How to read blueprints
As buildings and the systems within them have become increasingly complex, so have the two-dimensional drawings that describe all the details of the project. From a simple residence to a large commercial building project, the same basic drawings and related information are required in order to obtain permits, estimate costs, establish a construction schedule, and ultimately construct the project.
These basic terms should help you better understand how a set of plans is organized.
Similar to building a model or assembling something from written diagrams and directions, scan the entire set of plans first and read the various notes and specifications. This will give you an overall impression up front, before you start to drill down to specifics.
These are the basic views looking down at a horizontal plane.
- Site plans locates the building ‘footprint’ on the actual site and describes the required site work. Depending on the complexity of the project, there may be civil plan drawings that show existing site conditions; the proposed plan for re-grading the site; water drainage, water retention, sanitary and storm drain sewer systems; electrical, water and gas utility service locations; and parking lots, curbs, sidewalks, landscaping plans, and all details related to the site work.
- Civil drawings usually use an “engineering” scale with dimensions shown in increments of 10, for example 1”=50’ or 1”=100’. If the common “architectural” scales, such as ⅛”=1’ or ¼”=1’, were used, the drawings would be too large to be usable.
- Floor plans are simply that. Each floor of the building is drawn to scale (usual a ⅛” or ¼” scale). These plans show interior and exterior walls, door and window locations, room dimensions, stairs, cabinets, toilets and sinks, and other relevant information.
- Roof plans show dormers, hips, valleys, roof drains, roof pitch, roof-mounted equipment and other related details, such as materials to be used and planned penetrations like a plumbing or exhaust vent.
- Plumbing, mechanical and electrical plans are usually needed for larger projects, so each individual discipline can be shown on separate sheets without making the Architectural Plan too crowded and difficult to understand.
- Structural plans focus on the structural components of the building. In concert with ‘sections’ (see below), they describe the foundation work, framing and floor construction required, along with reinforcing and connection details.
Use the right scale and check that the scale shown is correct on the plans. As plans evolve and changes are made in haste, it is very common to see something that is dimension-ed (i.e. a wall that says it’s 24 feet long) but it is not drawn to scale. You must cross-reference the dimensions you read from your scale with the dimensions noted on the plans and make sure they agree.
Elevations are side views showing each of the exterior walls of the building. Usually the elevations are noted north, south, east, and west and they should be cross-referenced on the First Floor Plan.
Elevations show all windows, doors, roof lines, gutters and downspouts, and will also describe the exterior wall construction material, such as siding or masonry. Interior elevations are also included, typically to show cabinets and counter top work, bathroom walls and anywhere a plan view alone can’t communicate what is needed.
Compare various plans with the elevations. A common error is to assume that the architect has included every exterior wall elevation, but this is often not the case. The overall elevation view may not show an inset portion of the wall, so you must compare the floor plan to the elevations to ensure you have interpreted things correctly and missed anything.
Plan views and elevations are not sufficient to fully describe the various building components needed or how each component relates to the others. This is where ‘sections’ are used. Sections are basically ‘slices’ through a building or building component.
A common ‘section’ is a Wall Section. This is a vertical slice through the wall that shows the inside, outside and interior components within the wall itself, such as studs, sheathing, insulation, siding, or masonry, as well as how the wall engages the floor or foundation below, and the roof or floor structure above.
Other sections include cabinet and counter top sections to depict all dimensions, relationships to other elements and interior cabinet shelving and other features. Sections are cross referenced on plan views, and elevations, so the reader can understand where the relevant ‘slice’ was taken. A simple residence may only require a few wall sections, since the information will be typical. More complicated projects require dozens of wall sections to describe all the various conditions.
No set of plans is perfect. There are always conflicts between various sheets. It is difficult to coordinate every detail, plan and elevation so they all indicate exactly the same thing. To shift the risk of these conflicts to the builder, architects will often include language to the effect that “should a conflict arise, the contractor shall provide the greater QUALITY and/or QUANTITY of what was shown.” So it’s extremely important to make sure you understand how the various drawings relate to one another and to verify that the information called for is consistent.
Many building components are organized in simple matrices called ‘schedules.’ Door, frame and door hardware details will be described in a door schedule. The floor plan will have simple door number or mark, and that will correspond with the detailed information on the door schedule. Windows, finishes, lighting fixtures, and HVAC air flow requirements are all typically detailed in schedules.
Hundreds of abbreviations and symbols are used to convey building components and related information. While many are common and typically standardized, abbreviations and symbols can differ from one architect or engineer to another and from one discipline to another. For example a symbol used on an architectural plan, may mean something entirely different on the electrical plan.
To clarify their intent, the architect or engineer provides a key, typically on the first sheet, that relates the symbols and their intended meaning. As you start to review any construction plan, familiarize yourself with those symbols and what they mean.
The scale (or relationship between drawing dimensions and real dimensions) used for various drawings will change, depending on what information is being shown. Make sure you know what scale you should be using as you proceed with your estimate; using the wrong scale can drastically alter your quantities.
The most common architectural plan view scales are ⅛”=1’ and ¼”=1’. The specialized ‘rulers’ used to work with building plans are also called ‘scales’ and are either engineering scales or architectural scales.
Architects and engineers use some basic graphics to describe specific building elements. For example, a masonry wall when viewed in section will normally be shown with a 45-degree cross-hatching through the wall. Gypsum board is usually shown with small dots between the two faces. Rigid insulation is shown with a small cross-hatched grid, while batt insulation is shown as a continuous ‘S’ shape. These standardized graphics help the architect, engineer and builder communicate more clearly.
Building plans are not static and will typically evolve over the life of the project. The same chronological drawing progression is common:
- Preliminary or schematic plans are used to help the owner understand the size and appearance of the project; establish construction budgets; review with city planners with regard to zoning, aesthetics, and easements; and assist other related design disciplines to better understand what is planned.
- Issued for pricing and Issued for permitplans are basically what the names imply. These plans are complete enough to price or submit for building permits, respectively.
- Issued for construction is the final set of plans that is complete enough to build from.
The various sheets in any set of plans will have a sheet designation, typically Civil Engineering sheets will be called C-1, C-2 etc.; Architectural sheets are A-1, A-2, etc.; Structural sheets are S-1, S-2 and so on for Mechanical, Plumbing and Electrical Sheets (M, P and E).
Every drawing sheet will have a small “revision” block along the margin. This block is just a list that shows all of the dates the specific drawing was issued, as well as any applicable name, such as issued for permit, etc. Keep track of these dates to make sure you’re working with the most current set.
Changes, corrections and supplemental information are commonly added to the drawings as they evolve. Typically these are issued as “addendum’s” to the original set of plans. A good architect or engineer will draw a ‘bubble’ or ‘cloud’ around any portion of the drawing that has been changed and will mark each cloud with a small triangle with a number inside. This numbered triangle will correspond with a similar entry in the revision block, so changes can be tracked back to when that change was issued.
Addendums include only the sheets that have changed. Multiple addenda are common, and some sheets may be re-issued several times during the project. A good practice is to insert the new sheet, just in front of the sheet being updated or changed. Then fold back the lower corner of the older sheet, tape it on the back and mark it as VOID next to the sheet number. This insures the user has the current sheet and allows for quick reference to previous versions for comparison.
Architects are in a hurry like everyone else. Once they have provided a detail or building condition on the plans, they may add a note that says “typical” or “similar” to indicate that there are other locations where this same detail occurs, or where a very similar condition occurs. Many contractors have made the mistake of estimating only what was shown on the plans, missing a note that may say “typical at all floors.”