PLANNING
PERMISSION
A GUIDE FOR
EXTENDING A
DETACHED OR
SEMI-DETACHED
HOUSE
Introduction
Foreword by Councilor Dave Smith - Chair
of the Planning & Highways Committee.
Planning Permissions B
Owners of semi-detached & detached homes
often find it difficult to know how best to extend
their homes to provide much needed space for
growing and extending families.
This visual guide is intended to show how a
semi-detached/detached property can be
extended to add habitable space whilst
maintaining the right to light and privacy of
adjoining neighbours. The guide firstly explains
that there are a number of ways to extend a
semi-detached/detached property without the
need for planning permission, and the Council
would encourage homeowners to do this. Where
an owner wants to extend beyond the limits of
their Permitted Development Rights then
planning permission will be required. The guide
goes on to provide some ideas and options on
extensions to show what would, and what would
not, be appropriate.
Councillor Dave Smith
Councillor Jim Smith
1.
PLANNING PERMISSION IS NOT USUALLY REQUIRED FOR THE FOLLOWING:
Rear Dormer
•
•
•
•
•
Maximum additional volume of 50 cubic metres
Positioned below the ridge
Set back at least 20cm from the eaves
Materials must match the existing roof,
e.g. the dormer must be clad with tiles or slates
No verandas, balconies or raised platforms
20cm
Side Dormer
The same requirements as the Rear Dormer
apply, plus:
Windows must be non-opening unless the
opening is at least 1.7 metres above the fl
of the room
Roof Windows
The insertion of a roof window generally does not require
planning permission if it does not project more than 15cm
beyond the roof slope, or higher than the ridge.
However, if additional volume is created it may be treated as
an extension and seperate rules will apply.
15cm
Always Check!
Always check with the Council because there may be a restriction
on the property.
2.
PLANNING PERMISSION IS NOT USUALLY REQUIRED FOR THE FOLLOWING:
Single Storey Rear Extensions
Planning Permissions BwD
•
Projects no more than 4 metres beyond the rear wall of the original house,
•
Materials should be of similar appearance to the existing dwelling
•
Must not exceed 50% of the total garden area (including the front garden if there is one)
•
Must not include a veranda, balcony or raised platform
•
Maximum height 4 metres
•
Must not exceed the height of the existing dwelling
•
Maximum eaves height 3 metres if within 2 metres of the boundary.
•
The eaves height must not exceed the existing eaves height
Always Check!
Eaves the point where
the wall meets
the roof
Always check with the
Council because there
may be a restriction on the
property. If this is the case
Planning Permission will be
required.
3.
PLANNING PERMISSION IS NOT USUALLY REQUIRED FOR THE FOLLOWING:
Single Storey Side Extensions
Planning Permissions BwD
•
Must not extend beyond a wall which fronts a highway
•
Must not wrap around the rear of the original house
•
Must not exceed 50% of the original garden area
•
Maximum eaves height 3 metres if within 2 metres of the boundary
•
Must not exceed the height of the existing dwelling
•
Maximum height 4 metres
•
The eaves must not exceed the existing eaves height
•
Must not have a width greater than half the width of the original house
•
Must not include a veranda, balcony or raised platform
•
Materials should be of similar appearance to the existing dwelling
Always Check!
Always check with the
Council because there
may be a restriction on the
property. If this is the case
Planning Permission will be
required. For example, if the
property is in a Conservation
Area planning permission
will be required for a side
extension.
4.
PLANNING PERMISSION IS NOT USUALLY REQUIRED FOR THE FOLLOWING:
Two Storey Rear Extensions
•
Must not exceed 50% of the original garden area, including any
previous extensions
•
Must not exceed the height of the existing dwelling
•
The eaves height must not exceed the existing eaves height
•
Projects no more than 3 metres beyond the rear wall of the original
house, and must not be within 7 metres of the rear garden boundary
Planning Permissions BwD
•
Must not project beyond the side of the original house
•
Must not be within 2 metres of any boundary
•
Must not include a veranda, balcony or raised platform
•
Materials should be of similar appearance to the existing dwelling
Always Check!
Always check with the
Council because there
maybe a restriction on the
property. If this is the case
Planning Permission will be
required.
5.
PLANNING PERMISSION IS NOT USUALLY REQUIRED FOR THE FOLLOWING:
Porch (outside any external door of a house
Planning Permissions BwD
•
The ground area (measured externally) of the structure must not exceed 3 square metres
•
Must not exceed 3 metres height
•
Must not be within 2 metres of any boundary with the highway or pavement
New or Replacement Front Driveway
(over 5 square metres)
•
Must be made of porous materials which allows
rainwater to soak through, or rainwater run-off
must be directed to a porous area within the site
and not onto the road
Single Storey outbuilding
•
The total ground area covered by buildings must not exceed 50% of the
total area, excluding the original house
•
No part of the building must be situated on land which is forward of the
front wall of the house
•
Must not exceed 4 metres height (dual-pitched roof), 2.5 metres height if it
is within2 metres of the boundary, or 3 metres height in any other case
•
Eaves height must not exceed 2.5 metres
•
Must not include a veranda, balcony or raised platform
Always Check!
Always check with the
Council because there
may be a restriction on the
property. If this is the case
Planning Permission will be
required.
6.
PLANNING PERMISSION IS NOT USUALLY REQUIRED FOR THE FOLLOWING:
Renewable energy
Planning Permissions BwD
The planning system allows for certain types of renewable energy developments on houses to proceed without needing to apply
for planning permission as long as certain conditions are met. These include:
•
solar panels
•
ground source heat pump
•
water source heat pump
•
flue for a biomass heating system or
a combined heat and power system
•
air source heat pump
•
wind turbine not to exceed 15m
in height(detached houses only)
Always Check!
Please see the individual technology fact sheets
for further information via the Council website.
Please note: if the building is listed or within a
conservation area additional restrictions will apply.
To avoid confusion, it is always recommended
that you contact the council’s Planning
Department before installing any renewable
energy technology to confirm whether or not
planning permission is required.
7.
WHEN PLANNING PERMISSION IS NEEDED
All extensions
Planning Permissions BwD
The 45 Degree Rule
ELEVATION VIEW
The council applies the 45 degree rule as an indicator when assessing proposed
extensions, to ensure that a satisfactory relationship is maintained between existing
buildings and proposed extensions.
Extensions are measured at an angle of 45 degrees from the midpoint of the closest
window in a habitable room of a neighbouring property. If the extension lies within the 45
degree angle when measured horizontally or vertically, an unacceptable loss of daylight
and dominance may be caused and planning permission may be refused.

In the case where the neighbouring window is a patio door, the 45 degree angle is
measured from 1.6 metres above the ground on the centre line of the window.
45o


PLAN VIEW
4
5
o
)
Bathroom (non-habitable
450
Habitable rooms:
living rooms,
dining rooms,
kitchen/diner and
bedrooms
 45

0
8.
WHEN PLANNING PERMISSION IS NEEDED
All extensions
Planning Permissions BwD
Parking Requirements
Overdevelopment
Adequate parking space must be retained within the site in
accordance with the Council’s adopted Parking Standards. If new
parking spaces are to be created in the front garden area, at least one
third of the garden should be kept as a planted garden rather than
hard surfacing. For example 2-3no. bedrooms will require 2 spaces,
and 4no. bedrooms will require 3 spaces. The car parking standards
are available on the Council’s planning website.
Extensions should ensure that adequate garden space is left open for the
storage of bins, maintenance, clothes drying and to safeguard the health of
residents in respect of light and air.
Seperation Distances
A distance of no less than 21 metres must be maintained between facing
windows of habitable rooms, and a distance of no less than 13.5 metres must
be maintained between a habitable room window and a blank gable or wall
with only windows to non-habitable rooms.
9.
WHEN PLANNING PERMISSION IS NEEDED
Front Dormer
Planning Permissions BwD
Do

 Do not

the following pages aim to show examples of alterations
which require planning permission and how best to
achieve a planning approval.


•
At least two thirds
of the original roof
plane is retained
•
Matching Materials
•
No larger than existing windows
•
Pitched roof rather than flat roof
•
Leave 1 metre
distance to the
party walls
•
Do not exceed the
ridge height of the
original roof
•
Too big
•
Materials don’t match
•
Flat roof is a poor design
•
Windows too big
•
Box-shaped and too bulky

Always Check!
If the property is within a Conservation Area, or there are no other front dormers on the street, it is unlikely that planning permission would be granted.
WHEN PLANNING PERMISSION IS NEEDED
Rear Dormer
•
•
Planning Permissions BwD
Dormer covering all of the roof area and above the ridge.
Materials not matching the original roof

•
•
•
Dormer roof set lower than the original ridge height.
Set in from both side boundaries.
Clad in materials to match the original roof.
If the property is in a Conservation Area, dormer extensions are unlikely to receive
planning permission due to their impact on the character of the historic area.
11.
WHEN PLANNING PERMISSION IS NEEDED
ground Floor Rear extensions
Do
Planning Permissions BwD

•
Include a sloping roof
•
Prevent loss of daylight
or overshadowing of
neighbouring houses
•
Retain some rear
garden / yard space for
bins, maintenance and
clothes drying.
•
Consider 45 o rule
(see Page 8)



Do not
•
Flat Roof
•
Site where adjacent
properties have no
extensions
•
Project extension full length
of the garden
•
Overshadow the next door
rear window
NOT ALL DEVELOPMENTS ARE THE SAME
The following will have a bearing on whether extensions will be allowed.
• Number, location and size of extensions at adjoining properties.
• Position of the property in relation to the sun.
• Different ground level e.g Sloping site.
• Location of living room and bedroom windows in the next door property.
• Design of the extension and harmony with the original house
12.
WHEN PLANNING PERMISSION IS NEEDED
Two Storey Rear Extensions
Planning Permissions BwD
Two storey rear extensions usually require planning permission.
In many cases, planning applications are rejected because a two storey extension close to neighbouring houses can
significantly harm the living conditions of neighbours through overshadowing, loss of privacy, or dominance.
The following pages show five situations where two storey rear extensions may be acceptable, on semi-detached houses.
1. Sloping Site
Overshadowing and dominance can be minimised if the
site of the extension is lower than the immediate neighbour.
13.
WHEN PLANNING PERMISSION IS NEEDED
Two Storey Rear Extensions
Planning Permissions BwD
2. Joint extension across
two houses
Overshadowing and dominance can
be avoided if two houses build a joint
extension at the same time.
14.
WHEN PLANNING PERMISSION IS NEEDED
Two Storey Rear Extensions
Planning Permissions BwD
Bathroom
extension
Hallway
3. Nearest neighbouring windows are for non-habitable rooms
Overshadowing or dominance of a non-habitable room (such as bathroom or hallway) in some cases does not cause
significant harm to the living conditions of neighbours and may be acceptable.
Please refer to the 45 degree rule which is explained on Page 8.
15.
WHEN PLANNING PERMISSI0N IS NEEDED
Two Storey Rear Extensions
Planning Permissions BwD
4. Built next to an
existing extension
at an adjoining
house
Overshadowing and
dominance can be
minimised if the extension
is built next to an
existing extension at a
neighbour’s house.
(Subject to the adjacent
window serving a
non-habitable room)
Please refer to the 45
degree rule which is
explained on Page 8.
16.
WHEN PLANNING PERMISSION IS NEEDED
Two Storey Rear Extensions
Planning Permissions BwD
5. Outer Edge of Building
Overshadowing and dominance
can be minimised if the extension
is built at the outer edge of the
building, away from the nearest
neighbour.
17.
WHEN PLANNING PERMISSION IS NEEDED
Side extensions
Do
Planning Permissions BwD

Do not
•
Match the roof shape of the original house
•
Refer to the 45 degree rule (see page 8)
•
Do not project beyond the original front of the house
•
Have a lower ridge than original roof
•
Keep a gap of at least 1 metre between properties
•
Match materials, window styles and positions
•
For two-storey side extensions, the first floor should set
be
back from the front of the house by at least 1.5 m and
etres
the eaves level should match the existing eaves
level
•• Flat
Roof
Flat Roof

Create aa terracing
•• Create
terracingeffect
effect
• Project beyond the front build line
On corner
plots, do
project
•• Project
beyond
thenot
front
buildbeyond
line the side build line
•
On corner plots, do not project beyond the side build line
7

Two storey extensions up to the side boundary and flush
with the original front wall remove the visual separation
between the buildings and create the impression of a
continuous terrace

The preferred approach is to maintain a gap between
properties: this is the best way to prevent a terracing
effect. other options may also be available for extending
or gaining extra living space.
18.
WHEN PLANNING PERMISSION IS NEEDED:
Porches
Planning Permissions BwD
Conservatories
•
Match the roof shape of the original house
•
Match the style and the materials of the house
•
•
In keeping with the appearance of the street and
does not detract from the character of the street
Dwarf walls should be included with materials to
match the house
•
Refer to the 45 degree rule and separation distances
described on page 8.
•
Where a conservatory is adjacent to a boundary with
a neighbour, an acceptable degree of privacy should
be maintained by means of a solid side, obscure
glazing or screening by a fence or wall on the side
facing the neighbour.
19
.
GREATER FLEXIBILITY RELATING TO EXTENSIONS AND THE PRIOR
APPROVAL PROCESS
Class A
Single Storey rear extensions:
You may extend beyond the rear wall of the original dwellinghouse up to 8 metres (detached dwellinghouse), or 6 metres (semidetached dwellinghouse) subject to the following:
It must not exceed 4 metres in height
The enlarged part of the dwellinghouse would be within 2 metres of the boundary of the curtilage of the dwellinghouse, and the height
of the eaves of the enlarged part would not exceed 3 metres.
Materials must match the existing dwellinghouse
You must submit your notification to the local planning authority and include further information regarding the proposed extension to
enable the authority to determine the application. The authority has 42 days from receipt to notify you whether the proposed
development would be permitted development.
The new regulations are only temporary expiring on the 30th May 2016. All developments must be completed before this date.
Further guidance is available on the Council’s planning web page.
WHAT TO DO NEXT…
Planning Permissions BwD
Before starting any work you are advised to check to see if planning permission is required.
If planning permission is required, we can
offer you professional advice before you
formally submit a planning application. This
is a discretionary and chargeable service
offered by the Council. Having early
constructive discussions will help you save
time, avoid wasted expense and frustration
over any delays in the processing of your
planning application. Pre-application enquiry
forms and scale of fees can be downloaded
from the planning pages of the council’s
website www.blackburn.gov.uk/planning.
APPLY
If planning permission is required, you can complete and
submit your application yourself or you can employ an
agent to draw your plans and act as your representative
when dealing with the planning department. The Council
does not recommend particular agents however a list
of planning agents can be found on the Royal Town
Planning Institute’s website: www.rtpi.org.uk; and a
list of architects can be found on the Royal Institute of
British Architecture website: www.architecture.com.
Planning application forms and guidance notes can
be downloaded from the planning section of the
council’s website www.blackburn.gov.uk/planning,
which provides detailed guidance on the supporting
information and scale of fees. It is important to provide
as much relevant information as you can to avoid any
unnecessary delay in the progress of your application.
If in doubt please contact us.
When a planning application is submitted:
• We will write to your immediate neighbours
explaining your proposal to ask for their comments
• In some cases we may put up a site notice or
advertise the application in the press. e.g. in
Conservation Areas and/or Listed Buildings
• We will not make a decision until we have allowed at
least 21 days for comments to
be made. We will take account of all comments
received prior to a decision being made.
• The planning case officer will assess the application
against the relevant legislation and policies,
taking into account any comments received from
interested parties. The case officer will then make
a recommendation as to whether it should be
approved or refused.
• The final decision will be made by either the Director
of Regeneration or the Planning & Highways
Committee within a target timescale of 8 weeks.
• The decision notice will be posted to you (and your
agent if you have appointed one).
DECISION
There are two types of decision that can be made:
Permits or Refuses.
In most cases, planning permissions are subject to
conditions that are listed on the decision notice. For
example, you must commence work within 3 years of
the date of the permission.
If your application is refused, a revised application of
the same character and description can usually be
submitted within 12 months of the refusal date without
requiring a further planning fee.
Alternatively, you may wish to appeal to the Planning
Inspectorate against the Councils Refusal.
Please note:
You are advised to contact Building Control – their
separate permissions may be required for certain
internal and external alterations. Contact (01254)
505022 or email: bc@penninelancsplace.org
Blackburn with Darwen Borough Council
Development Management Team
Lower Ground Floor
Old Town Hall
King William Street
Blackburn BB1 7DY
www.blackburn.gov.uk
20.