Architectural Drafting Basics

What Goes Into A Plan Set

James Coppinger

Type Of Architectural Plans

Floor Plans

Architectural drafting is the development of all necessary construction information from the building envelope inwards. In other words, architectural drafting addresses everything within a building and leaves exterior design concerns to others. Architectural floor plans are the starting point for all architectural drafting. The initial layout begins with developing preliminary sketches to display to the client for comment and/or approval. These sketches form the basis of the floor plan. The floor plan is a detailed and dimensioned horizontal arrangement of all physical objects within the building. Floor plans will contain notes and callouts explaining specific materials or construction concerns that need to be brought to the builder's attention. Floor plans also act as an overall "key" to show the builder where to find specific information on various areas of the building. It is common practice to draft floor plans at a scale where the entire building can -hopefully- be displayed on a single page so that overall dimensions are easy to see, and then to create larger "blow-up" plans of areas that are information intensive, such as restrooms or stairwells.

References to these blow-up plans are made with dashed boxes surrounding the area in question and are labeled with call-out bubbles referring the builder to the title/sheet number where the enlarged plan is located. Floor plans will also make use of section and elevation bubbles that show not only the location of those details but also include arrow symbols that show the direction in which the detail is oriented. Lastly, a typical architectural floor plan will also contain notes and tables containing area, egress, volume, and structural calculations that show how the building's design meets all applicable construction code requirements.

Floor plans contain a large amount of information and can quickly become confusing. For that reason, drafters make use of various symbols, line weights, and hatch patterns to graphically differentiate what each line and/or area on the plan represents. For example, it is common practice to fill in the space between the two faces of a proposed wall with a hatch pattern (single line for brick, cross hatch for CMU) so that it can be easily seen, whereas existing wall spaces are usually left empty so that the viewer can quickly differentiate between the two. Symbols on a floor plan vary greatly depending on what information is being displayed. An electrical floor plan will show symbols designating outlet, light, and switch locations whereas an HVAC plan will show duct drops, thermostats, and pipe risers. Floor plans can be broken down to show only specific trade information on a single sheet or, if the project is small enough, they can be combined to show various trades on each sheet; for example, plumbing and HVAC are often combined.

Wall Sections

Wall sections are cut-away views of the walls (usually exterior) of the building. They are shown at a larger scale than the plans and give the drafter an opportunity to show detailed information on how the walls should be assembled, what materials are used, and how they are secured together. Wall sections usually show everything from the level of the soil below the footing, all the way up through the point where the roof connects to the top of the wall. In a multi-story structure, the wall section will also show the intersection of the flooring system and how it ties to the wall and the necessary support system needed. These sections commonly call out the reinforcing needed within concrete and masonry systems, exterior wall flashing to prevent water from seeping into the building, insulation types, and both interior and exterior finishes to be applied. All the sections necessary to construct a building are usually assembled onto a single sheet for ease of access.

Detail Sheets

Detail sheets are an assembly of enlarged sketches, referring to specific areas of the design that require very detailed information in order to be constructed. In architectural plans, these are normally drawn at large scale (1/2" = 1'-0" or larger) to allow sufficient area for notes and dimensions. Details are used when the construction requirements of a region are too complex to show on a wall section. For example, it is common to show footing types as a detail in order to show more information about the steel reinforcing, which would be difficult to read on a wall section. Many details are called out as "Typical" in their title, meaning that the information shown is standard for most instances of the condition being detailed. Any instance that varies from the "typical" is drawn as a separate detail and labeled accordingly.

Architectural Load and Bracing Concepts

Lateral Bracing

Lateral bracing is a method of reinforcing a structure to help it resist the forces of wind shear and seismic events. In lightweight, residential, construction the lateral bracing concept is carried very largely by the exterior sheathing of the structure. Plywood of varying thickness can be used to brace a stick frame structure, which is unstable in the lateral, into a monolithic structural component that uses all components of the interior frame to resist lateral motion. In addition, it's not uncommon and often required by code, to provide interior walls that are keyed into the exterior walls with no more that twenty-five foot (25') spacing. These interior walls act as lateral reinforcement that keeps the exterior walls from moving while under stress. In many cases, additional reinforcing of walls and joists are included in the structural design at key locations to reinforce potential weak points. This reinforcement, often called crossbracing, is commonly used within 18" of exterior corners, where structural failure is more likely.

It is often used to reinforce connection points between joists and exterior walls to ensure monolithic integrity of the structure between levels. When designing a multi-level structure it is important to keep in mind the need for the lowest levels to have more lateral bracing than the floor above it. This is due to the additional pressures added by the height and weight of the additional level. A standard rule of thumb is that a single story structure needs 20% lateral bracing and you need to add an additional 20% for each level added above it, i.e for a two-story structure the first floor would need 40% bracing and the second floor would need 20%. For a three-story structure the first level would need 60%, the second, 40% and the third 20%. These numbers are guidelines for initial design and are subject to the provisions of local construction does and the seismic region in which you are working.

Load Calculations

Load calculations are necessary values needed to determine the compressive load on the support members of your structure. Items such as the roof, snow load, weight of joist and flooring, etc. will all put additional compressive loads on your structure and must be accounted for when sizing your support members. Items that are static in weight (joists, flooring, etc.) are commonly referred to as "dead load", meaning that the amount of load they put on your supports do not change. Dead load calculations are achieved by multiplying the square footage of cover by the weight of the materials to determine the Pounds/Square Foot (psf) that needs to be supported. It is important to include all materials that are to be used in the construction during dead load calculations. For example, when calculating dead load for a roof, you need to account for the weight of the shingles, sheathing, rafters, and insulation as well as any interior finishes such as gypsum board.

Weights that can change are referred to as "live load" (snow, people, appliances, etc.) and are generally calculated using a minimum psf that allows for support of such loads within a reasonable range. For example, common Live Load psf allowance for a roof is 20 psf to account for potential amounts of drifting snow, while the live load for an internal floor is commonly 40 psf to allow for use by multiple people, furniture, and various appliances. The exact load numbers that are acceptable are governed by local building and zoning code requirements. It is important to note that loads are cumulative from the top down, i.e. the foundation of a two-story structure must be designed to support the dead load of the roof, ceiling, floors, and walls, as well as the live load for two full stories and snow load.