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Loft Conversions, 2nd Edition

ISBN: 978-1-118-40004-3
284 pages
February 2013, Wiley-Blackwell
Loft Conversions, 2nd Edition (1118400046) cover image

Description

Pressure 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.
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Table of Contents

Preface 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

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Author Information

John Coutts was educated at the City of London School and Brasenose College, Oxford. An author and journalist, he has worked with the BBC and Reuters in the UK and Dow Jones in South East Asia. He writes extensively on construction matters and advises leading multinationals on communications strategies for major infrastructure projects.

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