Why order matters
A retrofit is work done to improve an existing home, usually to make it warmer, healthier and cheaper to run. The individual jobs, such as insulating a loft, replacing windows or installing a new boiler or heat pump, can each be sensible on their own. The trouble starts when they are done in the wrong order.
Some examples of what can go wrong: a heating system sized for a draughty, uninsulated house may be larger than needed once the house is improved; new airtight work without a ventilation plan can cause damp and poor air; and a finished decorating job may have to be torn open to reach pipes or cables. Sequencing reduces wasted money, materials and effort.
There is no single correct order for every house, but a general logic works for most.
Step 1: Understand the house
Start with information. How old is the building and how was it built? Where is it cold, damp or draughty? Which rooms are used most? What do the energy bills look like? Reading your meter and bills helps you understand what you currently use, as the guide to energy meter readings explains.
A professional assessment, where available, such as an energy survey or a retrofit assessment, can show where heat escapes and which measures are suitable. A building survey also helps with older properties. Qualifications, schemes and grants vary by country, so check what exists locally, and be wary of anyone who pushes one product as the answer to everything.
At this stage, also check for hazards in older buildings. Before drilling, opening floors or removing coatings, read up on renovation hazards and test where advised.
Step 2: Fix the basics first
Water is the enemy of most building work. Leaking roofs, blocked gutters, failed pointing, faulty plumbing and rising or penetrating damp should be dealt with before anything else. Insulating over a damp problem hides it and can make it worse. Repairs of roofs, drainage and external walls come ahead of anything that would cover them.
Structural issues, electrical safety and gas appliance safety also belong here. These jobs typically need qualified tradespeople.
Step 3: Reduce heat loss
Once the building is sound, cut the heat loss. This is usually the most cost-effective stage because it lowers the amount of heating the home needs, whatever the heating system is.
- Draught proofing. Sealing gaps around doors, windows, floors and service entries is generally cheap and quick, and the basics of draught proofing are a good place to begin. It should be done with ventilation in mind, so do not block intentional vents or flues.
- Loft and roof insulation. Often a straightforward and effective measure where access allows.
- Wall and floor insulation. Cavity, solid wall and floor insulation depend on the construction. Solid walls need particular care in older buildings, so get advice.
- Windows and doors. Replacing windows is costly and has its own manufacturing footprint, so consider repair, secondary glazing, heavy curtains or other forms of window insulation first, and replace if they are beyond repair or the improvement is substantial.
The principles of home insulation, and the trade-offs between materials, are covered elsewhere. The key sequencing point is to do them before sizing new heating.
Step 4: Plan ventilation alongside airtightness
As a house becomes more airtight, moisture from cooking, bathing and breathing has fewer routes to escape. Without enough ventilation, this can lead to condensation and mould, and stale indoor air. So plan ventilation at the same time as insulation and draught proofing, not afterwards.
Options include extractor fans in kitchens and bathrooms, trickle vents, and in some projects whole-house mechanical ventilation. The right choice depends on the building and how airtight it becomes. The notes on condensation control explain why ventilation and warmth go together. Keep in mind that this is general information, and building regulations may set specific requirements.
Step 5: Choose and size the heating
After heat loss is reduced, you can see what heating the house really needs. Sizing heating after insulation avoids buying more capacity than necessary and lets lower-temperature systems work well.
If you are considering heat pumps, they generally work most efficiently when delivering heat at lower temperatures, so a well-insulated building with suitably sized emitters tends to suit them. Radiators, underfloor heating or pipework may need upgrading, and a qualified installer should perform a room-by-room heat loss calculation.
If you are not ready to replace an old boiler, you can still improve control, such as using heating zones and timers, which may reduce waste without major work. If the boiler fails unexpectedly, though, replacing it before other improvements may be unavoidable, and that is fine. It helps to think ahead so that the replacement can be sized for the improved house.
Step 6: Renewable generation and extras
Generation such as rooftop solar is generally considered once demand has been reduced, since you know your needs and your roof’s condition. If the roof needs repairs, do them before panels go on, to avoid removing and refitting them later.
Step 7: Internal alterations and finishes
Kitchens, bathrooms, plastering, flooring and decorating normally come last, after pipes, cables and insulation are in. If you are weighing up flooring choices or paints at this point, you can do so with the heating and ventilation already in place, and you can finish with low-emission products.
Working in phases
Few households can do everything at once. A phased plan lets you spread cost and disruption. Write a simple roadmap showing the final goal, then do each stage so that it does not need to be undone later. For example, if you will eventually fit internal wall insulation, think now about where sockets and radiators will go. Take photos of pipes and cables before they are covered, and keep records of products, installers and warranties.
Cost and expectations
Savings from retrofit are uncertain and depend on the house, the work done, how you use it, and energy prices. Be sceptical of precise promises. Comfort, health and resilience benefits can be as important as bill reductions, and some measures take many years to pay back, if they do so financially at all.
A good plan, drawn up before work begins and revisited when circumstances change, usually saves more than any individual product.