How to Make a Sash Window Pet Door

Dog peering out from a doorway
What You'll Need
Tape measure
Wood for a frame
Board for the window pane
Wire nails
Panel for the door flap
Staple gun and staples
Measure Your Pet

A window pet door can be a great alternative to installing a pet door in an exterior door. One benefit of building a window pet door is that there will be no evidence in your house door that you have a pet.

Before designing your door, measure your pet so that you know how big the door should be.

Step 1 - Examine the Window the Pet Door Will be Fitted Into

Check the window into which you want to install the pet door to ensure that there is enough room in the bottom pane. It is also a good idea to check how sound the window is. An animal passing to and fro is going to create extra strain on the window.

Step 2 - Make a Board to Fit in Place of the Window Pane

It is not wise to fit a pet door into standard window glass. Start by cutting out a board that can replace the glass. It needs to be exactly the same size as the glass and the same thickness if possible.

Step 3 - Mark the Outline for the Door

Mark on the board the outline shape of the door. Cut the shape into the board by drilling a hole in each corner of the shape and using a jig saw.

Step 4 - Check That Your Pet Can Get Through the Hole

Before going any further make sure that your pet can get through the hole. Testing at this stage will not only confirm that the hole is big enough but also introduce your pet to the door at an early stage. This can make it much easier to train your pet to use the door when it is finished.

Step 5 - Make the Pet Door Hinge

The easiest way to make a pet door hinge with motion in both directions is to use a strip of very heavy duty polythene. This material is remarkably durable and does not tear easily if you ensure that the grain of the polythene is vertical to the door.

Step 6 - Find the Grain in the Polythene

Polythene sheeting will tear in one direction only. With a piece of polythene cut off the piece you will be using for the pet door hinge. Hold it between two pairs of pliers and try to stretch it. If the polythene does stretch you will see that it will do so from two sides of the stretch. The grain is at 90º to the direction in which the polythene stretches.

Step 7 - Frame the Hole

Using strips of wood build a neat frame around the hole you cut for the pet door. Connect the frame to the board with adhesive and small nuts and bolts fitted with large washers. You will need to clamp the wood to the board and drill the holes for the nuts and bolts. Make sure you connect the frame to the side of the board that will be on the outside of the sash. This means that there will be no interference with the normal operation of the sash window. The wheels will still turn and you will have the benefit of sliding glass for ventilation.

Step 8 - The Top of the Frame

measuring a window frame

Make sure that you place your strip of polythene along the top of the frame and that it is held in place by the frame and adhesive.

Step 9 - Attach the Door Flap

The door flap will be attached to the polythene hinge with adhesive and whatever connectors are suitable. A thin plywood door, for example, could be attached with adhesive and staples from a stapling gun. Make sure the flap is free to move backwards and forwards through the maximum arc. Note that larger animals work better with a rigid door flap because they can see outside as soon as they raise the flap. A flexible flap will cover their eyes until they are through the door.

Step 10 - Finish Off

The door can be finished by grinding down the ends of the nuts to the level of the bolts. This makes for a much neater finish. Seal and paint the woodwork to match the door.

Step 11 - Fit Brush Strips

Drafts can be minimized by fitting brush strips around the inside of the pet door frame. The pet door is now finished.

Step 12 - Remove the Window Pane

Remove the glass window pane and clean off all the old putty and grit from the window frame to give the board a good seating.

Step 13 - Setting for the Board

caulking around a window

Before setting the board in the window put a bead of silicone sealer all around where the board is going to be fitted. This will give better adhesion and add water proofing.

Step 14 - Fit the Board into the Window Frame

Place the board into the window frame and press it home firmly. You can use fine wire nails to secure it to the frame. Apply window putty around the edge of the board and finish it off neatly. Let the putty dry before introducing your pet to the pet door.

All you need to do now is to introduce your pet to the new way in and out of the house and make sure it has safe access to the window both indoors and out.