Hello, I'm Kamino, a civil engineer and government employee who writes a blog.

One of the "Seven Wonders" of the construction industry: "mandatory" and "voluntary."

I think many people have a general understanding of the difference between these two, but when it comes to temporary structures in particular, almost no one can clearly explain the difference between designated and voluntary temporary structures. In some departments, they’re often applied incorrectly. That’s how vague these concepts are.

In this section, we’ll explain the official rules and why such incorrect practices have become common.

Definitions of "Required" and "Optional"

The basic provisions are set forth in Article 1 (General Provisions), Paragraph 3 of the Construction Contract Agreement, so let’s take a look at it.

Construction Contract

Article 1, Paragraph 3
With respect to temporary structures, construction methods, and all other measures necessary to complete the project (hereinafter referred to as “Construction Methods, etc.”), Party B shall determine such matters at its own responsibility, unless otherwise specifically provided in this Contract or the design documents.

Yes. The same text should be included in the documents for both municipalities. In principle, construction is optional.

The definitions of the terms are as follows.

・"Specified" refers to items that must be constructed in accordance with the design documents when building the project.In other words, these are the "terms of the contract." If the client has determined the construction methods, machinery to be used, and materials to be used in advance and has specified them in the specifications or drawings, the contractor must perform the work in accordance with those specifications.

・"Discretionary" refers to matters regarding which the contractor may freely carry out construction work at its own discretion when constructing the project.To put it simply, the philosophy is that “as long as safety, quality, and the final result are met, any construction method is acceptable.” Construction companies can select the optimal construction method based on their own technical capabilities, available equipment, and costs.

The key point is that, as a general rule, the construction method used to build the project’s intended structure is at the contractor’s discretion. Even if the design documents (cost estimate breakdown) specify backhoe specifications, detailed material specifications, or temporary work methods, those documents are treated merely as reference materials unless they are defined as “design drawings.” If something is not specified in the drawings or specifications, the contractor is not required to comply with it.

Oh, just to clarify.

The term "optional" sometimes leads people to think that they can "do whatever they want" during construction, but that is incorrect.

Even if it is an optional installation,
・Contract Documents (Contract, General Specifications, Special Specifications, Drawings, Site Instructions)
・Various rules, such as relevant laws and regulations
must be adhered to. Furthermore, it goes without saying that quality and workmanship standards must be met. While the choice of construction method is optional, this does not mean there is complete freedom regarding the quality of the work.

What should I do if I need to change the construction method?

For any type of work, the client prepares the design and cost estimate based on an assumed construction method (since they cannot otherwise determine the design cost), but since the contractor is free to choose the actual construction method, consultation is generally not required when changing the construction method. (Please be sure to submit a construction plan, though.) However, as an exception, if site conditions differ from what was explicitly stated and construction cannot be carried out using the method the client had anticipated, the original design cost will no longer be appropriate, so this will be subject to a design change.

On the other hand, for designated types of work, any changes to construction methods generally require consultation and must be approved by the client.

Item	Specify	Optional
Design Documents	Specify the construction methods and other details.	We do not specify construction methods or other details. We may include reference drawings.
Changes to Construction Methods, etc.	Requires instructions or approval from the client.	At the contractor’s discretion. (Amendments to and submission of the construction plan, etc., are required.)
Design Changes Due to Changes in Construction Methods, etc.	We will do so.	We will not do that.
Design changes resulting from changes to the site conditions originally specified	We will do so.	We will do so.

"Changes to the site conditions originally specified" refers to situations such as the following:

・The ground conditions were different than expected (sandy soil → gravelly soil; water, gas, and communication cables not shown on the design drawings were found underground)
・The impact of the surrounding environment was identified (construction began on an adjacent private lot, and it became necessary to switch to low-noise machinery as a measure against noise and vibration)
・There are safer construction methods

To summarize, if it becomes necessary to change the construction method—not due to the contractor’s circumstances—or if it would be better to do so, a design change may be approved, depending on the specifics. Of course, I think this also depends partly on the supervisor’s discretion.

How to Tell the Difference Between Mandatory and Optional Fields

As for how to distinguish between required and optional fields, as explained earlier,The items shown in the design documents are "specified."(If it says "Reference Diagram" or something similar, it's optional.) Everything else is optional. If you have any questions, you'll have to check directly with the client.

The problem is that these matters aren’t clearly defined in the design documents, or that operations are being conducted in violation of the rules.
Example 1: Although the construction method was decided during consultations with relevant agencies, it is included in the cost estimate but not specified in the design documents.
Example 2: There is a drawing for temporary construction work, but it is not labeled as a reference drawing.

For example, in the case of Example 2, if the scaffolding is temporary but not labeled as such in the reference drawing, please ask the client before construction begins, “Is it okay to use this scaffolding as a temporary structure?”

The next article explains what design documents are.

What will be specified?

I explained that, in principle, this is an optional construction requirement, so it becomes important to determine what is actually specified.

While some decisions are determined by established practices at specific government agencies, generally speaking, the construction method deemed most advantageous overall after comparing various options during the design phase is adopted, and the construction method specified is based on that premise. Let’s look at some specific examples.

(1) Designation of the Temporary Shoring Method
For example, in river construction projects,
・Temporary cofferdam using steel sheet piles
・Temporary closure using large sandbags
Even in the case of temporary structures, the safety of river temporary closures—including their design, materials, and construction methods—has been discussed and agreed upon through river consultation, and an overall plan has been established; as a result, they are almost always designated as temporary structures. The contractor cannot make changes at their own discretion.

② Specifications for Paving Construction Methods
For example, during paving work,
・Cutting Overlay Method
・Complete Replacement Method
The construction method has been selected either through a comparative evaluation that took site conditions into account or because it is the standard method specified by the local government.

③ Specification of Construction Equipment
For example,
・Low-noise, low-vibration, and emissions-controlled construction machinery
It’s not just common—I think the measures listed above are always specified. There are several criteria, so be sure to study them. Unless otherwise specified in the design documents, the choice of construction equipment is up to you.

④ Designation of Temporary Roads and Construction Yards
For example,
・Location and structure of temporary roads
・The construction yard must be set up on the ○○ side.
Temporary roads are the most critical element in developing the overall construction plan, and since their locations have typically already been agreed upon during various consultations, they are often designated in advance. In particular, detour routes intended for general traffic must always be designated. The location of construction yards may be designated based on constraints related to surrounding facilities and land use.

⑤ Specifications for Materials to Be Used
For example,
・The lower subbase consists of recycled crushed stone (RC-40)
・The structure is made of 24-12-40BB concrete
・Pipe material: GX-type ductile cast iron pipe
For example, the materials used are also part of the construction project and are generally specified in the drawings.

Examples of Inappropriate Responses

If you aren’t familiar with the mandatory and optional rules, you might end up handling things inappropriately. Here are two common examples of such situations. Please skim through them.

(1) For the earthwork, a construction plan was submitted specifying a 0.45 m³-class backhoe, but since the cost estimate was based on a 0.28 m³-class backhoe, the client instructed that the plan be brought to the job site.
→No, no, no!! The cost estimate is strictly a standard estimate. You are free to choose your construction equipment, and it is not subject to design changes. (Although one might question whether the original “standard estimate” was correct.)

② In an urban construction project, the contractor evaluated a soundproof enclosure (an optional temporary structure that the client had provided as a reference drawing) to house the plant. The evaluation revealed that, by streamlining the plant equipment and optimizing the construction methods, the structure could be built smaller than the one shown in the reference drawing. However, the client instructed the contractor to follow the reference drawing exactly, citing that this would be less expensive than the original design.
→No, no, no!! The cost estimate is based solely on the reference drawings for temporary structures. There is no requirement to construct the project exactly as shown in the reference drawings, and this does not constitute grounds for a design change. (Although one might question whether the original “standard cost estimate” was correct.)

Why Does This Lead to Incorrect Operation?

Unfortunately, as I just explained, there are cases where the information in the design documents is incorrect, the staff member in charge has misunderstood something, or the entire department has a mistaken understanding to begin with.

The reason this happens is that the current method for calculating design costs is so rigorous—tallying everything from 1 kg of rebar to a single bolt to items costing around 100 yen—that it makes you wonder, “Do we really need to break it down that finely?” That’s likely why so many people feel uneasy when there’s a discrepancy between the work methods used in the cost estimate and those actually employed on-site. Moreover, if the on-site construction method ends up being cheaper, there’s a higher chance that a third party will point out that the estimate was inflated.

That’s why, regardless of the drawings or specifications, people end up thinking, “We’re calculating the cost this way, so we can’t change it,” or “If you want to switch construction equipment, you’ll have to make a design change.” If you don’t know the rules regarding what’s mandatory and what’s optional, it’s not surprising that you’d think that way based on common sense.

People who are unfamiliar with the rules sometimes raise concerns during audits or accounting inspections, suggesting that “the details of the cost estimates may not match the actual situation,” but,As long as the scope of application of the cost estimation standards is appropriate for each individual project site, differences between the cost estimation standards and actual conditions generally do not pose a problem....is the conclusion reached. (That is precisely why establishing a sound basis for the initial cost estimation standards is so important—and why it’s a difficult situation for the staff members who must take responsibility for them.)

Everyone involved in civil engineering projects should make sure they fully understand this. Don’t let audits intimidate you—make sure to follow the rules correctly.

And,When creating design documents, make a clear distinction in your own mind between what is required and what is optional, and when including optional items in drawings or specifications, be sure to label them as “reference drawings” or “reference documents.”Let's do that. Even if it's optional, it's best to include reference diagrams and materials that reflect the client's perspective as much as possible. (Well, just follow the government agency's rules.)

That concludes this explanation. I hope it proves useful in your careers in civil engineering.

See you later.

 

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