Attic Conversions Dun Laoghaire Area Committee - 26th January 2015
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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.
SpanBuilding 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 * a minimum span of approximately 7.5 m
permission. * 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 mVentilation
The area of headroom at ceiling level (minimum The area A in red should be at
of 2.4m above floor level) should be at least 50% least 50% of area B in blue.
of the area at 1.5m above floor level.
This isas
This is asinTechnical Guidance
the Technical GuidanceDocument
Documents- Part
Part E, A
Building Regulations 1997), Diagram 5.
F (Building Regulations 2009, Diagram 3,Page 8.
Pg.11
B
2.4m
1.5m
Ceiling level minimum 2.4m above floor levelVentilation
In typical DLR dwelling dating from 1970’s
Inonwards,
Cois Cairn,
as Bray,as the illustration
the illustration showsshows the
the pitch
pitch is 40°
is 40° andand
the the span
span is 7.0m.
is 7m. The The
areaarea in red
in red
wouldbe
would be only
only approximately
approximately 1/4¼of of
thethe area
area in
in blue
blue.
2.4 m
1.5 mVentilation
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 HOMEBOND HOUSE BUILDING MANUAL It is possible to use purpose designed prefabricated Page. 181 dormer trusses at design stage. Structure However they involve "In dormer roofs the need to provide clear space (i) extra costs of adequate width and height to accommodate (ii) may have roof height and pitch implications and rooms means that the structural form of the roof (iii) planning implications 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
The typical headroom here before
inserting new floor joists at a pitch angle
Insulation to be inserted to of 35° and a span of 7.0m, is 2.2m, at 32°
building regulations standard pitch it is smaller. After inserting new
between and under rafters. 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 ductingAccess
Existing staircase
with landings
TYPICAL SECTION TYPICAL FIRST FLOOR PLAN
BEFORE ATTIC STAIRS INCLUDEDAccess
Attic floor space shown in blue hatch
New staircase Existing staircase with landings
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 PLANAccess
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 PLANFire Safety
BUILDING
BUILDING REGULATIONS
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 constructionFire 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 1.7 m
Max 1.1m,
min 0.6m
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
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