How To Replace An Old Window

  • By: Monica Shulz

Should your old windows be replaced by new ones? This guide will show you the process, what tools you need, and what steps you need to take to build an old window and replace it with a new one. If you have the gift of craftsmanship, you can do it yourself – ideally in pairs. Because this is the safest way to remove or hang heavy window sashes.


This is how you install a new window. Is the soffit of all walls in the house smooth and dust-free? If you install your windows, there must be an impeccable surface finish here. This is the only way to ensure that the sealing tape will remain in place later and to ensure installation in accordance with the RAL standard.


That is a simple overview of the whole process. You don’t have to be an expert when installing windows. Even the handyman can install his own window with the appropriate material and accessories.


However, to avoid many common mistakes, you will need step-by-step instructions and suitable installation tips and tricks. For example, when screwing the window frames, unwanted thermal bridges can occur if the frame is not optimally aligned.


The following instructions show you in detail how to do everything right and install your window professionally.

Tools you will need to replace a window

Although each project to change a window is different, you will need some or all of these tools:



Step 1 – Unhide The Old Casement

First mount the old window sash and possibly tighten existing frame anchor out. Be careful not to break the glass. Depending on the age of the house, it may also be necessary to remove old internal or external window sills and replace them with new ones.


First, remove the protective foil that is stuck on the window frame. It cannot be removed after installation and should therefore be removed in advance. The remaining films protect the surface during installation and remain first in place.

Mount the window handle on the window sash so that it can be opened. Then unhook the wing by removing the upper locking pin with a flat screwdriver. Now open the sash and pull it upwards.


Protect the suspended window sash from damage by placing it on a soft surface. Above all wood and aluminum as well as white and other light colors are susceptible to scratches, which are difficult to undo later.


Pro tip: Do the dimensions of the soffit openings match your windows? For successful installation of your window, adjust the lengths, widths and depths for safety again.


Step 2 – Saw Old Window Frames

Cut the old window frame in several places. It is best to use a foxtail or an electric saber saw. Then carefully knock out each part of the frame with a hammer, breaking the corners.


Step 3 – Remove Old Window Frame Tabs

Now screw out any existing frame anchors. Instead of these so-called tabs (also called wall anchors, or shaker) have been used previously, where you have attached the window frame. Either knock them out with a hammer and chisel or separate them with an angle grinder. When using an angle grinder you should always wear protective goggles.


Then, the window reveal is cleared of plaster. Any damage that has occurred can be remedied with the aid of quick-fixing repair mortar. Then, measure the wall opening for the new window exactly. When doing so, make sure that there is an approx. 20 mm wide construction gap between the window frame and the wall for foaming or clogging. Also, remember to include the height of the sill.


Step 4 – Mount The Window Handles And Stroke The Frame

Mount the window handle and then hang the new window sash out of the frame. Before installing pre-treated wooden windows, coat all areas that are no longer accessible and come into contact with masonry or mortar twice with thick-layer glaze.


Step 5 – Stick Decompression Tape To Window Frame

Now attach a decompression sealing tape to the outside of the window frame. This is usually included.


Step 6 – Insert, Fix And Align The Window Frame

Place the window frame in the wall opening by placing it on support blocks. Then fix the frame in all directions with wedges and spacers. Be sure to align the frame vertically and horizontally and maintain as symmetrical a distance as possible from the masonry. The distance should be around 20 mm all around. Remember to consider the height of the sill. Check the alignment with a spirit level.


Step 7 – Screw The Window Frame Into Place

As a rule, the new frames are already provided with mounting holes. If this is not the case, put the holes in the masonry through the side window fold. They should be about 10 to 15 cm from the inner frame corners, but no further than 70 cm apart.


If that’s not enough for your windows, drill another hole in the middle. It is best to use a long metal or stone bur. Now the frame dowels are set and screwed. Then hang the casements and check the function. If the windows can be operated well, the next step is filling the joints with foam.


Step 8 – Foam Joints, Install And Polish Windowsill

Fully foam the joints between the frame and the wall from the bottom up with two-component assembly foam and clean the frame immediately. After the mounting foam has cured, cut off the excess mass diagonally inwards with a craft knife. Only now, you can also remove the remaining supporting blocks and spacer wedges and foam the resulting gaps.


Cut the sill with a jigsaw and fit it. Apply adhesive mortar to the parapet and slide the windowsill under the window frame. Now you can re-plaster the window reveals or glue plasterboard. You may also need to finish the outside of the wall with plaster.


Step 9 – Seal Connecting Joints

Seal the connection joints to the masonry in the outer and inner areas with permanently elastic sealant, for example with silicone or acrylic. For smoothing, use a joint cleaner with detergent. Alternatively, you can also use a special cover strip. Finally, peel off the protective film from the window glass.


If you are a bit gifted, you can install and remove windows yourself. Nevertheless, it is best to work together with your friend.


Common “How to Install a Window” – Questions 

How To Frame a Window?

To frame a window (level horizontal surfaces, plumb vertical surfaces, and both equal diagonal measurements), you may need to make a fit. In general, a space of ¼ inch or less can be fitted. If the space is larger, a piece of filler should be installed to reduce the width to a dimension in which a fit can be placed. Cedar or composite shims are always used in pairs, with the angular sides facing each other. One fit is inserted from the outside, and the other from inside.

If the frame is not plumb, remove the screws and shims, and start again.

In frames, shims should be used wherever the new window is bolted to the frame (or jambs). In general, the holes of the jambs are pre-drilled in the replacement windows. The shims allow adjustment and prevent the sides of the window from arching when the windows are permanently fixed. Verify that the frames or jambs are plumb before and after inserting the shims and fixing the window. If the frame is not plumb, remove the screws and the shims, and start again (photo 4).

Fill any space around the perimeter with loose insulation.

To fit the bottom of the opening, place the shims approximately 1 inch away from either end and near the center of the opening. You may have to lightly hold one side of the window, by the head, with a 2-inch wood screw. Insert the screw just enough so that the window can open and close. Check the diagonal measurements of the window to make sure they are the same. Once checked, the window will be square, and should work and close normally.

Never put a shim on the head of a window or attach it to the frame. The windows are not structural and any type of fastening to the top of the rough opening could cause the window to break and / or to malfunction.

How To Make Accurate Mounting Holes For a New Window?

Drill holes with the drill. The masonry can be designed differently: In an old building, it can quickly come to the splinter solution, which furniture, windowsill or floor can be damaged. Bend in difficult cases with a frame anchor and careful approach.

Using the drill, screw in the screws. The window frame is now connected to the masonry. In the next step, the gaps are filled with foam to ensure good insulation.


How To Do Finishing On Window Replacement?

To complete the window installation, foam the cavity between the frame and the wall. Dose carefully, as the foam still swells. Glue the inner foil over the whole surface of the masonry (Fig. 6b) or grout the plane accordingly. Now, in a final step, the window sash has to be hung.



In this article, we have discussed about how you can replace an old window with a new one. It is an easy process if you know what you are doing. Don’t forget about the safety. We advise you to wear thick gloves to make sure you don’t scratch your hand with the glass or aluminium edges. Subscribe to Home RenoVision DIY here or better become RenoVision paying member and get extra perks.

If you prefer to see a video, you can watch it all below.

this post shows the reader how they can change the old window with; sawing the window out, put in insulation and put in a new window in nine steps.