20-Minute Fire-Rated Fiberglass Entry Door - 2 Panel (36" x 80")

Key Measurements & Sizing Information

This door is sold as a nominal 36" x 80" size, which is also commonly written as 3/0 x 6/8. The actual slab size is 35-3/4" wide x 79" tall, with a standard exterior door thickness of 1-3/4".

If purchasing with jambs to assemble a single prehung unit: this slab size typically pairs with a 36" head jamb. For inswing thresholds and saddle-style outswing thresholds, the matching leg jambs are 81-3/4", creating an assembled unit size of approximately 37-1/2" x 81-3/4" when using standard 3/4" jamb thickness. For bumper-style outswing thresholds, the leg jambs are 80-3/4", creating an assembled unit size of approximately 37-1/2" x 80-3/4".

If purchasing slab only to replace an existing door slab and keep your current frame: a 79" slab is the most common exterior slab height and is often the preferred choice even when the existing door measures 79-1/8" or 79-1/4" tall. In many replacement situations, a small height difference at the bottom can be addressed using an adjustable U-style door sweep, helping maintain proper sealing and smooth door operation within the existing frame. If your existing door measures a full 36" wide, is taller than 79-1/4", or measures exactly 36" x 80" (common with older wood doors), we also offer a line of oversize trimmable doors available in select styles.

Door Prep Options

Door prep refers to how the door slab is machined for hinges and lock hardware. We offer three options:

• Without prep (blank): no machining, ready for field preparation
• Standard prep: machined to common residential hinge and lock placements, and matched to the framing and jamb sets we offer for complete door systems
• Custom prep: hinge and lock locations machined to exactly match your existing door

If your existing door is prepped to specifications other than our standard layout, we recommend selecting custom prep so the new slab matches your existing door. See the diagram in the image gallery for a visual reference of standard hinge and lock placement.

Standard Hinge Prep

Standard hinge prep includes three hinge mortises on the hinge edge of the door, located as measured from the top of the door:

• Top hinge: 6-1/2" from top
• Middle hinge: 37-1/2" from top
• Bottom hinge: 68-1/2" from top

For Slab Only orders, standard hinge prep is reversible. The mortises are machined completely through the edge of the door so hinges can be mounted from either direction, allowing left-hand or right-hand swing installation without additional routing. This type of reversible hinge prep is compatible with 4" hinges in 5/8" radius (quarter-round), 1/4" radius (dime-round), or square corner profiles. Complete Door System orders come with standard hinge prep locations but will be mortised as hinge pockets to match selected swing and hinge shape.

Standard Lock Prep

Standard tubular lock prep is machined for a 2-3/8" backset lockset and includes two 2-1/8" bore holes spaced 5-1/2" apart. Each bore is centered 2-3/8" from the edge of the door:

• Deadbolt bore (upper): centered 40-3/8" from top of door
• Latch bore (lower): centered 45-7/8" from top of door

Fire-Rated Fiberglass Construction: Built for Safety and Code Compliance

Fire-rated fiberglass entry doors are specifically engineered to help slow the spread of fire and smoke, providing valuable time for occupants to exit safely. These doors are constructed using specialized materials and tested assemblies designed to meet building code requirements where fire-rated openings are required.

The fiberglass skins resist warping, rotting, denting, and rusting, while a fire-resistant polyurethane (PU) foam core is engineered to maintain structural integrity during fire exposure. Reinforced laminated strand lumber (LSL) stiles with maple wood caps provide structural strength and hardware support. Each door includes an applied 20-minute fire label verifying compliance with tested fire-resistance standards when installed as part of a properly rated door assembly.

20-Minute Fire Protection for Code-Compliant Applications

This door is designed to meet 20-minute fire-rating requirements when installed as part of an approved fire-rated assembly. A 20-minute fire rating indicates that the door system has been tested to withstand fire exposure for a minimum of twenty minutes, helping slow the passage of flames and heat.

This fire-rated door meets recognized testing standards including UL 10C, UL 10B, and NFPA 252 for positive pressure fire resistance with hose stream testing when properly installed in accordance with NFPA 80.

Where Fire-Rated Doors Are Commonly Required

Fire-rated doors are commonly required by building codes in locations where enhanced fire protection is necessary. Typical applications include:

• Between attached garages and living spaces
• Utility or mechanical room entrances
• Multi-family residential units
• Basement or stairwell separation openings
• Areas where local building codes require fire-rated assemblies

Hardware and Assembly Requirements

This fire-rated configuration is approved for single-door units only and supports cylindrical latch and deadbolt hardware with a maximum 2-3/4" backset.

Fire-rated doors must be installed in accordance with applicable fire-rated assembly requirements. Category "B" fire-rated doors require the use of a listed Category "G" gasket in positive pressure applications. Smoke and draft control applications require the use of a listed Category "H" gasket.

Surface Texture and Recommended Finish for Smooth Fiberglass Doors

This door features a Satin Smooth (white) surface with a fine linear texture and subtle vertical lines, similar to a woven linen or brushed fabric. This micro-texture provides built-in surface tooth that helps primer and paint adhere without the need for heavy sanding, reduces the visibility of brush marks and roller lines, and helps prevent runs and drips on vertical surfaces.

Before finishing, clean all door surfaces to remove dust, oils, and handling residue, then allow the surface to fully dry. For best results, we recommend using a high-quality bonding primer such as Sherwin-Williams Extreme Bond Primer, followed by a premium exterior-grade acrylic latex paint.

All six sides of the door must be finished, including the front, back, top, bottom, and both edges, to properly protect the door and maintain warranty coverage. When selecting paint colors, lighter to medium shades are typically recommended for doors exposed to direct sunlight, as very dark colors can increase surface temperatures and reduce long-term finish performance.

Fiberglass doors are shipped unfinished or factory-primed depending on selected options. Finishing should be completed promptly after delivery and before prolonged exposure to weather.

Installation Readiness for Fiberglass Door Slabs

Fiberglass door slabs are designed for installation into existing door frames or for assembly into new prehung units. Before installation, verify that the slab dimensions (width, height, and thickness) match the existing slab for replacements, or the jamb set for new assemblies.

When replacing an existing slab, the original door can often be used as a template. Align the existing door on top of the new slab to transfer hinge locations and hardware positions for accurate placement.

Minor trimming of fiberglass door slabs may be possible depending on the door construction, but allowable trimming limits should always be verified before cutting. Excessive trimming may affect performance or warranty coverage.

Fiberglass door slabs are heavy and should be handled by two or more people during installation. Always support the door evenly to prevent damage to corners or edges.

Complete all recommended finishing steps promptly after installation to protect the door surface and maintain long-term performance.

For complete step-by-step installation instructions, refer to the full installation guide available in the Resources section below.