Project 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.
Continue to step-by-step instructions
This D.I.Y. Advice is part of a series How to install a sash window

Step by Step Instructions

1 Install waterproof flashing onto the bottom of the sash window frame
2 Mark up and drill pilot holes for the sash window frame
3 Level the sash window
4 Install the sash window
  • Step 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.
  • Step 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.
  • Step 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.
  • Step 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.
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