How to Install a Dog Door in a Fiberglass Door (Step by Step)

Yes, you can put a dog door in most fiberglass doors. Here is how to install a dog door in a fiberglass door: check what the door maker's warranty asks for, confirm the door is not a fire-rated or garage-to-house door, mark a square, level opening at least 4 inches from the bottom and side, cut it with a reciprocating saw or a circular saw with a diamond blade while wearing a good dust mask, then sleeve a self-framing pet door through the opening, screw it together and caulk it.

The cutting and placement details below come from Hale's Door Model installation manual, which includes a note for fiberglass doors. Door construction, warranty, code and dust-safety points come from the sources linked in each section.

Can you put a dog door in a fiberglass door?

In most cases, yes. Hale's manual says plainly: "Fiberglass doors can be cut with a reciprocating saw or a circular saw with a diamond blade but be sure to wear a good dust mask! You do not want to be inhaling fiberglass."

The Hale Door Model pet door is listed to fit "seamlessly into wood, metal, and composite doors," and the manual describes it as self-framing, so there is no need to frame out the inside of the door. Before you mark anything, though, run through four checks.

What is inside a fiberglass door

A fiberglass entry door is not solid fiberglass. Door maker ODL's technical manual describes its fiberglass doors as two fiberglass skins over a polyurethane foam core, with LVL (laminated veneer lumber) side stiles, composite top and bottom rails, and a pine lock block on the lock side (ODL Door Tech Manual, PDF). Brands differ, but the idea is the same: thin skins and foam in the middle, a solid frame around the edges.

That matters for placement. A pet door opening belongs in the foam field of the door, not in the perimeter frame or near the lockset. Hale's 4-inch rule (below) helps keep the cut away from the edges.

Your door maker's warranty and the "inner sleeve" rule

Read the warranty on your fiberglass door before you cut. Some makers discourage it outright. Therma-Tru's FAQ, for example, says "we do not recommend drilling into the door." It adds that if you choose to add a pet door anyway, you should "use a product that contains an inner sleeve," and its warranty answer says a pet door "must have a water-resistant inner sleeve to protect the core of the door" (Therma-Tru FAQs).

The Hale Door Model has two aluminum frames that slide into the opening from each side and "sleeve together," per the manual. If your door's warranty has a specific requirement, check it against your door maker's wording, and call Hale at 1-800-646-4773 with your door's thickness and brand before you order.

Garage-to-house and fire-rated doors

Lowe's dog door guide says not to install a pet door "in designated fire doors, such as the one that leads from the house to the garage" (Lowe's, How to Install a Dog Door, PDF). The International Residential Code, Section R302.5.1, requires the door between a house and an attached garage to be solid wood or solid or honeycomb-core steel at least 1 3/8 inches thick, or a 20-minute fire-rated door, with a self-closing or automatic-closing device (City of Boise IRC handout, PDF). If a fiberglass door is in that spot, ask your local building department before cutting it.

Door thickness: 1 1/4" to 2" for the Door Model

Measure the door's thickness where you plan to cut. The Door Model is designed for doors between 1 1/4" and 2" thick. Hale's spec sheet lists the standard gap between the frames as 1 9/32" to 2", and the frame can be factory modified to collapse to as small as 3/4". If your door is between 1/2" and 1 3/8" thick and you did not order a factory cut-down, the kit should include a build-out that matches the frame color.

Sizing and placement in a fiberglass door

Choose the size first. Hale's manual says, "If in doubt, larger is better." Use the pet door sizing guide to measure your dog:

• Height: measure from the floor to the top of the shoulders (withers). The top of the flap should sit 1 to 2 inches above that.
• Width: measure the widest point and add an inch or two. Long hair can make a dog look wider than it is.
• More than one pet: the tallest pet needs shoulder clearance, and the shortest should not have to jump through.

Then check the manual's placement rules:

• Four inches from the edges. The rough opening should be "no less than four inches from both the bottom and the side of the door," to maintain the integrity of the door construction. The manual notes this can vary with the size and type of door.
• Room for the security cover. Nothing above the opening, such as a kick plate or door closer, should block the cover from sliding in. The Door Model page notes you can ask for a cover that slides to the right or left instead, at no additional cost.
• Square and level. The opening has to be square and level on both faces of the door so the flaps operate correctly.

One detail is specific to fiberglass. The photos in Hale's manual show a pet door installed much lower than four inches from the bottom, for a home with a Golden Retriever and a Chihuahua. The manual explains this "worked in this case because they were installing in a fiberglass door," and that the same cut in a wood door would have caused a structural issue. It also says each situation is different. Treat 4 inches as the default, and call Hale before going lower.

If your door is mostly glass, cutting through the panel is not an option. See our guide to putting a dog door in a French door, or the In-Glass pet door, which requires professional installation.

Rough openings for common dog sizes, from the sizing guide (width x height):

For all 11 sizes and the difference between flap, frame and rough opening, see our dog door rough opening guide. If you ordered a custom size, use the rough opening dimensions you gave Hale.

Tools and blades for cutting fiberglass

You need a drill to start the opening and drill the screw holes, a saw to finish the cut, and a screwdriver. Add a level, a pencil, masking tape, a tape measure and drop cloths, plus eye protection, gloves and a good dust mask. The kit includes 5/8" #6 Phillips screws and a 7/64" drill bit.

For the saw, Hale's manual gives fiberglass two options: a reciprocating saw, or a circular saw with a diamond blade. Here is how that compares with the manual's advice for other doors:

If you are working on a steel door instead, our metal door installation guide covers blade counts and priming the cut edges.

Fiberglass dust: protect yourself

Cutting the skins makes fine, itchy dust. The U.S. Agency for Toxic Substances and Disease Registry (ATSDR) says synthetic vitreous fibers, the group that includes fiberglass, can irritate the eyes and skin ("fiberglass itch") and the nose, throat and lungs, causing sore throat, nasal congestion and cough. It adds that these effects usually go away with time (ATSDR public health statement).

• Wear the dust mask Hale's manual calls for, plus eye protection and gloves.
• Cover bare skin. ATSDR's advice for people installing fiberglass insulation is to wear protective clothing and masks.
• Lay drop cloths on both sides of the door, then vacuum the area when you finish, as the manual's cleanup step says.

How to install a dog door in a fiberglass door, step by step

Need help mid-job? Hale's manual offers a free consultation with an experienced installer at 1-800-646-4773.

1. Check the kit. Confirm both frame halves, the security cover, the screws, the 7/64" bit and the instructions are there, plus a build-out if your door is thin.
2. Protect the area. Put drop cloths down on both sides of the door.
3. Mark the opening. Use a level and pencil to mark all four sides of the rough opening, at least 4 inches from the bottom and side. Outline it with masking tape and check the size and height one last time.
4. Drill starter holes. Drill at the corners, inside your lines, so a saw blade fits. The manual suggests holding a level on the drill bit so the inside and outside faces of the opening line up.
5. Cut the opening. Use a reciprocating saw or a circular saw with a diamond blade, with your dust mask on. Keep the cut square and level on both faces.
6. Test fit. Separate the pet door into its two halves and remove the security cover. Back out the pin-lock screws a few turns so they do not hold a corner off the door.
7. Sleeve the frames together. Put the inner frame, the one with the cover track, in from inside. Slide the outer frame in from outside and squeeze the halves together. If you use the optional raincap, hook it on the top of the outer frame first.
8. Level and screw it. Using the pre-drilled pilot holes and the supplied bit, drill one bottom hole and insert one screw loosely. Level the frames, tighten that screw, then drill and drive the rest. Retighten the pin-lock screws.
9. Caulk. Seal three sides of each frame, not the bottom (next section).
10. Finish up. Slide the security cover into its track, clean the frame and flaps with soap and water or an ammonia-free glass cleaner, and adjust the magnets if the flaps do not seal and swing freely.

Sealing the frame on a fiberglass door

Hale's manual says you can fill gaps or seal the edges with caulk once the pet door is in, but "do not caulk the bottom of the inside or outside frame." Tape the three sides first for a clean edge. For the most protection against water intrusion and for better energy efficiency, the manual recommends caulking both the inside and outside frames.

If your fiberglass door has molded panels, Hale's manual note on panel-look doors applies: center the pet door on the door or on a panel, then fill the gaps left by the panel grooves with caulking backer rod and caulk, keeping the filler back from the edge of the pet door frame.

When to call a pro

Call a professional if the door is fire-rated or leads to the garage, if your door maker's warranty limits what you can install, if you cannot fit the opening 4 inches from the edges, or if you are not comfortable with power tools. Hale's manual says anyone with a working knowledge of power tools and basic home construction can install the Door Model. If you would rather not, find a Hale installer near you. You can also compare door-mount options on Hale's dog doors for doors page. Hale has been making pet doors in the USA since 1985.

Frequently asked questions

Can you put a dog door in a fiberglass door?

Yes, in most fiberglass doors. Hale's manual says fiberglass can be cut with a reciprocating saw or a circular saw with a diamond blade, with a good dust mask. Check your door maker's warranty first, and do not cut a fire-rated or garage-to-house door without asking your building department.

What saw do you use to cut a fiberglass door for a pet door?

Hale's Door Model manual lists two options for fiberglass: a reciprocating saw or a circular saw with a diamond blade. Drill starter holes at the corners inside your marked lines first, and keep the cut square and level on both faces of the door.

Will a pet door void my fiberglass door warranty?

It depends on the door maker. Therma-Tru, for example, does not recommend drilling into its doors, and says a pet door must have a water-resistant inner sleeve to protect the door's core. Read your own door's warranty before cutting.

How far from the bottom of a fiberglass door should a dog door be?

Hale's manual says the rough opening should be no less than four inches from both the bottom and the side of the door, though this can vary with the door. Its photos show a lower install that worked in a fiberglass door, so call Hale before going below 4 inches.

Is fiberglass dust dangerous when cutting a door?

ATSDR says fiberglass fibers can irritate the eyes, skin, nose, throat and lungs, and that these effects usually go away with time. Wear a good dust mask, eye protection and gloves, and vacuum up the dust when you finish.

Sources

• Hale Pet Door, Door Model Installation Instructions (PDF)
• ODL, Door Tech Manual: fiberglass door construction (PDF)
• Therma-Tru, FAQs: pet doors and warranty
• Lowe's, How to Install a Dog Door (PDF)
• City of Boise, IRC Code Handout #435, Section R302 Dwelling/Garage Separation (PDF)
• ATSDR, Synthetic Vitreous Fibers public health statement