Description
Book SynopsisPressure on space and changes in planning law mean that loft conversions are now at the forefront in the race to improve the performance of Britain''s ageing housing stock. Since 1990, roof space conversions have increased UK housing capacity by more than 200 million square feet - a living area equivalent to a medium-sized city - without the loss of a single square foot of greenfield land.
Loft Conversions is the definitive technical guide to the conversion of roof spaces in single family dwellings. It brings together a wealth of practical and regulatory guidance in a form that is easy to read and comprehensively illustrated.
This fully revised and updated second edition is intended primarily for architects, builders, surveyors and others professionally involved in the process of loft conversion. The insights it provides are also invaluable to self-builders and to householders wishing to achieve a deeper understanding of what a loft conversion involves.
Table of ContentsPreface xiii
Acknowledgements xiv
1 Planning and legal considerations 1
Permitted development 1
Permitted development law 1
Commentary on permitted development provisions – England 4
Permitted development restrictions 10
Curtilage: raising party walls 10
Conservation areas 10
Article IV directions 11
Planning conditions affecting permitted development 11
Listed buildings 11
Other conditions affecting development 12
Restrictive covenants 12
Mortgage lenders 12
Buildings and contents insurance 12
Tree preservation orders 12
Bats 12
Lawful Development Certificate 13
Planning permission 13
Planning applications 13
Sources of planning guidance 15
Supplementary planning guidance 16
Supplementary planning documents 16
Design guides 16
Design codes 16
Local Development Framework 16
Unitary Development Plan 16
The Party Wall etc. Act 1996 16
Procedure 17
Disputes 18
2 The Building Regulations and building control 19
The Building Act 1984 19
The Building Regulations 19
Approved Document guidance 20
Compliance guides 21
Relationship between the Building Regulations and the Approved Documents 21
Building control 21
Local authority building control 22
Full plans 22
Building notice 24
Notification and inspection of work 25
Resolving Building Regulations disputes 26
Electronic building control applications 28
Approved inspector building control 28
3 External forms 30
Primary influences on form 30
Planning considerations 30
Pitch, plan and headroom 31
Stair access 31
Shallow-pitched roofs 31
Existing roof type 31
Conversion forms 33
Roof space only conversion 33
Box dormer conversion 33
Front box dormer conversion 34
Hip-to-gable conversion 34
Side dormer conversion 35
Full-width dormer with masonry flanks 35
Mansard conversion 36
Lean-to conversion 38
Half dormer 38
Existing attic rooms 38
Galleries and platforms 39
Traditional dormer forms 39
Gabled dormer 40
Hipped dormer 40
Flat dormer (small) 40
Cat slide dormer 42
Recessed dormer 42
Eyebrow dormer 42
Arched dormer 42
Segmental dormer 42
Pedimented dormer 42
Canted bay dormer 43
Design considerations 43
Fenestration 43
Roof detail 43
Vertical cladding and roofing materials 44
Chimney positions 45
Drainage 45
4 Fire safety 47
Regulatory framework 47
Main changes to Approved Document B (2006) 47
Fire resistance: basic requirements 49
Warning and escape 50
Floor height rules 51
Storey and floor numbering rules 51
Fire safety: common configurations – floor not more than 4.5 m above lowest ground level 52
Means of warning 52
Means of escape 52
One floor more than 4.5 m above ground level 54
Means of warning 54
First floor fire resistance 54
New floor (conversion) 54
Escape windows 54
Means of escape 55
More than one floor over 4.5 m above ground level 59
Galleries 59
Elements and terminology 62
Access room 62
AFD 62
Air circulation systems 62
Alternative escape route 62
Automatic self-closing devices (self closers) 63
Balconies and flat roofs 63
Cavity barriers 63
Doors – glazing in final exit 63
Emergency egress (escape) windows and external doors 64
Escape route 64
Final exit 64
Fire curtains 65
Fire detection and fire alarm systems 65
Fire doors 67
Fire stopping and the protection of openings 67
Habitable room 69
Inner room 69
Inner inner room 69
Loft conversion 69
Modified 30-minute protection 69
Open plan layouts 70
Passenger lifts 71
Sprinkler systems 71
Storey exit 71
Storey height measurement 71
Fire safety in context 72
5 Conversion survey 73
Survey procedure 73
Outline of survey elements 74
Survey elements in detail 76
Age of the building 76
Headroom and floor-to-ceiling height 76
External relationships 77
Internal layout 77
Roof form 77
Roof structure 77
Roof condition 79
Walls 80
Foundations 82
Internal walls and partitions 83
Floor and ceiling structure 84
Strength of existing timber elements 85
Water tanks 85
Drainage and services 86
Chimneys 87
6 Beams and primary structure 88
Approved Document guidance 88
Beam position relative to existing structure 88
Beam characteristics 89
Common structural steel sections 89
Engineered timber beams 91
Fire resistance of beams 94
Beam bearings 94
Mild steel bearing plates 95
Padstones 96
Beam penetration 98
Beam splices 98
Flange and web plate splice 98
End plate beam splices 99
Splice box 99
Inline box 99
PFC bearing 100
Beam-to-beam connections 101
Bolted connections 101
Grade 4.6 bolts 103
Grade 8.8 ‘high-strength’ bolts 103
HSFG bolt assemblies 104
Toothed plate connectors 105
Timber to masonry connections 105
Tension straps 105
Expansion bolts 105
Chemical anchoring 107
Disproportionate collapse 107
7 Floor structure 109
Role of the conversion floor 109
Elements of loft conversion floor design 110
Room height in the conversion (headroom) 111
Methods of support for floors 111
Beam-supported floors 112
Wall-supported floors 115
Floor joist selection 117
Joist spacing 117
Timber supplies 118
Machined (regularised) joist sections 118
Holes and notches in joists 119
Binders 119
New floor joist/existing ceiling clearance 122
Strutting 122
Trimming 123
Lateral support by floors 125
Floor fire resistance 128
Conversion floor (fire and sound resistance) 128
Floor materials and fixing 129
Conditioning 130
Staggered joints 130
Moisture and sound resistance 130
Fixing 131
T&G floor panels 131
Timber floorboards 131
Stairs 131
Headroom 131
Landings 132
Stair configuration 132
Structural implications 136
Stair provision: practical aspects 136
8 Wall structure 138
External stud walls 138
Stud arrangement and spacing 138
Elements of stud wall construction 141
Terminology 141
Openings 146
Supporting structural steel in stud walls 146
Vertical cladding 146
Fire resistance of dormer stud walls 148
Masonry walls (external) 149
Hip-to-gable conversion 150
Safety considerations during construction 151
Lateral restraint of flank gable walls 151
Brick selection and size 151
Solid blockwork 153
Mortar and brickwork 154
Parapet walls in loft conversions 155
Integrating new and old 155
Chimney cowls 159
Compartment (party) walls 159
Internal partitions 160
Window and door safety 160
Windows 161
Juliet balconies and balustrades 161
Glazing requirements for doors 162
Cleaning 162
Replacement windows 162
9 Roof structure 163
Roof types 163
The cut roof (common to about 1950) 163
The TDA roof truss (common 1947–1980) 163
Trussed rafter roofs (1965 to present) 165
Cut roof: structural forms 165
Single roofs 165
Double roofs 166
Cut roof: structural elements 167
Purlin 167
Ridge and rafters 170
Wall plates 172
Ceiling joists and collars 172
Cut roof: common conversion alterations 172
Modification of the roof structure 172
Reasons to remove a purlin 174
Replacement support for purlins 174
Rafters 176
Trimming 176
Sizing and loading of rafters 183
Hip-to-gable conversion 183
Notches and holes 184
Lateral support for gables 184
Replacement roof coverings 185
Flat roof: basic structure 186
Flat roof – warm deck (unventilated) 188
Flat roof – cold deck (ventilated) 189
Flat roof – hybrid warm roof (unventilated) 189
Roof ventilation 189
Continuity of airflow around roof windows 191
Ventilation – possible exemptions from the requirement 191
Approved Document guidance 192
Attic trusses 192
10 Energy performance 195
Methods of compliance 195
The reference method (elemental approach) 195
Area-weighted U-value method (optional approach) 196
Whole dwelling calculation method (optional approach) 197
Walls and roofs – performance requirements 197
U-values for new thermal elements 198
U-values for retained thermal elements 198
Standards for replacement thermal elements in an existing dwelling 199
Standards for renovation of thermal elements 199
Energy conservation – practical approaches 200
Insulation materials 200
Fixing internal insulation 201
Airtightness 203
Thermal bridging 204
Insulation for wall and roof elements 204
Existing (retained) solid brick masonry walls 204
New solid brick masonry walls 205
New solid blockwork walls 205
Existing (retained) cavity masonry walls 206
New cavity masonry walls 207
New tile hung stud walls 208
Existing (retained) or new pitched roof 208
New flat warm roof 209
New flat cold deck 210
Windows and other openings 210
Area of windows 213
Risks associated with insulation 213
Surface condensation 213
Interstitial condensation – all elements 214
Spalling risk – masonry walls 214
Electric lighting 214
Practical implications 214
Heating and hot water systems 215
Providing information about energy efficiency 216
Loft insulation when a loft is not converted 216
Ventilation for occupants 216
Background ventilation 217
Purge (rapid) ventilation 217
Extract ventilation 218
Ventilation – practical measures 218
All rooms 218
Habitable room (with external wall) 219
Habitable room (with no external wall) 219
Bathroom (with external wall) 219
Bathroom (with no external wall) 219
WC (with external wall) 220
WC (with no external wall) 220
Providing information about ventilation 220
11 Lofts in context 221
Why convert? 221
Loft conversion statistics 222
Underlying trends 222
The nature of the housing stock 222
Practical sustainability 223
Renewable energy 223
Reducing solar gain 224
Green roofs 225
Water conservation 225
Reducing construction waste and re-using materials 226
Energy Performance Certificates (EPCs) and insulating to a higher standard 227
Towards zero carbon 228
The Zero Carbon Loft 229
Appendix A Specification 233
Appendix B The Building Regulations: appeals and determinations 239
Appendix C Planning and curtilage 249
Glossary 252
Bibliography and useful contacts 260
Index 264
A colour plate section falls between pages 162 and 163
