How to Write a Substitution Request the Engineer Can Approve

Why this matters

A substitution request is the shop asking the design team to accept a product the spec did not name. The engineer who wrote the spec has no reason to say yes and every reason to say no: approving your product moves some of the design risk onto their stamp, and nothing in their fee pays them to study it. A request that says "equal to specified, better lead time" hands them nothing to check, so the safe answer is a denial, and the shop then buys the specified product late. A request built so the reviewer can verify equality in ten minutes gets approved far more often, and when it is denied, the denial says why.

Whether the spec permits a substitute at all, and what "or equal" binds you to, is covered in Specification Compliance and the Or Equal Question. This card is the paperwork that follows once the door is open.

Before you write: is it a substitution at all?

Three things look alike and travel through different paper:

• A listed manufacturer. When the spec names three acceptable manufacturers, the second and third are not substitutions. You submit them as an ordinary submittal (see related: How to Prepare a Submittal for Your Own Scope).
• A product that meets a performance spec. When the spec states only what the product must do (see related: Basis of Design, Proprietary and Performance Specifications), any product that does it is compliant, and again you submit rather than request.
• A substitution. The spec names a product or a short list and you want something not on it, or you want to change a requirement the spec states. This is the one that needs a request, under the project's substitution procedures section, commonly 01 25 00 in MasterFormat numbering.

Filing a request for something that was already allowed costs you a review cycle. Submitting something that was not allowed as an ordinary submittal is worse: if the reviewer misses it, the stamp does not accept a deviation you never called out, and the product is still the shop's problem when it is found.

The deadline is set in Division 01, and it is usually early

Read the substitution section before you price the job, because it sets two clocks:

• During bidding, many projects accept requests only up to a cutoff some days before bid opening, and approved ones are issued to every bidder by addendum. After that cutoff, you bid the specified product.
• After award, many projects allow requests only inside a window measured from the notice of award or notice to proceed, often 30 to 60 days, and only for stated reasons: the specified product is unavailable, has been discontinued, cannot meet the schedule, cannot be made to meet code or a warranty requirement, or the substitute offers a substantial advantage to the owner.

Those windows are common, not universal; the project's own section governs, and some specs say no substitutions after bid at all. Under AIA A201-style general conditions, where the contract uses them, the contractor may make a substitution only with the owner's consent, after the architect's evaluation, and through a change order or construction change directive (section 3.4 in substance; check the current edition and your contract). That is why an approved substitution often arrives as paper that changes the contract, not just a stamp. What the request legally commits you to is a question for your own attorney; what it buys you operationally is a dated, documented position.

Steps

1. Pull the exact requirement you are substituting against. Copy the spec section number, the article and paragraph, the specified product, and every performance value the section states for it: capacity, rating, dimension, material, listing, finish, warranty. Also check the drawings: the equipment schedule often carries values the spec does not (see related: How to Read a Schedule on a Drawing Set). Skip this and you will compare your product to a brochure for the specified one instead of the contract, which is the comparison the engineer will actually run.

2. Build the comparison line by line, specified against proposed. One row per stated requirement, the value the contract requires, the value your product delivers, and a source for your number: a page of the manufacturer's published data, a listing directory entry, a test report. Equality the reviewer cannot trace to a document is an assertion. Mark each row as meets, exceeds or differs. Do not leave a row out because it is unflattering: a hidden difference that surfaces at the review turns one denied row into a denied request and a reviewer who reads your next request line by line.

3. State every effect on other work. A different product changes things the spec never mentioned: a curb size, a weight on the structure, a voltage or a breaker size, a connection location, a clearance, a control interface. List each one and say who it touches and whether you carry the cost. This is where most approvable requests die, because the engineer has to protect the trades who are not in the room. Claiming no effect when the curb is a different size is the kind of statement that ends the engineer's trust in the rest of the form.

4. Compare warranty and service. Length and scope of the warranty against the spec's warranty article, and whether local service and parts exist. A shorter warranty is a difference to disclose, not a footnote.

5. Give the reason, using the spec's own list. Name which of the permitted reasons applies and attach the evidence: a supplier's written lead time, a discontinuation notice. "Contractor preference" is not on any list. If the reason is savings, many specs require you to state the credit to the owner; say it as the contract's numbers require, and do not promise one you have not priced.

6. Sign the representations, then submit through the channel Division 01 names. Most request forms ask the contractor to state that it has investigated the product, that it will coordinate any changes it causes, that it waives claims for added cost the substitution causes, and that the product is at least equal. Read those lines before signing; they are why step 3 cannot be guessed. Send it the way the section says, usually through the general contractor, and log it with a number like any submittal.

7. Do not order until you hold the answer in writing. An approved request is often followed by the substitute's own submittal. Ordering on a verbal yes is ordering the unspecified product on your own risk.

Worked example: the exhaust fan request

A light-commercial tenant improvement specifies a roof exhaust fan by one named manufacturer, no "or equal." The supplier quotes 14 weeks; the general contractor's schedule needs the fan in 6. Another manufacturer has a comparable fan in stock with 3 weeks delivery. All values below are illustrative of the method, not product data.

SUBSTITUTION REQUEST         No. SR-03     Date: day 18
Project: Tenant Improvement, Suite 140
Spec: 23 34 00 HVAC Fans, 2.3.A     Tag: EF-2 (M-601)
Specified: Mfr A roof exhaust, model per schedule
Proposed:  Mfr B roof exhaust, model per attached data

REQUIREMENT      SPECIFIED     PROPOSED      SOURCE
Airflow          1,200 cfm     1,200 cfm     B curve p.4
Static pressure  0.5 in wc     0.5 in wc     B curve p.4
Sound, max       12 sones      11.4 sones    B data p.5
Motor            1/2 hp 120/1  1/2 hp 120/1  B data p.2
Listing          UL 705        UL 705        directory
Curb, outside    22 x 22 in    20 x 20 in    B p.7 DIFFERS
Weight           95 lb         88 lb         B data p.7
Warranty         2 yr          2 yr          B warranty

EFFECT ON OTHER WORK
- Curb: specified curb is 22 in. Proposed needs a curb
  adapter supplied by this contractor; roofer flashes
  the specified curb unchanged. No change to roofing.
- Structure: 7 lb lighter. No change.
- Electrical: same motor, same disconnect. No change.

REASON: Specified product cannot meet schedule.
Supplier letter attached: 14 wk vs 6 wk required.
Credit to owner: none offered.

Why the reviewer can approve it. Every row has a page reference, the one difference is flagged in the row itself, and the only effect on another trade has an owner and a fix. The engineer can check airflow, static and sound against the curve in minutes and does not have to call anyone about the roof.

What would have sunk it. The first draft said "meets or exceeds all specified requirements, curb adapter if needed." "If needed" told the reviewer the shop had not checked; the reviewer would have had to look up both curbs, and on a no-equal spec the easier answer is no.

What changes the answer. If the proposed fan had rated 14 sones at the same airflow, over the 12-sone maximum, the sound row would fail outright and no schedule argument would fix it: the request becomes a request to change the design criterion, which the engineer may refuse on principle. Submit it anyway, honestly, only if the schedule loss is worse than the denial.

How to tell the request is ready

• Every value in the specified column can be found in the spec or the schedule, cited by paragraph or tag.
• Every value in the proposed column has a document behind it.
• Every row marked differs has an effect line, an owner and a cost bearer.
• The reason matches a reason the substitution section allows, with evidence attached.
• It is dated inside the window Division 01 sets, or the cover explains why it is late.

References

• See related: Specification Compliance and the Or Equal Question
• See related: Basis of Design, Proprietary and Performance Specifications
• See related: The MasterFormat Divisions a Service Trade Lives In
• AIA A201 General Conditions, section 3.4 (Labor and Materials, substitutions), as incorporated by your contract
• CSI MasterFormat, Section 01 25 00 Substitution Procedures, as written in your project manual