Uninsulated sliding glass doors can allow UV radiation and heat into your home and cause drafts, increasing your energy usage in summer. Homeowners can help reduce or eliminate both UV radiation and heat by insulating the frame and treating the glass with reflectors.

Sliding glass doors are often located in the rear of the home and serve as egress exits in the event of an emergency. Most sliding glass doors are made from aluminum or vinyl and include the frame, two doors, and mounting hardware.

Insulating a sliding glass door involves insulating the frame with fiberglass, foam rope, or spray foam, while adding treatment to the glass. Treatment can include window film, heavy curtains, and ensuring the seals are effective and not causing drafts.

Here we will discuss why insulating your sliding glass doors is important, which insulation works best, and offer a few installation tips. You will need a couple of hand tools, and most of all, personal protection equipment to keep yourself safe.

What Insulation Do I Use to Insulate a Sliding Glass Door For Summer?

Most sliding glass door frames are insulated with fiberglass batts, foam rope, or spray foam. The insulation is installed behind the casing, which is the trim across the top and sides on the frame. If the gaps are less than ¼” wide, foam rope or fiberglass batts are often used as neither material expands after installation.

Larger gaps (more than ¼” wide) are usually good candidates for low rise spray foam, also known as closed cell spray foam. Open cell spray foam is rarely used to insulate sliding glass doors because even a small overexpansion of the foam can break the glass.

Avoid spray foams that claim 3x or 5x expansion (open cell foam) unless the gap is wider than 1”. Overfilling a gap is very easy with open cell spray foam as the foam exits the nozzle quickly and begins to expand immediately, making control more difficult .

Closed cell spray foam will only expand about double its size so it is much easier to control in a small area. Closed cell foam also offers about twice the R value (R-7/inch) of open cell foam (R-3/inch), so you need less closed cell foam to achieve the same insulation value.

How Do I Insulate a Sliding Glass Door For Summer?

To insulate a sliding glass door, you will be adding insulation around the frame and/or applying reflective film to the glass. Most sliding glass doors sit inside a frame with two tracks attached at the bottom. You will also be inspecting the seals and checking the door(s) for level.

Insulating a sliding glass door frame is quite simple, but using the correct tools will make the job easier and look better. Here’s a sample list of the tools you’ll need to insulate a sliding glass door frame for summer:

  • Trim Pry Bar
  • Hammer
  • Sharp Knife
  • Brad nailer or finish nails
  • Caulk and Caulk Gun
  • Paint and paint materials (if required)

Insulating a Sliding Glass Door Frame 

1. Score the Caulk Around the Casing

To begin, first score the casing with the sharp blade. Use the blade to score the caulk between the drywall and the back of the casing. Make sure you go all the way through the caulk to avoid tearing the drywall paper when you remove the casing. Also score the joints between the vertical side casing and the horizontal casing over the top of the door.

2. Remove the Casing

Using a small, flat pry bar, remove the casing completely. Place a thin book or towel between the back of the pry bar and the drywall to avoid cracking the drywall. Gently pry off all three pieces of casing and set them aside.

3. Install the Insulation

Install the insulation between the sliding glass door frame and the rough opening, being careful to fully fill the gap. If you are using fiberglass batts, just pull the fiberglass from the batts as needed to fill the gap. Allow the fiberglass to remain as fluffy as possible.

If you are using foam rope, like this one, use a screwdriver or pencil to stuff the foam rope into the gap. You don’t have to worry about compressing the foam rope, so stuff the gap full. If needed, you can apply adhesive caulk to the foam rope to help it remain in place.

If you are using spray foam from a can, make sure both the sliding glass door frame and the rough opening are completely dry. Next, apply a steady bead of spray foam to the gap, but keep the can moving. It is better to apply a second layer of foam than to accidentally overfill the gap.

4. Reinstall the Casing and Caulk

Allow any spray foam to cure before reinstalling the casing by following the directions on the can. Reinstall the casing using a hammer and finish nails or a brad nailer if you have one. Make sure the casing goes back into the same location as before to avoid gaps in the casing.

Pro Tip For Caulking the Casing: If your casing and walls are different colors, use a clear caulk to avoid repainting. For the rest of the casing, use a color matching caulk or simply repaint the casing.

Applying Summer Treatments to Sliding Glass Doors

Select only those treatments appropriate for your sliding glass door. Remember that one door slides behind the other, so you can’t attach drapes, curtains, or blinds directly to the door that slides. 

Most sliding glass door treatments are in the form of vertical blinds attached to the wall above the door. Vertical blinds are popular over sliding glass doors because they pivot and push out of the way when more light is needed.

Other treatments like reflective curtains and shades are also commonly found over sliding glass doors to block the UV radiation that can pass through the glass. Glass films are ideal for insulating a sliding glass door because the film will filter or reflect the UV radiation without affecting the operation of the door.

Glass films are available at most home improvement stores and can be installed by a do-it-yourselfer using simple tools. Most glass films either filter the UV radiation (providing a slightly dark tint), or reflect it, which prevents most of the UV radiation from ever reaching the inside of the glass.

Should I Buy An Insulated Sliding Glass Door?

Modern sliding glass doors are almost always designed to be energy efficient, especially where the glass is concerned. Most sliding glass doors contain low-e glass, which is made from two panes of glass with an inert gas in the middle. Low-e glass can reduce UV radiation and heat gain through the glass as much as 95%, compared to regular single pane glass.

If your sliding glass door is cloudy, noisy, and seen its better days, often a replacement sliding door is the best solution. Replacement sliding glass doors are often preinsulated with low-e glass, energy efficient seals, and a sturdier frame than the original.


Evan has decades of experience as a project manager for large-scale commercial renovation home-building projects throughout the US. Currently, Evan runs a successful construction management company in Virginia.

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