Ask anyone who's had an extension built and they'll usually have a story about the gap between two trades. The plasterer who couldn't start because the electrician hadn't been. The kitchen sitting in boxes in the garage for a week while everyone waited on the plumber.
Energy upgrades are no different, and they often involve more trades than people expect. A heat pump isn't one person's job. Neither is external wall insulation. The part that gets the least thought, how all those people fit together, is usually where a job is won or lost. You can have a first-class electrician and a first-class heating engineer and still end up with a heat pump that doesn't work properly, simply because nobody was in charge of the space between them.
Short Answer: Most energy-efficient home improvements need more than one trade, and the trouble tends to start where one person's work meets the next. A good team sorts that out before anyone arrives. It plans the job as a whole, books people in the right order and stands behind the finished result. So before you sign, find out who's actually turning up, and who you'd ring if something wasn't right.
Key Facts at a Glance
- An air source heat pump installation typically involves a heat pump installer, an electrician and often a plumber, and sometimes other specialists too.
- Under MCS rules, the certified installer remains responsible for the whole installation at handover, even if parts were subcontracted, and must have a written contract with each subcontractor.
- PAS 2035, the UK standard for retrofitting homes, sets out specialist roles for assessing, coordinating, designing and installing the work.
- PAS 2035 is mandatory for government-funded schemes such as ECO and the Warm Homes programme, and coordinators must be registered with a TrustMark-approved scheme.
- In October 2025 the National Audit Office found major issues in around 98% of homes given external wall insulation under the ECO4 and GBIS schemes.
Why Does an Energy Upgrade Need a Whole Team?
Because most upgrades touch several parts of the house at once. Wrap a house in insulation and suddenly you're dealing with window sills, gutters, drainpipes and the edge of the roof as well. A heat pump brings the pipework, radiators, a hot water cylinder and the electrics into play. None of that is a one-person job.
Roughly, it breaks down like this. The last column is the one to keep an eye on.
| Upgrade | Trades usually involved | Where it goes wrong if they don't work together |
|---|---|---|
| Loft insulation | Insulation installer, sometimes an electrician | Cables buried under insulation, vents at the eaves blocked |
| Cavity wall insulation | Surveyor and insulation installer | Unsuitable walls filled without a proper check first |
| External wall insulation | Scaffolders, insulation and render specialists, roofer, sometimes a plumber and electrician | Gaps at windows and roof edges, pipes and cables not moved properly |
| Air source heat pump | Heat pump designer and installer, plumber, electrician | Wrong size system, pipework not flushed, blame passed between trades |
| Solar PV and battery | Scaffolders, roofer, electrician | Damaged tiles, leaks, wiring not properly certified |
| Renovation with energy upgrades | Builders, joiners, plasterers, plus the trades above | Insulation missed because each trade assumed someone else was doing it |
What Goes Wrong When Trades Don't Work Together?
More often than not, it's the joins. Everyone can do their own bit well and the job still comes unstuck, because the bit in between belonged to nobody.
Homebuilding & Renovating has a good description of what happens when a heat pump job is split between several firms. The installer blames the plumber. The plumber blames whoever fitted the underfloor heating. Meanwhile the homeowner is paying someone else to flush the system out. At its worst you get a heat pump sat in the garden, radiators on the walls upstairs, and no pipes joining the two.
The Gap Between Your Bit and My Bit
On an external wall insulation and rendering job, the big flat walls are the easy part. It's the edges that cause trouble. Every window sill needs extending so rain drips clear of the new, thicker wall. The roofline sometimes has to come out a little. Gutters, downpipes, the satellite dish, the light by the back door: all of it comes off and has to go back on. If the renderer thinks the roofer is sorting the top edge, and the roofer thinks it's the renderer's job, water will find its way into that gap sooner or later.
It's small details like these that decide whether insulation keeps a house dry or lets damp in. We've looked at what happened when they went wrong on a large scale, in the government insulation schemes, in our guide to why experience matters when choosing an energy efficiency company.
Who Do You Ring When Something's Not Right?
Picture it six months on. The radiators upstairs are only lukewarm. Is that the heat pump, the pipework, the controls or the radiators themselves? If four different firms were involved, you could spend weeks being bounced between them, each one fairly sure it's someone else's problem. If one team did the lot, you ring them, and it's theirs to sort out.
What Does a Retrofit Coordinator Do?
Think of them as the person keeping an eye on the whole project, from the first assessment to the final checks, making sure the different bits of work don't trip each other up. The role comes from PAS 2035, the UK standard for retrofitting homes. Its starting point is that a house is one connected system, so changing one part affects the others. You'll often hear that called the whole-house approach.
According to the Retrofit Academy, PAS 2035 sets out these core roles:
| Role | What they do |
|---|---|
| Retrofit Assessor | Carries out a detailed assessment of the property |
| Retrofit Coordinator | Oversees the whole retrofit process and makes sure it meets the standard |
| Retrofit Designer | Prepares a design suited to that particular house |
| Retrofit Installer | Fits the energy efficiency measures on site |
Do You Need One for a Job You're Paying for Yourself?
Not usually. PAS 2035 is mandatory for government-funded schemes such as ECO and the Warm Homes programme. For work you're funding yourself, it isn't a legal requirement, although building regulations still apply. Someone still needs to do the coordinating, though. On a privately paid job, that's normally your main contractor. If you hire every trade separately, guess who it ends up being.
What Makes a Team Experienced?
Years in the trade count for something, of course. What counts for more is having worked on houses like yours, alongside the same trades, enough times to know where the snags usually are. It shows up in small ways. An experienced team will usually:
- Know your type of house as soon as they walk in, and what tends to go wrong with it.
- Spot the knock-on work at the survey, like a soil pipe in the way or a fuse board that won't cope, instead of finding it halfway through the job.
- Book the trades in the order the work actually needs.
- Get the scaffolding up once, not three times.
- Treat it as a home people are living in. Dust sheets down, rooms sealed off, the kettle still within reach.
- Own the finished result, not just their slice of it.
Why Does the Order of Work Matter?
Because one job changes what the next one needs. Once the walls are insulated, the house loses less heat, so a heat pump fitted afterwards can be smaller and cheaper to run. Fit the heat pump first and you could be paying for one that's bigger than the house will ever need.
On a larger project, a sensible order looks roughly like this:
- Survey and design. Measure heat loss, check the structure and ventilation, and plan everything together.
- Repairs first. Fix any damp, roof problems or failing render before covering them up.
- Fabric next. Loft, walls and floors, with ventilation planned in at the same time.
- Scaffolding jobs together. Wall insulation, roof work and solar panels while the scaffold is up.
- Electrics checked. Make sure the supply and fuse board can cope with a heat pump, battery or car charger.
- Heating last. Size the heat pump or boiler for the improved house, then commission it and set up the controls.
Scaffolding Is the Classic Example
Scaffolding Is the Classic Example
Scaffolding isn't cheap, and wall insulation, roof repairs and solar panels can all need it. Book them as three separate jobs and you could end up paying for scaffolding three times, and living behind it three times too. A team that's done this before will usually spot that at the survey and suggest lining the jobs up back to back, even if you only go ahead with one or two of them for now.
None of this means doing everything in one go. Plenty of people spread the work over a few years, and our guide to what home energy upgrades cost and save might help you decide where to start. The point is to get the order right, so nothing has to be pulled out and redone later. That, really, is the whole-house approach in practice.
One Main Contractor or Several Separate Trades?
Either can work. It mostly comes down to how much time you've got, and how happy you'd be running a building job yourself. Here's how they compare, warts and all.
| What to compare | One main contractor | Hiring separate trades yourself |
|---|---|---|
| Contracts | One contract for the whole job | A separate contract with each trade |
| Who coordinates | The contractor | You |
| If something goes wrong | One company is responsible for the result | Each trade answers only for its own part |
| Paperwork and sign-off | Usually arranged for you | You chase each certificate yourself |
| Cost | Includes the cost of managing the job | Can be cheaper if everything goes to plan |
| Your time | Much less | Calls, scheduling and checking work |
What About Subcontractors?
There's nothing wrong with a firm bringing in a specialist for part of a job. Lots of good ones do. You just want to know about it up front, and you want someone to still be answerable for the whole thing. On heat pumps, the Energy Saving Trust's installer guidance spells this out. The MCS certified installer stays responsible for the installation at handover. They need a written contract with any subcontractors, and they have to check those firms are competent and insured.
So ask which parts of your job, if any, are going to another firm, and who'll be keeping an eye on them on site.
How Does Building Experience Help With Energy Upgrades?
More often than you'd think, an energy upgrade turns into building work halfway through. A doorway needs moving to make room for a cylinder cupboard. The window sill turns out to be rotten. There's re-plastering to do after new pipework, or the roof needs attention before solar panels can go anywhere near it. A team with building experience just carries on and deals with it, instead of downing tools while someone goes looking for a joiner.
It's a big help when the energy work is part of something larger, too. If an extension, a loft conversion or a full home renovation is on the cards, that's the moment to build the insulation, heating and electrics in properly from the start. With one team doing the lot, there's a single plan to work from, and nobody arguing afterwards about whose job the insulation was.
How Should a Good Team Keep You Informed?
Regularly, and without you having to chase them. Living in a house while building work goes on around you is tiring enough. Not knowing whether the water's going off tomorrow makes it worse. On a well-run job, you'd usually expect:
- You know who's coming each day and roughly when they'll start and finish.
- You're told in advance when the heating, water or power will be off, and for how long.
- Any extra work is explained and agreed with you, with a price, before it's done.
- You get photos of work that will end up hidden, such as insulation before it's rendered over or pipework before the floor goes back down.
- There's one person you can message with questions, who knows the whole job.
Those photos are worth asking for, by the way. Once a wall is rendered or a floor is back down, they're the only record of what's underneath, and they're handy if you ever sell the house.
What Should You Ask About the Team Before You Sign?
You can learn a surprising amount from a handful of plain questions.
- Who'll be on site each day? And will it be the same people from start to finish?
- Do they work for you directly, or are any of them subcontracted? If so, for which parts?
- Who's my main contact? Someone who can answer questions about the whole job, not just one part.
- Who's responsible for the finished result? Including work done by any other trades.
- Who arranges the scaffolding, building control sign-off and any grid notifications?
- What accreditations does each trade hold? For example MCS, Gas Safe or an electrical competent person scheme.
- What happens if one part of the job runs late? How does it affect the others, and how will you be kept informed?
If you'd like to see what happens at each stage on one of our jobs, from the first visit through to aftercare, here's how our home energy improvement process works.
Getting Expert Help in the West Midlands and Wales
In the end, reliable energy-efficient home improvements come down to people. Good trades, booked in a sensible order, with someone who keeps an eye on the whole job and is still answering the phone once it's finished. Get that right and a list of separate jobs turns into a warmer house that costs less to run.
Greentek Energy Ltd is one accredited team for building work and energy upgrades, from insulation and rendering to heat pumps, solar PV, battery storage and full renovations. You can read more about Greentek and the way we work. We cover the West Midlands and Wales, including Coventry, Birmingham, Solihull, Wolverhampton, Dudley, Cardiff and Swansea. Give us a ring on 0333 533 4567 or book a free consultation.
