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Exterior wood entry door with sidelites and stone facade

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Door Fundamentals

Complete this page before moving to Door Anatomy. Every term and concept here comes up in every customer conversation and every quote.
Before quoting any door, a rep must understand the two basic product categories and how door sizes are communicated in the industry. Getting this wrong leads to quoting the wrong product and missing critical fit details.

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Slab vs. Prehung

This is the first and most important question to answer on every job.
A slab is the door panel only. It does not include the frame, hinges, threshold, or any jamb components.When to use slab:
  • The existing frame is in good condition and structurally sound
  • The customer only needs a new door panel
  • The frame is still square and the existing hinge locations match the new slab
What you must capture for a slab order:
  • Exact panel width, height, and thickness
  • Existing hinge backset and count
  • Lock bore location and backset
  • Whether the frame is wood, fiberglass composite, or metal
Always verify that the existing frame is square before recommending a slab replacement. An out-of-square frame will cause fit and operation problems regardless of slab quality.
A rep cannot build an accurate quote until they know whether the customer needs a slab or a prehung unit. This single question changes measurements, hardware options, pricing, and install assumptions.

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How Door Sizes Work

Door sizes use a four-digit shorthand that is standard across the industry. The first two digits are the width in feet and inches, the last two are the height.
When a customer says “I need a 3068 door,” always confirm whether they mean the slab size or the full unit callout. For prehung units, the unit is typically 2” wider and 1” taller than the slab to account for the frame. Do not assume.

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Interior vs. Exterior

Exterior and interior doors have fundamentally different construction and performance requirements. Always confirm which application the customer needs before recommending a product.

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Exterior Doors

  • Weather-rated construction required
  • Threshold and weatherstripping included
  • Higher core density for insulation and security
  • Glass units must be insulated (IGU)
  • Brickmould or casing may be required
  • Finish must be rated for sun and moisture exposure

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Interior Doors

  • No weather resistance required
  • No threshold standard
  • Lower core density acceptable
  • Glass can be single-pane or decorative
  • Casing is standard trim detail, not weather seal
  • Paint-grade or stain-grade finishes both common

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New Construction vs. Replacement

There is no existing door unit. The rough opening is being framed to size and the door unit goes in as part of the build. The rep needs the rough opening dimensions from the builder’s plans and must confirm framing specs. No existing frame condition to assess.
An existing door unit is being removed and replaced. The rep must account for the existing opening dimensions, the frame condition (square, rotted, damaged?), trim reuse, and whether the new unit will cover any existing damage or gaps at the rough opening edge.

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The Four Qualifying Questions

Every customer conversation should answer these four questions before any measurement discussion begins.
1

Slab only or full prehung unit?

Determines the entire scope of the order and what measurements you need.
2

Interior or exterior application?

Sets performance requirements, glass specs, threshold needs, and material options.
3

New construction or replacement?

Determines whether you are working from framing plans or field measurements.
4

Single, double, or door with sidelites?

Changes the total configuration width, active panel sizing, and handing reference point.
Print this page or save it to your phone. Run through these four questions at the top of every intake call before you open a quote.