Basic, Supplemental, and Additional Services under B101: the three service tiers

One-line orientation

B101 defines three service tiers with different timing, authorization, and fee implications — the supplemental-vs-additional distinction is the most frequently tested trap in this topic.

Key points

• Basic Services:
  • The five standard phases: SD, DD, CD, Bidding/Procurement, CA.
  • Included in the base fee; the architect must provide them under the signed agreement.
  • No additional authorization or compensation required to proceed through the phases.
• Supplemental Services:
  • Services beyond the five phases that are agreed upon and written into the contract at signing.
  • Pre-priced: fee and scope are defined before the project begins.
  • Examples can include sustainable design consulting, measured drawings, specialized programming, on-site project representation, or other extra scopes when the parties agree up front to include them.
  • Designated in the Section 4.1 table of B101-2017 (described there or in an attached exhibit such as a B2xx scope document) before signing.
• Additional Services:
  • Arise after the contract is signed due to changed conditions, owner requests, or unforeseen events, and fall under Section 4.2 of B101-2017 — the counterpart to the Section 4.1 table.
  • Additional Services generally require prompt notice and owner authorization. For specified services needed to avoid delay, B101 may allow the architect to begin and notify the owner promptly; the owner can direct the architect not to continue.
  • Compensated separately — outside and above the base fee.
  • Common triggers: owner-requested scope changes, extra evaluations, extra services caused by delay or changed project conditions, or a service such as programming / certification support / on-site representation that was not selected at signing but is requested later.
  • The architect must notify the owner when an Additional Service is needed; the owner then authorizes (or declines) in writing.

Confusions / comparison

Tier	When defined	Written into contract?	Extra fee?	Owner authorization to proceed?
Basic Services	At signing	Yes — the five phases	No (included in base fee)	No
Supplemental Services	At signing	Yes — in Sec. 4.1 table or B2xx exhibit	Yes (pre-agreed amount)	No — already authorized at signing
Additional Services	After signing	No — arise later or are authorized by amendment	Yes (negotiated when authorized)	Generally yes; check B101’s notice-and-delay exception

Related

• pp-aia-b101-owner-architect — full B101 article structure, including Article 4 Additional Services
• pp-aia-document-families — B-series overview and where B2xx exhibits fit
• pp-aia-c401-architect-consultant — how consultants handle additional service requests under C401