NBS Chorus has been the default specification tool for UK architects for good reason. It is cloud-based, it integrates with Revit and ArchiCAD, and it provides a structured library of pre-written clauses organised by Uniclass classification. For practices that have used NBS products since the days of NBS Create, the transition to Chorus felt natural. You pick your classification, select your clauses, edit what needs editing, and publish.
The strength of Chorus is its content library. NBS employs a team of specification writers who maintain and update clauses to reflect current British Standards, building regulations, and product data. When a standard changes, NBS pushes an update notification. That is a real advantage for practices that don't have the capacity to track every amendment to the Approved Documents themselves.
Chorus also works well as a collaboration tool. Multiple team members can work on the same specification, mark sections as complete, and track progress through a simple visual dashboard. For larger practices running several projects simultaneously, that visibility matters.
For all its strengths, Chorus is fundamentally a clause library with a good interface. You still need to know which clauses to select. You still need to manually cross-reference your specification against your drawings, schedules, and material selections. And you still need to read every clause to make sure it actually applies to your project rather than a generic version of it.
This is where the time goes. Not in the writing itself, but in the thinking around it: checking that the window schedule matches the specified ironmongery, confirming that the fire rating in Section 3 doesn't contradict the detail on Drawing 45, making sure the acoustic performance specified for the partition system is actually achievable with the product you've chosen.
NBS Chorus doesn't do any of that for you. It gives you well-written clauses and trusts you to assemble them correctly. For a senior architect with decades of experience, that might work. For a Part III who has been handed their first specification at RIBA Stage 4, it is a steep learning curve with expensive consequences if something gets missed.
Avoice takes a fundamentally different approach. Rather than providing a library of clauses for you to select from, Avoice uses AI agents that generate specifications based on your actual project data. You feed it your drawings, schedules, material libraries, and previous project documentation. The AI then produces a draft specification that is grounded in what you have already decided, not in generic template content.
The difference is subtle but significant. A clause library assumes you know what you need and can find it. An AI agent looks at what your project contains and works out what the specification should say. It can flag when your door schedule specifies a fire rating that doesn't match the partition system in your spec. It can catch when you have referenced a product that has been discontinued or when a performance requirement contradicts another section of the document.
Avoice generates specifications classified under Uniclass, CAWS, NATSPEC, and CSI MasterFormat. That means it works for UK practices using Uniclass, Australian firms on NATSPEC, and North American offices using MasterFormat. NBS Chorus, by comparison, is primarily built around Uniclass and the UK market.
One of the persistent frustrations with any clause library is that it is generic. NBS Chorus gives you industry-standard clauses, but they don't know that your practice always specifies Schuco curtain walling, or that your preferred acoustic consultant requires a specific STC rating in all your healthcare projects, or that your last three school projects all used the same roofing system because the client trust prefers it.
Avoice addresses this by ingesting a firm's existing documentation. Historical project specifications, material libraries, preferred product lists, and internal standards all become part of the knowledge base that the AI draws from. Over time, this means the specifications it generates reflect how your practice actually works, not how a generic clause library thinks you should work.
This is particularly valuable for practices with a signature approach to detailing or material selection. If you always specify standing seam zinc roofing with a specific substrate build-up, Avoice learns that. NBS Chorus will give you a zinc roofing clause, but you will need to edit it every time to match your preferred system.
Both tools support Uniclass classification, which is now a requirement for BIM projects in the UK. NBS Chorus has deep Uniclass integration, which makes sense given that NBS and Uniclass are maintained by the same organisation. The classification structure is built into the clause library, so you are always working within a recognised framework.
Avoice also classifies output under Uniclass, but adds CAWS classification alongside it. Many UK practices still use CAWS internally, particularly for cost planning and coordination with quantity surveyors. Having both classification systems available in a single tool removes the translation step that often causes errors when moving between specification and cost documentation.
For practices working internationally, Avoice's support for NATSPEC and CSI MasterFormat is a clear advantage. NBS Chorus is primarily a UK and Australasian product. If your practice has projects across multiple jurisdictions, maintaining separate specification tools for each market creates unnecessary complexity.
NBS Chorus pricing has been a sore point for smaller practices. Subscription costs have risen significantly in recent years, with some firms reporting year-on-year increases of 30% or more. A single Chorus licence sits in the region of £1,500 to £1,700 per year plus VAT, depending on the package. For a five-person practice, that is a meaningful line item, especially when only one or two people actually write specifications.
NBS has responded with lower-cost options like Chorus for Small Works and the Designer licence, which provides view-only access for team members who need to reference specs without editing them. These help, but they also mean paying for multiple licence types to cover your team.
Avoice takes a different pricing approach, though both tools require a subscription. The relevant comparison is not just the licence fee but the total cost of specification writing: the hours your team spends selecting clauses, cross-referencing documents, and reviewing for consistency. If an AI-first tool reduces that time by even a third, the subscription cost becomes secondary to the labour savings.
The choice between NBS Chorus and Avoice depends on how your practice works and what problems you are actually trying to solve.
If you have experienced specifiers who know exactly which clauses they need, who are comfortable with manual cross-referencing, and who value a familiar interface backed by NBS's content team, Chorus remains a solid choice. It does what it has always done, and it does it reliably.
If your practice is spending too many hours on specification coordination, if you want your project data to drive the specification rather than the other way around, or if you work across multiple classification systems and jurisdictions, Avoice offers something materially different. It doesn't just store clauses. It reads your project, understands your standards, and drafts a specification that reflects both.
The architectural profession has been through this kind of shift before. Hand drafting gave way to CAD. 2D drawing gave way to BIM. In each case, the older tool didn't stop working overnight, but the newer approach changed what was possible. Specification writing is at that same inflection point. The question for your practice isn't whether AI will play a role in how you write specs. It is whether you want to start adapting now or wait until it is no longer optional.
If you want to see how AI-driven specification works on a real project, Avoice's AI Spec Agent is worth trying.
