How to Specify Windows for a Custom Home: A Drawing-to-Order Checklist

A window specification for a custom home records ten decisions for every opening: size and mark, operation, frame material, finish, glass package, performance targets, hardware, screens and shades, code-driven requirements, and delivery constraints. Work through them in that order, because each decision narrows the next, and write them into one document the supplier can price and the building official can read.

Start from the openings on the drawings

List every window and door opening from plans and elevations, then group identical openings under one mark. The schedule that results is the backbone of the specification: it holds the mark, quantity, size basis, operation and the elevation each opening belongs to. Resolve conflicts between plans and elevations before anything is priced.

The mechanics of marks, size bases and conflicting drawings are covered in a dedicated planning guide, the Fenestry window schedule guide, which is the tool to use for building the schedule itself. This checklist picks up where the schedule ends and records everything the schedule does not.

Choose operation for each opening

Operation drives hardware, clearances, egress and furniture layout. The options in European systems include tilt-and-turn, casement, fixed, and lift-and-slide doors for large glass walls. Decide which bedrooms and basements need emergency escape openings now, because operation and size both change to meet that requirement. For inward-opening sashes, check swing arcs against furniture, curtains and screens on the plans.

Choose frame material

Pick the material per elevation or per project: thermal-break aluminum, aluminum-clad wood, solid wood, uPVC or real steel. The materials guide compares them. Real steel and steel-look aluminum are different products and should never share a line in a specification. Material also determines minimum visible frame width, achievable sizes, finish options and maintenance, so decide it before sizing glass.

Set finish and color

State interior and exterior finish separately, since many European systems allow different colors on each side. Give the finish type (powder coat, anodized, or a wood finish), a color reference from a named color system, and the gloss level. Ask for physical samples before approval: color on screen and in catalogs differs from color on a finished profile.

Set the glass package

Specify the number of panes, low-e coatings, gas fill, spacer type and any laminated or tempered requirement. Safety glazing is a code item (see below). Acoustic, solar-control and privacy needs belong here too. Where possible, state the performance target and let the supplier propose the build-up that reaches it, then check it against the whole-window rating.

Set performance targets by climate zone

Performance targets belong to the whole window, not to the glass alone. NFRC certifies whole-product ratings through accredited laboratories and licensed inspection agencies, and the NFRC label lists U-factor, solar heat gain coefficient (SHGC), visible transmittance, air leakage and condensation index. European catalogs often show Uw; the conversion is explained under U-factor for windows.

The 2021 IECC prescriptive limits for residential fenestration, as summarized by PNNL, are:

The 0.32 value applies in zones 5 to 8 and Marine 4 to vertical fenestration above 4,000 feet or in windborne debris regions. Many jurisdictions use other editions or amendments, and compliance can also be shown through trade-off paths, so these values are a starting point only.

ENERGY STAR Version 7.0, effective October 23, 2023, sets whole-window criteria by four zones:

The Northern zone also offers equivalent-performance options that pair higher U-factors with higher SHGC. ENERGY STAR is voluntary and requires NFRC certification first, so cite it as a target only when the project wants it.

Structural performance is a separate line. The North American Fenestration Standard defines performance classes (R, LC, CW and AW) and performance grades tied to design pressure. The standard states that the performance class is chosen independently of the building's use, so the designer or engineer states the required class and design pressure from the project's wind loads rather than leaving it to the supplier.

Set hardware

Specify handle style and finish, locking points, key-lockable handles where needed, hinge type and the handing convention used on the schedule (viewed from outside or inside). State hardware finish separately from frame color. For tilt-turn windows, check whether the handle position at each mode matches the owner's expectations, since conventions differ between manufacturers.

Decide screens and shades

Screens and interior shades interact with operation. Screen options for inward-opening sashes differ from those for outward-opening windows, so decide early whether screens are fixed, removable or integrated, and who supplies them. Integrated blinds or shades inside the glazing, and motorization, need electrical rough-in planned with the builder.

Check code items

Name the code edition adopted locally and list the items that affect windows:

• Emergency escape and rescue openings: the 2021 IRC section R310 requires a net clear opening of at least 5.7 square feet (5 square feet at grade floor), at least 24 inches clear height and 20 inches clear width, with the bottom of the clear opening no more than 44 inches above the floor. Details are in the egress requirements guide.
• Fall protection: the IRC section R312.2 addresses operable windows in dwellings whose openings lie more than 72 inches above grade, requiring the lowest part of the clear opening at least 24 inches above the floor unless a compliant opening limiter or fall prevention device is used. Opening devices must not defeat required escape openings.
• Safety glazing: IRC section R308.4 lists hazardous locations, such as glazing near doors, tubs and showers, stairs, and large low panes next to walking surfaces. Confirm the exact criteria in the adopted edition.
• Energy: the IECC or the state energy code, as in the tables above.
• Wind and impact: required in some regions; confirm with the local building official.

States and cities amend these codes, and enforcement is local, so verify each item with the building official before ordering.

Plan delivery constraints

Record how units reach their openings: street and driveway access, truck size, crane or lift needs, weights of large panes and lift-and-slide panels, door and stair widths, protected storage and the sequence relative to framing and weather barrier. Delivery constraints change glass size limits and packaging, so they belong in the specification, not in a conversation after the order. The order process shows where they land in the sequence.

What the finished specification contains

• The schedule with marks, quantities, sizes and operation.
• Frame material, finish and color by elevation.
• Glass package and performance targets, stated as whole-window ratings.
• Hardware, screens and shade requirements.
• Code items and the adopted code edition.
• Delivery and storage constraints.
• A list of documents required from the supplier, such as shop drawings, NFRC documentation and warranty terms.