Retrofit Done Right: Guide to Energy-Efficient Building Upgrades

What is retrofit ?

Retrofit is a buzzword in construction, but it’s more than jargon – it’s about transforming existing buildings to boost performance. This often means enhancing energy efficiency, accessibility, or functionality.

Our focus here is on energy efficiency, using a fabric-first approach. By insulating, draught-stripping, and upgrading the building’s fabric, we maximise energy savings. These improvements, known as Energy Efficiency Measures [EEMs], are tailored to enhance a building’s sustainability and comfort.

This mini-guide simplifies retrofit into 15 key areas, ideal for smaller buildings like homes or small commercial spaces. For deeper insights, you can either consult specialised resources on your own, or why not get in touch with us at Ikonografik Design and let us bring our extensive expertise to your sustainable retrofit project.

Insulation

Insulation is a cornerstone of improving a building’s energy efficiency, acting like a cosy duvet that wraps the structure to prevent heat loss. We prefer organic, bio-based materials like sheeps wool, wood fibre, hemp, and cork, which are minimally processed and free from harmful chemicals or fossil fuels. These sustainable options enhance a building’s warmth and eco-friendliness, making them ideal for retrofitting projects.

Installation can occur inside or outside the building, but older structures often have walls, floors, or roofs that create gaps or “bridges” in the insulation layer, allowing heat to escape. A thoughtful retrofit strategy minimises these gaps. Internal wall insulation may reduce floor space and usually requires door frame adjustments.

Image credits: Thermafleece.

Ventilation

Ventilation, which is often misunderstood, is vital for a building’s energy efficiency and health of the occupants. It involves exchanging stale indoor air with fresh outdoor air to manage moisture, remove pollutants, and enhance comfort. Poor ventilation can lead to mould, dampness, and health issues, while good ventilation ensures clean, dry air that heats faster, saving energy. Effective ventilation also boosts productivity by maintaining fresh air for work and socializing, making it a key part of any retrofit project.

Ventilation can be provided by natural means [using windows, trickle vents, or air bricks / wall vents] or mechanical, with systems like Mechanical Ventilation with Heat Recovery [MVHR] capturing heat from stale air to pre-warm incoming air, reducing energy loss. Retrofitting older, drafty buildings often reduces natural ventilation, risking dampness and poor air quality, so assessing overall ventilation provision is important.

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Air Tightness

Air tightness is crucial in retrofit design, minimising unwanted air leakage from buildings to create energy-efficient and comfortable spaces. By reducing drafts and controlling ventilation, air tightness lowers heat loss, decreasing the need for heating and cooling. This leads to lower utility bills and a reduced carbon footprint, while ensuring consistent indoor temperatures, better air quality, and enhanced occupant comfort, making buildings more pleasant for living, working, or leisure.

Beyond energy savings, air tightness protects structural integrity by preventing moisture damage, extending a building’s lifespan. Strict air leakage tests can be undertaken, using fans to ensure compliance with Building Regulations or standards like Passivhaus to help ensure a building’s air tightness. Importantly, air tightness differs from breathability—older buildings can be vapour-permeable to manage moisture while still being airtight, ensuring both durability and optimum efficiency.

Glazing

When updating windows and doors in older houses, the goal is to make them more energy-efficient and practical while keeping their charm.

Here’s what to focus on: Choose windows with special low-emissivity glass [like Pilkington K glass] that helps keep heat inside. Use warm edge spacers and frames designed to block heat loss. Triple glazing keeps things cozy, but usually takes more energy to make than double glazing, so double glazing is often a smarter choice. Vacuum glazing is also becoming more common place but the benefits vs drawbacks needs further consideration. To stop chilly drafts and save energy, insulate around the window frames well and use foam tape [not gooey sealants] to seal gaps tightly.

You’ll also need to check if the window frames and surrounding structure are strong enough—sometimes old beams need replacing. For safety, go for toughened or laminated glass and secure locks [look for “Secured by Design” standards]. In historic homes, secondary glazing [an extra layer of glass inside] can boost efficiency without changing the original look. If possible, bigger windows can let in more sunlight and warmth, and choosing different frame materials or styles can make the house look better while working more efficiently, all while respecting the home’s unique character.

Heating

Even with excellent insulation and air tightness, retrofitting UK buildings rarely eliminates the need for heating, due to the cool climate. Early planning for heating ensures a warm, comfortable environment for occupants. Calculating heat loss, versus heating output is crucial to sizing heating systems appropriately, maintaining energy efficiency while keeping spaces cozy for families or workplaces.

Heating options include traditional hot water radiators, electric radiators, hot water or electric underfloor heating, and innovative infrared systems like ultra-thin panel heaters or films embedded in walls/ceilings.

Zoning and smart controls enhance efficiency by independently managing different areas. While wood burner stoves are less favourable due to pollution and incompatibility with airtight buildings, choosing the right system early optimises comfort and sustainability.

Cooling

As UK summers get hotter, updating older homes to stay cool is essential, especially in rooms with big windows or south-facing glass areas, like conservatories or modern large windows.

When upgrading windows, think about their size and direction to reduce unwanted heat from the sun. This can be figured out with simple planning tools. While new buildings follow rules to prevent overheating, older homes need thoughtful updates to keep people comfortable during hot weather.

Cooling can be done without using extra energy through passive methods, like adding internal or external blinds, sunshades [brise soleil], shade sails, shutters, or special solar control glass to block heat. Opening windows at night to let cooler air replace the hot air, or using insulation materials like wood fibre or cork that absorb heat, can also help. For more powerful cooling, active systems like air conditioning or reversible heat pumps work well but use electricity, so they need careful planning. By calculating how much heat comes in and what cooling is needed, you can choose the right system to keep your home comfortable and energy-efficient.

Energy Sources

A “fabric-first” approach to retrofitting older homes focuses on adding insulation, sealing drafts, and improving the building’s structure to cut down on energy use. However, for historic or listed buildings, these upgrades must be done carefully to avoid harming their unique features. Even with these improvements, homes still need heating, cooling, and power for things like lights and appliances. Most UK homes currently use gas or oil boilers, but with gas boilers being banned in new homes after 2025, switching to eco-friendly energy options is key for sustainable upgrades.

Renewable energy sources are great alternatives, especially for older buildings where structural changes are limited. Practical options include heat pumps [which pull heat from the air, ground, or water], solar panels for electricity [PV panels], solar water heaters [evacuated tube panels], and batteries to store energy. Small wind turbines can also be used but are not so popular at the moment. Less common choices like biomass and combustion boilers, are generally avoided now due to pollution concerns. Adding renewable energy to retrofit plans helps ensure homes stay energy-efficient and sustainable while meeting heating and power needs for the long term.

Money

When upgrading older homes, balancing costs with comfort and environmental benefits is key. A payback calculation helps figure out if energy-saving upgrades, like insulation or renewable energy systems, are worth it by showing how long it takes for savings on energy bills to cover the initial cost. For example, spending £20,000 on a heat pump and solar panels that saves £2,000 a year on bills would take 10 years to pay off, which is reasonable because it’s less than 15 years. Plus, selling extra energy back to the grid can bring in some cash.

The materials you choose also affect the cost a lot. Modern materials are often cheaper but can have a bigger environmental footprint, while natural or organic materials usually cost more but have a reduced environmental footprint. Natural or organic materials are usually better for historic homes as well. Government programs like the Boiler Upgrade Scheme, ECO4, Great British Insulation Scheme, Home Upgrade Grant, Social Housing Decarbonisation Fund, and VAT relief on energy-saving upgrades [available until 2027] can help lower costs, but you’ll need to meet specific requirements. For more details check out, gov.uk or ofgem.gov.uk.

Deep retrofit – Whole building approach

A deep retrofit means thoroughly upgrading an older home to make it super energy-efficient, comfortable, and eco-friendly. It involves major improvements like adding top-notch insulation, sealing drafts, upgrading windows, and installing renewable energy systems. The goal is to drastically cut energy use while keeping the home cozy and preserving its character, especially for historic buildings.

A deep retrofit usually involves a full strip back to the structural frame, back to bare brick etc. This is very disruptive and messy, especially if you want to continue living in the house at the same time.

Key steps include using high-quality insulation [like wood fibre or cork] to keep heat in, choosing energy-saving windows [like double or triple glazing with special coatings], improving ventilation and reducing unwanted drafts, and adding in heat pumps or solar panels for heating and power.

Deep retrofit is often very expensive and the payback period is often not realised in a reasonable timeframe, but the energy, comfort and wellbeing benefits for occupants are usually well worth it.

A house in a state of disrepair awaiting a retrofit

Example of a light retrofit, door with engraved flower

Shallow Retrofit – light touches

A shallow retrofit involves small, low-disruption changes to make an older home more energy-efficient, offering clear benefits with minimal hassle. These are often called “low-hanging fruit” because they’re easier and cheaper than major renovations. Unlike deep retrofits, shallow retrofits focus on specific improvements without needing a full building overhaul, though planning the upgrades together works best.

Common upgrades include swapping out old doors and windows for energy-efficient ones, adding draught-proofing strips to stop leaks, putting insulation in the loft or walls, switching to modern heating systems like heat pumps, adding solar panels for electricity, installing smart thermostats, or adding single-room ventilation systems to improve air quality. These changes are budget-friendly and let people stay in their homes during the work.

However, since these upgrades are often done one at a time, the energy savings may be smaller, and some changes could cause unexpected issues if not planned carefully. Shallow retrofits are a great way to start improving comfort and cutting energy bills, but combining them into a bigger plan will give better results in the long run.

Benefits of Retrofit

You may be wondering why bother with a retrofit in the first place? Fortunately, upgrading an older home through retrofitting brings many rewards. First, it lowers energy bills, saving money as energy prices climb. It makes homes cozier by keeping them warm and free from chilly drafts, while also improving health by creating better air quality, less dampness, and a drier living space. Retrofits help the environment by cutting down carbon emissions and using fewer of the planet’s limited resources.

On top of that, smart retrofits keep homes cooler during hot summers, reducing the risk of overheating. They also need less upkeep, saving time and effort, and can even boost the value of the property. Better insulation can make homes quieter by blocking out unwanted noise, creating a more peaceful and comfortable place to live or work. All these benefits make retrofitting a smart choice for home that is over 10 years old.

A modern shelving unit custom built into an older house alcove

Mouldy wall showing the potential dangers of a bad retrofit

Potential Problems

Retrofitting older homes can bring big benefits, but poor planning or trying to save money the wrong way can cause problems. If moisture risks aren’t properly checked, you might end up with condensation, damp, or mould, which can damage the building and harm people’s health. High costs for some upgrades might not pay off quickly enough, and adding insulation inside walls could make rooms feel hotter or smaller. Using the wrong materials, like insulation that lets water seep into walls, can also cause dampness.

Other issues include wooden beams rotting, increased fire risks from flammable materials, or crumbling brickwork if walls stay wet. Blocking natural airflow can worsen indoor air quality or even raise levels of harmful Radon gas. Changes to your building might cause dampness in your neighbour’s shared wall. Doing upgrades one at a time, dealing with disruption during work, or facing mistakes with no one to fix them can make things tricky. Carefully, well-thought-out pro-active retrofit design is essential to avoiding these problems and making retrofits work well.

Post-Occupancy Evaluation

Post-Occupancy Evaluation [POE] is a key step to see how well a retrofit actually works compared to its energy-saving goals. Plans often make a home seem more efficient on paper than it is in real life, with energy use sometimes higher than expected once people move in. POE tracks how much energy a home uses before and after the retrofit to check if it’s really saving energy as planned.

Even though POE is important, it’s often skipped. It helps spot problems in planning, design, installation, or setup of energy-saving upgrades, like insulation or new heating systems. By finding these issues, POE lets you fix things in your current project and to learn for future ones, avoiding the same mistakes. This ensures retrofits work as well as possible, saving energy and keeping the home comfortable.

Man with clipboard giving post-occupancy evaluation

A gallery showing different stages of the building progress from PAS2035

Standards + Assessments

When retrofitting older homes, following specific methods and processes ensures the upgrades are high-quality and energy-efficient. In the UK, Building Regulations, especially Approved Documents Part L1 and L2, set basic requirements for improving things like insulation, floors, walls, roofs, and energy-saving doors and windows.

BS 40104 is a relatively new British Standards framework for assessing homes prior to retrofit work. This methodology ensures that retrofit designs are appropriate for the specific characteristics, context, and usage of each home.

Also for homes where the building work is publically funded [such as council homes and housing associations etc.] then the recommendations outlined in technical guides PAS 2030 and PAS 2035 must be followed to ensure the retrofits are designed and installed properly, and to secure the funding. PAS 2038 provides similar guidance for non-residential, commercial buildings.

There are also optional standards to aim for. The AECB CarbonLite Retrofit and New Build Standards encourage eco-friendly, low-energy practices. Passivhaus EnerPHit is a tougher, optional standard for super-efficient retrofits. TrustMark, a government-backed program, ensures workers are skilled and follow PAS 2030/2035 rules, which is important for qualifying for funding, like for heat pumps or solar panels. These standards help make retrofits reliable, effective, and energy-saving.

Further information + resources

There is a huge amount of information available online and in written guides. When referring to information to help you make decisions on your retrofit journey try to ensure that the information you are using is reliable, accurate and suitable for your unique set of circumstances. The list below makes reference to some well-respected industry organisations, who, we feel, know what they are talking about.

This list is also not exhaustive or complete but should provide a head start to some good resources to find out more information, to help you on your retrofit journey. We have a longer, more comprehensive list on our more in depth guide Retrofit done Right downloadable e-book guide. More details coming soon!

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