How to Insulate and Seal Window Trim

What You'll Need
Fiberglass insulation rolls or rigid foam insulation
Cutting shears
Pry bar
Foil tape

You may have used the best of materials on your window to ensure that it is properly insulated, but all of this effort and expense is negated unless you check the condition of your window trim as well. In order to install a window, you essentially have to cut an opening in the walls of your house and then fit the window in that opening. However, if there is any gap between the sides of your window and your walls, it will let in air into your home. Since this gap is covered by a window trim, it is important to ensure that this trim is well insulated. 


Step 1 – Check Your Window Trim

If your trim is not damaged, do not fix it. Before you decide to remove your window trim and pry into the innards of your window, check whether the insulation actually needs replacing. All you need to do is run your hand over the window trim on a cold day, when the window is shut. If the trim and surrounding woodwork feels cold to touch, chances are that it is not properly insulated. 

Step 2 – Remove the Trim

Use the pry bar to carefully remove a section of the window trim and check the insulation inside. Be very careful while doing this as it is very easy to damage the trim. In fact, the trickiest parts of this do-it-yourself job are when you are removing and replacing the window trim. If it seems that your window is lacking in insulation, remove all of the trim. Do not try to remove part of the trim and then try to fill in the insulation by pushing it in with a stick. Although this may seem a lot easier, you will not really be able to ensure that the insulation reaches all the way through, and all your hard work will be negated. 

Step 3 – Fill the Insulation

The next step is to stuff the insulating material into the window sills. There are different kinds of insulating materials available. If you have a large window without any insulation, you should use rigid foam insulation. If you just need to pack in some more insulation, fiberglass insulation rolls may be a better option. Use the cutting shears to cut the rolls to the proper size. Remember not to overstuff the insulation into the window frames. Insulating material expands over time and you need to leave some room for this expansion. 

Step 4 – Tape the Edges

Use foil tape to cover the insulation and the edge of the window frames. This not only ensures that the insulating material does not move, but also prevents air and moisture from entering into the small gap between the insulating material and the edge of the window sill. Be sure that the tape is not too thick because then you will have a problem putting the window trim back on. 

Carefully put back the window trim and you have a fully insulated window that will not let cold air in and keep your home warm during the winters.