Critical construction dimensions

Temperature limits for cold weather working

2 °C

Construction work should not proceed if the air temperature is, or is forecast to fall below, 2°C, unless specific cold weather precautions are rigorously implemented

Building settlement limits on fill

25 mm

Total settlement of a building foundation on engineered fill should generally not exceed 25mm over its 60-year design life

Cavity Fill Below DPC

150 mm

Where partial or full fill cavity insulation is used, it should terminate at least 150mm below the lowest damp-proof course (DPC)

Concrete cover to reinforcement cast against the ground

75 mm cast against soil; 50 mm cast against blinding

Reinforced foundations, ground beams and ground-bearing slabs.

Damp-proof course height above finished ground level

150 mm

External masonry wall, adjoining finished external level

Damp-proof membrane lap and seal

150 mm

Ground-supported slab, membrane above or below the concrete

DPC and Cavity Tray Locations

150 mm

Damp-proof courses (DPCs) must be installed at the base of walls, at least 150mm above the external ground level, and linked to the damp-proof membrane (DPM) in solid floors to prevent rising damp

DPC and DPM Lapping in Timber Frame

100 mm

Foundation depth during cold weather

450 mm

When construction occurs in cold weather, foundations should be at least 450mm below existing ground level, or adequate measures must be taken to prevent ground freezing

Low-Level Protection for Timber Frame and SIPs

150 mm

For closed panel timber frame and structural insulated panels (SIPs), the lowest timber element must be positioned at a minimum of 150mm above the finished ground level

Minimum depth of a strip foundation

450 mm minimum; 750 mm or more in shrinkable clay, deeper near trees

Strip and trench fill foundations on non-aggressive ground, subject to the ground conditions on site.

Minimum foundation depth in frost-susceptible ground

450 mm

To prevent damage caused by frost heave, foundations in frost-susceptible ground must extend to a minimum depth of 450mm below the finished ground level.

Minimum thickness of a strip foundation

150 mm, and not less than the projection beyond the wall face

Plain concrete strip foundations to Approved Document A.

Minimum thickness of strip and trench fill foundations

150 mm

The thickness of a strip foundation must be equal to its projection beyond the wall face or a minimum of 150mm, whichever is greater, typically ranging from 150mm to 500mm

Minimum Timber Clearance and Drainage Holes

150 mm

The lowest timber components of a structure must be at least 150mm above finished ground level, or 75mm where conditions permit

Percolation test procedure for small soakaways

150 mm

The standard percolation test for small surface water soakaways involves boring a 150mm diameter hole, filling it with 300mm of water, and recording the time taken for it to soak away

Pipe support spacing and thermal movement

110 mm

Horizontal drainage pipes, typically 110mm diameter, require support at regular intervals, often around 900mm to 1000mm centres, or at every joint/socket

Ready-mixed concrete temperature and curing

5 °C

Ready-mixed concrete delivered to site should have a minimum temperature of 5°C, as specified in BS EN 206

Timber Sole Plate Height Above Ground

150 mm

The lowest timber elements of a building, such as sole plates, should be positioned a minimum of 150mm above the finished ground level

Traditional manhole construction

100 mm

Traditional manholes feature a concrete base at least 100mm thick and walls constructed from brick, blockwork, or concrete appropriate to ground conditions

Waterproofing around retaining elements

150 mm

Walls and/or floors require waterproofing where structural elements like retaining walls, buried podiums, or raised external ground levels greater than 150mm create a risk of contact with groundwater

Waterproofing for specific structural configurations

150 mm

Specific architectural and structural configurations, such as stairs adjacent to the building, stepped floor slabs where retained ground exceeds 150mm, or raised external ground levels, necessitate careful consideration of waterproofing

Backfill compaction protocols

300 mm

Trench backfill must be well compacted in layers no deeper than 300mm to achieve stable ground

Depth of cover to a buried drain

600 mm under gardens and other areas not subject to vehicles; 900 mm under roads and driveways

Buried foul or surface water drain outside the building footprint

Distance from a soakaway to a building

5 m

Surface water soakaway serving a dwelling

Drainage bed and manhole location

10 mm

Substructure drainage pipes must be laid on a suitable bed of granular material, such as 10mm pea gravel, to provide stable support and protect the pipes from ground movement

External drainage outlet and DPC clearance

150 mm

External rainwater downpipes must discharge at least 150mm below the damp proof course (DPC) level, typically into a gulley or soakaway, to prevent moisture bridging across the DPC into the substructure

Gradient of a 100 mm foul drain

1 in 80 (steeper for runs with fewer appliances)

100 mm foul drain serving at least one WC

Ground drainage pipe support

100 mm

Underground drainage pipes require proper support, either on a minimum 100mm deep granular bed or a carefully hand-trimmed trench bottom

Height of a ventilating stack terminal above an opening

900 mm above the top of any opening within 3 m horizontally

Open ventilating stack terminating at roof level or on an external wall

Minimum cover for mechanical compaction

150 mm

Before mechanical compaction of trench backfill, a minimum of 150mm of material should be placed above the pipe to prevent direct damage.

Minimum WC connections per pipe diameter

100 mm

For peak flows exceeding 1.0 litre per second, a 100mm diameter pipe serving multiple WCs should have a minimum of one WC connection

Pipe clearance for movement

50 mm

When a pipe passes through a structural element, it typically requires a minimum 50mm annular space around it to allow for movement and prevent stress transfer

Spacing between drainage access points

45 m

Straight run of buried drain between access points

Ground-bearing floors over deep fill or sulphate-rich ground

600 mm

When a concrete floor is constructed over deep fill exceeding 600mm, it should be designed as a suspended floor rather than ground-bearing

Ground-supported floor slab thickness

100 mm

Ground-supported concrete floor slab on hardcore

Maximum depth of a hardcore bed under a slab

600 mm

Ground-supported concrete floor slab on a hardcore bed

Minimum thickness for ground-bearing floors

100 mm

Ground-bearing floor slabs, where applicable, must have a minimum thickness of 100mm

Minimum thickness of a polythene damp-proof membrane

0.3 mm (1200 gauge)

Polythene sheet used as a damp-proof membrane below or above a ground-bearing slab.

Sub-floor ventilation opening area

1500 mm² per metre run of external wall, or 500 mm² per square metre of floor area — whichever is the greater

Suspended ground floor with a ventilated void

Ventilated void depth under a suspended timber floor

75 mm to the underside of the wall plate and 150 mm to the underside of the joists

Suspended timber ground floor over a ventilated void

Air temperature limits for laying masonry

Stop at 3 °C and falling; do not restart below 1 °C rising

Masonry and render work in cold weather.

Cavity drainage and DPC extension

150 mm

Cavities in external walls must extend at least 150mm below the damp-proof course (DPC) level to allow for proper drainage and collection of moisture

Cavity tray installation and weep holes

450 mm

Weep holes at not more than 450 mm centres, with at least two over every opening

Cavity tray upstand height

150 mm

Cavity tray over an opening, abutment or cavity interruption

Cavity wall tie horizontal spacing (full-fill insulation)

900 mm

For cavity walls incorporating full-fill insulation, wall ties must be placed at maximum 900mm horizontal centres

Cavity wall tie horizontal spacing (partial-fill insulation)

600 mm

horizontal tie spacing for partial-fill insulated cavities does not exceed 600mm.

Cavity wall tie vertical spacing

450 mm

vertical spacing of cavity wall ties does not exceed 450mm.

Chimney wall thickness and construction

100 mm

The minimum wall thickness for block, brick, or stone chimneys, excluding flue lining, is typically 100mm

Concrete Placement Conditions and Technique

5 °C

Concrete should not be placed if its temperature at the point of use is below 5°C, as fresh concrete is vulnerable to frost damage

Coursing and Jointing in Rubble Stone Masonry

450 mm

For squared or random rubble stone masonry, it is essential to incorporate coursing at regular intervals not exceeding 450mm to maintain structural integrity and a consistent appearance

External chimney breast air spacing

40 mm

for the presence of a minimum 40mm air space or equivalent non-combustible separation within external chimney breasts where thickness is less than 200mm.

Garage wall weather resistance and DPC

150 mm

Lintel end bearing length

100 mm for spans up to 1200 mm; 150 mm for longer spans

Masonry openings — confirm against the lintel manufacturer's schedule for the specific span and load

Lowest fixing position for straps

150 mm

For any structural strap, the lowest fixing into the masonry or supporting structure must be positioned no more than 150mm from the bottom of the strap

Nominal mortar joint thickness

10 mm nominal

Brick and block masonry laid to a gauge rod.

Residual clear cavity width with partial fill insulation

50 mm

Masonry cavity wall with partial fill insulation board

Structural element tolerances

12 mm

the deviation from specified edges or alignments to ensure it remains within the maximum allowable tolerance, e.g., 12mm.

Temperature limits and protection for masonry

3 °C

Brickwork and blockwork should generally not be laid when the air temperature is below 3°C and falling; work can resume when temperatures rise to 1°C with an expectation of exceeding 3°C

Wall tie embedment and slope

50 mm

Wall ties are critical for connecting masonry leaves and must be long enough to achieve proper embedment into both leaves, typically a minimum of 50mm in the mortar bed

Wall tie embedment into each masonry leaf

50 mm

Cavity walls built with ties to a suitable length for the cavity width.

Wall tie spacing at reveals and movement joints

Additional ties at 300 mm vertical centres within 225 mm of the opening

Within 225 mm of an unbonded vertical edge — reveals, movement joints, wall ends

Wall tie spacing in a standard cavity wall

900 mm horizontally, 450 mm vertically (2.5 ties per square metre)

Masonry cavity wall, cavity width up to 100 mm, wall height up to 15 m

Weep hole spacing above a cavity tray

900 mm maximum centres, with at least two weep holes over every opening

Over lintels, cavity trays and at the base of the cavity

Breather membrane lap on a timber frame

100 mm

Horizontal laps shingled downwards; vertical laps over a stud, taped where the manufacturer requires it

Cavity barriers at timber frame panel junctions

At every compartment junction and opening edge

Barriers tight to both faces of the cavity, fixed and continuous

Clear cavity behind the breather membrane in timber frame

50 mm

Clear residual width, measured from the face of the breather membrane to the back of the outer leaf

Lateral restraint strap spacing at floor and roof level

2 m

Straps at floor and ceiling level, carried over at least three joists with solid noggins

Racking board fixing centres

150 mm at board edges, 300 mm at intermediate studs

Fixings kept at least 10 mm from the board edge; pattern to the frame designer's specification where it is tighter

Sole plate DPC height in a timber frame wall

150 mm

Measured from finished external ground or paving level to the underside of the sole plate DPC

Timber moisture content before closing up

20 %

Measured with a calibrated meter at several points, including sole plates and the base of studs

Wall tie spacing to a timber frame

Max 600 mm horizontally (at stud centres) and 450 mm vertically

Ties screwed into studs, not sheathing alone; closer spacing at reveals and movement joints

Floor deck fixing centres

300 mm at supported edges, 500 mm at intermediate joists

Boards laid with the long edge across the joists and joints staggered

Floor joist end bearing on masonry

90 mm

Bearing directly onto masonry or a wall plate; joist hangers follow the hanger manufacturer's seating instead

Joist bearing and pointing

90 mm

Timber joists require a minimum bearing surface, typically 90mm, on supporting masonry or timber to ensure stable load transfer

Lateral restraint for concrete floors

90 mm

Concrete floors offer lateral restraint to walls when they bear a minimum of 90mm onto the masonry

Lateral restraint for timber floors

90 mm

Timber floors can provide lateral restraint to masonry walls if joists have a minimum 90mm bearing onto the wall

Light steel floor joist spacing and design

600 mm

Light steel floor joists should typically be installed at a maximum spacing of 600mm centre-to-centre, although wider spacings may be permitted if specifically engineered

Strutting rows by joist span

One row over 2.5 m span; two rows over 4.5 m

Herringbone or solid strutting, tight between joists and restrained at the ends

Clear air gap above insulation in a cold flat or shallow roof

50 mm

Cold flat roofs and cold roofs pitched below 15 degrees.

Equivalent ventilation areas for a cold roof

10,000 mm²/m at pitched eaves; 25,000 mm²/m at low level on flat or shallow roofs; 5,000 mm²/m at the ridge

Cold roof construction with the insulation at ceiling or deck level.

Flue outlet height at a ridge

600 mm

Solid fuel flue passing through a pitched roof at the ridge

High-level and ceiling air permeability for ventilation

5,000 mm

High-level ventilation, typically 5000mm²/m, is necessary for pitched roofs where the pitch exceeds 35°

Holding-down strap fixing and dimensions

30 mm

Roof holding-down straps should be 30mm x 2.5mm in cross-section and at least 1 metre long

Hybrid roof ventilation and AVCL

25 mm

Hybrid roof constructions require a minimum 25mm clear airflow path below the underlay to ensure effective ventilation

Hybrid roof ventilation with air permeable coverings

25 mm

the presence and continuity of the 25mm clear air gap, the specified eaves and ridge ventilation, and the correct installation of the AVCL.

Minimum eaves ventilation for pitched roofs

7,000 mm

For specific pitched roof constructions, a minimum continuous eaves ventilation opening of 7000 mm²/m is a common requirement

Minimum masonry thickness around a flue

100 mm around the flue; 200 mm between flues serving different dwellings

Masonry chimneys built with a suitable liner.

Minimum strap dimensions for holding down

30 mm

A strap used for holding down purposes, particularly in roof structures, must have a minimum cross-section of 30mm x 2.5mm and be at least 1000mm long to effectively resist uplift forces.

Minimum tile or slate width at a verge

150 mm

All verges on plain tiled, interlocking tiled and slated roofs.

Roof underlay horizontal lap

100 mm at pitches of 15° and above; 150 mm below 15°, and at least 150 mm where the underlay is unsupported

Pitched roof underlay beneath tiles or slates

Separation between a flue and combustible material

200 mm from the flue face, or 40 mm from the outer face of the masonry

Masonry chimneys and fireplace recesses serving combustion appliances.

Specification and fixing of lateral restraint straps

30 mm

Lateral restraint straps must conform to design specifications for length, size (typically 30mm x 5mm), and corrosion protection

Strap material compatibility and fixing height

150 mm

strap and fixing materials are compatible and that the lowest fixing is within 150mm of the strap's base.

Thickness of Code 4 milled lead sheet

Code 4 = 1.80 mm

Milled lead sheet to BS EN 12588 used for flashings and weatherings.

Typical timber roof member dimensions

50 mm

Standard timber roof member sizes, such as minimum 100x50mm for struts, 32mm thick for valley rafters, and rafter cut plus 25mm for ridges and hips, are generally acceptable

Upstand, Warm Roof, WFRL, Waterproofing, Zero Fall Roof definitions

150 mm

An upstand provides perimeter waterproofing continuity between a flat roof or deck and vertical wall construction, typically 150mm high, but potentially 75mm at accessible thresholds

Ventilated batten space beneath a roof underlay

25 mm

Roofs designed with a ventilated space beneath the underlay, including counter-battened details.

Ventilated Cold Roof Construction Diagram

50 mm

In a ventilated cold roof construction, a clear void, typically a minimum of 50mm, is maintained between the insulation layer and the roof deck

Ventilation openings to a cold pitched or flat roof void

25 mm continuous at the eaves; 5 mm at the ridge for pitches of 15° or more; 25 mm at both sides of a cold flat roof

Cold roof construction with insulation at ceiling level

Background ventilator equivalent area

8000 mm² equivalent area to habitable rooms; 4000 mm² to kitchens, utility rooms and bathrooms

Dwelling with background ventilators, including window replacement work

AVCL jointing requirements

100 mm

Joints in air and vapour control membranes must be adequately lapped, typically with a minimum overlap of 100mm, to ensure continuity of the membrane

Clearance for walkways above insulation

50 mm

Boarded walkways and working platforms within roof spaces must be securely fixed and maintain a minimum 50mm clearance above the insulation

Limiting air permeability for a new dwelling

8 m³/(h·m²) at 50 Pa

New dwelling air pressure test at completion

Limiting fabric U-values for a new dwelling

Roof 0.16; wall 0.26; floor 0.18; party wall 0.20; window, roof window and door 1.60 W/(m²·K)

New dwelling, individual element limiting standard

Cavity barriers around openings in a cavity wall

Continuous around the full perimeter of the opening

Includes windows, doors, and any duct or vent passing through the cavity

Cavity subdivision in a roof void

20 m

Maximum distance between cavity barriers in a concealed roof space

Doors onto a protected stairway in a three-storey house

Fire doors to every habitable room opening onto the stair

Applies where any floor level is more than 4.5 m above ground level

Fire barrier at the party wall and roof junction

Continuous to the underside of the roof covering

Gaps at truss positions and at the tile battens closed with a fire-resisting material

Fire resistance of a compartment floor between flats

60 minutes

Includes the ceiling line, service voids and any penetrations through it

Fire resistance of a wall separating dwellings

60 minutes

Applies to the wall and to its junctions with floors, roofs and external walls

Fire stopping at a service penetration

Reinstate the full fire resistance of the element

Sealed with a system tested for that substrate, aperture size and service type

Maximum pipe diameter through a compartment wall or floor

40 mm

Nominal internal diameter for a non-fire-rated pipe; larger pipes need a tested sleeve, collar or non-combustible material

Maximum unbroken cavity before a barrier is needed

20 m

Concealed cavity in a wall or roof of a dwelling

32mm waste pipe support

32 mm

Independent 32mm polypropylene discharge or waste pipes, conforming to relevant British Standards such as BS 5254 or BS EN 1451, must be adequately supported with pipe clips throughout their run to the soil stack or manifold

Clearance from combustible materials

75 mm

Appliances that generate heat, such as solid fuel burners, must maintain a minimum separation distance of 75mm from any combustible materials to prevent fire

Constructional hearth thickness and extent

125 mm thick, at least 840 × 840 mm on plan, extending 500 mm in front of the appliance and 150 mm each side

Solid fuel appliance on a constructional hearth

Ductwork Fixing and Condensate Management

750 mm

MVHR ductwork must be securely fixed at appropriate intervals to prevent sagging, typically no more than 750mm apart, or as per manufacturer guidelines

Electrical accessory spacing

100 mm

Electrical socket outlets and switches should be installed with a minimum spacing of 100mm between their centres to ensure adequate access and compliance with wiring regulations

Exceptions to combustible material clearance

75 mm

Exceptions to the standard 75mm clearance from combustible materials are permitted under specific conditions

Fixing Plywood to Battens

150 mm

Plywood sheets fixed to battens require 10-gauge nails or screws, placed at 150mm centres along perimeters and 300mm centres on intermediate supports

Flue liner requirements for new builds

250 °C

Flue liners must be selected based on the expected flue gas temperature; for temperatures unlikely to exceed 250°C, requirements for gas flues apply, while for higher or unknown temperatures, solid fuel flue pipe standards are used

Gradient of a branch discharge pipe

18 to 90 mm per metre for a 75 mm or 100 mm branch

Measured along the branch from the appliance to the stack

Headroom over a stair

2000 mm, reducing to 1900 mm at the centre of a loft conversion stair and 1800 mm at the side

Stairs and landings within a dwelling

Maximum length of a WC branch to the stack

6 m

For a 100 mm branch serving a single WC, with no more than 90 mm/m fall

Minimum Hot Water Storage Capacity

60 °C

Domestic hot water storage systems must provide a minimum capacity to adequately supply hot water at a target temperature, typically 60°C

Permitted notches and holes in floor joists

Notches: max depth 0.125 x joist depth, only between 0.07 and 0.25 of the span. Holes: max diameter 0.25 x joist depth, on the centreline, between 0.25 and 0.4 of the span, at least 3 diameters apart

Solid timber floor joists — engineered joists follow the manufacturer's zones instead

Protection of gas pipework through timber

1 mm

Gas pipework that penetrates timber studs or joists must be protected by steel plates, typically 1mm thick, to prevent accidental damage from screws or nails during subsequent fit-out

Screed Cover for Buried Pipes

25 mm

A minimum of 25mm screed cover is required over pipes and insulating material, and where pipes cross, a duct may be necessary to maintain this cover

Separation of flues from combustible materials

25 mm

Flues must be adequately separated from combustible materials to prevent fire hazards, typically requiring a minimum clearance of 25mm

Smoke alarm siting distances

Within 7.5 m of the door to every habitable room, within 3 m of every bedroom door, and at least 300 mm from any wall or light fitting

Ceiling-mounted mains-powered alarms on circulation routes

Stair rise and going relationship

550 mm

Staircases must be dimensioned such that the relationship between the rise (R) and the going (G) falls within prescribed limits for safety and comfort, typically expressed as 2R + G between 550mm and 700mm

Cable depth in a wall before extra protection is needed

50 mm

Measured from the finished surface on either side of the wall

Plasterboard fixing and fire resistance

300 mm

Plasterboard must be fixed to light steel studs with self-drilling, self-tapping screws at specified centres, typically a maximum of 300mm

Safe zones for cables buried in a wall

Within 150 mm of the top of the wall or of a corner, or vertically/horizontally in line with the accessory

Applies to cables concealed in a wall or partition at a depth of less than 50 mm

Flatness of a finished plasterboard surface

Within 3 mm under a 1.8 m straightedge

Measured on the finished surface in any direction, away from internal corners

Plasterboard fixing centres

200 mm to ceilings, 300 mm to walls, and 150 mm at board ends

Fixings kept at least 10 mm from cut edges and 13 mm from bound edges

Appliance space, general storage, and unit installation

600 mm

Design specifications should account for standard appliance depths, typically 600mm, even if appliances are not supplied

Carbon monoxide alarm position

Ceiling mounted at least 300 mm from any wall and 1–3 m horizontally from the appliance, or wall mounted above the height of any door or window and at least 150 mm from the ceiling

Room containing a fixed combustion appliance

Cistern access requirements

520 mm

Adequate access must be provided to cold water storage cisterns located in roof spaces and voids, through an opening of at least 520mm in each direction

Clear opening of an escape window

0.33 m² clear openable area, at least 450 mm in both height and width, with the bottom of the opening 800–1100 mm above floor level

First floor and loft rooms served by an escape window

Clear opening width of an internal door

750 mm from a corridor at least 900 mm wide; 775 mm from a 825 mm corridor; 900 mm from a 750 mm corridor

Internal doorway on the entrance storey of a dwelling

Conditions for Pipe Freezing Calculations

6 °C

Calculations for pipe insulation to prevent freezing are based on specific assumed conditions, typically including an external air temperature of -6°C and an internal water temperature of +7°C

Critical locations for safety glazing

Below 800 mm from floor level in walls and partitions; below 1500 mm in doors and in side panels within 300 mm of a door edge

Internal and external glazing in a dwelling

Door Clearances and Fire Door Installation

10 mm

Internal doors, including fire doors, must be installed with sufficient clearance from the finished floor level to accommodate flooring, typically around 10mm for non-fire doors

Door swing clearance at stair landings

400 mm

door swings on or near landings do not impede safe passage, particularly verifying the 400mm minimum clearance from the first tread on private stair bottom landings.

Electrical Accessory Clearance Elevation Detail

300 mm

Elevation diagrams specify the minimum 300mm horizontal separation required between electrical accessories and the edges of sinks or wash basins

Electrical Accessory Clearance from Water Diagrams

300 mm

Diagrams illustrating the required 300mm minimum horizontal clearance for electrical accessories from water sources, such as sinks and wash basins, are commonly used in guidance documents

Electrical socket outlet distance from water source

300 mm

all socket-outlets are located at least 300mm horizontally from the edge of any sink or basin.

Flue pipe horizontal run limit

150 mm

A short horizontal section, typically up to 150mm in length, is permitted within a flue pipe system to connect a back-outlet liquid fuel appliance to the main flue, provided the primary run remains as vertical as possible.

Going of a tapered tread

Measured at the centre of the flight; at least 50 mm at the narrow end

Winder or tapered tread in a private stair

Guarding height in a dwelling

900 mm to stair flights; 1100 mm to landings, balconies and external edges

Single-family dwelling

Handrail height on a stair or ramp

900–1000 mm above the pitch line or floor

Private stair, landing or ramp in a dwelling

Handrails for Tapered Treads and Winders

600 mm

For stairs incorporating tapered treads or winders, any handrail provided on the outside of the turn must offer a safe handhold for the full rise of the stair, particularly if the total rise exceeds 600mm

Hearth Provision and Floor Finishes

225 mm

A hearth may not be necessary if an appliance's flame or incandescent material is positioned at least 225mm above the floor

Hearth Thickness for Appliances

12 mm

Hearths for appliances, other than specific solid fuel or gas-specific cases, must be constructed from non-combustible materials with a minimum thickness of 12mm.

Intermittent extract rates by room

Kitchen 30 l/s next to the hob or 60 l/s elsewhere; utility room 30 l/s; bathroom 15 l/s; WC 6 l/s

Intermittent mechanical extract in a wet room

Landing length at the top and bottom of a flight

At least equal to the least width of the flight, kept clear of door swings

Landing at the head or foot of a private stair

Maximum gap in guarding

No opening should allow a 100 mm sphere to pass

Guarding to a stair, landing, balcony or floor edge in a dwelling

Maximum hot water temperature at a bath

48 °C

Hot water supply to a fixed bath in a dwelling

Private stair rise, going and pitch

Rise 155–220 mm, going at least 220 mm, maximum pitch 42°, and twice the rise plus the going between 550 mm and 700 mm

Private stair within a single dwelling

Purge ventilation opening area

One twentieth (1/20) of the floor area of the room for a hinged or pivot window opening 30° or more

Habitable room ventilated by openable windows

Soundproofing Measures for Soil Pipes

25 mm

Sound insulation for soil pipes involves either encasing them in boxing made from a material with a minimum mass of 15kg/m², or wrapping them with at least 25mm of unfaced mineral wool, typically 10kg/m³ density

Stair Handrail Height and Clearance

600 mm

A handrail is mandatory for flights of stairs where the rise exceeds 600mm

Staircase guarding requirements

600 mm

Staircases and landings require adequate guarding where there is a drop of more than 600mm

Tread overlap for open-riser stairs

16 mm

For stairs with open risers, each tread must overlap the one below by a minimum of 16mm, or 15mm in Scotland, to meet safety requirements and prevent foot entrapment.

Water seal depth at appliance traps

75 mm for baths, basins, sinks and showers on a branch; 50 mm for a WC trap

Appliance trap on a branch discharge pipe

Accessible threshold upstand

15 mm maximum total upstand, chamfered or pencil-rounded above 5 mm

Principal entrance to a dwelling designed to be accessible

Additional flue terminal separation rules

300 mm

Beyond standard table distances, all flue terminals must maintain a minimum 300mm clearance from any combustible material, such as window frames

Gutter bracket spacing

600 mm

gutter brackets are spaced no more than 600mm apart along the gutter run.

Handrails for external steps

600 mm

A handrail is required for external flights of steps when the total rise exceeds 600mm and the individual step going is less than 600mm

Landscaping Levels and DPC

150 mm

External ground levels, including landscaping finishes such as turf, must be maintained at a minimum of 150mm below the damp proof course (DPC) level

Specific guarding requirements for level changes

600 mm

Guarding is mandated for retaining structures where the drop is greater than 600mm to an accessible lower level

Water efficiency limit for a new dwelling

125 litres per person per day (110 where the tighter optional requirement is imposed by condition)

New dwelling water efficiency calculation