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Attic Conversions
Dun Laoghaire Area
Committee
26th January 2015
Considering Attic Conversions
The possibility of providing an attic conversion as a means of
offering a solution has been considered by Dún Laoghaire
Rathdown County Council.
The conversion of uninhabitable roof space into habitable
accommodation requires full adherence with statutory building
regulations. Part A (Structure), Part B (Fire), Part F (Ventilation),
Part K (stairs) and Part L (Energy) are of particular relevance to
attic conversions
The following information clearly illustrates that in most
circumstances it is not possible to facilitate this option based on
one or more technical issues
Typical Roof Profile
Typical roof pitch angle of 32° to 35°.
Trussed rafter (more recent roofs)
Headroom
35°
Main ceiling joists usually 125/150x50mm.
Span
Building Regulations 1997
Technical Guidance Document F,
Ventilation
Section 1: Means of Ventilation
Sub-section 1.2.1.8 states:
“Ceiling height is one of a number of
factors which affects ventilation of habitable
rooms. The suggested dimensions in
Diagram 3 are consistent with good room
design, the use of standard materials and
good building practice”
Ventilation
To achieve 2.4m clearance under the ridge
the following is required :Dormer window dependent on planning
permission.
* a minimum span of approximately 7.5 m
* at a minimum roof pitch of 35°
or a minimum span of 8.4m at a roof pitch of 32°
2.4 m
35°
Ceiling level minimum 2.4m above floor level
(Technical Guidance Document Part F)
7.5 m
Ventilation
The area A in red should be at
least 50% of area B in blue.
The area of headroom at ceiling level (minimum
of 2.4m above floor level) should be at least 50%
of the area at 1.5m above floor level.
This is
the Technical
GuidanceDocument
Documents- Part
Part E,
This
isas
asinTechnical
Guidance
Building
Regulations
1997),
Diagram
5.
Page
8.
F (Building Regulations 2009, Diagram 3,
Pg.11
A
B
2.4m
1.5m
Ceiling level minimum 2.4m above floor level
Ventilation
In typical DLR dwelling dating from 1970’s
Inonwards,
Cois Cairn,
the illustration
the
as Bray,as
the illustration
showsshows
the pitch
pitch
is 40°
span
is 7.0m.
in red
is 40°
andand
the the
span
is 7m.
The The
areaarea
in red
wouldbe
be
only
approximately
area
would
only
approximately
1/4¼
of of
thethe
area
in
in blue
blue.
2.4 m
1.5 m
Ventilation
1.1m
2.4 m
2.0 m
35°
2.2m
2x1.1 maximum
Span of approximately 8.5 m required for 2.2m
wide room in attic. Prior to deeper floor joists
and insulation works allowed for.
Structure
Typically prefabricated roof trusses are used in
houses at 600mm centres.
To facilitate attic conversion , the trusses need
to be removed, this requires expensive alteration
and replacement structural members to be
inserted.
Structure
It is possible to use purpose designed prefabricated
HOMEBOND HOUSE BUILDING MANUAL
dormer trusses at design stage.
Page. 181
However they involve
Structure
(i) extra costs
"In dormer roofs the need to provide clear space
(ii) may have roof height and pitch implications and
of adequate width and height to accommodate
(iii) planning implications
rooms means that the structural form of the roof
differs significantly from a conventional roof space.
The design of the roof structure must take this
into account, and ensure that sizing and disposition
of members is adequate".
Structure
Insulation to be inserted to
building regulations standard
between and under rafters.
The typical headroom here before
inserting new floor joists at a pitch angle
of 35° and a span of 7.0m, is 2.2m, at 32°
pitch it is smaller. After inserting new
floor joists in lieu of ceiling joists this
figure is reduced.
Trusses strengthened
with extra members
Main ceiling joists not strong enough to support
floor loads of attic room. New stronger deeper floor
joists have to be inserted.
Equipment and Services
Services and equipment that may have
to be altered, relocated or replaced
- chimney stack
- flues -gas boiler etc.
- water storage
- electrical cabling/trunking, equipment
- ventilation/extraction ducting
Access
Existing staircase
with landings
TYPICAL SECTION
TYPICAL FIRST FLOOR PLAN
BEFORE ATTIC STAIRS INCLUDED
Access
Attic floor space shown in blue hatch
Existing staircase with landings
New staircase
with landings
Existing staircase
with landings
New staircase with landings
taking up space of twin bedroom
and now only useable as single.
SECTION
FIRST FLOOR PLAN
Access
Attic floor space shown in blue hatch
New staircase required minimum
headroom of 2.0m required
Existing staircase with landings
New staircase
with landings
Existing staircase
with landings
New staircase with landings
taking up space of bathroom, that
now has to be relocated.
SECTION
FIRST FLOOR PLAN
Fire Safety
BUILDING
REGULATIONS
BUILDING
REGULATIONS
19972006
Technical Guidance Document B - Fire safety
Section B1 :- Means of Escape in Case of Fire :-
Sub-section 1.5.3. - provisions that have to be included in cases where the
new attic storey floor will be more than 4.5m above ground level (probably a
two storey house). It stipulates the folowing requirements :- fire resisting enclosure construction be provided to form protected
staircase enclosure
- fitting fire resisting doors
- automatic smoke detection and alarm system
- provision of escape window/doors from the new third storey
- layout and configuration of the escape/stairs to comply with the
requirements of this section.
- separate attic floor by fire resisting construction
Fire Safety
Escape window to comply with
Building Regulations TGD S.1.5.6.
Clear opening minimum 0.33 sq.m.
and minimum 450mm high
Max 1.1m,
min 0.6m
Max 1.7 m
Area beneath window should be clear of obstructions
to enable escape and/or rescue. For example :
conservatory/back addition.
Conclusion
Technical Issues which can prove problematic in relation to
Attic Conversions:
•
•
•
•
•
Ventilation
Structure (roof trusses etc.)
Equipment/Services located in the attic
Access and its adverse affect on existing living space
Fire Safety
End of
Presentation
26th January 2015