Last updated November 6, 2026
General information, not tax or legal advice. The rules depend on your country and your situation, so check anything with a tax or legal consequence with your accountant.
Additional services in architecture are work outside the scope of your appointment. Spot the change, tell the client what it will cost before you start, get their agreement in writing, log it, and invoice it as its own line. A fee agreed before the work is a bill. A fee raised after it is a negotiation.
What counts as an additional service?
An additional service is anything your appointment doesn't already include, so the test is the wording of your scope, however much or little work it feels like. If the scope is vague, almost nothing is clearly extra, which is why this starts back at the fee proposal.
The RIBA Plan of Work gives you a useful line for UK work. Its 2020 overview says functional changes after the Stage 2 sign-off, such as relocating a space or changing its size, aren't design development and belong under change control procedures. Tweaks that come from developing the design don't count.
| What happened | Additional? | Why |
|---|---|---|
| Client changes an approved concept during Stage 3 | Yes | Approved work is being redone |
| Client adds a garage or another storey | Yes | The project got bigger |
| Client wants a third concept option when you agreed two | Yes | Your scope set the number |
| Planning resubmission after the client changed the brief | Yes | The client's change caused it |
| Planning officer asks for a small amendment | Depends | Many appointments include dealing with routine comments, so read yours |
| Build overruns the contract period you assumed | Usually | Only if your proposal stated the period |
| Coordination error in your own drawings | No | That's your cost |
How do you agree an additional service with a client?
Agree an additional service in writing before doing the work, stating what it is, what it costs and how it affects the programme. In the UK, ARB's guidance on terms of engagement says amendments to the initial terms should be recorded in writing by the architect with a copy to the client. It also says inadequate terms are the most common cause of complaints about architects.
In the US, AIA's B101-2017 agreement has a notice and authorisation process for additional services, with an exception for work needed to avoid delay in construction. AIA's G801 form exists for exactly this notice. Check which form your own appointment uses, since standard forms get amended.
An email is often enough for small items, if your appointment allows it. Something like this:
Additional service AS-04: revised kitchen layout and rear elevation, following your email of 12 May. This is outside the services in our appointment dated 3 February. Fee: £1,200 plus VAT, fixed. Programme: adds about one week to Stage 3. We'll start when you reply to confirm. Until then we'll carry on with the approved design.
The last sentence does the most work. It tells the client what happens if they don't answer, and it stops you drifting into the change while you wait.
Pick the fee basis by how well you can define the task. Use a fixed sum when you can describe the output. Use an hourly rate with a cap when you can't, such as "£85 an hour, up to 20 hours, and we'll ask before going further". The guide to lump sum vs hourly fees covers the trade-off in more detail.
How should you record additional services?
Record additional services in a single register per project, because a year later the invoice alone won't tell you who asked for what. Here's an invented example:
| Ref | Asked for by | What | Basis | Fee | Client agreed | Invoiced |
|---|---|---|---|---|---|---|
| AS-01 | Client, site meeting 2 Mar | Third concept option | Fixed | £650 | Email 3 Mar | INV-2026-0031 |
| AS-02 | Client, email 18 Mar | Planning resubmission after brief change | Fixed | £900 | Email 19 Mar | INV-2026-0038 |
| AS-03 | Client, phone 7 Apr | Review of neighbour's party wall notice | Goodwill | £0 | Not needed | Shown at nil |
| AS-04 | Client, email 12 May | Revised kitchen and rear elevation | Fixed | £1,200 | Email 13 May | To bill |
| AS-05 | Engineer's revision 20 May | Coordination of revised beam layout | £85/h, cap 20 h | 14 h so far | Email 20 May | To bill |
Log the goodwill items as well. A line at nil on the invoice shows the client what they received for free, and it gives you something to point at when the next request isn't free.
How do you invoice additional services?
Invoice additional services as separate lines below the stage fee, each with its reference, so the client can tie every amount to something they agreed. Here's the invented job above, billing Stage 3 with both open items, with VAT at the UK standard rate:
| Line | Quantity | Price | Net |
|---|---|---|---|
| RIBA Stage 3, Spatial Coordination: stage fee | 1 | £8,000 | £8,000 |
| AS-04: revised kitchen and rear elevation, agreed 13 May | 1 | £1,200 | £1,200 |
| AS-05: beam coordination, hours to 31 May, agreed 20 May | 14 | £85 | £1,190 |
| Subtotal | £10,390 | ||
| VAT at 20% | £2,078 | ||
| Total | £12,468 |
If an additional service brings costs with it, such as a specialist's survey, bill those on their own line too. The guide to invoicing reimbursable expenses covers how.
What if you've already done the work?
If you've already done the work without agreement, write to the client now, set out the facts and ask them to agree a fee. Say when the request came in, what you did and why it fell outside the appointment. Keep it factual, and offer a sum you can defend from your hours.
You may have to accept less, and you may end up writing some of it off. What you shouldn't do is put it on the next invoice without warning, because that's when an otherwise friendly client starts reading every line. If a large sum is in dispute, take advice, since the outcome depends on your contract and what was said.
Recording and billing additional services in ERPFlow
ERPFlow has no variation register or stage budgets, so the register above stays in a spreadsheet, or as cards in a column on the project's board. The documents around it are ordinary ones:
- The agreement. Send each additional service as a small quote with its own PDF. There's no e-signature or online acceptance: you mark it accepted by hand when the client replies, and attach their email to the quote.
- The rate. A service holds your hourly rate and tax, so it fills in on any line. You enter the hours as the quantity.
- The work. A card on the project's board can carry the assignees, the deadline and the time spent, typed in as hours and minutes. ERPFlow doesn't have a timer or timesheets today. Time tracking, including converting tracked time into invoices, is coming soon.
- The invoice. Convert the quote to a draft invoice, or add its line to the stage invoice. A nil-priced goodwill line is allowed. Issuing the draft gives it its number and makes it final.