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CONSTRUCTION KNOWLEDGE  >> GENERAL TECHNICAL KNOWLEDGE >>

BLUEPRINT READING
 

1. How Do I Learn to Read Blueprints?
2. Why Should I Think "Plan, Elevation and Section"?
3. What is an Architectural Scale?
4. What is an Engineering Scale?
5. Why Specs Should be Read?
6. Why aren't CAD Drawings all Done in 3D?
7. What Public Domain Documents are Available for Further Study?
8. Tricks of the Trade & Rules of Thumb for Blueprint Reading:
 

How Do I Learn to Read Blueprints?

My high school physics said the language of science is mathematics. Since I never spoke that language too well, I wasn’t much of a scientist. I’ve been an effective contractor, though, and have learned the language of construction: drawings. We communicate in job trailers by pointing to the significant sections of drawings. We make sketches, often quite rough, to show what we’re trying to say.

 In short, if you want to advance in construction, learn to read drawings well and to make rough sketches. It’s a simple language to learn (I’m the least visual person I know and I learned it), but it does take some studying.

So, how do you learn to read blueprints? It's a little like eating elephants. You might ask me, "How do you eat an elephant?" The answer, of course, is "One bite at a time."

Novice blueprint readers look at the entire page of words, lines and weird symbols and get overwhelmed. It's easy at that point for your brain to shut down and you just say, "I can't read blueprints." If you tried to read an entire page of words at the same time, you couldn't do that either. You simply have to calm down, start at one corner and begin figuring out what you can learn from the blueprint. The main difference between a blueprint and a page of text is that you know to start at the top left corner on a page of text, then to left to right till the bottom of the page. Blueprints don't have a place you need to start.

So where should you start?
 

Why Should I Think "Plan, Elevation and Section?

The most basic concept about reading blueprints, and the one to keep in mind no matter how good you get at reading blueprints, is "Plan, Elevation and Section". Your first thought when looking a drawing should be, "Is this a Plan, an Elevation or a Section?" First, some quick definitions:

1. Plan: a view looking downward on the object, usually the horizontal plane cut at 30" above the floor.
2. Elevation: a view looking sideways at the object, usually from the north, the west, the south or the east.
3. Section: a cut-through view of the object, usually an imaginary view that shows how something will be built.

When I'm standing in a job trailer, and we are trying to resolve some problem and someone starts drawing a sketch, my first question almost always is, "Are you drawing a plan view, a side view or a section view?" I know many people don't ask that question and often just looks at lines on the paper, having no idea what the sketcher is trying to  convey. Learn to ask that question first, whether you are looking at a new set of blueprints or a sketch done by a friend.

The rest of the information below will help you understand some other specific aspects of understanding blueprints. The most important thing to remember, though, is just to do one thing at a time. Don't try to understand everything at once, no one can do that, so you won't be able to either. Take some time, relax, look at each symbol and word and try to understand what it's there for. Most everything on a blueprint is there for a purpose, so just slowly go through the symbols and words, getting their purpose into your head.

I often go through a new set of blueprints on a project with a yellow highlighter, reading and highlighting every word, number or symbol. When I've highlighted an entire sheet, I've got a fairly clear idea of what the designer and draftsman were trying to convey.

What is an Architectural Scale?

We use an Architect's Scale when dimensions or measurements are to be expressed in feet and inches. So the gradations on an Architect's Scale are as follows:

1. 1/8" = 1'
2. 1/4" = 1'
3. 1/2" = 1'
4. 1" = 1'
5. 3/8" = 1'
6. 3/4" = 1'
7. 1 1/2" = 1'
8. 3" = 1'
9. 3/32" = 1'
10. 3/16" = 1'
11. Regular inch scale with  gradations to the 16th of an inch

What is an Engineering Scale?

We use an Engineer's Scale whenever dimensions are in feet and decimal parts of a foot, or when the scale ratio is a multiple of 10. So an Engineer's Scale has an inch broken into 10, 20, 30, 40, 50 and 60 gradations.

Why Specs Should be Read?

The most boring part of Construction Supervision may be reading Specs and General Conditions. So lots of folks just don't do it. They make that decision lightly, but the ramifications can be huge. Too many times Design Professionals hide little time-bombs in the Specs, or Special Conditions, that become important as the project progresses.

Perhaps it's a milestone in the schedule that must be achieved by a certain date. Or a requirement to never work before 8am in the morning or on weekends. Sometimes the project clean-up requirements can be quite different from what might make sense to you, but those are the rules for that project.

So at the start of a project, the Construction Supervisor should obtain his or her own copy of all the project documents and read them. After doing this on a couple of projects, you will learn what you can skim through and what needs more careful attention. Don't just blow off this duty, though.

The Project Specifications, General Conditions, Special Conditions and Construction Contracts constitute the rules for the project. It's easier to win the game when you know the rules.

Why aren't CAD Drawings all Done in 3D?

Blueprints traditionally got drawn as two dimensional (2D) drawings. Architects and Engineers drew in 2D because 3D was too complicated. When Computed Aided Design (CAD) became popular in the 1980s and 1990s, we assumed most drawings would now get drawn in 3D. But they don't. Things tend to change slowly in the design and construction industry. The typical set of plans produces today don't vary that much from plans produced generations ago. 

So why aren't most projects designed in 3D? I believe most Design Professionals are proficient at producing 2D drawings, but often don't understand the details of how contractors build buildings. As a young Design Professional working in a Design Office, I know I didn't.

So the complexity of producing 3D drawings carries the task of actually knowing how the project will be built. The level of understanding must be much higher for the draftsman. The technology works, but the learning curve for the Design Professionals is steep. On the other hand, many Owners try to limit their design costs and don't feel 3D drawings would add enough value to cover the cost of production of the documents.

The current state of affairs, then, has most projects being built on 2D drawings. The more complex projects, though, increasingly use 3D for architectural, structural, mechanical and electrical. Perhaps the main advantage of 3D is the crash feature. By modeling all the elements, the hundreds of crashes between beams, columns, ducts, pipes and the many other features in a building can be determined during design, then resolved in the office rather than in the field, with crews standing and waiting.

The future will belong to 3D...it's just not clear how long it will take for us to get there.

What Public Domain Documents are Available for Further Study?

The US Department of Army Carpentry Field Manual does a great job in the first three chapters explaining basic drawings, construction planning and bills of materials. If you are somewhat new to construction, take some time and review this excellent resource. The official name is US Army FM 5-426.

The US Navy produced a Blueprint Reading and Sketching course that has 200 pages of good basic instruction. The technical name of the course is NAVEDTRA 14040 May 1994. I've included a few paragraphs below that are helpful.

A building project may be broadly divided into two major phases, the design phase and the construction phase. First, the architect conceives the building, ship, or aircraft in his or her mind, then sets down the concept on paper in the form of presentation drawings, which are usually drawn in perspective by using pictorial drawing techniques. Next, the architect and the engineer work together to decide upon materials and construction methods. The engineer determines the loads the supporting structural members will carry and the strength each member must have to bear the loads. He or she also designs the mechanical systems of the structure, such as heating, lighting, and plumbing systems. The end result is the preparation of architectural and engineering design sketches that will guide the draftsmen who prepare the construction drawings. These construction drawings, plus the specifications, are the chief sources of information for the supervisors and craftsmen who carry out the construction.

GENERAL PLANS
General plans contain information on the size, material, and makeup of all main members of the structure, their relative position and method of connection, as well as the attachment of other parts of the structure. The number of general plan drawings supplied is determined by such factors as the size and nature of the structure, and the complexity of operations. General plans consist of plan views, elevations, and sections of the structure and its various parts. The amount of information required determines the number and location of sections and elevations.

FABRICATION DRAWINGS
Fabrication drawings, or shop drawings, contain necessary information on the size, shape, material, and provisions for connections and attachments for each member. This information is in enough detail to permit ordering the material for the member concerned and its fabrication in the shop or yard. Component parts of the members are shown in the fabrication drawing, as well as dimensions and assembly marks.

ERECTION DRAWINGS
Erection drawings, or erection diagrams, show the location and position of the various members in the finished structure. They are especially useful to personnel performing the erection in the field. For instance, the erection drawings supply the approximate weight of heavy pieces, the number of pieces, and other helpful data.

FALSEWORK DRAWINGS
The term falsework refers to temporary supports of timber or steel that sometimes are required in the erection of difficult or important structures. When falsework is required on an elaborate scale, drawings similar to the general and detail drawings already described may be provided to guide construction. For simple falsework, field sketches may be all that is needed.

CONSTRUCTION PLANS
Construction drawings are those in which as much construction information as possible is presented graphically, or by means of pictures. Most construction drawings consist of orthographic views. General drawings consist of plans and elevations drawn on relatively small scale. Detail drawings consist of sections and details drawn on a relatively large scale; we will discuss detail drawing in greater depth later in this chapter. A plan view is a view of an object or area as it would appear if projected onto a horizontal plane passed through or held above the object area. The most common construction plans are plot plans (also called site plans), foundation plans, floor plans, and framing plans. We will discuss each of them in the following paragraphs. A plot plan shows the contours, boundaries, roads, utilities, trees, structures, and other significant physical features about structures on their sites. The locations of the proposed structures are indicated by appropriate outlines or floor plans. As an example, a plot may locate the comers of a proposed structure at a given distance from a reference or base line. Since the reference or base line can be located at the site, the plot plan provides essential data for those who will lay out the building lines. The plot also can have contour lines that show the elevations of existing and proposed earth surfaces, and can provide essential data for the graders and excavators.  A foundation plan (fig. 7-9) is a plan view of a structure projected on a imaginary horizontal plane passing through at the level of the tops of the foundations. Framing plans show the dimension numbers and arrangement of structural members in wood-frame construction.  A wall framing plan provides information for the studs, corner posts, bracing, sills, plates, and other structural members in the walls. Since it is a view on a vertical plane, a wall framing plan is not a plan in the strict technical sense. However, the practice of calling it a plan has become a general custom. A roof framing plan gives similar information with regard to the rafters, ridge, purlins, and other structural members in the roof. A utility plan is a floor plan that shows the layout of heating, electrical, plumbing, or other utility systems. Utility plans are used primarily by the ratings responsible for the utilities, and are equally important to the builder. Most utility installations require that openings be left in walls, floors, and roofs for the admission or installation of utility features. The builder who is placing a concrete foundation wall must study the utility plans to determine the number, sizes, and locations of openings he or she must leave for utilities.

ELEVATIONS
Elevations show the front, rear, and sides of a structure projected on vertical planes parallel to the planes of the sides. Elevations give you a number of important vertical dimensions, such as the perpendicular distance from the finish floor to the top of the rafter plate and from the finish floor to the tops of door and window finished openings. They also show the locations and characters of doors and windows. However, the dimensions of window sashes and dimensions and character of lintels are usually set forth in a window schedule.

SECTION VIEWS
A section view is a view of a cross section. The term is confined to views of cross sections cut by vertical planes. A floor plan or foundation plan, cut by a horizontal plane, is a section as well as a plan view, but it is seldom called a section. The most important sections are the wall sections.  Starting at the bottom, you learn that the footing will be concrete, 1 foot 8 inches wide and 10 inches high. The vertical distance to the bottom of the footing below FIN GRADE (finished grade, or the level of the finished earth surface around the house) varies-meaning that it will depend on the soil-bearing capacity at the particular site. The foundation wall will consist of 12-inch concrete masonry units (CMU) centered on the footing. Twelve-inch blocks will extend up to an unspecified distance below grade, where a 4-inch brick facing (dimension indicated in the mid-wall section) begins. Above the line of the bottom of the facing, it is obvious that 8-inch instead of 12-inch blocks will be used in the foundation wall. The building wall above grade will consist of a 4-inch brick facing tier, backed by a backing tier of 4-inch cinder blocks. The floor joists consist of 2 by 8s placed 16 inches OC and will be anchored on 2 by 4 sills bolted on the top of the foundation wall. Every third joist will be additionally secured by a 2 by 1/4 strap anchor embedded in the cinder block backing tier of the building wall.  Flooring will consist of a wood finished floor on a wood subfloor. Inside walls will be finished with plaster on lath (except on masonry, which would be with or without lath as 7-16 directed). A minimum of 2 vertical feet of crawl space will extend below the bottoms of the floor joists. The middle wall section gives similar information for a similar building constructed with wood-frame walls and a double-hung window. The third wall section gives you similar information for a similar building constructed with a steel frame, a casement window, and a concrete floor finished with asphalt tile.

DETAILS
Detail drawings are on a larger scale than general drawings, and they show features not appearing at all, or appearing on too small a scale, in general drawings. The wall sections are details as well as sections, since they are drawn on a considerably larger scale than the plans and elevations. Framing details at doors, windows, and cornices, which are the most common types of details, are nearly always shown in sections. Details are included whenever the information given in the plans, elevations, and wall sections is not sufficiently “detailed” to guide the craftsmen on the job.

SPECIFICATIONS
The construction drawings contain as much information about a structure as can be presented graphically. A lot of information can be presented this way, but there is more information that the construction craftsman must have that is not adaptable to the graphic form of presentation. Information of this kind includes quality criteria for materials (for example, maximum amounts of aggregate per sack of cement), specified standards of workmanship, prescribed construction methods, and so on. When there is a discrepancy between the drawings and the specifications, always use the specifications as authority. This kind of information is presented in a list of written specifications, familiarly known as the specs. A list of specifications usually begins with a section on general conditions. This section starts with a general description of the building, including type of foundation, types of windows, character of framing, utilities to be installed, and so on. A list of definitions of terms used in the specs comes next, followed by certain routine declarations of responsibility and certain conditions to be maintained on the job.

Tricks of the Trade & Rules of Thumb for Blueprint Reading:

1. Think "Plan, Elevation or Section" when looking at any drawing.
2. Read the Project Specifications, General Conditions, Special Conditions and Construction Contracts at the start of any project.