Are you a first-time property developer or investor looking for affordable and high-potential opportunities in the UK’s property market? You might be missing one of the biggest opportunities—right above your head.
Welcome to the world of airspace development, where unused rooftop space can be converted into profitable new homes. Since June 2020, changes to UK planning law have made this type of development faster, easier, and more accessible—even for beginners.
In this article, we’ll break down what airspace development is, how the new permitted development rights (PDRs) under Part 20 of the GPDO work, the benefits and risks, and how you can use refurbishment bridging loans to finance your project. Whether you’re looking to expand your portfolio or kick off your first development, this is your essential guide.
What is Airspace Development?
Airspace development is the construction of new residential units—usually flats—on top of existing buildings. In simple terms, you’re adding one or two new storeys using the unused rooftop space.
This strategy is especially useful in densely populated urban areas like London, Birmingham, Manchester, and other cities where land is limited and expensive. With no need to purchase additional land, airspace projects often deliver higher ROI per square metre.
Why First-Time Developers Should Consider Airspace Projects
For new investors and developers, airspace projects offer:
- Lower entry costs (no land purchase required)
- High GDV potential in urban areas
- Access to underutilised space with growing demand for flats
- Shorter build times compared to ground-up developments
- Easier permitted development approval process under Part 20
You’re essentially building value out of thin air.
Government Support: The GPDO Part 20 Breakdown
In June 2020, the Government updated the General Permitted Development Order (GPDO) with a new section—Part 20. This opened the door to vertical expansion by allowing upward extensions on many types of buildings without full planning permission.
✅ Key Criteria Across All Part 20 Classes:
- Existing building must be at least 3 storeys
- Maximum roof extension of 7m
- Total building height (excluding plant): 30m max
- Floor-to-ceiling height of new flats must not exceed 3m
- New units must be self-contained flats
- No external support structures permitted
- Applies only outside conservation areas (Article 2(3) land)
- HMOs cannot be created via this route
Breakdown of Airspace Development Classes
Here’s a simplified view of the six PDR classes under Part 20:
| Class | Applies To | Permits |
| Class A | Blocks of flats | 2 storeys of flats above existing flats |
| Class AA | Detached commercial or mixed-use | 2 storeys above existing roof |
| Class AB | Semi-detached or terraced commercial | 1–2 storeys depending on existing use |
| Class AC | Terraced or semi-detached houses | New flats above homes |
| Class AD | Detached houses | New flats above detached houses |
| Class ZA | Redevelopment opportunity | Demolish and rebuild with 2 extra storeys |
Each has specific conditions—height limits, surrounding context, and building use types—so expert guidance is crucial.
Step-by-Step: How to Start an Airspace Development
- Identify Suitable Property
- Urban area with strong demand
- Existing 3+ storey structure
- Not in conservation or protected zone
- Assess Feasibility
- Structural integrity of the building
- Air rights ownership
- Existing tenant agreements (if any)
- Secure Prior Approval
- Submit application under the correct Part 20 Class
- Allow 8–12 weeks for approval
- Arrange Finance
- Use refurbishment bridging finance to fund the project
- Commence Build
- Use trusted contractors with rooftop extension experience
- Exit Strategy
- Sell completed flats or refinance into a long-term mortgage
Don’t Build Until You Know It Can Hold: The Importance of Structural Surveys
One of the most critical (and often overlooked) steps in an airspace development project is ensuring the existing building can physically take the weight of additional floors.
Before you apply for prior approval or commit to purchase, you must commission a comprehensive structural survey by a qualified structural engineer. This is non-negotiable.
Why a Structural Survey Is Essential:
- Load-bearing capacity: The existing foundations and structural framework must be able to support the new storeys.
- Material integrity: Older buildings may suffer from weakened concrete, corrosion, or inadequate design standards.
- Temporary works planning: The build may require support scaffolding, bracing, or other temporary structures during construction.
- Strengthening works: You may need to retrofit steel frameworks, reinforce walls, or install additional columns inside the existing building.
These factors can significantly increase the project cost, which is why it’s essential to engage a Quantity Surveyor (QS) to cost not just the construction, but also the structural upgrades, temporary works, and any necessary party wall agreements.
Pro Tip:
You’ll want your QS and structural engineer to work together early in the process, ideally before you submit for prior approval. This will help you assess whether the project is viable and financially sensible—before you commit funds.
At Sunrise Commercial Finance, we encourage all our clients to have a “costed viability pack” ready before we apply for finance. This shows lenders you’re serious, professional, and understand the risks—making funding more likely to be approved on favourable terms.
Why Refurbishment Bridging Loans Are Ideal for Airspace Projects
Traditional mortgages are slow, rigid, and unsuitable for most property development projects—especially ones involving planning and construction.
A refurbishment bridging loan offers:
- Fast access to capital (usually within 7–14 days)
- Funds for both purchase and build costs
- Flexible repayment terms (typically 6–18 months)
- Interest can be rolled up, so no monthly payments
- Easier approvals based on project viability, not personal income
At Sunrise Commercial Finance, we work with specialist lenders who understand development risk and can offer tailored finance solutions even for first-time developers.
Potential Risks & Considerations
While airspace development is promising, it’s not without risk:
- Structural feasibility: Not all buildings can support new floors.
- Neighbour objections: Though it’s PDR, you still need approval.
- Delays: Prior approval and construction may take longer than expected.
- Exit strategy: Sales or refinancing can be impacted by market conditions.
- Cost overruns: Always budget for contingencies.
Having an experienced broker by your side can help mitigate these risks and structure your finance to fit your timeline and budget.
Real-Life Use Case Example
Case Study: Retail-to-Rooftop in East London
A developer purchased a 2-storey terraced retail unit in East London for £750,000. Using Class AB under Part 20, they added 2 new storeys to create 4 self-contained flats, generating an estimated GDV of £1.5M.
We arranged a £850,000 refurbishment bridging loan covering 100% of build costs and 75% of the purchase price. The loan was repaid after 10 months via a development exit bridging loan, allowing time for unit sales.
Conclusion: Sky-High Potential with the Right Support
Airspace development is one of the most underrated and profitable strategies in today’s market. Whether you’re looking to build your first property or grow your investment portfolio, learning to spot and fund these rooftop opportunities could be your next big win.
At Sunrise Commercial Finance, we help investors and developers—new and experienced—secure fast, flexible funding for airspace, refurbishment, and mixed-use developments across the UK.
Get Expert Help from a Trusted Property Finance Broker
📞 Call us: 07939 091418
📧 Email: john@sunrisecommercial.co.uk
🌐 Visit: www.sunrisecommercial.co.uk
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