Application of Part L to Conservatories
attached to existing dwellings
Introduction
The introduction of the new Part L has caused
Building Control Bodies and industry difficulties
in deciding what constitutes a conservatory in
order to be exempt from making a Building
Regulations application. The definition of a
conservatory previously contained in AD L1B of
the April 2006 edition is no longer included in the
2010 Approved Document.
This best practice note is intended to provide
guidance that will promote a consistent
approach to defining what a conservatory is, for
the purposes of being considered exempt from
the need to make a Building Regulations
application.
What is a conservatory?
To establish whether the conservatory extension is
mainly exempt, we must look to Class 7
of Schedule 2 to the Building Regulations 2010.
This tells us that in order to be exempt it must:
• be at ground level
• not exceed 30m2 floor area
• be thermally separated from the building it is
attached to
• have an independent heating system from the
main building
• have glazing meeting Part N in critical zones.
The question now arises as to what constitutes
a conservatory as opposed to any other type of
extension.
In the absence of a specific definition in the
Building Regulations of a conservatory, reference
can be made to dictionary definitions which give a
variety of options as to the description and
purpose of a conservatory.
A common factor in many descriptions is of a
glazed structure often used for growing plants,
and sometimes reference is made to it being an
extension, but there is no indication as to the
amount of glazing that should exist for the
structure to be considered as a conservatory. It
must also be borne in mind that at no point do the
regulations stipulate what the space should be
used for, albeit various uses are suggested in
dictionary descriptions.
In the vast majority of situations these structures
are built as a form of living extension to homes,
with in many instances ancillary heating provided
for those times when it is occupied.
In the interest of national consistency of
interpretation, the guidance on levels of glazing
contained in the superseded Approved Document
L1B 2006 still gives a valid basis for a decision. In
other words an ‘exempt conservatory’ should:
• have at least 50% of external wall area formed
from translucent materials (not including walls
within 1 metre of boundary*)
• have at least 75% of roof area formed from
translucent materials
• be at ground level
• be effectively thermally separated** from the
main part of the dwelling.
But after establishing a fit with the exempt criteria
of Schedule 2 class 7 it must be remembered that
Regulation 9 still enables control under
Requirement P1 (electrical safety), G1 (cold water
supply) and G3(2) and (3) (hot water systems)
if they are applicable.
Approved Document L1B
The exemption status for conservatories is slightly
complicated by virtue of Paragraph 3.16 of
Approved Document L1B which removes
exemption if the heating system of the dwelling is
extended into the conservatory.
www.labc.uk.com
LABC represents Local Authority Building Control in England and Wales.
The removal of such exemption should only apply
control in relation to requirement L1 –
Conservation of fuel and power. In this way an
owner would be required to submit a Building
Regulation application but control would be
restricted to demonstrating compliance with
Part L only.
In such cases the extent of control will depend on
whether the conservatory’s heating system has
independent temperature and on/off controls***.
If it has, there is no limit on the area of glazing, but
all glazed and solid elements should meet the
thermal performance specified in Tables 1 and 2 to
L1B and the heating system should comply with
the Domestic Services Compliance Guide 2010.
If independent control is not provided then the
limits on glazed area in L1B section 4 apply in
addition to the above.
Conclusion
Legislation and guidance on this subject leaves
room for interpretation, hence a potential for
variance in application between local authorities
around the country can arise.
Adoption of this guidance will serve to promote a
consistent approach when dealing with
conservatories, this being in our own interests and
most importantly those of our customers.
Definition of conservatory
It is proposed the use to which a conservatory is
put is the choice of the occupier, with the proviso
that should any fitting or controlled service be
installed the definition may well change.
Permitted areas of glazing
The permitted area of glazing to roofs and external
walls is as described above.
Notes
* There is a potential for excessive
unprotected areas where external walls are
in a boundary situation. Consideration for
fire safety as opposed to the need to meet a
specified level of glazing should form part of
the assessment in relation to the permitted
area of glazing in the external walls of a
conservatory. It is considered that where
external walls to conservatories are within
1 metre of an adjacent boundary it is more
important to achieve reasonable fire
separation than to insist upon a minimum
level of glazing in such a wall simply to assist
achieving exemption status.
** Effective thermal separation means that
walls, doors and windows between the
dwelling and the extension are insulated and
draft proofed to at least the same extent as
the existing dwelling’s external elements.
***Independent temperature and on off
control could typically be achieved using
thermostatic radiator valves within the
conservatory.
www.labc.uk.com
LABC represents Local Authority Building Control in England and Wales.
Reference code 0001-05-2011
