What We Found Under the Floor: A Victorian Retrofit Story

A Lower Clapton Victorian terrace, a broken sewer, and the case for understanding a building before you try to improve it.

Some projects start with a design brief. This one started with an emergency.

When we began work on a Victorian mid-terrace in Lower Clapton,  brought to us with a clear ambition to transform a cold, damp, inefficient house into a sustainable family home, we knew the building had problems. What we didn’t know, until we properly investigated, was quite how serious they were.

Rotten ground floor joists. Soil erosion caused by a broken sewer running beneath the property. Structural vulnerability that previous owners and previous contractors had, for whatever reason, worked around rather than resolved. The house hadn’t just been uncomfortable to live in. It had been quietly deteriorating for years.

Before a single insulation board was specified or a heat pump discussed, we had to stabilise the building. Emergency underpinning. Sewer repairs. Structural remediation. None of it appeared in the original brief. All of it was essential.

This is the project we come back to whenever someone asks us why we always start with diagnosis, not design.

Why Victorian terraces deserve particular scrutiny

Who doesn’t love a Victorian property with their good proportions, period character, adaptable layouts? However they are also among the most likely to be carrying hidden problems.

Built at a time when subsurface drainage, damp-proof courses, and structural surveying weren’t what they are today, many have spent a century slowly accumulating issues. Some have been patched repeatedly. Some have had well-intentioned improvements; insulation, extensions, new kitchens, all installed without anyone properly checking what was going on underneath.

When you’re planning a retrofit, this history matters. A retrofit that improves the thermal performance of a building with unresolved structural or moisture problems doesn’t just fail to fix those problems, it can make them worse. Sealing a building that has active damp, for example, traps moisture rather than allowing it to escape. The energy performance numbers may improve. The building underneath may continue to deteriorate.

What a proper pre-retrofit diagnosis looks like

On the Lower Clapton project, our pre-work investigation covered several areas that wouldn’t typically appear on a standard architect’s checklist. We consider all of them essential for any serious retrofit of an older property. Read our blog for more on this here.

Substructure and foundations. The ground floor joists were in a significantly worse condition than a surface inspection would have suggested. Soil movement caused by the broken sewer had undermined the structure in ways that wouldn’t have been visible without opening up. We took on the project as CDM Principal Contractors, responsible for coordinating health and safety across the whole site. The structural work at this stage was non-negotiable. Nothing else could proceed until we’d finished it.

Drainage and services. The broken sewer wasn’t just a structural problem. It was a moisture problem, a health problem, and a long-term risk to everything built above it. Identifying and repairing it at the outset rather than discovering it mid-retrofit when floors were down and insulation was going in saved significant time, cost, and disruption later.

Damp and ventilation. The property had persistent damp issues, some of which were related to the drainage problem and some of which were independent. Understanding the source of damp before specifying insulation is critical and it’s something that’s easy to get wrong if you’re in a hurry to get to the more interesting parts of the project.

Existing fabric performance. Only once the structural picture was clear did we begin the assessment of the building envelope , that means the walls, roof, floors, windows, that would inform the retrofit specification. U-value calculations, SAP modelling, and a clear picture of where heat was being lost and where moisture was at risk of accumulating.

What we specified, and why the diagnosis shaped it

With the structural work complete and a thorough understanding of the building in hand, we could specify the retrofit with confidence.

Internal and external insulation was used in combination,  a decision that often raises questions, but which was clearly the right approach for this particular building. The solid brick walls needed meaningful improvement to their thermal performance. Mixing internal and external insulation let us treat each elevation on its own terms, while managing the risk of trapped moisture building up inside a wall that needs to breathe.

New timber and aluminium windows improved energy performance while respecting the Victorian character of the house, a balance that matters in a conservation-aware context like Lower Clapton. Below-ground ventilation resolved the residual damp. An air source heat pump and underfloor heating, sized accurately to the now well-understood heat demand of the building, provided the low-carbon heating system the family needed.

Photovoltaic solar panels, permeable paving in the courtyard, locally sourced and low-carbon materials, and rigorous waste management practices rounded out the project. Together, these measures made the retrofit genuinely whole-house. The building had been properly understood first, and every measure that followed built on that understanding.

What this means if you’re planning a retrofit

The Lower Clapton project is an unusually dramatic example of what pre-retrofit diagnosis can uncover. Most projects won’t involve emergency underpinning. But the principle that you ‘ understand the building before you try to improve it ‘ applies every time.

If you’re planning a retrofit of a period property, these are the questions worth asking before any design work begins:

Has the substructure been properly inspected,  not just visually, but with opening up where necessary? Are there any signs of drainage problems, past or present? Where is damp coming from, and what’s causing it? What does the existing fabric actually perform at, not what you’d expect from a building of this age and type, but what it actually achieves?

A good pre-retrofit survey costs money and takes time. It also routinely saves more of both and occasionally, as in Lower Clapton, it saves the building.

A note on how we work

We’re a design and build practice with a fabric-first approach to sustainable retrofit. That means we think about the building before we think about the technology. And it means we take pre-retrofit diagnosis seriously, even when it surfaces things that make a project more complicated.

If you have an older property and you’re thinking about a sustainable renovation, we’d love to talk.

We’ll always be honest about what we find and about what needs to happen before the interesting work can begin.

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