length of the latch can be adjusted to ensure it is secure in the striking plate.


Mortice Latch 1
Mortice Latch 2

Doors

Hinges

Hinges are used to attach door to a frame so that they are able to swing about one edge.

  • Steel Butt Hinge - This is the common type in general use.
  • Rising Butt Hinge - Used to make the door rise as it is opened to clear carpets or fall on a floor.
  • Tee Hinge - These are used mainly for hanging matchboarded doors and gates.
Hinges

Section 3

Windows

Introduction

Windows are primarily designed to enable daylight to enter rooms and building occupants to see outside, however, windows require other factors to be considered within their design.

Other factors may include, ventilation, solar gain, heat loss, sound insulation, fire resistance, fire escape and prevention of water ingress.

There are a wide variety of window types and styles available. Traditionally window frames were made of wood, however, uPVC windows now have a large market share.

Windows

Sliding Sash

Sliding Sash

Traditional windows are of the type shown opposite. These are known as 'sash in case' or 'sliding sash' windows.

They are constructed of timber and opening and closing of both the lower and upper window frames (sashes) is assisted by the use of pulleys.

Rope cord or metal chains connected to a counterweight of metal(often iron) at one end and to the sliding frame at the other enables even heavy window frames to be opened and closed with relative ease.

Windows

Vertical Sliding Sash

Vertical Sliding Sash

The vertical sliding slash window is often called a double hung or box window owes its name to box framing, it is usually found in older properties. The top sash slides between a parting bead, or slip and the outer casting.

The bottom sash slides between the other side of the parting bead and a baton rod, or staff bead, mitred around the inside of the frame. Both sashes are operated by a cord fastened inside a groove on the edge of each sash, and passing through a pulley fitted flush at the top of the pulley stile.

Lead or cast iron weights, equal to the weight of the sash and the glass, are tied to the cord that passes through the pulley. They are housed inside the box frame.

Windows

Casement Windows

Casement Windows

Hinged windows are much more common and are produced primarily as 'casement' windows.

Great care in the detailing around the openable parts must be taken to ensure that water is excluded, see opposite.

Door types 2

Windows

Elevation

Elevation

Windows

Sections (modern stormproof)

Modern stormproof

Windows

Tilt and Turn Technology

Most modern windows offer a range of opening directions through 'tilt and turn' technology.

Windows located in upper floors must be able to be cleaned easily from the inside and there may be a requirement to enable occupants to escape or be rescued from upper windows, in which case, window openings must allow for this.

Tilt and Turn

Section 4

Stairs

Introduction

Stairs are required to enable movement of people between levels in buildings. Stairs must be designed to ensure people using stairs can do so safely.

Stairs will therefore be designed that the pitch (angle) of the stairway is not too steep nor to shallow, be of sufficient width to enable people to pass and to move furniture, etc, have sufficient headroom, have edge protection, and each step must be of a safe and comfortable size.

Building Regulations specify the design criteria for stairs in both domestic and non-domestic buildings.

See section 4.3 of the Domestic Technical handbook found at the following web address: www.scotland.gov.uk/Resource/Doc/217736/0117120.pdf

Stairs

Types of Stairs

Sliding Sash

Stairs within houses (private stairs) are normally constructed of timber.

There are many types of stairs, including straight flight stairs, that lead from one level to the next, they may also be formed between landings of half turn stairs or quarter turn stairs.

Other types include winding stairs and spiral stairs.

Some stair terms are shown opposite.

Stairs

Building Regulations

Steps

All stairs must comply with current Building Regulations. If unsure, advice should be sought from your Local Authority to ensure compliance with the regulations.

There are many rules and regulations relating to stairs but one of the main ones being ease of going up (ascending) and going down (descending) a stair safely.

Stone stairs and landings should be strong, hard and durable. Certain stones are more suitable than others but something like York stone or Caithness slabs would be ideal choices.

Stairs

Design principles - basics

The rise and going of each step should be uniform throughout the stair. There should be no more than 16 continuous rises.

A handrail must be provided if there is a change in level of more than 600mm. All stairs must comply with the formulae 2 x R + G = 550mm to 700mm. See table for minimum and maximum rise, pitch and going.

A few general points

  1. Landings must be provided where there are more than 16 continuous steps.
  2. The tread width should be equal throughout the stair.
  3. The rise of each step should be equal throughout the stair.
  4. 2 x R + G = 550mm to 700mm
Rise, Going & Pitch of Flights in Stairs
Description Maximum rise (mm) Maximum going (mm) Maximum pitch
Private stair 220 225 42°
Any other stair 170 250 34°

Stairs

Plan views

Fig. 1 shows a stair with 6 steps, then a landing, then another 6 steps then another landing. This combination of flight of stairs and landings is sometimes termed a "dog-leg stair". These steps are normally made from pre-cast concrete and lifted into position on site with the aid of a crane.

Fig. 2 shows a similar example but this time there is a space between the two flights of stairs. This stair is termed an "Open well" stair. The purpose of this well is to allow light into the stair well. Commonly used in flats and tenement buildings.

Fig. 3 is another example of an "Open well" stair but this time with landings which are termed as quarter space landings. The two above show half space landings. Quarter space landing will turn the stairs through 90 degrees whereas a half space landing will turn the stair through 180 degrees. The use of a particular stair will determine which is more appropriate. This stair will be easier to climb as there are more landings to rest on.

Plan views Plan views Plan views

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