The number on the contract looked fine. Seven percent of the build cost, my London architect said, standard for a project like mine. What nobody spelled out was that seven percent of a moving target moves too. By the time the build finished over budget, the fee had quietly climbed with it.
When you hire an architecture firm in London, how they charge matters as much as what they charge. I learned this the slow way across two projects. The first taught me what a percentage fee really means. The second, on a fixed fee, was a completely different and far calmer experience.
Im not saying percentage fees are a trick. They arent. But I didnt understand the mechanics, and that ignorance cost me. So here is the honest version of how architect fees actually behaved on my real projects, not the tidy table you see everywhere.
How the Percentage Fee Crept Up
On my first extension, the architect charged a percentage of the construction cost. Simple enough on paper. The problem was the construction cost didnt stay still.
We hit poor ground. Steel prices rose. I changed my mind on a couple of things. Each pushed the build cost up, and because the fee was a percentage, it rose alongside. The final fee was noticeably higher than the figure I had budgeted.
None of it was dishonest. The architect did more work as the project grew. But I hadnt grasped that signing up for a percentage meant signing up for an open ended number. That was on me, but I wish someone had been clearer.
Why Percentage Fees Exist At All
To be fair, the percentage approach has logic. When a project starts and nobody knows the final scale, a percentage flexes with the work involved. More build, more design effort, more fee.
It suits complex jobs where the scope genuinely cant be pinned down upfront. The architect isnt penalised for the extra work a growing project demands, and you only pay for what the project actually becomes.
For my first job, which was fairly involved, it wasnt an unreasonable structure. I just didnt understand the risk I was carrying. The fee rising with the build felt like a surprise, when really it was the model working exactly as designed.
The Fixed Fee That Felt Different
My second project, a couple of years later, I insisted on a fixed fee. The architect quoted a set amount for the whole service, agreed upfront, regardless of how the build cost moved.
The difference was psychological as much as financial. I knew the architect number from day one and it never changed. When other costs wobbled during the build, at least that one stayed put.
It also changed the incentives subtly. On a fixed fee, the architect had no reason to let scope creep. They were motivated to design efficiently and keep things tight, because their fee didnt grow with the build. That alignment suited me far better.
When Each Approach Makes Sense
Having lived both, I think the choice depends on the project. For a straightforward extension with a clear brief, a fixed fee gives certainty and I would pick it every time.
For a large or genuinely unpredictable project, where the scope really cant be known early, a percentage can be fairer to everyone. You pay for the work that actually emerges rather than a guess.
The key is understanding which youre signing up for and why. A well coordinated design and build route can also bundle the design and construction together, which gave me more cost certainty on the second project than juggling separate parties had on the first.
The Questions I Now Ask Upfront
Before signing anything now, I ask exactly how the fee is calculated. Fixed, percentage, or hourly. Then I ask what happens to the fee if the build cost rises.
I ask what is included at each stage and what counts as extra. Revisions, site visits, dealing with planning conditions. The vague areas are where surprise costs hide.
And I ask for the fee in writing, broken down, so there are no assumptions. My first project taught me that a single percentage figure hides a lot. Clarity upfront prevents the awkward conversation later.
What I Wish I Had Known at the Start
A fee isnt just a price. It is a structure, and the structure shapes how the whole project feels. Percentage ties your architect cost to a number that can move. Fixed locks it down.
Neither is wrong. But you should choose with your eyes open, understanding the trade off, not just glancing at a percentage and assuming its fine.
Six to eight months per project, two very different fee experiences. The first taught me how a percentage behaves when a build grows. The second showed me the calm of a fixed number. Ask how your architect charges before you sign. It matters more than the headline figure suggests.
