The Core Rule
Always use written dimensions on plans — never measure the drawing. Plans are printed at reduced scales and physical measurement is unreliable.
A dimension that reads 12\'6" on the plan is 12 feet 6 inches regardless of how large or small it looks on paper. Drawings marked "NTS" (not to scale) are illustrative only. Every dimension decision during construction must reference the written number, not a tape measure held to the printed plan.
9 Blueprint Sheets — What Each One Covers
A complete residential plan set contains these sheets. Know what to look for on each one.
Shows the lot from above — property boundaries, setbacks, the house footprint, driveway, utilities, and grading. The site plan tells you where the house sits on the land and how it relates to property lines.
The most-used sheet — a top-down view of each floor showing room layout, wall locations, door and window openings, stairs, and dimensions. Every room is labeled and dimensioned.
Four drawings showing the exterior of the house from each side — front, rear, left, and right. Elevations show rooflines, window and door placement, siding patterns, and the overall appearance of the exterior.
Cross-section cuts through the house showing interior heights, floor-to-ceiling dimensions, roof pitch, structural elements, and how floors and walls connect. Sections reveal what you cannot see on a floor plan.
Shows the foundation layout — footings, foundation walls, piers, beams, and post locations. Specifies concrete strength (typically 3,000–4,000 PSI), rebar size and spacing, and waterproofing requirements.
Top-down view of the roof showing ridge locations, hip and valley lines, dormers, skylights, and drainage directions. Also shows roof pitch notation (e.g., 6/12 means 6" rise per 12" run).
Floor plan overlay showing outlet, switch, and fixture locations. Uses standard symbols for receptacles (circle with two lines), switches (S), and fixtures (various). Panel schedule lists all circuits.
Shows drain, waste, and vent locations, supply line routing, fixture locations, and water heater placement. Often shows isometric (3D) diagrams of the drain-waste-vent stack.
Shows duct layout, register locations, equipment placement, and return air sizing. The HVAC plan is based on a Manual J load calculation that determines the tonnage needed for your home size and climate.
Common Blueprint Symbols and What They Mean
Frequently Asked Questions
How do I read dimensions on a house plan?
Dimensions on house plans are typically shown in feet and inches (e.g., 12'6" = twelve feet six inches). Exterior dimensions measure to the outside face of the framing. Interior dimensions measure between finished walls. Always use the written dimensions — never measure the drawing itself, as plans are often printed at non-standard scales.
What is the difference between a floor plan and a blueprint?
"Blueprint" is a colloquial term for any construction drawing. A floor plan is one sheet within a set of blueprints — the top-down view of each floor showing room layout and dimensions. A complete blueprint set includes site plan, floor plans, elevations, sections, foundation plan, roof plan, electrical plan, plumbing plan, and HVAC plan.
What should I look for before approving my house plans?
Walk through the floor plan mentally for daily routines. Verify ceiling heights on sections. Check window locations match on floor plans and elevations. Confirm outlet placement in every room. Verify all rough-in for future spaces (bathrooms, wet bars) is shown. Check setback dimensions on the site plan against local zoning. Verify roof pitch and valley locations.
Do I need to understand blueprints before meeting with a contractor?
You do not need to be an expert, but understanding the basics lets you have productive conversations, catch discrepancies, and verify what you are paying for. A contractor who cannot walk you through the plans sheet by sheet is a red flag. You should always be able to ask "show me where that is on the plan."
What does NTS mean on a blueprint?
"Not to scale" means the drawing is illustrative and dimensions should be read from the written notes, not measured from the printed drawing. House plans are often printed at reduced scales (1/4" = 1' or 1/8" = 1') and physical measurement of a printed plan is unreliable. Always use the written dimensions.
Kerem is a construction cost analyst and architectural graduate with a degree from the Illinois Institute of Technology. He has spent over a decade analyzing residential and commercial build costs across all 50 U.S. states, and leads the cost methodology team at Equin Global LLC — the company behind CostToBuildHouse.com.
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