An architect designs your extension and can submit the planning application. A planning consultant does not design anything; they build the strategy and the case to get an application approved. For most straightforward home extensions you need an architect, and for difficult or previously refused sites you may need both. Searching for architects near me is usually the right starting point, because the design and the application are the same conversation, but the honest answer depends entirely on your site.
So rather than define the two roles in the abstract, here is how the decision plays out across four real situations.
First, the One Line Difference
Keep this straight and the rest follows.
An architect works in the world of design. They survey the house, design the scheme, produce the drawings, and on most householder projects they also submit the planning application and manage the build.
A planning consultant works in the world of policy. They do not draw. They assess whether a scheme is viable against local planning policy, build the planning argument, and act as your agent with the council, which carries weight because officers treat a represented application more carefully.
Most architects offer a planning service. Few planning consultants offer design. That asymmetry is why the starting point is usually an architect.
Now the scenarios.
Scenario One: A Standard Rear Extension on an Unconstrained Plot
You want a single storey rear kitchen extension on a 1930s semi, not in a conservation area, not listed, with permitted development rights intact.
You need an architect, or an architectural technologist, and nothing more. The scheme either falls under permitted development or needs a simple householder application, and the design plus the drawings is the whole job.
A planning consultant here would be money spent on a problem you do not have. There is no policy battle to fight, no objection to pre empt, no refusal to overturn. The design is the project.
This covers the large majority of home extensions.
Scenario Two: A Conservation Area or Listed Building
Now the same extension, but the house sits in a conservation area, or it is listed.
You still start with an architect, because the design has to be right, materials and proportions become part of the planning case, and a heritage statement is needed. But the planning complexity has risen, and this is where the two specialisms start to overlap.
The practical answer is an architectural practice that offers both design and planning in house. You get the design led by someone who understands heritage constraints, and the application handled by someone who knows the policy, without managing two separate firms who blame each other when something stalls.
A standalone planning consultant becomes worth it here only if the heritage position is genuinely contentious.
Scenario Three: Green Belt, or a Policy Fight
Your plot is in the Green Belt, or the scheme pushes against local policy in a way that needs arguing, not just drawing.
This is where a planning consultant earns their fee. Green Belt applications turn on whether an addition is a disproportionate addition over the original dwelling, which is a policy argument before it is a design one. The case has to be built against the development plan, and sometimes negotiated with officers or defended at committee.
The ideal here is both, engaged at the same time. The planning strategy is set first, and it informs the design, so the architect is drawing something that already has a route to consent rather than a beautiful scheme that policy will refuse.
Getting the planning guidance at the very outset, and letting it shape the design rather than fight it, is what avoids abortive costs and resubmissions.
Scenario Four: A Site That Has Already Been Refused
You, or a previous owner, had an application refused on this site, and you want to try again.
A refusal changes the calculation. The reasons in the notice are specific, and the task is now partly strategic, understanding exactly why it failed and building an application that answers each point. A planning consultant, or an architect experienced in reading refusal notices, is valuable here precisely because the design alone did not succeed last time.
Extension Architecture took on a South Croydon project that had already been refused, amended the scheme to answer each reason in the notice directly, and secured approval on resubmission. That is the pattern: a refusal is a list of specific, addressable problems, not a verdict on the whole idea, and someone who reads it properly is worth more than someone who simply redraws it.
Guidance on exactly when you need an architect and planning consultant together, rather than one or the other, is worth reading before you commit to either.
Who Do You Hire First?
The sequence matters, and it depends on which scenario you are in.
For scenarios one and two, the standard and the heritage extension, start with an architect. The design leads, and planning is folded into it.
For scenarios three and four, the Green Belt fight and the refused site, get the planning view first, ideally alongside an architect from the outset, so the strategy shapes the design rather than the design hitting a policy wall later.
The practice that offers both under one roof removes the sequencing question entirely, because the planning and the design happen together.
The One Thing to Remember
Do not pick between an architect and a planning consultant by title. Pick by how much planning risk your specific site carries.
Low risk, an architect is all you need. High risk, Green Belt, heritage, a previous refusal, you need the planning strategy and the design working together from day one. Match the team to the difficulty of the site, and the question answers itself.
