NBS Chorus vs Avoice
An honest comparison for UK practices: how each tool writes specifications, how they handle classification, model links and checking, where each is strongest, and which suits the way your practice actually works.
What is the difference between NBS Chorus and Avoice?
NBS Chorus is the established UK specification platform, where specifiers build specifications from NBS's maintained clause library with strong collaboration and model links. Avoice uses an AI model fine-tuned for specification writing to draft from the project's own information and then check the result for contradictions and gaps, inside a wider practice workspace.
Which is right depends on how your practice writes specifications and where its time and risk actually go. This page replaces our two earlier comparisons with one up-to-date view. We make Avoice, so we have tried to be fair to NBS and to state only what NBS says about its own product.
Chorus starts from a maintained library and relies on the specifier to review. Avoice starts from project information and adds an automated check before issue.
What is NBS Chorus?
NBS Chorus is NBS's cloud-based platform for creating, managing and collaborating on construction specifications. It runs in a web browser, so nothing is installed locally.
NBS says over 3,400 practices use NBS and that 93% of AJ Top 100 architects do. According to NBS, Chorus provides:
- Maintained content. NBS writes and maintains the specification content and notifies users when it changes.
- Uniclass as standard. NBS describes Uniclass as Chorus's native classification. CAWS content is also offered, including a CAWS library in Chorus for Small Works.
- Real-time collaboration across organisations and locations, with external user invitations, permissions and audit trails on higher tiers.
- Masters, so practices can build master specifications from their commonly used clauses.
- Model integration. A plug-in connects specifications to design models. The Designer licence lets team members view and annotate specifications inside Revit, Archicad or Vectorworks without editing them.
- NBS Source integration for adding manufacturer products.
- Tiers and packages: Core, Pro and Premium, plus Designer, Small Works, Preliminaries, Early-stage specification, Domestic and Schedules.
NBS does not publish standard prices. Cost depends on plan, content and user numbers, and is quoted on request. NBS describes revision tracking, update notifications and audit trails, but does not describe automated checking for contradictions or spec-to-drawing mismatches as a Chorus feature.
What is Avoice?
Avoice is an AI workspace for UK architecture practices. Specification writing is one part of it, alongside QA/QC, schedules, construction administration, a project record, compliance registers and practice management.
For specifications, Avoice:
- Drafts from project information (drawings, briefs, product data and the practice's past work) using a model fine-tuned for specification writing. The architect reviews and edits.
- Applies Practice Voice, turning a practice's preferred clauses, products and phrasing into rules every new specification follows.
- Supports CAWS and Uniclass with NBS-compatible output, and also MasterFormat, NATSPEC and BCA for international work.
- Writes MEP specifications alongside architectural ones, since October 2026.
- Marks gaps as explicit TBCs with reasons that roll into a per-project TBC register, instead of guessing values.
- Checks the result for contradictions, broken references, leftover content, open items and spec-to-drawing mismatches, through built-in QA/QC.
- Connects to models through Revit and Archicad plugins.
NBS Chorus and Avoice side by side
The two tools overlap on classification, model links and practice standards. They differ most on where content comes from, whether checking is automated and how far the tool reaches beyond the specification.
| NBS Chorus | Avoice | |
|---|---|---|
| Approach | Specifier selects and edits clauses from NBS's library | AI drafts from project information; architect reviews and edits |
| Content source | NBS-authored and maintained content | Practice's own information and Practice Voice rules, drafted by a fine-tuned model |
| Classification | Uniclass (native) and CAWS | CAWS and Uniclass, plus MasterFormat, NATSPEC, BCA |
| Collaboration | Real-time co-authoring, external users, permissions, audit trail (by tier) | Shared workspace across specs, drawings review and project record |
| Model links | Plug-in; Designer licence for Revit, Archicad, Vectorworks | Revit and Archicad plugins |
| Practice standards | Masters | Practice Voice |
| Automated checking | Not described by NBS as a Chorus feature | Built-in QA/QC across spec and drawings |
| Open items | Handled by the specifier | Explicit TBCs with reasons, rolled into a TBC register |
| MEP | Engineering content available (Uniclass) | MEP spec writing since October 2026 |
| Wider scope | Specification-focused, with related NBS products (Source, Uniclass, LCA) | Specs plus QA/QC, CA, schedules, compliance registers, practice management |
| Pricing | Quoted per plan, content and users | Published at avoice.co/pricing |
NBS entries reflect what NBS says about Chorus. Compare total cost including the staff time spent on drafting and checking, not licence fees alone.
Where each tool is strongest
Chorus has real advantages in content authority, industry familiarity and large-team workflows. Practices that look for an alternative usually describe one of four problems that a clause library does not solve.
Where NBS Chorus is strongest
- Authority of content. NBS has written UK specification content for decades. For practices that want clauses written and maintained by a dedicated technical team, that matters.
- Industry familiarity. Contractors, QSs and clients know NBS specifications. Many public-sector and framework clients expect them.
- Mature collaboration. Real-time co-authoring, permissions, audit trails and revision tracking are well developed, especially on Pro and Premium.
- Large-team workflows. Practices with dedicated specification writers and established masters can run a consistent, auditable process at scale.
- Uniclass depth. NBS maintains Uniclass itself, so classification and content stay aligned.
Why practices look for an alternative
- Time goes on coordination
- Selecting clauses is the visible part of the job. Checking fire ratings against details, matching window types to ironmongery and confirming the specification still agrees with the drawings after the last revision take longer, and a clause library does not do those checks.
- Defects still reach tender
- Specifications written in dedicated specification software carried the same defects as those written in Word in our 2026 study.
- Setup is heavy for small teams
- Building a master, learning the tool and licensing it is a significant investment. NBS addresses this with Chorus for Small Works, a reduced CAWS or Uniclass library for simpler projects.
- One place for the project
- Practices that also need QA/QC, construction administration and a project record sometimes prefer one workspace to several tools.
From Avoice's State of UK Specifications 2026. The report concluded that a better library does not remove these defects; a check before issue does.
We also ran our QC on NBS's own published sample specification and found 36 findings in each of the CAWS and Uniclass editions, including a facade fire classification conflict: see the sample spec review. Sample specifications are illustrative documents, but the exercise shows how easily contradictions survive manual assembly.
A clause library helps you write the specification. It does not check that the specification still agrees with itself and the drawings.
Which should your practice choose?
Choose on how your practice writes and checks specifications, not on features alone. Many practices will find that using both is the practical answer.
NBS Chorus fits if
You have dedicated specifiers, an established Chorus master, clients or frameworks that expect NBS documents, and a review process that already catches contradictions and drawing mismatches before issue.
Avoice fits if
Your architects write specifications alongside design work, coordination and checking take more time than drafting, or you write MEP specifications, work internationally, or want specs in the same workspace as QA/QC and CA.
Using both makes sense if you are committed to Chorus but want an independent check on what you issue.
Using Avoice and NBS Chorus together
Avoice's QA/QC works on specifications from any source, flagging contradictions, orphan references, leftover content, open TBCs, drawing mismatches and withdrawn standards. Some practices keep writing in Chorus and use Avoice to check the output against itself and the drawings before issue. Avoice produces NBS-compatible output, which helps practices that move between the two or work with consultants on Chorus.
Ask NBS for a Chorus quote for your team size and content, and compare it with Avoice pricing on total cost, including staff time spent on drafting and checking.
Where Avoice fits
Avoice is built for practices where coordination and checking, not clause selection, take most of the specification effort. It can replace Chorus or sit after it as the final check.
You can see Avoice spec writing and QA/QC on one of your own projects, or send an existing specification, including one written in Chorus, to hello@avoice.co for a free check.
Software can draft, compare and flag. The architect and specifier still decide what the project requires and sign off what is issued.
Draft and check specifications in one place
Specifications drafted from your project information in CAWS or Uniclass, then checked against themselves and the drawings before issue.
This comparison is for general information. NBS Chorus details reflect NBS's own published descriptions at the time of writing; check current features and pricing with NBS before deciding.