An assessment tells you what a building is. A retrofit design tells you what to actually do about it – which measures, built to what detail, in what order, without one measure undermining another. That’s the Retrofit Designer’s job: taking the data a Retrofit Assessor collects and the options a Retrofit Coordinator has agreed, and turning them into a specification an installer can actually build from.
In this blog, you’ll learn:
- What a Retrofit Designer’s role actually covers
- How it fits between assessment, coordination and installation
- Why resolving interface risk is the core of the job
- How we deliver retrofit design that survives contact with the installer
What is a Retrofit Designer?
A Retrofit Designer takes the agreed improvement options for a property and specifies the actual technical solution: which measures, built to what junction detail, in what sequence, to what performance standard. It’s a distinct role from both the Assessor, who gathers the site data everything else is built on, and the Coordinator, who oversees the whole project and holds continuous compliance oversight rather than producing the design themselves.
A single person can hold accreditation across more than one of these roles, but under PAS 2035 they remain distinct responsibilities — and on a well-run project, the design gets checked by someone other than the person who produced it.
What Does a Retrofit Designer Do?
Design is where a retrofit project either holds together or falls apart at the seams — literally, at the junctions between measures. Here’s what the role covers:
- Translating agreed options into a buildable specification: taking the improvement options already agreed (usually via an Improvement Option Evaluation) and turning them into detailed drawings and specifications an installer can actually work from — not a general recommendation, but exact materials, thicknesses, and fixing details.
- Resolving interface risk: this is the part of the job that catches problems before they’re built in. Insulation without adequate ventilation traps moisture; external wall insulation meeting a roofline wrong creates a thermal bridge; a junction detail that works on paper can still fail if it’s not buildable on site. A good design resolves these interactions before installation starts, not after.
- Setting performance targets per measure: specifying the actual standard each measure needs to hit — a target U-value, an airtightness figure, a ventilation rate — so installation and post-completion evaluation have something concrete to check against.
- Sequencing the work: deciding what gets installed in what order, since some measures depend on others being in place first (ventilation before airtightness improvements, for example).
- Buildability review: working with installers to confirm a design that looks right on paper can actually be delivered on the property in front of them, and revising it where site conditions differ from what the assessment recorded.
The Importance of PAS 2035 in Retrofit Design
PAS 2035 exists precisely because retrofit measures interact with each other in ways that aren’t always obvious — a fabric improvement that reduces heat loss can just as easily trap moisture if ventilation isn’t addressed alongside it. The Designer’s job is where that interaction risk actually gets resolved on paper, before it becomes a problem on site. A design that’s been through proper interface and buildability review is what stands between “the numbers worked in the model” and “the building actually performs as intended.”
What Sets Us Apart
Where we’ve carried out the assessment and coordination ourselves, our designers work from that same data directly, so a design decision can be traced straight back to the condition data that justified it. We’re just as happy stepping into a project alongside other assessors, coordinators or contractors already involved, advising on interface risk and buildability wherever we’re brought in. Either way, every design goes through interface and buildability review before it reaches site, catching thermal bridging and junction risks on paper rather than as a costly on-site discovery.
The role that sits above Design, holding the whole project to PAS 2035 standard from assessment through to post-installation evaluation:
What’s Next?
A retrofit is only as good as the design behind it — the point where good assessment data either turns into a specification that performs as intended, or doesn’t. Whether it’s a single property or a portfolio-wide programme, that’s the stage we treat with the same rigour as the assessment and coordination either side of it.
We carry out PAS 2035 retrofit design – specification, interface risk resolution and buildability review – for portfolios and programmes nationwide.
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