If your neighbour has already built a new wall for their extension and you now want to build off it rather than erecting your own independent wall, you’ll encounter the Party Wall concept of “making use”—often called enclosure costs. Far from being a penalty, this payment is a fair contribution for benefitting from a substantial structure your neighbour has already funded. In many cases it’s actually a net saving and helps you achieve a wider, more efficient extension.
Below, we demystify when enclosure costs apply, why they’re good value, and how surveyors work them out.
When do enclosure costs apply?
Under Section 11(11) of the Party Wall etc. Act 1996, enclosure costs become payable when:
- Your neighbour (the earlier Building Owner) has built a wall that you later use for your works; and
- Your use amounts to enclosing upon or deriving structural benefit from that wall—e.g., tying in your new extension, roof, or floor, or relying on its foundations rather than building your own separate wall.
Typical scenarios:
- Your neighbour has built a new wall along (or astride, with consent) the boundary. You now want to abut your extension to this wall instead of constructing a standalone wall on your side.
- A party fence wall or previously-constructed party wall exists; you now enclose off it (for example, tying your rear extension in).
If your works structurally rely on that wall, enclosure costs are due.
Why enclosure isn’t a “cost”—it’s usually a saving
Think of enclosure as paying your share instead of footing the full bill for your own independent wall. With enclosure you typically:
- Save on materials and labour for a new wall and its foundations.
- Gain internal width: a shared/party wall can remove the need for a gap and separate construction, so your extension can be slightly wider and more efficient.
- Simplify weathering and detailing: fewer junctions, flashings and interfaces generally mean cleaner detailing and lower risk.
Bottom line: enclosure is cost-sharing after the fact. You tap into a wall that already exists and pay a fair, proportionate contribution, not the whole cost of building your own.
How surveyors calculate enclosure costs
Surveyors assess a “due proportion” at present-day rates for the part of the wall (and foundations) you’re benefitting from. While each case is fact-specific, the calculation usually follows these steps:
- Define what’s being used
- The length/height/thickness of wall your works rely on.
- The foundations beneath that segment (where relevant).
- Any structural elements that directly benefit your extension (e.g., concrete strip foundations, blockwork, cavity wall, DPC course).
- Apply present-day rebuild costs
- Costs are assessed at current market rates, not historic spend.
- Materials + labour for the relevant portion of wall/foundations.
- A fair share of associated preliminaries (scaffolding, access, reasonable professional fees directly linked to that wall’s construction).
- Apportion fairly
- Typically a 50/50 split where the wall is party and both owners derive similar benefit.
- Where use or benefit differs (e.g., one owner relies on extra height or thickness), surveyors adjust the share to reflect the actual benefit.
- Exclude owner-specific finishes
- Decoration, fixtures and features that serve only one side are generally excluded from the shared calculus.
- Add practical terms
- Payment timing (usually on enclosure).
- Any interest if payment is late.
- Clear description of what structures you may connect to.
The result is recorded in a Party Wall Award (or a supplemental award if the wall already exists)—giving both parties a clear, enforceable record.
What if I just touch the wall lightly?
Whether you owe enclosure costs hinges on benefit. If your works do not rely structurally on the neighbour’s wall (for example, non-structural flashing only, or a freestanding wall with a movement joint), you may avoid enclosure. But it’s easy to misjudge: a “light touch” detail can still turn into structural reliance. Get a party wall surveyor to review your drawings before you commit.
Does enclosure always mean a bigger extension?
Often, yes. Using the boundary wall (instead of creating a gap and building your own wall) can unlock valuable internal width—especially on tight city plots. That extra 100–200mm across the full depth of your extension is material: more layout freedom, better kitchen runs, improved furniture placement, and a space that simply feels larger.
Key takeaways
- Enclosure costs apply when you make use of next door’s wall for your works.
- It’s not a penalty—it’s a fair share, typically cheaper than building your own separate wall.
- You usually end up with a wider, better extension and fewer interfaces to detail.
- Surveyors calculate a present-day, proportionate contribution for the part you benefit from, formalised in a Party Wall Award.
Keep it smooth and cost-effective with Simple Survey
We make enclosure straightforward, fair and fast:
- Party Wall Notice service: £25 per adjoining ownership (multi-notice bundles discounted)
- Act administration as Agreed Surveyor (single surveyor): typically £300 fixed-fee (depends on complexity and number of notices/owners)
- Two-surveyor route (we act for the Building Owner): fixed-fee proposals from £325 for our side (we work to keep your neighbour’s surveyor’s hourly fees reasonable and contained)
Next step (fastest route):
Email your drawings (drafts are fine) and the site address to team@simplesurvey.co.uk. We’ll confirm whether enclosure applies, outline an expected contribution range, serve any required notices, and agree a robust Party Wall Award so you can get on with building—confidently and compliantly.
Simple Survey — the most cost-effective Party Wall service in England & Wales.