Basis of design, or equal, and substitutions.

What basis of design means

The basis of design is the specific product, maker and model, that the drawings and spec were built around. Its size, weight, power, connections and performance are what the engineer coordinated with every other trade. The schedule on the drawings usually names it, and the spec section often names it again with the phrase "basis of design." Everything else on the job is measured against it.

The ways a spec can name products

• 1One product, no substitutions. Only the named product. Anything else is rejected. Owners use this for standardized equipment they already maintain.
• 2Basis of design, plus listed makers. The named product is the reference, and the other makers listed may be submitted if their product matches it. This is the most common form in MEP specs.
• 3Or equal. The named product, or one the reviewer accepts as equal. The contractor carries the proof.
• 4Performance only. No maker named, just the values the product has to meet. Any product that meets them, with the data to show it, can be submitted.

Read the spec section's PRODUCTS article to see which one applies. The same project can use all four in different sections.

What an or-equal product has to prove

Equal doesn't mean similar. It means the same in every way the drawings and spec fix: capacity, size, power and connections, listing and certifications, material and finish, warranty. The submittal has to show it, side by side, on the maker's own sheet. A reviewer can't approve an equal they have to take on faith.

Here's what that looks like on our sample project. The basis of design for an under-sink tempering valve was listed to ASSE 1070. The submitted valve from a different maker matched on inlet size, minimum flow and lead-free brass body. It differed on three: it was listed to ASME A112.18.1 instead of ASSE 1070, its adjustment range was narrower, and it had two outlets instead of one. Three matches don't make it equal. The listing difference alone is a decision only the reviewer can make.

When a different product becomes a substitution

A product from a maker the spec doesn't list, or one that differs from the basis of design in a way the spec fixes, isn't a submittal. It's a substitution. Division 01, usually Section 01 25 00, sets the procedure: a written request, the comparison it asks for, the reason, the cost and schedule effect, and often a deadline after award. The design team decides, and only an approved substitution can then be submitted.

Sent as an ordinary submittal instead, it does one of two things. It gets rejected, which costs a review cycle. Or it slips through unnoticed and turns up later, when the trades argue over a product nobody actually accepted. The spec usually puts the cost of coordinating a substitution, including changes to other trades' work, on the contractor who asked for it.

How to keep it clean

For subcontractors: check the maker against the spec's list before you price it. A maker that isn't there needs a substitution request, filed early with the comparison done. For reviewers: read every submitted product against the basis of design, not just against the maker list, and say in the comment which values differ. "Approved as noted" on a product that differs in a fixed value is how the argument starts later.

How Beem handles it

Every item we check gets one verdict: it matches the basis of design, or it differs, with the reason and the page behind it. A different product from the contractor goes beside the basis of design value by value, so the reviewer sees exactly where it holds up and where it doesn't. The call on whether it's equal stays with the reviewer, and the brand choice stays with the contractor.

Questions people ask