Building Regulations Approved Document A (Structure) sets out requirements for structural safety, stability, and durability of buildings in England and Wales. Updated for 2026, Part A ensures buildings can safely withstand all imposed loads including dead loads, live loads, wind loads, and snow loads throughout their design life without excessive deflection or collapse.
This comprehensive guide covers Part A requirements for foundations, walls, floors, roofs, structural alterations, and compliance with British Standards including BS 5628 (masonry), BS 8110 (concrete structures), and Eurocodes for structural design calculations.
Overview of Part A Requirements
Building Regulations Part A contains five main sections covering all structural aspects of building construction. Compliance ensures buildings remain structurally sound under normal use and predictable extreme conditions.
Section A1: Loading
Requirement: Buildings must sustain and transmit all loads safely
Includes: Dead loads, imposed loads, wind loads, snow loads
Standards: BS 6399 series, BS EN 1991 (Eurocodes)
Design Life: Minimum 50 years for residential buildings
Section A2: Ground Movement
Requirement: Buildings must not be adversely affected by ground movement
Covers: Subsidence, landslip, frost heave, swelling/shrinkage of clay
Standards: BS 8004 (foundations), BS 8002 (earth retaining structures)
Key Factor: Foundation design based on ground investigation
Section A3: Disproportionate Collapse
Requirement: Building must not suffer disproportionate collapse from localized failure
Applies To: Buildings over 5 storeys or high consequence
Methods: Effective horizontal and vertical ties, alternative load paths
Standards: BS EN 1991-1-7 (accidental actions)
Sections 1C-2E: Practical Guidance
Section 1C: Sizes of structural elements (deemed-to-satisfy provisions)
Section 2C: Thickness of walls for various heights and exposure
Section 2E: Strip foundation widths for soil types
Purpose: Simple rules for common construction without calculations
Structural Loading Requirements
Section A1 requires buildings to sustain all predictable loads during construction and use. Structural design must account for combinations of dead loads (permanent), imposed loads (variable), wind loads, and snow loads according to British Standards and Eurocodes.
Standard Loading Values for Design
| Load Type |
Standard Value |
Application |
British Standard |
| Domestic floor imposed load |
1.5 kN/m² |
Residential rooms, bedrooms, hallways |
BS 6399-1 / BS EN 1991-1-1 |
| Domestic roof imposed load |
0.6 kN/m² (no access) |
Pitched roofs, tiles/slates |
BS 6399-3 |
| Flat roof with access |
1.5 kN/m² |
Accessible flat roofs, roof terraces |
BS 6399-3 |
| Partition allowance |
1.0 kN/m² |
Allowance for internal partitions (if not designed specifically) |
BS 6399-1 |
| Staircase |
2.0 kN/m² |
Domestic stairs and landings |
BS 6399-1 |
| Balcony |
2.5 kN/m² |
External balconies, private use |
BS 6399-1 |
| Point load (concentrated) |
1.4 kN |
Single wheel/furniture load on floors |
BS 6399-1 |
| Snow load (UK typical) |
0.6-0.75 kN/m² |
Ground level snow, varies by location and altitude |
BS 6399-3 / BS EN 1991-1-3 |
| Wind pressure (basic) |
Variable 0.5-1.5 kN/m² |
Depends on location, height, building shape |
BS 6399-2 / BS EN 1991-1-4 |
Domestic Floor Load
Imposed Load
1.5 kN/m²
Application
Residential rooms
Standard
BS 6399-1
Domestic Roof Load
Imposed Load
0.6 kN/m²
Type
No access
Standard
BS 6399-3
Staircase Load
Imposed Load
2.0 kN/m²
Application
Domestic stairs
Standard
BS 6399-1
Balcony Load
Imposed Load
2.5 kN/m²
Application
External balconies
Standard
BS 6399-1
📊 Load Combination Factors (Partial Safety Factors):
- Dead Load Factor: 1.4 (permanent loads - structure weight, finishes)
- Imposed Load Factor: 1.6 (variable loads - people, furniture, snow)
- Ultimate Limit State: 1.4 × Dead Load + 1.6 × Imposed Load
- Serviceability Limit State: 1.0 × Dead Load + 1.0 × Imposed Load (deflection checks)
- Wind Load Combinations: Consider dead + imposed + wind with appropriate factors
Wall Thickness Requirements
Section 2C of Approved Document A provides deemed-to-satisfy thickness requirements for masonry walls based on height, length, exposure, and construction type. These provisions allow construction without structural calculations for straightforward buildings.
Minimum Wall Thickness - Cavity Walls
| Wall Height |
Internal Leaf (Loadbearing) |
External Leaf (Non-loadbearing) |
Cavity Width |
Max Storey Height |
| Up to 3.5m (single storey) |
100mm blockwork |
102.5mm brickwork |
50-100mm |
2.7m |
| Up to 7m (two storey) |
100mm blockwork (7N blocks min) |
102.5mm brickwork |
50-100mm |
2.7m each |
| Up to 10.5m (three storey) |
140mm blockwork OR 100mm (10N+ blocks) |
102.5mm brickwork |
50-100mm |
2.7m each |
| Over 10.5m (four+ storey) |
Structural calculations required |
Calculations required |
Design specific |
Engineered |
Single Storey (up to 3.5m)
Internal Leaf
100mm blockwork
External Leaf
102.5mm brick
Cavity
50-100mm
Two Storey (up to 7m)
Internal Leaf
100mm (7N blocks)
External Leaf
102.5mm brick
Max Height Each
2.7m storey
Three Storey (up to 10.5m)
Internal Leaf
140mm OR 100mm 10N+
External Leaf
102.5mm brick
Max Height Each
2.7m storey
Solid Wall Thickness Requirements
| Wall Type |
Height Range |
Minimum Thickness |
Block Strength Required |
| Single storey external wall |
Up to 3.5m |
190mm (solid) or 215mm brick |
3.5N/mm² minimum |
| Two storey external wall |
Up to 7m |
215mm (solid) or 327mm if over 6m |
7N/mm² minimum |
| Internal loadbearing partition |
Up to 3.5m |
90mm minimum (lightweight blocks) |
2.8N/mm² minimum |
| Internal loadbearing (two storey) |
Up to 7m |
140mm minimum |
7N/mm² minimum |
Single Storey Solid Wall
Height
Up to 3.5m
Thickness
190-215mm
Strength
3.5N/mm² min
Two Storey Solid Wall
Height
Up to 7m
Thickness
215-327mm
Strength
7N/mm² min
⚠️ Wall Thickness Limitations:
- Maximum Unsupported Height: Wall height must not exceed 12 times thickness (slenderness ratio)
- Maximum Unsupported Length: Wall length between supports ≤ 30 times thickness
- Lateral Support: Walls require roof/floor lateral restraint at maximum 2.7m vertical intervals
- Parapet Walls: Additional thickness required, typically 215mm minimum regardless of height
- Wind Exposure: Increased thickness required for severe/very severe exposure zones
- Calculations Required: When exceeding these limits or in complex situations
Floor and Roof Span Tables
Section 1C provides deemed-to-satisfy span tables for common timber floor joists and roof rafters. These tables allow construction without calculations for standard residential buildings using readily available timber sizes.
Timber Floor Joist Spans (C16 Timber)
| Joist Size (mm) |
400mm Centres |
450mm Centres |
600mm Centres |
Max Clear Span |
| 38 x 147 (6" x 2") |
3.10m |
2.94m |
2.65m |
3.10m |
| 38 x 170 (7" x 2") |
3.61m |
3.42m |
3.08m |
3.61m |
| 38 x 195 (8" x 2") |
4.16m |
3.95m |
3.56m |
4.16m |
| 38 x 220 (9" x 2") |
4.72m |
4.48m |
4.04m |
4.72m |
| 47 x 195 (8" x 2.5") |
4.47m |
4.24m |
3.82m |
4.47m |
| 47 x 220 (9" x 2.5") |
5.07m |
4.82m |
4.34m |
5.07m |
38 x 170mm Joist (7"x2")
400mm centres
3.61m span
450mm centres
3.42m span
600mm centres
3.08m span
38 x 195mm Joist (8"x2")
400mm centres
4.16m span
450mm centres
3.95m span
600mm centres
3.56m span
47 x 220mm Joist (9"x2.5")
400mm centres
5.07m span
450mm centres
4.82m span
600mm centres
4.34m span
Structural Alterations Requirements
Part A applies to structural alterations in existing buildings. Any work affecting loadbearing elements requires Building Regulations approval and often structural engineer involvement to ensure building stability is maintained.
Removing Loadbearing Walls
Requirement: Structural calculations and Building Control approval mandatory
Beam Required: Steel beam or reinforced concrete lintel to carry loads
Support: Padstones or padded steel posts transfer loads to foundations
Engineer Fee: £400-800 for beam design calculations
Creating New Openings
Windows/Doors: Lintel required over all openings in loadbearing walls
Lintel Specification: Based on opening width and wall load above
Building Control: Approval required before work commences
Typical Lintel: Concrete or steel, 150mm bearing each end minimum
Loft Conversions
Floor Upgrade: Existing ceiling joists usually inadequate for floor loads
Options: Strengthen existing or install new floor joists alongside
Calculations: Structural engineer assessment of existing structure required
Roof Structure: May require modification to create headroom
Extensions & Structural Connection
Foundation Design: Must prevent differential settlement with existing building
Wall Connection: Tie into existing structure or provide movement joint
Roof Connection: Load paths must be clearly defined and adequate
Engineer Input: Recommended for all but smallest single-storey extensions
Steel Beam Sizes for Common Applications
When removing loadbearing walls, steel universal beams (I-beams) are commonly specified. Beam size depends on span, loading, and support conditions. Always use structural engineer calculations for final specification.
Typical Steel Beam Sizes (Indicative Only)
| Span |
Single Storey Load |
Two Storey Load |
Beam Weight |
Approx Cost |
| 2.5m |
152x89x16 UB |
203x102x23 UB |
16-23 kg/m |
£150-250 |
| 3.0m |
203x102x23 UB |
254x102x28 UB |
23-28 kg/m |
£200-350 |
| 3.5m |
203x133x25 UB |
254x146x31 UB |
25-31 kg/m |
£250-450 |
| 4.0m |
254x102x28 UB |
305x102x33 UB |
28-33 kg/m |
£350-550 |
| 4.5m |
254x146x31 UB |
305x127x37 UB |
31-37 kg/m |
£450-700 |
| 5.0m |
305x102x33 UB |
305x165x40 UB |
33-40 kg/m |
£550-850 |
3.0m Span Beam
Single Storey
203x102x23 UB
Two Storey
254x102x28 UB
Cost
£200-350
4.0m Span Beam
Single Storey
254x102x28 UB
Two Storey
305x102x33 UB
Cost
£350-550
5.0m Span Beam
Single Storey
305x102x33 UB
Two Storey
305x165x40 UB
Cost
£550-850
⚠️ Steel Beam Installation Requirements:
- Never Assume Sizes: Always use structural engineer calculations - indicative sizes only shown
- Padstones Required: Concrete padstones minimum 440x215x100mm distribute beam load
- Bearing Length: Minimum 100mm bearing on each support, 150mm preferred
- Fire Protection: Beams require fire protection boarding in critical locations
- Building Control: Inspection required before beam installation and after completion
- Temporary Support: Adequate propping required during wall removal and beam installation
Disproportionate Collapse Requirements
Section A3 requires buildings to resist progressive collapse from localized damage. Requirements apply primarily to buildings over 5 storeys or buildings where consequences of collapse are severe (public assembly, hazardous materials storage).
🔒 Disproportionate Collapse Prevention Methods:
- Class 1 Buildings: Houses up to 4 storeys - no specific measures required beyond normal structural design
- Class 2A Buildings: 5-storey buildings or public assembly - effective horizontal ties required
- Class 2B Buildings: Larger buildings - horizontal + vertical ties, or alternative load paths
- Class 3 Buildings: High-risk buildings - systematic risk assessment and key element design
- Tie Force Requirements: Calculated based on floor area and number of storeys
- Key Elements: Critical structural members designed to resist 34 kN/m² accidental loading
Structural Engineer Involvement
While simple residential buildings can use deemed-to-satisfy provisions from Part A, many projects require structural engineer input. Engineer fees vary based on project complexity and design requirements.
When Structural Calculations Are Required
| Project Type |
Engineer Required? |
Typical Scope of Work |
Typical Fee Range |
| Simple 2-storey house, good ground |
Not usually |
Use Part A standard details |
£0 |
| 3-storey house or complex layout |
Yes, recommended |
Foundation + superstructure design |
£1200-2500 |
| Removing loadbearing wall (single beam) |
Yes, mandatory |
Beam sizing and support design |
£400-800 |
| Removing multiple walls (open plan) |
Yes, mandatory |
Multiple beams + structural analysis |
£800-1500 |
| Loft conversion |
Yes, recommended |
Floor upgrade + roof assessment |
£600-1200 |
| Single storey extension (simple) |
Often not needed |
Foundation design only if required |
£300-600 |
| Two storey extension |
Yes, usually required |
Complete structural design package |
£800-1500 |
| Basement construction |
Yes, mandatory |
Structural + waterproofing design |
£2000-4000+ |
Simple 2-Storey House
Engineer?
Not usually
Approach
Use standard details
Fee
£0
Single Beam Installation
Engineer?
Yes, mandatory
Scope
Beam + support design
Fee
£400-800
Loft Conversion
Engineer?
Yes, recommended
Scope
Floor + roof assessment
Fee
£600-1200
Basement Construction
Engineer?
Yes, mandatory
Scope
Full structural design
Fee
£2000-4000+
Building Control Approval Process
All structural work requires Building Control notification and inspection. Failure to comply results in enforcement action, difficulty selling property, and potential requirement to expose completed work for inspection.
✓ Part A Building Control Inspection Points:
- Foundation Inspection: Excavation depth, width, concrete grade verified before pour
- DPC/DPM Installation: Damp proofing inspected before covering
- Steel Beam Installation: Beam size, padstones, bearing checked before building over
- Floor Joist Installation: Sizes, spans, support verified for new floors
- Wall Plate/Restraint Straps: Lateral restraint fixings checked
- Completion Inspection: Final check before issuing completion certificate
Part A Structure FAQs
Do I need Building Regulations approval for removing a wall?
Yes, removing any loadbearing wall requires Building Regulations approval. Even if wall appears non-loadbearing, Building Control notification mandatory before work. Structural engineer calculations required to specify beam size and support requirements. Non-compliance results in enforcement action and affects property sale. Internal non-loadbearing partitions (stud walls not carrying floor/roof loads) can be removed without approval.
What size steel beam do I need to replace a loadbearing wall?
Beam size depends on span, wall load above, and support conditions - structural engineer calculations mandatory. Indicative sizes: 3m span single storey = 203x102x23 UB, 4m span two storey = 305x102x33 UB. Never assume beam sizes - incorrect sizing causes dangerous structural failure. Engineer fee £400-800 includes beam specification, padstone design, and Building Control submission.
What is the maximum span for floor joists without calculations?
Part A Section 1C span tables provide deemed-to-satisfy spans for C16 timber joists. Example: 38x195mm (8"x2") joists span 4.16m at 400mm centres, 3.56m at 600mm centres. Tables assume 1.5 kN/m² domestic loading + 0.25 kN/m² dead load. For longer spans, larger joists or engineered solutions (I-joists, steel beams) required with calculations. C24 timber permits slightly longer spans.
Do I need a structural engineer for a loft conversion?
Yes, strongly recommended. Existing ceiling joists designed for ceiling weight only (0.25 kN/m²), not floor loading (1.5 kN/m²). Engineer assesses existing structure and specifies floor strengthening method - typically new joists alongside existing or complete replacement. Also checks roof structure modifications and ensures adequate support. Cost £600-1200. Without engineer input, Building Control unlikely to approve and structural failure risk exists.
What wall thickness is required for a two storey house?
Cavity wall construction: 100mm internal blockwork (minimum 7N blocks) + 102.5mm external brickwork with 50-100mm cavity. Solid wall: 215mm minimum thickness. Maximum height 7m total with maximum 2.7m per storey. Walls require lateral support from floors/roof. These are deemed-to-satisfy provisions - structural calculations may permit variations or required if exceeding limits.
What are padstones and why are they needed?
Padstones are concrete blocks (typically 440x215x100mm minimum) placed under steel beam ends to distribute concentrated beam loads across multiple bricks/blocks. Without padstones, beam point load crushes masonry. Padstones essential for all steel beams bearing on masonry walls. Minimum 7N/mm² concrete strength. Structural engineer specifies exact size based on beam load - larger beams need larger padstones.
Can I use Part A standard details to avoid engineer fees?
Yes, for straightforward construction: two-storey houses on good ground using cavity walls, standard spans, and simple layouts can use Part A deemed-to-satisfy provisions without calculations. However, engineer required for: three+ storeys, poor ground, removing walls, complex layouts, unusual loadings, or anything outside standard details scope. Using standard details when inappropriate is dangerous and won't satisfy Building Control.
What is disproportionate collapse and when does it apply?
Disproportionate collapse is progressive structural failure where localized damage causes collapse disproportionate to original cause. Part A Section A3 requires prevention in buildings over 5 storeys or high-consequence buildings. Methods include effective horizontal/vertical structural ties, alternative load paths, or key element design. Houses up to 4 storeys (Class 1) exempt from specific measures beyond normal structural design standards.
How long does Building Control approval take for structural work?
Full Plans application: 5 weeks standard, 8 weeks for complex projects. Building Notice (if permitted): no upfront approval but inspections during work. Structural engineer calculations submission adds 2-4 weeks for engineer design time. Book Building Control inspections 24-48 hours in advance. Inspections required at foundation stage, beam installation, and completion minimum. Total project timeline: 6-12 weeks from initial application to completion certificate.
What happens if I do structural work without Building Regulations approval?
Local authority can issue enforcement notice requiring work exposure for inspection or complete removal. Property sale affected - solicitors require completion certificate or indemnity insurance (expensive and difficult to obtain). Mortgage providers may refuse lending. Structural failure risk if work inadequate. Retrospective approval possible but expensive - Building Control may require opening up completed work. Always notify before starting. Non-compliance is false economy.
