CarbonLite, Clearly: How AECB’s Standards Help Us Design Low-Energy Buildings That Actually Work

What is CarbonLite?

CarbonLite is the AECB’s practical framework for creating buildings that are genuinely low-energy, comfortable and healthy. It takes Passivhaus thinking (modelling with PHPP, focus on fabric, ventilation and airtightness) and packages it into standards that UK designers and builders can deliver cost-effectively. 

Ribbon House exterior view showing rear extension in Queen’s Park with precast concrete canopy, large glazing and landscaped garden as part of an AECB CarbonLite retrofit.

The three strands at a glance

1) CarbonLite New Build
For new homes and non-domestic buildings using widely available tech and construction methods. The AECB estimates this route can cut operational CO₂ by around 70% versus typical UK stock — a big win without exotic materials or methods. 

2) CarbonLite Retrofit (full)
For deep retrofits that meaningfully reduce energy demand and winter bills while improving comfort and air quality. It uses Passivhaus methodology (PHPP) and independent AECB Approved Certifiers to quality-assure the design and built outcome, with projects uploaded to the Low Energy Buildings Database on certification. Typical airtightness is far tighter than UK Building Regs, with published guidance and targets to suit different project contexts. 

3) Step-by-Step (‘Step 1’) Retrofit
A pragmatic pathway when budgets, access or sequencing make a full retrofit in one go unrealistic. The crucial idea: your first step is planned so nothing you do now blocks later measures; each phase is modelled in PHPP to stay on track technically and financially.

Targets (in plain English)

• Energy + comfort are modelled, not guessed. All CarbonLite projects use PHPP, the same calculation engine behind Passivhaus, so we predict performance before we build and verify afterwards. 

• Airtightness matters. Retrofit pathways reference achievable, real-world levels (for example, guidance around ~5 m³/hr·m² @50Pa for an entry step and tighter targets where feasible; some full retrofits work to around ~2 ACH@50Pa). In new build, we design detailing to deliver excellent airtightness reliably — and we test it. 

• Fabric first. Insulation, thermal-bridge control and high-performance windows/doors are coordinated as a system, not as isolated upgrades, which is how you get comfort without penalty elsewhere (condensation, summer overheating, etc.). 

• Ventilation with brains. MVHR (or well-designed mechanical extract where MVHR isn’t yet viable) is planned from day one so indoor air is clean, filtered and consistent — especially vital in deep retrofits. 

The CarbonLite ethos is simple: design with evidence, build with care, prove it works.

Indoor–outdoor connection at Ribbon House with sliding timber doors, dining area and landscaped garden, designed to AECB CarbonLite standards.

Why we like CarbonLite at RISE

• It’s rigorous without being dogmatic. CarbonLite gives clear, testable outcomes yet allows the design freedom we need for context, character and craft.

• It scales. From single London terraces to community/cultural buildings, we can calibrate ambition: Step-by-Step for staged budgets, or full New Build/Retrofit when the brief supports it. 

• It’s certifiable. Independent AECB certifiers review the PHPP model, details and evidence; successful projects are recorded in the Low Energy Buildings Database — transparent, comparable, accountable. 

How we deliver a CarbonLite project (our workflow)

1. Brief → Feasibility
   We map your goals (budget, phasing, comfort issues, bills, carbon priorities) against the most suitable CarbonLite route and sketch early options.

2. PHPP pre-design modelling
   We model the building’s energy balance early, testing fabric upgrades, window specs, shading, airtightness and ventilation to find the sweet spot between performance and cost. 

3. Detail design for performance
   We coordinate junctions and services to make airtightness and moisture-safe insulation “buildable”, not just desirable; we plan testing and QA with the contractor from the start. (AECB’s airtightness guidance informs our site strategy and checks.)

4. Procurement with the right team
   We tender to contractors who understand low-energy delivery and agree the testing/commissioning plan up front.

5. On-site verification
   Blower-door tests, MVHR commissioning and evidence gathering for certification — managed so handover isn’t a scramble.

6. Certification & monitoring
   With the AECB certifier we close the loop and, where helpful, add light-touch post-occupancy checks.

FAQs we hear from clients

Is CarbonLite just Passivhaus by another name?
No — it’s built on Passivhaus methodology and PHPP but tailored as a flexible framework for the UK market, with routes for new build and different retrofit realities.

What if I can’t afford a full retrofit now?
Start with Step-by-Step. We plan the destination and deliver logical phases that don’t trap you later. Think of it as “retrofit without regrets.” 

Will it look ‘boxy’ or compromise design?
Not with RISE. We integrate performance with material honesty, daylight, and craft. CarbonLite defines outcomes; we design how you get there.

How “tight” is ‘airtight’?
It depends on your route and building. As a guide, entry-level step targets can be around 5 m³/hr·m² @50Pa, with deeper retrofits aiming tighter (e.g., ~2 ACH@50Pa). We’ll set the right target for your project and make it buildable, then test it.

What this means for you

• Lower bills and carbon with measurable results — not just green labels. 

• Year-round comfort: warm, even temperatures and filtered air.

• Future-proofing: designs that anticipate policy, grid decarbonisation and heat-pump readiness, with staged pathways where needed.

Ready to explore CarbonLite for your home?

Whether you’re planning a new build or upgrading a much-loved Victorian terrace, we’ll help you choose the right CarbonLite pathway — New Build, full Retrofit or Step-by-Step — then design the details so it works in the real world.

Let’s talk about your brief → Reply with your address, goals (budget, comfort, bills) and timeline. We’ll suggest the best route and next steps, including PHPP pre-design modelling and (if you wish) AECB certification. 

Building for the future

At RISE, we believe CarbonLite isn’t just a badge. It’s a promise — to design buildings that are comfortable, low-energy and built to last. Homes that set a higher bar for performance and craft. That answer to both climate and character. That are bold enough to lead and humble enough to belong.

Curious which CarbonLite pathway fits your project — New Build, Retrofit or Step-by-Step?
Let’s map it together and design a home that gives back more than it takes.

→ Email us at architects@risedesignstudio.co.uk
→ Or call the studio on 020 3947 5886

RISE Design Studio, Interior Designers + Sustainability Experts

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