Retrofit Myths & Jargon Buster: Christmas Countdown Collection.
Throughout December, we shared a daily series unpacking some of the most common retrofit myths and clarifying technical terms.
This page brings all 13 posts together in one place. From thermal bridging and fRsi, to whole-house plans, resident engagement and performance risk.
Whether you’re a housing provider, asset manager or retrofit practitioner, the aim is the same: to make the core principles of good retrofit clearer, more practical, and easier to share with your teams.
We hope you find this resource useful!
Retrofit Myths & Jargon Buster:
JARGON BUSTER: “Thermal Bridging”
Thermal bridges are areas where heat escapes faster: junctions, corners, windows, and structural links.
Often invisible. Always important.
They can cause:
• cold spots
• surface condensation
• mould growth
• reduced efficiency
Thermal modelling helps identify risks early, so they can be addressed through design.
JARGON BUSTER: Fabric-first approach
The Fabric First approach is a strategy in building retrofitting that focuses on improving the physical fabric of a building, before considering other energy efficiency measures.
A fabric-first approach focuses on three essentials:
• Insulation – effective insulation to reduce heat loss in winter and prevent overheating in summer, improving comfort and lowering bills for residents.
• Thermal bridging – reducing heat loss at junctions and edges, where problems often begin.
• Air tightness – reducing uncontrolled draughts and help the building maintain st stable temperatures – while always pairing this with appropriate ventilation.
This is the foundation of PAS 2035: a whole-house method that ensures each decision supports the next.
JARGON BUSTER: BRPD vs PD (CDM)
Two roles. Similar name. Different responsibilities.
BRPD — Building Regulations Principal Designer
• Defined by the Building Safety Act 2022
• Ensures compliance with Building Regulations
• Required where design work triggers Building Control
PD (CDM) — Principal Designer under CDM 2015
• Defined under the Health & Safety at Work Act
• Manages health & safety risks in the design phase
• Required on most construction projects, including retrofit
MYTH: “One approach works across the whole stock.”
Stock diversity makes that impossible.
Solid-wall, mixed-age estates, non-traditional construction, each behaves differently.
Good retrofit respects those differences. It doesn’t apply a blanket solution.
JARGON BUSTER: fRsi — Internal Surface Temperature Factor
fRsi = Internal surface temperature factor (0–1).
It indicates how likely a junction is to drop to a temperature where condensation and mould could form.
Low fRsi = higher risk of:
• surface condensation
• mould
• cold spots
• resident discomfort
It’s an important, yet commonly overlooked indicator of building health.
Good design raises fRsi at critical junctions, ensuring warm, dry internal surfaces.
JARGON BUSTER: Whole-house plan
For social housing stock, this is essential. It ensures future-proofing, minimises rework, and gives your organisation clarity on budget cycles.
It sets out:
• the right long-term measures
• the right order
• the risks to manage
• the benefits for residents
A good plan gives you control. Not guesswork.
MYTH: “Retrofit ends once the installer leaves.”
Retrofit is not install-and-go. It’s only complete after monitoring & evaluation.
Did the home perform as intended?
Are residents comfortable?
Are there new moisture risks?
Retrofit isn’t install-and-go, it’s a full performance cycle.
JARGON BUSTER: EWI & IWI
External Wall Insulation (EWI) wraps the building in a continuous thermal layer.
Internal Wall Insulation (IWI) improves performance from the inside when EWI isn’t suitable.
Both approaches work, but both require careful consideration of moisture, detailing and ventilation.
Good design selects the right system for the right building.
MYTH: “Once the retrofit is installed, residents will automatically get the benefits.”
Not quite.
Even the best-designed retrofit won’t perform as intended if people don’t know how to use the new systems, controls, or ventilation strategy.
Comfort, health, and energy performance all rely on how the home is lived in day to day.
This is where good communication matters just as much as good design, to help residents feel confident, supported, and in control of their upgraded home.
Clear explanations.
Simple, usable guides.
Post-install check-ins.
And retrofit advice delivered in a way that’s relevant, accessible and timed to when residents actually need it.
Retrofit is technical; yes. But it’s also deeply human.
It succeeds when the people living in the home feel the difference, understand the changes, and experience the comfort the design intended.
Scheduled up until this post::
JARGON BUSTER: Archetypes
In retrofit, an archetype is a way of grouping homes that share similar construction, age, layout, and performance characteristics.
For housing providers, archetypes help simplify complexity. Instead of assessing every property from scratch, you create representative groups.
Why it matters:
• Smarter planning Archetypes allow you to forecast risks, costs and measures at scale.
• Consistent design If an upgrade works for one home in the archetype, it can often be adapted safely for the others.
• Better sequencing They help coordinate fabric, ventilation and heating decisions across whole portfolios.
Archetypes don’t replace whole-dwelling assessments, but they make programme design more efficient, predictable and manageable.
SPECIAL: Skeilings — The Small Detail That Can Cause Big Problems
Skeilings; the sloped ceilings between loft and wall, are frequently overlooked but technically sensitive.
Common issues we find:
• no eaves ventilation
• no insulation, or inconsistent insulation
• insulation packed too tightly to allow ventilation
• shallow rafters (often 75 x 50mm) limiting available depth
Good retrofit design ensures:
• continuous ventilation
• robust thermal performance
• mitigated thermal bridging
JARGON BUSTER: Performance gap
Housing providers know this all too well, a home performs differently once lived in.
The performance gap reflects the difference between design intent and actual outcomes.
Closing it means:
• better assessment
• better coordination
• better monitoring
• better communication with residents
Stronger data means stronger decisions.
Welcome to the final day of our Myth & Jargon Buster Countdown
JARGON BUSTER: U-Value
• U-value = how fast heat escapes. Lower = better.
• R-value = how well a material resists heat loss. Higher = better.
Both matter. But U-value tells you about heat loss through an element, while R-value describes the material’s resistance. way in retrofitting homes that are compliant, efficient, and, most importantly, make a lasting difference to the people who live in them.
