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How to install a sash window

Driving screws through the pilot holes and into the frame of the house

Overview

Sash windows are a classic design seen in many homes. We will show you how to install them into a wall yourself. You will see how to prepare the window before you put it in, plus we will teach you how to get the window level before you screw it in place.

Steps

1

Install waterproof flashing onto the bottom of the sash window frame

Staple a strip of waterproof flashing onto the rear of the window frame so it can fold underneath the frame and cover the base. Be sure to leave yourself plenty of overhang on both sides of the frame. Staple that overhang tightly into position onto the sides of the window frame. This holds the flashing in place but leaves it loose at the front of the frame.
Bunnings team members installing waterproof flashing onto the bottom of the sash window frame

2

Mark up and drill pilot holes for the sash window frame

Remove the beading from the window jamb. Mark up drill points about 40-50mm back from the window jamb and 75-100mm from the top and bottom of the frame. Slide the sash windows out of the way and drill where you have marked.
Drilling pilot holes for the sash window frame

3

Level the sash window

Slide the sash back into place and lift the frame into your wall. If it is a big window, make sure you have someone help you with this. Once the window is in place, use your spirit level to check the window is level. If the window isn't plumb, use masonite packers to level it up. Then use your ruler to make sure the frame is flush with the internal wall face.
Using a spirit level to check the window is level.

4

Install the sash window

Once the frame is sitting in the proper position, slide the sash windows out of the way again. Then drive screws through the pilot holes and into the frame of the house. To give your job the best finish, countersink the screw head just below the surface of the timber. Finish by sliding the sash window back into place and reinstalling the timber beading on the jamb.
Driving screws through the pilot holes and into the frame of the house
Health & Safety

Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page.

When following our advice in our D.I.Y. videos, make sure you use all equipment, including PPE, safely by following the manufacturer’s instructions. Check that the equipment is suitable for the task and that PPE fits properly. If you are unsure, hire an expert to do the job or talk to a Bunnings Team Member.