How-to Install Double-Glazed Windows

You can save a bit of money by fitting replacement windows yourself. It is not a difficult DIY task, but there are certain things the professionals know that will make it easier and more secure when it comes to installing your replacement windows safely, so if you feel in over your head call them. Until then, here’s how to fit a window yourself.

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Fit a Double Glazed Window

To fit double glazed window, you will need:

  • Drill
  • Chisel
  • Screwdriver
  • Spirit level
  • Frame fixings
  • Silicon sealant

You may also need a saw to trim down the sill for a tidy finish. Before you remove the old windows measuring the new frames to make sure they will fit. Once you are satisfied they are the correct size, score along the edge between the wall and the window frame to break the existing bond. This will makes removal easier and you are less likely to pull a chunk of plaster out the wall.

Remove old fixings with a screwdriver and break external silicon seal with a blade. Remove external brick corners to remove old frame and clean off old sealant and debris from the brick wall aperture. Make sure surfaces are smooth and even then prepare the external sill for the new frame. You may have to cut the sill to size to make it fit around the brickwork.

Screw the sill on to the bottom of the frame using screws that will not penetrate the skin of the frame. Be sure to seal the ends of the sill and frame assembly to prevent moisture tracking along the edge of the sill and into the brickwork. You can do this using a window sealant. They are not very expensive.

Image source: Master Designs via DesignMine

Framing the Window

Carefully position the new frame into the aperture. You may need some help guiding the window into place as they are bulky and awkward to position. Once you have centred the window frame, insert packers underneath to level it and maintain the 5mm extension gap. Check the frame is both level and plum and drill at least two fixing holes on all four sides of the frame. Drill holes should be approximately 150mm from top and corners and around 600mm centres in between.

Suitable fixings for this job are nylon sleeve frame anchors or self-tapping masonry screws. Do not over-tighten the fixings as it is important to position packers between the frame and the brickwork to prevent distortion and maintain the 5mm expansion gap. Ensure that any holes drilled through the bottom of the frame are sealed with silicon around the screw heads to reinforce the frame and prevent water ingress.

Again use packers round the frames and break off the excess length with a chisel to give it a neat finish. Before finishing off the final stages, clean any brick dust or debris from the frame and surrounding area. Glaze the frame ensuring that appropriate glazing platforms are fitted around the aperture. These will centralise the glass and allow free passage of water into the draining slots.

Slot the pane into position noting that where opening casements are hinged from the sides they should have the glass packed at opposing corners to keep the casing square. Using a nylon mallet, tap the beads into place. Clean the area down and seal the frame to the internal wall. You may fit a trim using a bead of silicon to tidy the gap between replacement window frame and the interior window sill.

Finally, seal the walls using an acrylic sealant. Run a strip of masking tape across the internal walls beside to prevent sealant smudging on to your paint work. Do you the same on the outside frame and apply the end caps to the sill. Then you can step back and admire your handy work.

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