Introduction to Blueprint Reading for Inspectors

by Nick Gromicko and Kate Tarasenko

Whether you are performing residential new-construction inspections or a commercial property inspections, you'll need to be able to read and understand blueprints.  Blueprints are mechanical drawings of technical details and architectural plans that are used for reference by various parties in everything from small homes to large industrial complexes. The ability to read and interpret blueprints is a useful skill for inspectors in order to gain an accurate understanding of the architect’s intent, and to be able to interpret the building’s specifications properly.

Plans and Specifications Defined

Blueprints, known generically as "plans," show the construction details of a completed structure.  And although the plans may be complete in every respect, many details, such as the materials to be used and the standards of workmanship desired, cannot be conveniently shown on the plans, so they are usually described only in the specifications, also referred to as “specs.”  Collectively, the plans and specs, along with any other supplemental information and drawings, are known as the construction documents.

The set of plans and specifications is the “bible” of the construction trade. Nothing should be changed without the approval of the architect and building official. Only information that can be shown graphically is presented on the plans. Detailed descriptions of the materials and methods to be used are written in the specs. The specs, which are often considered more important than the plans, describe every step of construction.  The specifications should describe anything that is not shown on the plans. Whatever is not described fully in the specifications should be shown clearly on the plans.

The only way to improve one’s blueprint-reading abilities is to start with a simple set of plans and go on to more complicated ones for more complex building projects.

The Purpose of Plans and Specs

Specs usually include the scope of the work to be done, a description of the exact type and grade of equipment, materials and fixtures to be used, the method and level of workmanship required by each trade, and guarantees of completion. The specs, including any sketches and working drawings, along with the written contract, become the basis for agreement between the owner and the contractor.

A set of plans and specifications must be prepared for each building so that the contractor can complete the project accordingly. Although it is up to the building official to determine whether a building is meeting its planned specifications during and after construction, it is useful for the commercial building inspector to be acquainted with a building’s plans and specs so that s/he can observe and inspect, where appropriate, the various intended features of the building.  For example, if the plans call for egress windows and fire doors, this information will give the inspector a heads-up as to their locations.  The specs will provide the materials and dimensions, along with other relevant details. 

The plans and specs should be in agreement.  But if a conflict exists between them, the specs will govern, so the inspector should obtain the proper answer from the specs.

Plans and Specs in Action

Specs supplement the plans with detailed, technical information about the work to be done.  Even the simplest type of construction project should have specs.  They are usually presented in a booklet or notebook (or several large volumes for large projects), which cover a number of subjects in comprehensive detail.

The specifications include the general conditions, which are the broad provisions of the contract between the owner and contractor. The responsibilities of the architect, contractor and subcontractors are outlined. The guarantees of completion, performance, and quality of work are described in precise detail.

Following the general conditions section, the specs are usually written in the same sequence in which the various trades will commence their work on the project. The first section usually describes the demolition, site clearance, or excavation procedures, depending on which of these would best fit the particular job. Then the “rough” and “finish” work are described for each trade.

The architect is responsible for the contents of the specs and must account for all its details. The specs will also describe the inspection procedures that will be used by the architect during construction.

Who Uses the Specs?

The owner uses the specifications to determine his or her part in the contract, and to verify the things s/he specifically wants in the finished building.  The owner should review the guarantees of performance and workmanship for future reference, in the event that the structure or equipment fails or does not prove satisfactory.

The specifications provide the contractor and subcontractors with detailed information so that they know exactly what they are bidding on and can estimate the costs of labor and materials that are both competitive and realistic.  They must use the drawings in measuring the materials needed in the actual phases of construction. By planning ahead, they can achieve many economies in the use of materials. The plans must indicate the precise location of building features, such as windows, doors, mechanical equipment, fixtures, and electrical circuits. The workers must study the prints to solve any problems that require the cooperation of the various trades

Material suppliers can study the specifications to accurately determine the quantity, quality and types of materials to be used. The suppliers of fixtures and appliances can find detailed descriptions with catalog numbers and names for the items they will need.

Building officials from city and county building departments use the specifications and working drawings to determine their compliance with zoning and building codes and fire and health standards.

Banks and loan agencies use the information in the specifications to help appraise the value of the building. Lenders, which might provide part of the financing, require a copy of the specifications for their approval.

The importance of complete and concise specifications cannot be overemphasized because they are part of the legal contract, and may be used in court in the event of a lawsuit.

Understanding Plans and Specs

To properly interpret plans or blueprints, the inspector must have a thorough understanding of how to read plans in general. This skill can only really be developed by reading many sets of plans from different types of construction projects.

The sections and details are sometimes the most difficult to master, but they are the more important parts of the plans. The details must be matched carefully with the main sections of the plans, and also with the plan views and elevations. As the inspector studies the plans, he must visualize how each section and detail will fit in the completed building.

Just as a traveler must rely on a key to understand how to read a map, a schedule is shown in a box on the plans for the inspector to see. The schedule contains a complete list of symbols and abbreviations that are used throughout the set of plans. A door schedule will show the length, width and thickness of each door, the type of each door, and the material of which it is made. A window schedule lists all the windows by number or letter.  It gives the type, quantity, material, size, model number and rough-out opening for each window. A room finish schedule lists each room and the materials to be used on the walls, ceilings, floors and trim.

The schedules may have notes containing important information. General notes are found on the plans and must be read carefully; they will not appear anywhere else on the plans or specs. Most general notes appear on the first page of the plans.

Symbols, abbreviations and notes are used on plans to save time and space in making up the plans and to improve their clarity. They are used extensively on all types of plans. They usually are not difficult to interpret, except that sometimes an architect may use a different meaning for a particular abbreviation or symbol. That is why it is important that each architect furnish a schedule of all the symbols and abbreviations used throughout the set of plans.

The working plans and specifications should contain all the necessary information to build the structure. Everyone concerned with and involved in the construction of a building should read and interpret them to learn the exact requirements of the job. There should be no need for guessing. All answers must be substantiated from information gleaned from the plans and specifications.

Each person on the job must be able to read the parts that pertain to his or her work or trade, as well as have an overall sense of how the other trades will contribute to the construction. Cooperation between different trades is essential because one trade’s efforts are affected by those of the other trades, in most instances. When all trades work together in harmony, a building is completed in a most efficient manner.           

Before tackling blueprints, the inspector should be aware that there are other different types of documents relating specifically to the construction of a building, and they have various purposes.

Supplements to Plans and Specs

On large construction jobs, especially commercial projects, an architect and his staff plan and prepare what are known as the architectural working drawings.  Structural drawings are prepared by a structural engineer; they show the details of the steel or reinforced concrete skeleton. Another set of drawings is called the electrical set, which illustrates the details regarding electrical equipment and circuits. Another set of working drawings shows the mechanical work, which includes the plumbing, heating, air-conditioning, sheet metal, and fire sprinkler systems. 

Architectural Drawings

Architectural drawings show the floor plans, interior and exterior elevations, sections and details that represent to the builder or contractor the owner’s ideas of what the building will look like. The architect has transferred these ideas to the drawings in terms of the sizes and shapes needed to produce the desired result.

Structural Drawings

Structural drawings are the floor plans, elevations, sections and details that represent the construction needed to give the building its strength to support the dead load of the building, plus the live load of its contents. The building’s strength must withstand wind, snow, earthquakes, and other natural occurrences. All buildings must be designed to conform to their state and local building codes. The sizes, shapes and dimensions on structural drawings must coincide with those on the architectural drawings.

Shop Drawings

Shop drawings include all plans and details prepared by the subcontractors for work to be done away from the construction site. Shop drawings are completely detailed and drawn to scale. They must be large enough to clearly indicate the methods of construction, installation and fastening. The drawings must be submitted to the architect for his approval before any work can be fabricated. Individual items may be fabricated in the shop while general construction is in full progress. This allows the job to proceed according to schedule.

Carpenters provide openings in the walls and floors to accommodate the ducts and pipes.  The fabrication plans and details prepared by the subcontractors who do the structural steelwork, miscellaneous ironwork, and millwork are a few examples of what are included in shop drawings.

Electrical Drawings

On large construction jobs, another set of working drawings is called the electrical set. These drawings, prepared by an electrical engineer, present the details regarding the electrical equipment and circuits.  Electric heating systems are installed by electricians, who also install wiring for furnaces or boilers in other systems. 

An electrical layout should show the number and location of outlets, switches, incoming lines, distribution panels, and fuses. The sizes of wire and other pertinent information may be given in the accompanying specifications, or listed on the drawings. All electrical devices and materials used should have the approval of the Underwriters Laboratories, Inc.

The electrician must proceed with the work of providing an efficient and safe electrical installation. A fundamental knowledge of electrical theory, and a thorough knowledge of the many kinds of conductors, wiring devices, and electrical appliances, is required. The electrician must be familiar with the National Electrical Code, which sets the standards covering the design and manufacture of electrical devices and materials, and the manner of their installation. The fire insurance policy generally is written on the assumption that the building is constructed in accordance with this electrical code. The electrician also must know the state and local codes and ordinances. The specifications dealing with electricity must be followed. When planning the layout, the electrician uses basic knowledge of installation practices, plus the information supplied by the wiring diagrams or blueprints.

Mechanical Drawings

Another set of working drawings illustrates the mechanical work; this includes plumbing, HVAC and sheet metal work. Subcontractors make shop drawings for work that will not be done at the job site; however, the architect must approve these shop drawings before the work can be started. 


Gas lines are provided by the plumbers.  Hot-water and steam systems are installed by pipefitters (who are usually plumbers).  Additionally, the building ordinances in some cities require that the architect prepare a drawing to show the plumber how to connect the drainage system. After studying the plans of the building, the plumber will read the architect’s specifications. The specifications should include:

1.  the scope of the work;
2.  a list of materials to be used for water, drain and gas pipes;
3.  installation information;
4.  a list of all the fixtures, giving complete descriptions, including brand names and sizes; and
5.  information on the types of tests to be performed on the water and sewer systems.

The plumber also must study the blueprints of a building to note the layout of the plumbing system. The plumbing system is the least understood installation in a building, yet it is perhaps the most important convenience. The plumbing provides a steady supply of clean, clear water and carries away the waste water.  The plumber is the one who is responsible for this system. If the piping and sewers were not designed correctly, a health hazard could be created. Most cities and states require plumbers to be certified or licensed before they can work at their trade.

The plumber must abide by the National Plumbing Code and city and state ordinances pertaining to the trade. The installation and operation of the water supply system, the drainage system, vents, sewer disposal system, storm drains, drain tiles, leach fields and gas piping are the responsibilities of the plumber.

Sheet Metal

The ducts for forced-air heating and air-conditioning systems are installed by sheet metal workers.

The sheet metal workers obtain the installation information about the heating unit and its controls from the specifications. The architect rarely gives a detailed layout of the ducts or pipes. This is the responsibility of the heating contractor. A heating, ventilation and air-conditioning or HVAC engineer makes a layout of the ductwork and piping in detail, and indicates the size of the ducts, pipes, radiators, convectors and diverters that are required to deliver the correct amount of heat and cooling to each room. The sizes are determined by careful calculation of heat loss and gain in each room that result from window areas and other factors. The installation of the furnace or boiler is not a difficult task. The difficult part usually is the fitting of ducts and pipes. The installers have to follow the engineer’s layout and solve the problems presented by the structural makeup of the building.

Other sheet metal work includes installing flashing to protect a building from water damage, constructing and installing gutters and leaders (downspouts), and building sheet metal canopies and decks. In commercial buildings, the sheet metal crew might install such things as conveyors, which are complex duct systems for heating and cooling, and guards and hoods for machinery.

Exterior sheet metal items generally are described on the elevation, section, or detail views. The specifications written by the architect amplify the drawings with instructions as to the type of metal to be used, and the methods of installations.

As-Built Drawings

As-built drawings are the additional drawings required by the mechanical trades.  The purpose of these drawings is to show exactly how and where certain equipment has been installed. The trades most concerned with these drawings are the electrical, plumbing, heating, and air-conditioning trades.

As-built drawings will include all minor changes in the location and elevation of underground pipelines, conduits, cleanouts, overhead valves, junction boxes, power line locations, and so forth.  They show any changes and additions to the original set of plans and specifications. These drawings must be submitted to the architect or owner because they serve as references for future additions and repairs.

Code Compliance

As inspectors know, the International Standards of Practice for Inspecting Commercial Properties does not require the inspector to confirm code compliance; this is the domain of the building official and licensed professionals, depending on the trade and component being inspected.  However, by expanding their knowledge in this area, especially with regard to commercial building projects, inspectors can be aware of potential code violations, which may bear directly on the items that they actually are responsible for inspecting.  Problems may be identified and will need to be called out as defects, which may have been the result of some previous code violation.

Building Code Requirements

All building designs must be approved by the local building inspection departments, and checked for compliance with the building code and zoning ordinances, before a building permit can be issued. For this purpose, a set of plans must be filed with the building inspection department. They may be retained by the department for future reference, but not always.

Electrical Code Requirements

The installation of electrical wiring and outlets should conform to the National Electrical Code. The installation must pass inspection by the local building department or fire inspection bureau.

The National Electrical Code specifies detailed rules for computing electrical power loads. The size of the main service is often determined by the utility company. Local ordinances usually require that electrical installations be made by licensed electricians. These precautions have been set up for reasons of safety and fire prevention. If such precautions are carefully observed, fire insurance should be more readily obtainable and less costly.

Plumbing Code Requirements

The building ordinances in some cities require that the architect prepare drawings to show the plumber how to hook up the drainage system. This can be in the form of an elevation or isometric drawing. The plumber must be familiar with the National Plumbing Code, and the local codes and ordinances. The codes cover items such as the type and size of pipes, drains and vents. Testing provisions will be specified; for example, soil pipe must be filled with water and tested for leaks.

The efficient disposal of waste and contaminated water is the most important function of plumbing. A system of soil and waste stacks of specified sizes must be set up to carry water away from each fixture. These and many other requirements must be met by the plumber to conform to the national and local codes.

Although the inspector is not required to know the codes that govern the plumbing and electrical systems, it is good to have a basic understanding of the responsibilities of these trades. The inspector should generally know who is responsible for the different stages of construction.

Where Can an Inspector Find Plans and Specs?

If an inspector is involved in a particular building project, there are various sources from which to obtain copies of the project’s specs and plans, such as from the owner or the building official.  The specs and plans for building projects are often retained by the local building department for future reference. This policy protects the general public and the property owners in that municipality.  But not all specs and plans become part of the public record or general files of the building department, depending on the municipality.  This void can create problems, especially if something goes wrong down the line. 

In May of 2009, the practice facility for the Dallas Cowboys, located in Irving, Texas near Dallas, collapsed.  The accident injured a dozen people, leaving one man paralyzed.  But city and law enforcement officials were prevented from discovering the cause of the collapse because the building’s plans and specs were no longer on file with the city.  The only planning document for the structure that the city had on file was the general site plan, which merely indicated the facility’s location.  Texas state law was erroneously interpreted by the city of Irving’s building department to mean that they were to retain only building permits and certificates of occupancy.  But the Texas State Library and Archives Commission, which oversees state document retention requirements and interprets state law, contend that the law also includes building blueprints and specifications.  As a result, Irving and other cities around the country have been reviewing their document retention policies.

In summary, InterNACHI inspectors should learn how to read plans and specs, understand who uses them and why, and become familiar with how and from where they can be obtained.  InterNACHI inspectors who spend time building on their knowledge surrounding the various aspects of existing and new construction will enhance their expertise as inspectors, and can pass the value of their skill and knowledge on to their commercial property and new construction clients.