Sustainable BuildingsRetrofittingShallow & Deep – Different Dives into Retrofitting

Shallow & Deep – Different Dives into Retrofitting

Karl Dickinson
Karl Dickinson
Change matters. It takes courage. As a writer - and citizen - I am inspired by stories of those who challenge the 'we've always done it this way' attitude. We can do better - it's time to listen to those who go against the grain.

There is no one-size-fits-all solution to decarbonising older properties. Each building has its own character, history, and flaws that need to be considered when choosing appropriate measures to make them energy efficient. These can be done in one go or piecemeal. That’s the fundamental, but not only, difference between shallow and deep retrofitting.

Buildings are unique entities. Even those apparently identical in design hide a lived history that alters the needs of each: wear and tear, historic maintenance, extensions, weather strain, vibration damage, etc. As such, retrofitting must be a bespoke application. How we choose to future-proof our homes, offices, commercial and industrial complexes, and public buildings hangs on several factors: budget, time, tastes, extent of disruption and filth it causes, and the local climate being among the primary concerns.

But we don’t have to endure inconvenience to be an environmentally conscious citizen. There are options. From all-in-one to step-by-step, we’ll take you through the ins and outs of the two major schools of retrofitting approaches.

A Tale of Two Retrofits

The best energy makeover for a build is one that’s tailored for its individual needs.

There’s little value in rushing to add external cladding to a building already boasting insulated walls when the untreated roof and floor are leaking the most heat. By understanding the specific shortfalls of each build, we can identify a responsible retrofitting portfolio. Then decide how to approach it.

Your plan will fall into one of two retrofitting camps: shallow and deep. Let’s take a closer look at each.

Shallow Retrofits – A Piecemeal Approach

Proof that every little change makes a difference. Shallow retrofits offer micro-solutions to individual problems, focusing on the minutiae of energy efficiency, rather than the complete building system.

According to Colin Bebbington from Ireland’s Bord Gáis Energy, low-impact examples that offer decent results include:

  • Converting to more efficient lightbulbs.
  • Draught exclusion – such as properly fitting doors.
  • Cavity wall insulation.

Then, of course, there’s the classic: adding loft insulation to fix that heat-leaking roof we mentioned. Or triple glazing.

Shallow upgrades are perfect for smaller budgets or buildings already on their way to net zero needing that extra tweak. Notably, they concentrate more on renewable energy creation than overall efficiency.

Shallow Retrofits – The Ups and Downs


  • Pick and choose individual solutions that can be added in stages when time, budgets, and expertise allow.
  • Minimum disruption – occupants rarely need to vacate a property for work to be conducted.
  • Powerful for meeting short-term energy goals – a boon for city councils and property owners who want quick ROI.
  • Quick payback: savings of 10-20% are reflected in energy bills in just over a year.
  • Small changes are easy to incorporate during routine household maintenance/redecorating.


One other disadvantage: Incremental upgrades delay holistic impact, minimising potential gains. For example, installing triple glazing one year provides benefit. But if insulation comes 2 years later, that’s 48 hours of better efficiency levels lost.

Deep Retrofits – A Whole-House Approach

Maximising energy efficiency and tackling a reliance on fossil fuel. That’s a deep retrofit agenda. With their (almost) 100% efficiency rating, passive house renovations fit snugly into this category. Or, if the purse strings allow, we can indulge in adding centralised ambient controls.

Ideally, deep retrofits start with a whole-building evaluation, which identifies complete and complementary improvements. This provides 50-100% carbon and energy efficiency[1] and is exactly what a spot of retro-commissioning can accomplish – the addition and calibration of, say, an HVAC or light and heat sensors to perfect the ambient comfort.

Colin explains this option is “more intrusive” and covers “upgrades such as external or internal wall insulation, airtightness and mechanical ventilation, renewable heating systems such as heat pumps” or solar heating. We can also install photo-voltaic units for electricity generation. And the batteries to store it in. In other words, investing in some pretty hefty hardware.

Deep Retrofits – Advantages and Disadvantages


  • A comprehensive package of benefits. Immediate and holistic impact.
  • Other than routine maintenance, further disruption is unlikely.
  • Pay once. No additional investment required.
  • Pre-construction evaluation ensures all changes complement – rather than contradict – all others.


  • Possible major disruption, requiring evacuation of buildings for extended periods – can be worrisome or prohibitive for those with nowhere else to go.
  • Expensive. The Deep Retrofit Pilot Programme in Colin’s native Ireland cost €58,722 per home to renovate to the highest energy rating. Passive House improvements can be twice that.
  • A difficult sell, especially in the public sector, due to the long-term nature of ROI (5-7 years on average).
  • Equipment can encroach on space, such as duct piping and water heaters.

No Such Thing As a Bad Retrofit

Diana Ürge-Vorsatz, Vice Chair of Working Group III of the Intergovernmental Panel on Climate Change (IPCC), has been quoted saying “shallow retrofits need to be avoided”. That we should wait until enacting its deep counterpart is possible.

But that is time lost. Carbon emitted. Energy wasted. Money burned. Years of unnecessary discomfort. Why wait? Even small changes made on a budget have an impact. Plus, retrofitting of any kind encourage upscaling and potentially improved affordability.

Shallow and deep is not a matter of good vs bad. They both keep energy consumption, environmental harm, and costs down. The trick to getting it right is defining the purpose of your project first.

But don’t take our word for it. Let’s see this in action!

Deep Retrofit Case Study – Victorian Semi-Detached House, UK

Think Victorian and what comes to mind? Poverty. Workhouses. A starving Oliver Twist. Pretty bleak. So maybe it’s no surprise that their abodes, while built to last, are an energy efficiency nightmare.

At least they can be pretty. Zetland Road in Manchester is a prime example. At 125 years old, Europe’s first Passivhaus EnerPHit Plus Home is a period property. The retrofit had to preserve the heritage aesthetic. Rewiring original chandeliers for LEDs bulbs, triple glazed stained glass, and copper drainpipes – that will last 120 years! – are an authentic touch.

A comprehensive, heritage-respecting refurb was achieved using new-to-market tech, materials, and innovations. An ultra-efficient domestic water heater that only warms the water required is fully powered by rooftop solar panels and can be controlled by an app. Filtration in the heat recovery ventilation system ensures constant fresh air without heat loss. Cladding and rear windows are angled for increased heat absorption. Greywater from handwashing is stored for flushing the toilet.

Biomaterials were used in place of synthetics: insulation made from recycled paper and wood fibre. Through biomimicry, natural solutions create an airtight, dry, warm residence.

A neat touch was to house ventilation pipework in chimney cavities, encroaching on no living space whatsoever.

The result? Absolutely no energy costs. None! Minimal maintenance. Cost savings of £50,000 in the first decade alone. The efficiency is so succinct that by using A+++ rated appliances, the house is designed to generate more energy than it consumes!

The homeowners were reluctant at first: “Our biggest fear was how we would live in it, what we would need to do and learn; but the fact is, you don’t need to do anything – the house does it all for you.” Indeed, a lot of the trepidation in undertaking such an extensive refurbishment is being ill-informed. Experience is a wonderful teacher. “If anything,” continues the satisfied resident, “the house has changed us rather than us changing for the house.”

With such a strong case for deep retrofits, it’s hard to imagine an alternative. But there is…

Shallow Retrofit Case Study – Phased Home Upgrades in Florida, USA

About as far from the chilly northern English winters as one can get, Florida’s problem is humidity. And the infernal heat. And America’s high energy consumption culture.

In 2013, the Building America Partnership for Improved Residential Construction trialled easy-to-install efficient cooling, lighting, and water heating technologies on several properties.

Energy saving and LED bulbs were required in half the homes. Cladding (‘wrap’) was added to water storage tanks and pipes. Showerheads were replaced with low-flow alternatives. Refrigerator cooling coils and vents were cleaned.

The entire makeover and cleanse was completed in an average of 4 hours per property. Material and labour cost of just $374. Raking in savings of $180+ annually, these upgrades paid for themselves in just 2 years. The impact was immediately measurable. Replacing lamps resulted in 50% energy savings; 31% for the hot water solutions. Overall, whole-house efficiency was improved by 9% with “very favourable economics”.

Almost unique to the Sunshine State retrofit was applications of timers to pool pumps. Yes, the device that keeps swimming water circulating. This gave the most instantaneous alteration, at 16% more efficient. Although, resident interference was later found to counteract any good.

It’s true that passive house renovations would be more reliable. Regardless, there is clear, measured evidence that proves shallow retrofits work.

Shallow and Deep Retrofitting in a Nutshell

One thing’s for certain: inaction would be the worse response to an ageing population of buildings. With existing stock producing so much of the world’s harmful emissions, modifications are needed to stabilise the threat. But more than that, we’re living and working in builds that could be better suited for our use, health, and happiness.

A whole-house approach creates a huge impact, but piecemeal changes make energy renovations a sinch! Whichever we choose, it’s important to see the bigger picture – to ensure no measure undermines another and undoes all that good work.

Now you know the differences between retrofitting options, you’re well on your way to getting started with your own renovation project. Don’t fear! We tell you exactly how, right here.

[1] Volans, Re:Pattern and APPG on Fair Banking. (2021). Bankers for Net Zero briefing: The Retrofit Revolution.

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