Turnkey vs Split-Delivery Retrofit: Which Model Is Right?

When a housing provider commissions a retrofit programme, one of the first decisions is how to structure the delivery. Do you appoint a single accountable contractor to handle the whole journey, or split the work across separate specialist suppliers? Both can be fully compliant. The difference is where the risk sits, and that is worth understanding before you procure.

The two models

Turnkey means one contractor is accountable for the whole journey, from assessment and coordination through design, installation and post works evidence, under a single contract.

Split delivery means you appoint separate suppliers for different stages, for example one organisation for assessments, another for coordination and another for installation, and you hold the pieces together yourself.

Neither is inherently right or wrong. The best choice depends on your in-house capacity, how much coordination risk you want to carry, and how your evidence trail needs to hold together.

Split delivery, strengths and trade-offs

The appeal of split delivery is control and, sometimes, cost. You can select a specialist for each stage, put each part out to competition, and keep suppliers honest against each other. For providers with a strong in-house asset team that can manage the interfaces, it can work well.

The trade-off is that the seams between suppliers are where retrofit programmes tend to fail. When the assessor, the designer, the coordinator and the installer all answer to different organisations, the gaps between them become your problem. If the evidence trail breaks between two suppliers, or a design decision does not survive into installation, it is the provider left reconciling it, often at the point a funder is asking for proof. Coordination overhead sits with you.

Turnkey, strengths and trade-offs

The appeal of turnkey is accountability. With one contractor responsible end to end, there is a single point of ownership for compliance, for the retrofit design surviving into installation, and for the evidence reaching the funder intact. The interfaces that cause problems in a split model are handled inside one organisation rather than across contracts. For programmes at scale, or where in-house capacity is stretched, that reduces both risk and management burden.

The trade-off, and the honest one, is the question of independence, which we come to next.

The independence question, addressed honestly

PAS 2035 designed the retrofit coordinator role to be independent of the installer, so the client gets impartial technical advice without anyone having an agenda to push a particular product. On the face of it, that sits in tension with a turnkey model where the same organisation both coordinates and installs.

The standard anticipates this. PAS 2035 permits one organisation to hold multiple roles, provided the people are suitably qualified and any potential conflicts of interest are declared and managed. So the question to ask a turnkey provider is not whether they do both, but how they keep the coordinator's independence intact, how conflicts are flagged, and how impartial advice is protected. A good turnkey partner will have a clear answer. A provider who cannot explain how they manage that tension is the one to be wary of, not the model itself.

How to choose

Weigh three things. Your in-house capacity to manage supplier interfaces, because that is the hidden cost of split delivery. How much coordination and compliance risk you are willing to carry yourself. And how important a single, unbroken evidence trail is for your funding, which for most funded programmes is very important indeed.

If you have the team to manage the seams and want maximum control of each stage, split delivery is defensible. If you want one organisation accountable for compliance and evidence, and you want the interfaces handled for you, turnkey is usually the lower-risk route. Whichever you choose, insist on a qualified retrofit coordinator with clear independence, and a proper retrofit assessment at the start.

Where we fit

Greener Solutions Group delivers the turnkey model, with assessment, coordination, design, installation and post works EPC evidence under one accountable contract, and coordinator independence maintained within it. It means the compliance and the evidence sit in one place rather than being stitched across suppliers. You can see the full journey on our PAS 2035 retrofit services page.

Talk it through

If you are weighing up how to structure a retrofit programme, we are happy to talk through the options, whichever model you lean towards. Explore our PAS 2035 retrofit services or get in touch.