When should one specify by Basis of Design? It seems when there is:
Difficulty finding equivalent products, assemblies, or systems that meet the specific, necessary performance requirements or criteria.
A desire to keep the spec open (non-proprietary).
When one is lazy (to keep looking beyond the one specified item).
Is there more to it? What are your thoughts?
(I could not find other 4specs discussion on this topic, and the project delivery practice guide has only two instance use of this term - I, unfortunately, do not have the specifying practice guide).
I started using basis of design in 1988 for elevator specifications, as information for the contractor. “Standard” Shindler elevators wouldn’t fit a hoistway or machine room that was designed to fit an Otis elevator and vice versa.
On the other hand, Shindler was capable of making elevators of comparable quality.
It was done with a desire to keep the spec open while avoiding change orders when a “standard” elevator from an “acceptable” manufacturer wouldn’t fit the spaces allotted.
Basis of design specifying can be a useful tool, if done correctly. Identify one specific product as basis of design by listing manufacturer name, brand name, model number and similar characteristics that uniquely identify the product. Include in the specification only those descriptive, reference standard and performance requirements that identify salient characteristics of the product. Salient characteristics are those that are important in keeping the design intent. Confirm that there are comparable products by comparing the listed salient characteristics of the basis of design to comparable products.
Once the basis of design product is chosen and the salient characteristics that will be used to judge comparables are specified, the specifier has two options for comparables. One is to keep the specification open, allowing any other manufacturer who has a product that meets the salient characteristics. While a list of comparable manufacturers is not needed, it is often helpful for bidders to list those known comparable manufacturers [or products] following language such as Comparable manufacturers [products] include:
The second option is to write a closed specification, listing the manufacturers that are known to provide comparable products following language such as Provide the specified product, or a comparable product manufactured by one of the following:
So to answer your three points:
The specifier should have already found equivalent products, assemblies, or systems that meet the specific, necessary performance requirements or criteria. If not, be intellectually and professionally honest and write a closed proprietary specification with the one product you know will work. Trying to write a basis of design spec without knowing there are comparables just invites needless work on the part of the contractor team in looking for nonexistent products, and on the part of the A/E in reviewing submissions for non-comparable products.
A basis of design specification is not necessarily open. It can be closed as in allowing the basis of design product, and ONLY three comparable products listed. Its still proprietary if you list multiple manufacturers, but limit it to only those listed.
Lazy specifiers create more work for themselves see 1 above.
Use basis of design specifying when there exists a product whose salient characteristics meet the design intent. Define those characteristics, and use them to judge whether other products are in fact comparable. Merely listing a product as basis of design without defining what characteristics are important leaves the decision on what is comparable open to interpretation. Its unfair for the bidders, and spells trouble for the A/E when submittals are made.
Also CSI practice guides and Regener’s book. Main topic - Product Requirements. Secondarily - Substitution Requirements.
Be careful not to confuse “comparable products” with “substitutions”. Read how it is defined in the applicable master specifications and the PROJECT’S Division 01.
Do the salient characteristics represent the minimum requirements that must be met, or do they represent the characteristics of other proposed assemblies/systems they will be judged on as being “close enough”?
The way I see it, if it is the first, then, why not just eliminate the term and list a generic description with the salient characteristics? (along with any optional, approved manufacturers and their respective “items”).
If the second, then it seems there could be a lot of gray area in comparing equivalents. Are the General Conditions or Division 01 section on product requirements supposed to address the authority decision-making on ‘basis of design’ issues?
Regener’s book addresseds “Quality Basis” but I don’t see “basis of design”.
It also seems Basis of Design specifying is giving preferential treatment, and should not exist for public works projects. Shouldn’t due diligence by the designer include researching sufficient and appropriate systems, and listing a minimum of two (preferrably three)?
I will admit to using the “Basis of Design” fairly casually, but I do find it very useful especially when there are very specific details shown on the Drawings, but the products can be interchanged without difficulty (I like to think of aluminum storefront). Using a comparable product should not take a lot of retinkering with the details.
Having said that, certain there are items like elevators that changing from one manufacturer to another can cause major headaches for systems with the same nominal capacities. Relatively slight changes in hoistway size can require additional engineering, especially when the project is more than a few stories high.
I would not see basis-of-design being practical with elevators, as Peter points out. But for many accessory items and some finishes it is really a good solution. Using a basis-of-design rather than a completely thorough description makes everyone’s job easier. For many of these products, each manufacturer already has produced an equivalency chart showing their products against their competitors (though this is not always publicly available).
“…a generic description with the salient characteristics” is the definition of a descriptive specification and therefore it wouldn’t even require listing manufacturers - although listing them as you suggest as “approved manufacturers” or even better “available manufacturers” is an option to keep the specification open.
Division 01 - probably in the “Products” section - is where you would define the rules of the game for evaluating comparables. As always, the more specific you can be about this, the easier the evaluation will be.
Basis of Design - and correct me if I am wrong any of you more experienced specifiers - is a relatively recent evolution. I think it may have started, or at least leapt to popularity, with ARCOM MasterSpec introducing it into their masters. If you have access, their Division 01 is a good example of the type of language for defining and evaluating Basis of Design.
When John did the revision to Rosen’s original book, Basis of Design was probably not as prevalent, and therefore was absent. I don’t know if Mark Kalin’s recent version covers it in more detail. I know CSI has not caught up in the Practice Guides as much as we should have, and the issue will certainly be addressed in upcoming revisions especially in the Construction Specifications PG.
As far as Basis of Design giving preferential treatment - the architect/engineer is hired by the Owner to select materials, products, and systems with salient characteristics (theres that term again!) that meet the Owners definition of quality. So I see using a storefront system, for example, as a Basis of Design as being precisely what you should be doing for product selection. Just because you use YKK instead of Kawneer doesnt limit competition or create an unfair environment for bidding.
And in theory, there is no reason why you shouldnt be able to write a Basis of Design specification for elevators, although in practice, I agree with John and Peter. It would be a difficult specification to write effectively, as compared to the storefront example. In theory, there is no difference between theory and practice. In practice, there is a big difference.
Per MasterSpec:
Basis-of-Design Product Specification: A specification in which a specific manufacturer’s product is named and accompanied by the words “basis-of-design product,” including make or model number or other designation, to establish the significant qualities related to type, function, dimension, in-service performance, physical properties, appearance, and other characteristics for purposes of evaluating comparable products of additional manufacturers named in the specification.
They don’t provide a definition for that, but apparently the terminology is used to distinguish between a Basis of Design product and a Basis of Design document that records the Owner’s Project Requirements.
Based on what I understand, it seems the main reason for using “basis of design” is when details need to be drawn, but cannot be done so without reflecting a single manufacturer’s product (since other acceptable products would need to be drawn differently).
But on the other hand, it seems to me that drawing it one way, to reflect the “single-named” product is also acceptable without using the term “basis of design.”
What does the term basis of design add?
I say, list:
Its salient characteristics.
The words “or equal” or a list of the other acceptable manufacturers.
Ensure the design will accommodate other proposed products. If complicated, item 2 should ideally be designed around the few manufacturers listed (e.g., sized), such that would be acceptable.
If so, then you HAVE a basis of design specification.
I see “Basis of Design” most frequently when it’s an aesthetic issue, and most frequently, that’s an interior issue. (Not always, though; recently there was only one manufacturer offering the desired sight-line for a rated curtain wall, so that was the Basis of Design; other manufacturers were welcome to custom produce)
Back to the usual: the salient characteristics then are the design, color, the appearance, etc., even though many other manufacturers can produce a product that would function as well. “Or equal” absolutely will not work, since the product has to coordinate with many additional products. The only way another product could be used would be with approval of the designer/architect.
I’ve also seen Basis of Design used when the physical characteristics of the products to be installed are completely different. For instance, the DOD and State Department require the engineer to use to a certain product as a basis of design for a pop-up vehicle barrier, as there are significant differences among the different manufacturers of those products when it comes to height, width, depth, etc. As long as the vehicle barrier meets the K-12 rating and the specified duty cycles, and the contractor is willing to bear the cost of redesigning the system (even with the re-work, bids have been competitive), the product is acceptable.
I agree with Lynn and Michael, “Basis-of-Design” is used either for an aesthetic issue or a “this one fits in the available space” issue.
The aesthetic issue is pretty obvious, particularly for interior finishes. Products specified in many different Sections have been selected because they work together and are often presented to the client for approval together on a color board. Everything needs to hang together. I have had a designer change (slightly) all of the wall paint colors when faced with a different corner guard manufacturer than they expected.
I think that the “this one fits in the available space” use is the more critical application because it can often be very subtle and not even something you could expect to be considered by person making the selection. I can recall where we selected a specific roof top cooling tower because only that one and a couple others in the same configuration fit into the building’s maximum allowable height limit. MEP engineers and bidders aren’t used to taking a criteria like that into consideration.
For these reasons we always try to say in the spec “why” something is the basis of design. That is a good exercise because if you can’t clearly state why, then it probably doesn’t need to be a “Basis-of-Design”.
Ok, “or equal” would not work. I meant to say “or approved equal”
But, my point is… isn’t it up to the designer to define the essential characteristics? If you require a certain color match, a certain size, or configuration, define it and require it. And with approval authority over any alternate submission, you essentially have a basis of design specification (this assumes the designer has properly vetted each manufacturer’s product with each essential characteristic).
If you do public work, you will usually need to include “or equal” or “or approved equal” or … There are relatively few instances where you cat legally restrict product selection.
The reasons I like “basis of design” for public work is that it lets the Bidders and Contractors know what we actually drew without unduly restricting pricing options. The one area that I can think of is storefront systems. The standard 2 by 4-1/2 inch system is a comodity product as far as I am concerned, but there are minor differences from product to product. When Architects download specific sets of details from a specific manufacturer, a really good storefront person knows who makes that particular extrusion. What I am interested in is thermal performance, water and air infiltration restrictions, wind load, impact resistance, glazing requirements, and finish. I don’t really care if it is EFCO, Kawneer, OldCastle, or Tubelite (sorry if I didn’t mention your favorite system). The basis of design says, “Here’s what we drew, but we are open to other stuff that meets our requirements without a formal substitution.”