The mechanical insulation specification is an important but often overlooked part of the overall design process. Too often, mechanical insulation specifications are developed by "dusting off" the specification from a previous project. This often results in confusion, delays, and increased costs. Good specifications should communicate the design objectives, materials, thicknesses, finishes, securements, and other systems requirements.

This section on specification writing was originally published from the North American Commercial and Industrial Insulation Standards. It is reproduced here with permission of the Midwest Insulation Contractors Association.

The industry standard in the commercial/building segment for specification organization and writing style is the Construction Specifications Institute1 (CSI) Project Resource Manual (PRM), which has evolved over more than 30 years, while the industrial segment does not follow any specific format.

The PRM discusses overall organization of contract documents. Understanding the organizational principles of construction contract documents is essential to writing clear and concise specification sections without creating conflicting requirements within the whole set of documents, which includes the drawings.

This specification writing guide provides an overview of the concepts contained in the PRM, as well as application techniques used by most architects and engineers, and the majority of commercially available master guide specifications. This includes MasterSpec® Specification System 2. There are other master-type specifications available, including (but not limited to):

MasterSpec is a product of the American Institute of Architects (AIA). AIA MasterSpec is an industry-standard product research and specification resource for design professionals for producing specifications. With MasterSpec master guide specifications, users can delete what does not apply and add their own customizations.

MasterSpec is exclusively developed by Deltek, a strategic partner of AIA.

MasterSpec provides the design professional unbiased, objective information on building products. It is written by professional architects and engineers, and vetted by AIA-sponsored architectural and engineering review committees.

Whether the insulation project is a part of a complex building project or a simple contract that includes only mechanical insulation, these principles apply. In every case, a contract identifies the contracting parties and defines their duties, responsibilities, and relationships. Contract provisions may be a series of complex standard documents or simple provisions written on the back of a work order. There are usually some administrative requirements for performance of the contract and procedures to follow during the execution of the contract. These are included in a series of specification sections in Division 01 – General Requirements. Division 01 specifications can sometimes be combined with the contract provisions or can be omitted when they have been established in a previous relationship between the owner and contractor.

Along with these contract requirements and general requirements (Division 01), the drawings and specifications form the complete set of construction contract documents. Drawings communicate the quantitative requirements and show graphically the shape, location, joining, and general arrangement of construction. Specifications set the quality requirements for materials and workmanship.

Specifications are organized into groups, subgroups, and divisions. Each division is further subdivided into sections, with each section divided into three parts. For example, mechanical insulation appears in one or more sections in:

  • Division 21 – Fire Suppression,
  • Division 22 – Plumbing, and
  • Division 23 – Heating, Ventilating, and Air Conditioning (HVAC).

This organizational concept helps to locate particular information for easy retrieval. Organized in a standard sequence, each document in the set of construction contract documents fulfills a particular and unique function. Each document must precisely perform its function without encroaching on the function of the other documents. This principle avoids creating conflicting requirements within the overall set of documents and reduces the chances for duplications and omissions. Construction contract documents organized by this principle must be read together to obtain the complete meaning and to understand all the contractual requirements associated with the work or a portion of the work. Therefore, a specification section for duct, equipment, or pipe insulation must be read with the agreement and conditions, Division 01 specifications, and all drawings to know all the requirements that apply to insulation work. This is true whether the insulation contractor is the prime contractor, a subcontractor, or a lower-tier subcontractor.

The following paragraphs generally describe the role of each document within the set of documents. Even if the project is a simple contract without a full set of drawings and specifications, these principles remain valid.

  • Contract Documents: The entire set of documents that make up the contract. Contract documents include the form of agreement, conditions of the contract, specifications, and drawings. They also include addenda issued during bidding and contract modifications (such as change orders, construction change directives, and others) issued after contract execution.
  • Agreement: The document that identifies the project, the owner, the architect and engineer, and the contractor. Among other provisions, it briefly describes the project and includes the contract time and amount and method of payment. This document sets the obligations of the contracting parties. The agreement usually has several attachments, such as bonds (performance and labor and material payment bonds) and certificates (e.g., insurance certificates).
  • Subcontract Agreements: Created between the contractor and the subcontractor, or between a subcontractor and a lower-tier subcontractor, these agreements obligate the subcontractor to the owner the same as the contractor is obligated. Therefore, all the contract documents apply equally to the subcontract as they do for the contractor. The specific scope of work for subcontracts must be described in the subcontract agreement or its attachments and not delineated on the drawings or described in the specifications. So, identification of who performs particular work is not described in well-written specifications.
  • Conditions of the Contract: General conditions are usually standard documents that apply to any project. Supplementary or special conditions modify the general conditions to make them project specific. New electronic documents available from AIA provide the ability to modify the standard general conditions within the documents but do so in a way that the modifications are clearly identified. These documents set the rights, responsibilities, and relationships for the involved parties. Along with the form of agreement, the conditions of the contract set the requirements for the contractor to provide materials, workers, tools, and equipment; and to perform the work described in the rest of the documents. The conditions also set the requirements for the owner and the architect and engineer to perform certain tasks during construction (such as reviewing submittals and applications for payment, interpreting documents, and making payments).
  • Division 01—General Requirements: The first division of the specifications, Division 01 includes administrative and procedural requirements that apply to all the work, whether performed by the prime contractor or subcontractors. Division 01 specifications help eliminate the need to repeat requirements throughout the rest of the specifications. Therefore, insulation specification sections in Divisions 21, 22, and 23 must be read together with sections in Division 01 to know all of the contractual requirements.

In Division 01, some sections discuss the rules for product selection, such as what is meant by the phrase "or equal" if that phrase is used in the specification. Other sections include the procedures for submitting shop drawings, product data (also known as manufacturers' cut sheets), and samples. Other sections set general requirements for execution of the work and procedures for project closeout.

All these documents are important for insulation contractors to know and understand (whether they are the prime contractor or a subcontractor) because they contain requirements that apply to their work. If each document is written without encroaching on the functions of other documents, it not only avoids conflicts, duplications, and omissions, but it also allows specification sections to be written without repeating information. Specification sections then focus on the technical requirements for a particular portion of the work (e.g., duct, equipment, or pipe insulation systems). Many contract provisions are omitted from technical sections because they are already stated in the agreement, conditions of the contract, and Division 01 specification sections. This is the keystone of specification writing principles.


Specification Section Numbers and Titles: The CSI and Construction Specifications Canada (CSC) jointly publish a document called MasterFormat®, which is the master list of numbers and titles for organizing information about construction requirements, products, and activities into a standard sequence. In addition to other applications, MasterFormat is the de facto North American standard for assigning numbers and titles to specification sections. CSI and CSC periodically update MasterFormat according to the changing construction industry. MasterFormat expands the divisions by assigning numbers to construction subjects known as specification sections. The system of numbers is open and flexible to allow user-assigned numbers for additional subjects.

MasterFormat has been adopted by all federal government agencies and the private-sector design and construction industry throughout the United States and Canada.

Mechanical insulation is located in several divisions: Division 21–Fire Suppression, Division 22–Plumbing, and Division 23–HVAC. The first two digits of the section number are the division number, followed by two pairs of digits that provide the standard location of mechanical insulation within these divisions. The standard location within each of these divisions is identified by the second pair of numbers in the section number—e.g., "XX 07 XX." The benefit of this standard location is that duct, equipment, and pipe insulation can always be found in these locations from project to project and from region to region across the United States. The objective is ease of information retrieval. Standard numbers and titles for mechanical insulation are as follows:

  • 21 07 00 – Fire Suppression System Insulation
    • 21 07 16 – Fire-Suppression Equipment Insulation
    • 21 07 19 – Fire-Suppression Piping Insulation
  • 22 07 00 – Plumbing Insulation
    • 22 07 16 – Plumbing Equipment Insulation
    • 22 07 19 – Plumbing Piping Insulation
  • 23 07 00 – HVAC Insulation
    • 23 07 13 – Duct Insulation
    • 23 07 16 – HVAC Equipment Insulation
    • 23 07 19 – HVAC Piping Insulation

Notice the similarity of the numbers and titles within each division. This similarity, and the apparent redundancy, end at the numbers and the titles of articles and paragraphs within the sections. The requirements for insulation vary among applications—i.e., the internal temperatures and conditions are different for each application, and they often require different materials or installation requirements.

Specification sections can be written using the higher-level number (numbers ending in “00”) or using the lower-level numbers (ending with specific numbers in the third pair of numbers). Specifications for a specific project in a particular division should not be written using both higher- and lower-level numbers (i.e., 23 07 00 and 23 07 13). A project specification written using 23 07 00 would be inclusive of duct, equipment, and piping insulation as applicable to the project. This would be the choice when the project is simple and requires only one or two different types of insulation systems. When there are multiple types of insulation systems for ducts, equipment, and piping, using the lower-level numbers affords the ability to focus on each application comprehensively, while keeping the subject matter easy to find and read.

Standard arrangement of information within specification sections is the objective of the CSI/CSC SectionFormat®. Retrieval of information continues to be the objective for this concept. Each specification section is divided into three parts. These parts are Part 1 – General, Part 2 – Products, and Part 3 – Execution. Each part includes particular information about the subject of the section. These three parts are fixed in number and title and are included in all specification sections.

Part 1 – General supplements the "general requirements" in Division 1 sections by setting particular requirements about the materials and workmanship included in the section. In the case of mechanical insulation, it sets particular requirements for submittals, quality assurance, and other administrative requirements for mechanical insulation.

Example: Division 01 Section "Submittals" specifies general requirements for the procedures, including quantities, distribution, and actions to be taken by each party. In the Part 1 "Submittals" article of a specification section, particular requirements about what to submit are specified.

Part 2 – Products contains provisions that set the quality requirements by describing materials, products, equipment, and, if applicable, manufacturing tolerances and factory testing requirements.

Part 3 – Execution specifies how the products described in Part 2 are incorporated into the work, specifies workmanship quality requirements (without dictating contractor means and methods), and sets field quality-control testing requirements.

In each of the three parts, a standard sequence of articles and paragraphs exists. Suggested articles and paragraphs should be retained only if they apply to the subject of the section; and, when retained, they should be arranged in the recommended sequence to meet the objective of easy information retrieval.

Page layout and article and paragraph numbering are presented in CSI/CSC PageFormat©. This document suggests alternative article and paragraph numbering schemes, recommendations for margins, spacing between articles and paragraphs, and other formatting considerations. The most important feature of this document is the article and paragraph numbering schemes that provide an address for specification text. This addressing feature helps users reference information when communicating among contracting parties and addressing changes to the documents through addenda, requests for information, and change orders.

Methods of Specifying

Several methods exist for writing specification requirements to describe products. These methods are presented here in summary only, and each method is described in its purest sense. Most specifications employ combinations of these methods to create a complete set of requirements.

  • Descriptive: This method is a detailed written description of the required properties of a product, material, or piece of equipment; and the workmanship required for its proper installation. In its purest form, proprietary information is not used. This method results in lengthy specifications. The burden of performance of the described product, material, or workmanship rests with the specifier. This method should be used when proprietary information is prohibited (e.g., on public-funded projects), when adequate standards are not available to use as references, or when at least three manufacturers and products can be included in the specifications to maintain a competitive bidding environment.
  • Reference Standards: Nationally recognized standards are used by reference in this method to eliminate writing lengthy descriptions. ASTM is one of many recognized standard-producing organizations in the United States, for example. Standards are developed by consensus and usually set minimum requirements that may not be sufficient to suit project needs. Both poor and good standards exist, and most standards include hidden choices that must be made and included in the citation within the specification. Such choices include grades, types, classes, and other parameters to allow for various levels of quality and alternative or optional attributes. Standards are constantly updated, withdrawn, or replaced by other standards. Use of this method requires the specifier to know the standard and to incorporate it correctly and completely in the specification. Reliance on citations used in previous project specifications without current knowledge of the cited standard can result in inaccurate, incorrect, or obsolete references; resulting in inaccurate contractual requirements.
  • Performance: The end results are specified in this method, rather than the way to achieve the end result. A performance specification also must include criteria by which performance is verified. Contractors are free to use products of their choosing that comply with the performance requirements. The burden of performance rests with the contractor. Specifiers should not include unnecessary restrictions on how to achieve the results.
  • Proprietary: Use of proprietary information provides the specifier the most control over what products will be used on a project. This method is the simplest and shortest to write. As with the descriptive method, the burden of performance of the specified products rests with the specifier, and this method often limits competition. For this reason, single-source proprietary specifications are normally prohibited on public-funded projects. Proprietary specifications can be open or closed. Open proprietary specifications are used to allow the consideration of substitution requests, and closed proprietary specifications are used if substitutions are prohibited. Nonrestrictive proprietary specifications include the use of proprietary information to set a level of quality by which other products are judged when substitutions are proposed. This requires rules about how other products will be evaluated, who will evaluate and decide, and how decisions will be documented. These rules are generally included in Division 01 specifications.

Defining the Scope of Work

The function of specifications is to define the quality of products, materials, and workmanship. The function of the agreement and conditions of the contract is to set obligations for contract performance. Therefore, specification sections should not include "scope of work" statements. These statements belong in the form of agreement (between the owner and contractor, and between contractor and subcontractor). Excluding scope statements from specifications allows specification sections to focus on the technical requirements without encumbering them with contract requirements. This practice avoids the problem of attempting to determine who performs each task. Division of the work varies among contractors, depending on many factors. For the benefit of the reader, opening articles and paragraphs in most specification sections include statements about what is included in that section—similar to an executive summary for a report. Avoiding assignment of the work within the specification section also allows for more concise and direct sentence construction, and it helps make the specifications easier to read and understand.

Typically, specifications are intended to provide information related to design or quality, whereas drawings, piping and instrument drawings (P&IDs), isometric drawings (ISOs), equipment drawings, and orthographic drawings provide information related to quantitative measurements.

The information on drawings pertaining to mechanical insulation varies between the commercial/building and industrial sectors.

As an example, in the industrial sector, the extent of insulation information on P&IDs can vary. Some will show the insulation type (and maybe thickness) for piping, some will also include the insulation type (and maybe thickness) for equipment, while others will not show any insulation information. Most of the process industry includes some insulation information on the P&IDs.

There are also different approaches to what is included on isometrics. Typically, they only show the insulation type (and any applicable limits), thus requiring the reader to use the latest piping line list to determine insulation thickness. Insulation thickness tables may be in the specification or other contract documents; or piping insulation thicknesses are in the line lists, and equipment insulation thicknesses are defined on item-specific equipment coating, insulation, and fireproofing data sheets (CIFDS).

The line (or line schedule), equipment list, and instrument index—to name just a few—are also vital components to be referenced in conjunction with other drawings and the specifications. They may include information like type and thickness of insulation.

Very rarely, if ever, do mechanical and plumbing drawings prepared for commercial construction projects show duct, equipment, and pipe insulation. Insulation requirements are usually described in an application schedule that is included in the specifications.

The variances between industry segments are great, but in all cases—especially from a contractor's perspective—drawings can be vital components used in conjunction with the specifications.

Specification Language and Writing Style

Vocabulary (Terminology): Writers of specifications should use terms with precise meanings and avoid jargon and ambiguous terms. Additional rules of thumb include:

  • Avoid the use of abbreviations, unless they are well-known industry standards or are defined in the specification.
  • Avoid the use of symbols.
  • Use numerals consistently.
  • Set particular rules for capitalization.
  • Set rules for spelling and select a particular dictionary for specification production. If there are optional ways to spell a word (e.g., calk and caulk), the shorter spelling is preferred.

Writing Style: Short, simple sentences are easier to read and understand. Specifications are contract requirements written as communication between the two contracting parties: the owner and the contractor. The communication in these documents is in one direction: from the owner to the contractor. With this in mind, sentences in specifications can be written assuming that they are directives from one party (the owner) to another (the contractor). Sentences should be simple declarative statements. For this reason, statements that assign work can be eliminated (e.g., “The mechanical contractor shall…”), along with the phrase "the contractor shall." Style also means passive or active voice. Active voice is when the subject of the sentence acts; if the subject is acted on, the voice is passive. Active voice uses fewer words and is more direct. Passive voice nearly always takes more words and is less direct. Active voice is preferred in most cases but is not always appropriate.

Example: If the subject does not take action but is something being described (such as a product), passive voice is clearer. If the subject is "the contractor," directed by the document to take action, the active voice is shorter and clearer.

Grammar Rules: English grammar rules apply. Proper sentence construction means that the subject and verb must agree; that the sentences have parallel construction for both parts of compound subject or predicate; and that the style for nouns, adverbs, or prepositional phrases are identical. Use of unnecessary words and excessive use of prepositional phrases should be avoided.

Part 1 Writing Style: General requirements here expand on Division 01 – General Requirements as applicable to address the subject of the section only. So, unique requirements are included here. This includes requirements for what specific submittals are required, as well as quality assurance requirements that apply only to the products and installations of this section. The writing style is directive in nature, similar to the content of Part 3. Simple, declarative statements are applicable here. Streamlining is also employed, with the use of paragraph titles followed by a colon—which is, in turn, followed by descriptive content and, sometimes, subordinate paragraphs.

Part 2 Writing Style: Product and materials are described in Part 2 – Products. When describing products, use streamlining to make clear and concise sentences. Streamlining employs a title (preferably a generic, descriptive term for a product or material) followed by a colon, and then a concise description. The title of the paragraph should match the term on the drawings used to identify the product being described. Within the context of construction documents, this presents concise statements and avoids duplicating requirements from the agreement, the general conditions, and Division 1 specifications. As previously stated, these other documents set the obligation to provide all labor, materials, tools, and equipment to perform the work of the contract. Specifications do not need to repeat these requirements. Sentences can be limited to describing products and materials.

Part 3 Writing Style: Part 3 – Execution should concisely describe the qualitative requirements for installation and application of products described in Part 2 – Products. These are the actions the owner is directing the contractor to perform as a part of the work of the contract. Writers should use imperative mood and active voice to create concise, declarative statements. Since specifications communicate requirements from the owner to the contractor, the understood subject of these sentences is "the contractor" or "you." Begin sentences with the action word (predicate).

Example: Install insulation materials, accessories, and finishes with smooth, straight, and even surfaces; free of voids.

In the example above, the subject of the sentence is "you," which, in the context of specifications, means "the contractor."

It is also important to avoid dictating means and methods.

Coordination with Drawings

The drawings are normally mute on the subject of mechanical insulation, except for the inclusion of an insulation schedule that identifies services to be insulated, locations and sizes of the services (because these items potentially determine materials and thicknesses), and the required insulation materials and thicknesses. These schedules also include required jackets, when applicable. These insulation schedules can also be included in the specifications.

Designers must consider the internal temperatures of the equipment or systems being insulated, the ambient conditions in which the insulated equipment or system exists (or passes through), and the physical abuse the insulation system must withstand. In addition, the primary objective of the insulation system must be determined, along with secondary and tertiary objectives. Pipe materials sizes must be determined before insulation systems can be designed. All these factors must be known to determine the appropriate insulation materials, thicknesses, and required coverings.

As an example, any given piping system will have multiple insulation materials and thicknesses along its route from central equipment to terminal equipment. This situation makes creating an insulation schedule a complex undertaking.

Periodic maintenance of system components, which may require the periodic removal and replacement of portions of the insulation system, must be included in the design considerations. These situations must be identified on the drawings to make all aware of the maintenance requirements.

Coordination with Other Specification Sections

Specification sections that specify the equipment and systems to be insulation should be carefully coordinated with the insulation sections. This coordination includes compatibility of the surfaces to be insulated with the insulation materials chosen for the application. Also, the installation requirements for equipment and systems to be insulated must specify adequate clearance requirements for proper insulation application.

A provision can be included in Part 3 – Execution for duct, equipment, and piping specifications sections to alert the installer of that equipment or system that the equipment or system will be insulated and refer the installer to the insulation specification that details the materials and thicknesses to be applied to the equipment or systems described.

Adequate Clearance for Proper Insulation Application

Insulation systems are designed to accomplish certain objectives (which includes freeze protection, personal protection, condensation control, fire safety, sound control, and energy efficiency). There can be multiple objectives identified for each insulation system. If proper clearances are not allowed, the insulation system thickness and other system components will be compromised, and the insulation system will not achieve its designed objective. Inadequate clearances can occur because of pipes and ducts that are too close together or too close to the structure or other architectural features or engineered system components.

Piping and duct systems are often not drawn to scale in construction drawings. To ensure proper installation of mechanical insulation, adequate clearances must be designed into the mechanical equipment and systems to be insulated. However, single-line schematics are often all that is provided for bidding and construction. Design professionals often do not properly consider the application of insulation systems, so clearances are often not specified. When this occurs, it is up to the installing contractors of all structural, architectural, mechanical, and electrical systems to work together to achieve the necessary installation clearances. When modifications must occur to provide adequate clearance, the owner and architect/engineer must be included in the discussions. In some cases, inadequate clearances can cause some parts of a system to not be insulated, such as pipes or ducts installed against a wall, ceiling, or equipment. Below-ambient systems must have a complete and uninterrupted insulation installation to achieve condensation control. This includes wall or floor penetrations. To achieve condensate control through the penetration, insulation must be installed continuously through the penetration; otherwise, vapor retarding insulation components will be compromised, resulting in failure of the insulation system as well as damage to architectural finishes. Thus, size of sleeves and the sleeve seals must be selected to allow for the specified insulation material and thickness.

It is essential that clearance for equipment and systems to be insulated be discussed in construction and pre-installation meetings. The construction team, including the owner, must be made aware of the requirements for adequate clearance and application access for insulation installations.