Do I need an architect, a structural engineer, or neither?

These are different services that people treat as a single expensive category and then skip entirely. In practice, one of them is a technical necessity on structural work and the other is a design and strategy investment that pays for itself on some projects and not on others. Knowing which is which is most of the decision.

Step by step

1. Get a structural engineer whenever load moves.Removing or opening a load-bearing wall, forming a new opening, removing a chimney breast, altering roof structure, underpinning, or foundations near trees. They calculate and specify the beam, the padstones and the connections, and building control requires that design.
2. Understand what an engineer does not do.They are not designing the room, choosing the layout or handling the planning application. Their output is calculations and structural details, and it is usually a small fee relative to the work it governs.
3. Consider an architect where design or planning is hard.A difficult site, a listed building or conservation area, a project that needs to work as a whole rather than as a set of rooms, or a planning position where refusal is a real risk. An architect's fee buys strategy, not just drawings.
4. Know the cheaper middle options.Architectural technologists and architectural designers produce planning and building regulations drawings at lower fees than a full architectural service, and many domestic extensions go through on their drawings perfectly well.
5. Decide what service level you are buying.Drawings only, drawings plus the planning application, or a full service through to administering the contract on site. These are very different fees for very different amounts of help.
6. Get a structural survey where the question is about the building rather than the project.Cracking, movement, sagging floors or subsidence concerns are a structural engineer's report, not a builder's opinion, and the report is what any insurer or buyer will want.
7. Ask for fee proposals in writing from more than one.Fees vary widely for the same scope, and the scope varies more than the fee does. Compare what is included, particularly whether the planning application, building regulations drawings and site queries are inside the fee.
8. Check registration and insurance.The title architect is legally protected in the UK and registration is checkable on the register. Engineers should carry professional indemnity insurance, and it is reasonable to ask.
9. Get them involved early enough to matter.An engineer brought in after the builder has decided where the steel goes is being asked to justify a decision rather than to make one. Early is cheaper.

Tips

• A builder's opinion on a beam size is not a substitute for calculations. Builders install what engineers specify, and building control asks for the calculations, not the opinion.
• Ask a prospective architect or designer to show you a project like yours that got planning permission in your council's area. Local track record is genuinely predictive.
• The engineer's fee is usually small compared with the cost of the steel, the padstones and the making good. It is the wrong place to economise.

Common mistakes

• Skipping the engineer because the builder is confident — Building control needs the design, and an undersized beam is a structural risk that shows up as cracking, deflection and sticking doors months later.
• Commissioning full drawings before checking the planning position — Design fees are the main sunk cost when a scheme turns out to need permission it will not get. Check permitted development and policy first.

Alternatives

• Structural engineer only: The right answer for most straightforward structural jobs — a beam over a new opening, a wall removal, a chimney breast. Calculations and details for building control, at a modest fee.
• Architectural designer or technologist: Planning and building regulations drawings at lower cost than a full architectural service. Suits conventional extensions and loft conversions with no unusual planning difficulty.
• Architect, full service: Design, planning strategy, building regulations package and contract administration on site. Worth it on complex, listed, or planning-difficult projects, and where the design of the whole matters.

Questions people ask