Previous Article
The Ultimate Composite Fencing Installation Guide
A rooftop deck can enhance, elevate, and maximise your current space, adding a true “wow factor” and a place to relax. However, in our years of supplying composite decking, we have seen that this project must be correctly checked, organised, and executed to avoid falling into the trap of complications and legal issues down the line.
When building a rooftop deck, you are not just dealing with enhanced aesthetics; you are dealing with wind loads, weight restrictions, and strict fire regulations.
To help you make the safe choice, we have drafted this engineer’s guide to the best materials for the job.
⚠️ The Golden Rule: UK Fire Regulations
Before you choose a material, you must know the height of your roof or balcony. In the UK, laws are strict regarding what materials can be used on high-rise buildings (Building Regulations Approved Document B).
- Above 18 Metres (approx. 6 storeys): You are legally required to use Class A Non-Combustible materials. This usually means Aluminium or Porcelain only. You cannot use standard timber or composite.
- 11 Metres to 18 Metres (The “Grey Area”): The rules are tightening here. Many new builds now require Class A materials even at this lower height. This is driven heavily by Insurers and Warranty providers (like NHBC) when selling the property.
- Below 11 Metres (Garden Roof Terraces): You generally have more freedom to use Class B (Fire Rated) or standard materials, but you should always check with your local building control first.
- The “1 Metre” Boundary Rule: Even if you are below 18 metres, pay attention to your neighbours. If your balcony is within 1 metre of a boundary, regulations change to prevent fire spread. In our personal view, you are better off opting for Class A (Aluminium) or Class B (Fire Rated Composite) in these zones to safeguard yourself and your property.
Experience Tip: When building below 18 metres—especially in the 11 to 18-metre zone—Warranty and Insurance are key. Before opting for any material, look ahead and check if it will affect your building insurance or ability to sell. This has become a huge issue in the press, and you don’t want to be stuck with a flat you cannot sell.
Option 1: Aluminium Decking (The Commercial Standard)
If you are in a high-rise building or want the ultimate in safety, this is the gold standard. In our personal view, for anything over 11 metres, you should be using Aluminium or Porcelain to protect yourself and safeguard your property for the future.
- Fire Rating: Class A (Non-Combustible). It creates no smoke and does not burn. It is the only option that “future-proofs” your home against changing regulations.
- Durability: Unrivalled. It is rot-proof, rust-proof, and immune to UV damage.
- The Downside: It is expensive (approx. £120+ per sqm) and can get hot in direct summer sun.
-
Engineer’s Note: Don’t make the error. Never install aluminium directly onto pressure-treated timber joists, as the chemicals in the wood can corrode the metal. Use an aluminium subframe.
Option 2: Composite Decking (The Residential Choice)
For low-rise residential roofs (e.g., a single-storey extension or garage roof), Composite is often the preferred choice due to its balance of comfort and competitive composite decking prices. If you are leaning this way, reading our ultimate guide to choosing the right board is the perfect next step.
- Fire Rating: Standard boards are Class D/E. However, you can purchase Specialist Fire-Rated Composite (Class B). Always check the spec sheet before buying.
- Performance: Excellent resistance to wind and rain. Unlike timber, composite decking offers excellent weather resistance; it won’t rot or warp, which is critical for rooftops where maintenance access is difficult.
- Aesthetics: It feels warmer and more natural underfoot than aluminium. Capped boards offer excellent fade & stain resistance for increased sunlight and entertaining family and friends on the roof.
Expert Tip: In our experience, we see many consumers opt for the cheapest option and ask questions about fire resistance after installation, when it is too late. Check your building regulations before building and ask for the correct certification reports before you even start.
Option 3: PVC Decking
PVC is a 100% plastic board. ASA PVC decking is changing this category with its enhanced aesthetic appearance and improved scratch resistance. However, note that ASA PVC generally falls into the same fire resistance category as composite (Class B being the max).
- Pros: Extremely lightweight (great for roofs with weight limits) and waterproof.
- Cons: It expands and contracts significantly in the heat. On an exposed rooftop in full sun, this movement can cause issues if not installed with large expansion gaps. It is also not an eco-friendly product.
⚠️ The “American” Trap: You may see some PVC brands claiming a “Class A” rating. Be very careful. This often refers to the American ASTM standard (flame spread), NOT the UK Euroclass A1 standard. In the UK, plastic decking generally cannot achieve Class A1. Always get the UK certification.
Option 4: Timber Decking (Avoid)
We generally do not recommend timber for rooftop decks.
- High Maintenance: You do not want to be hauling buckets of stain and sealant up to a roof every year.
- Fire Risk: Timber is a high fire risk.
- Rot Risk: Rooftops are exposed to extreme weather. Timber will dry out, crack, and eventually rot much faster than at ground level.
Conclusion: Which Material is Right for You?
The choice comes down to Height and Budget.
- If you are above 18m (or want total peace of mind): You must choose Aluminium Decking (Class A). It is expensive, but it is the only option that meets strict fire safety laws and future-proofs your property.
- If you are on a low-rise residential roof (<11m): Composite Decking is the best all-rounder. It offers the warmth and beauty of wood without the maintenance and is far more affordable than aluminium or PVC-ASA.
- Final Checklist: Ensure you check if your local council requires a “Class B” fire-rated board, check the right certification before starting, and pay attention to the 11-18m and boundary rules.
Previous Article
Next Article 
A UK Homeowner's Guide to Replacing Wood Decking with Composite
