Phone: 314.966.9988   |   Toll Free: 888.845.5637

Replacing old, tired-looking windows can make a big difference to the overall appearance of a house, not to mention that it can also help to improve the energy efficiency and security of the property. But replacing a window and installing a new one can seem like a daunting task, especially in a home with vinyl siding which will need to be removed to facilitate the installation. 

What is Vinyl Siding

Before we get further into the process of installing a new window into a house with vinyl siding, it’s important to first understand what vinyl siding is. Vinyl siding is a plastic exterior siding used for houses and small scale apartment buildings. Vinyl siding provides a consistent aesthetic appearance as well as weatherproofing against the elements and is also fire resistant. Most vinyl siding is designed to replicate the look of wooden clapboard, board and batten or shakes and comes in fairly neutral colors, though the number of colors available is increasing. Vinyl siding first appeared on the market in the late 1950s as a replacement for aluminium and fibre cement siding and is made from polyvinyl chloride (PVC) resin. It has since become a very popular material as it is cheap and readily available and it is used widely in the property manufacturing industry throughout the United States and Canada. You may also come across vinyl siding in the UK and New Zealand though it often comes under a different name, and is often referred to as ‘PVC Weather boarding’. When installed correctly vinyl siding can be very durable and a long-lasting alternative to other building materials. 

How to install a new window in a house with vinyl siding

1. Measure the existing window to purchase a replacement.
If you are replacing a window then the first thing you will want to do is to measure the existing window so that you can order a replacement. Measure the width, height, and diagonal of the window from frame edge to frame edge, ensuring not to measure the trim as this is installed separately. Most windows can now be ordered in set sizes; however, if you cannot find an existing window to fit your measurements then you may need to have one custom made.

2. Prepare the inside of the old window area.
To remove the old window you will need to remove the old window surround and trim; do this carefully and you may be able to reuse them for the new installation. The drywall surrounding the window inside the house can also get in the way of the window removal process and so in some cases it is best to remove it, though do be aware that this will add time to the project as it will need replacing. To remove the drywall, use a utility knife to make shallow incisions – also known as to score – the area of drywall that you wish to remove; this will weaken these areas making it easier to remove the drywall section. Next, use a crowbar or chisel to gently and carefully remove the drywall areas. To avoid damaging areas of the drywall that you do not need to remove, ensure to score carefully and go back and score again if pieces to not come away easily. 

3. Remove the old window.
The goal is to remove the old window without causing damage to the frame of anything else around the window. Start by removing any nails or screws that may be holding the window in place, and remove any wooden supports you find between the window and the wooden studs around the window. Knock the supports out with a hammer, or unscrew them if they are screwed in place. Next, from the outside of the property make cuts around the seal of the window frame using a utility knife, this will loosen the frame and make it easier to pull out. Finally, pull out the frame from the window hole – you may need to use a crowbar or a chisel if it is still in there tight. Remember to have plenty of spare help on hand as windows can often be heavy and difficult to maneuver.

4. Remove the vinyl casing.
Windows installed into houses with vinyl siding usually have an exterior vinyl casing which holds the window in place. This vinyl casing can usually be found in the same color as the siding and can be found on the perimeter of the open space in the wall after the window is removed. If there are nails holding the vinyl casing in place then remove them with a hammer before pulling the casing out.

5. Remove any damaged vinyl siding.
If the vinyl siding around the window area has been damaged or needs replacing then now is the time to remove it. Don’t cut it; instead, remove any nails, then use a siding removal tool to separate the siding panels. Now is also the time to add or replace a vinyl sill if you would like a window sill feature. Remember to add the end caps to the window sill and to glue them in place in order to hide the hollow interior and protect it from the elements.

6. Check the window area.
Having removed the old window and any damaged vinyl siding, you can now check the window area substrate for any signs of rot in the wood; you can do this by running a flat blade screwdriver along the frame to probe for soft or crumbling areas. If you find any rot then these areas will need replacing before installing the new window. If there is rot in the wood beneath a new window this will continue to worsen until eventually the window will sag or could come loose.

7. Add sill flashing tape.
Because the vinyl siding on the exterior of the window does not provide a 100% waterproof barrier, it’s important to also install building paper and flashing to avoid water getting in and rotting the wood beneath the window. Add building paper which should extend behind the window’s nailing fin. If you see any holes in the building paper then patch them with house wrap tape. Next, install the flashing; the flashing should extend along the bottom of the window and overlap the nailing hem. It should also extend partway up the sides to ensure that any water that gets in will be directed away from the dry wood beneath. As a general rule, the flashing along the sides of the window should extend around five inches out from the edge, two inches past the top and overlap the bottom flashing by at least two inches.

8. Dry fit the new window.
Carefully lift the new window into the window area to check if it fits. There should be a small ½ or ¾ inch gap around the edge of the window. If it fits remove it and set it aside. If the window is too small then you can add furring strips to match the new window size. If the window is too big then it is best to return it and get the right size – otherwise you will need to cut into the raw opening, which is a job best left to the professionals.

9. Fit the window.
Once you are confident your window fits and have prepared the dry opening, it’s time to run a bead of caulk along the exterior stops. This should follow the edges of the window opening. Next, lift the window – the more hands the better – and fit it into the gap, ensuring that the corners sit flush. Once the window is in place, screw the fasteners into place and seal any gaps with frame sealant for a neat finish. If there are some larger gaps you may wish to fill them with foam first. Once the foam is dry, trim it back with a craft knife so that it does not bulge out from the frame and then cover it over with frame sealant. It’s important that all exterior gaps are filled to avoid water penetration.

10. Add a new J-channel to the window frame.
In order to re-fit vinyl casing around the exterior of the window, you will need a J-channel. Vinyl casing requires a J-channel to slide into; having removed the old vinyl casing, it’s time to install a new J-channel. To add more architectural detail to the window frame you can also use moulding and casing, which will hide the J-channel whilst providing an original colonial facade. If you are using vinyl casing then ensure that the angle of the casing matches the angle of the sill by cutting it to fit. Fit the J-channel or vinyl casing to the window and secure with nails and sealant.

11. Re-install the vinyl siding.
With the window installed the last thing you will need to do to the exterior of the window is to replace any removed vinyl siding. You may be able to reuse the old siding if it is not damaged, otherwise you may need to cut new sections. Vinyl siding can be cut with either tin snipper or a utility knife. Tin snippers can be used in much the same way as a pair of conventional scissors, though you should try to avoid closing them completely to give a smoother cutting finish. Alternatively, Vinyl siding can also be trimmed by scoring them with a utility knife at the point at which you wish them to be trimmed and then snapping the piece off along the scoreline. Each piece that is adjacent to the window should slide neatly into the J-channel that you have installed. Remember to leave about a ¼ inch for expansion. The vinyl siding should lock into one another with the siding locking edge locking into the coursing below. Then secure the panels with nails leaving 1/16 of an inch to 1/8 of an inch of the nail exposed to allow the vinyl siding to move as it expands. This will prevent buckling.

12. Fill in the gaps around the inside of the window.
Sealing isn’t just important on the outside of the window but on the inside too. To help the window fit into the rough gap it is often made to be slightly smaller than the gap it is being inserted into. This excess gap can be filled with jammers and then sealed with expanding foam from a foam gun. Be sure to use a 1-1 expanding foam so that it doesn’t expand too much, pushing the window out of place. Once the foam has dried you can then trim off any excess with a craft knife before sealing over it with frame sealant. Properly sealing the interior of windows can help to reduce drafts, improve the energy efficiency for the window and keep the window in place.

13. Finish up the inside aesthetics.
Finally, it’s time to finish off the interior aesthetics by replacing the trim to cover the foam and sealant filling the gaps. If you managed to carefully remove the trim from the old window, then this can be reinstalled. If the trim was damaged or you are looking to upgrade the aesthetic then you will need to purchase, cut and fit a new interior window trim. Whichever trim you use, secure it with pin nails and sealant and if necessary paint it for a professional finish. 

14. Test the windows.
With your new window installation complete it’s time to test that everything opens and shuts as it should. Once you are happy with the installation let the windows rest for at least 24 hours so that all of the sealants can dry properly before you begin excessively using the windows.


And there you have it. Window installation can look easy when watching someone else do it but the process itself can be long and technical. To ensure you get it right and achieve the finish you want, take it slow and pay attention to the details. Window installation is better done right the first time around to avoid costly re-fits and future repairs.