Insulation works best when it is a continuous blanket, wrapping a building against the elements. If the weather is either too cold, or perhaps too hot, sometimes neither is comfortable.

There are weak spots in every house, and doors are areas that are especially vulnerable to heat transfer. On new builds this area is likely to be taken care of, but in a renovation project it could easily be overlooked.

The good news is that insulating these areas is a simple and straightforward project. Insulating a door frame can be completed quickly and cheaply, with regular DIY skills and tools.

Here’s our guide to a successful door frame insulation job.

Why Is the Lack of Insulation Around the Door Frame a Problem?

Your front or back door frame is usually fitted into a structural opening that would normally be built at least a half inch wider and higher than the frame; to ensure the carpenter has enough room to adjust the door-set to fit.

The carpenter uses the space all round to pack and shim the frame so that it sits plumb in the structural opening. In older properties the gaps between the shims might be covered with drywall, backed up with a twist of newspaper, before being covered with door trim.

This is the weak spot in a building’s thermal envelope that you can close up in an afternoon with a few tools and some spray foam.

Tools Required

You will need the following: a craft knife, a small pry bar, hammer, wide putty knife, pliers, eye protection and gloves. You will also need a safe set of low-rise steps, perhaps from the kitchen. Never use a chair or other item not designed as a working platform.

Working in a doorway can be inconvenient for people who need to come and go, so make sure everyone in the house either has alternative access or will be out for the duration of the work. It will save you time and stress.

Ensure the floor finish is protected with a drop cloth, or newspaper, anything to keep cleaning up to a minimum.

Insulating a Door Frame Step by Step

Whether the door trim is painted, or varnished, carefully score the joint between it and the frame. Keep your hands behind the direction of the blade at all times, and don’t rush. If the blade comes up against resistance it is likely that you are using too much pressure or you have a dull blade.

Remember, you might want to re-use the trim in the same place, and gentle scoring on both the frame side and the wall side, will ease the removal of the trim and prevent damage to finished surfaces.

Next, place the wide putty knife flat against the wall to protect the internal plaster finish from the pry bar.

Slide the blade of the pry bar between the putty knife and the back of the trim. Again, be gentle and the trim will reward you for your patience and should spring off without too much trouble. 

Remove both side and head trims.

Next, with the flat edge of the pry bar and the hammer, knock out any plaster and paper build-up adjacent to the frame. The chances are that after several years of use that the plaster will be loose from the vibrations caused by the door opening and closing.

In fact, the plaster is likely to be most resilient where it has come into contact with the original packers and shims slotted in by the carpenter who fitted the door back in the day. Take additional care here in order to not loosen or split the shims and packers.

Once you have cleared away all the plaster a gap will be revealed that runs right around the door frame. It might even be possible for you to see daylight where the external siding and trim has come or worn away over time.

There might be spiders. Deal with that however you see fit, but for thoroughness it is a good idea to vacuum out the space between the structural members and the frame, then clear up the plaster, paper, and other debris before moving onto the next stage.

There are a number of spray foam products developed specifically for door and window installation, and these will be used in new construction work in exactly this situation every day. For a standard door expect to use up to two cans of low-rise foam.

Starting at the bottom of the door frame slowly fill the space with foam between the shims and packers. Foam expands to approximately two to five times the bead that comes out of the can so do your best not to overfill the cavity. Check the manufacturer’s advice on the can.

Once the foam has cured gently push the expanded foam back into the gap with the putty knife. Cut off any that has over-expanded, then replace the door trim.

Check the exterior for areas where the foam might have leaked out through any minor gaps between the siding and exterior door trim. Cut off the excess and clean off. Any visible spray foam should be removed with acetone to avoid UV light damage.

While you are working on the front door it is also an opportunity to also check the door seal within the frame. Timber is a natural material and shrinks and expands with the weather. In wetter weather any gaps usually close up, cutting off drafts, but likely not all of them.

Use a foam tape on a roll between the face of the door and the stop. Stick the foam roll to the doorstop. When the door closes onto it, it will make a seal, adding to the continuous insulation effect that you have recently augmented between the structural opening and the door frame.

What Spray Foam Can I Use for Door Frame Insulation?

Great Stuff, Window and Door Insulating Spray Foam Sealant can be bought at Walmart for $17.50 for a 12 ounce can, which is probably enough to get you three quarters of the way around an average size front door, so it’s sensible to get more than one can, or upgrade to a 20 ounce.

It is a low-rise foam insulator that will cure in about fifteen minutes but will remain flexible enough to deal with the vibration and movement associated with a regularly used front or rear door access.

Loctite Foam, Window and Door foam sealant boasts a heavier density than its rivals, which it claims gives a better insulating performance than other foams on the market. However, it pays to shop around for this brand as prices for a 12 ounce can vary wildly from $11.99 to $35.00.

General Electric foam sealant is the least expensive window and door foam sealant, often on sale at just $3.88 but be mindful to follow the instructions on the can to the letter whichever spray foam insulation product you choose.

Tips for Using Window and Door Spray Foam

Keep a water mister handy. Perhaps you have one for your plants? Use it to speed up the curing process of the spray foam.

Use masking tape to protect the door frame before installing the foam. Spray foam is very sticky and is stubborn to remove from finished surfaces.

But don’t worry if you have made a mess as acetone cleans off spray foam from most surfaces.

It is worth getting a pair of single use plastic gloves. Either remove your work gloves or pull them on over the top. As mentioned earlier, spray foam is very sticky and will be difficult to remove from either your hands or regular work gloves.

Likewise, wear old work clothes that can take any mess.

When the instructions tell you to ‘shake the can well before use’ it means it. The gasses inside the can have to be excited if you want them to work properly and distribute the foam correctly. Shake the can vigorously for at least five minutes, perhaps longer on cold days. That way the contents will go further.

Some spray foam manufacturers have developed their product so that shaking a can is unnecessary, and the product can be used, then left for a time before being used again without clogging the applicator. Check the manufacturer’s instructions before you buy, as it could save you both time and money.


Justin's been in construction for over 20 years in both new build and renovation. With experience in both commercial and residential construction, he specializes in healthier and more energy-efficient homes.

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