Where Not To Caulk Around Windows: Dos & Don’ts Explained


Windows are the weakest part of a house in terms of insulation. That’s because they do not only welcome light and sunshine; they also have potential to let outside temperature in, not to mention moisture from precipitation.

Window makers glue the various parts of window frames together for structural strength. That’s how new windows are also usually temperature and moisture resistant. However, this insulation eventually weakens, meaning it is time to caulk the windows again!

Replacing the caulking on an old window keeps the outside temperature where it belongs, saves on energy bills, and helps control internal humidity too. However, you should only put the sealant where it belongs. The best way to do this is to remember:

  • DO NOT block the weep holes on the inside and outside of the window frame.
  • DO NOT seal around the trimming out frame on the exterior of the building.
  • DO NOT apply caulk to any moving parts. Rather replace the rubber seals.

Caulking Around Windows: The Basics

View of an exterior window. Image: Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy

When we examine the above image carefully we can see the component parts the factory glued together, and hopefully weather-sealed within an outside frame:

  • The window frame comprising of the head, the side casing, and the bottom sill, in this case surrounding a double casement module.
  • Standardization means the owner could swap those moving parts out for another configuration, for example side-opening casements, or fixed panes.

What Is Caulk And How Do You Use It

The word ‘caulk’ means to seal a gap in something, alternatively the sealer you are going to use. In olden times, seafarers used bitumen to close the gaps between planks on sailing ship hulls, in case you wondered where the word comes from.

However, the purpose of caulk in terms of modern windows is to prevent heat loss from the inside, and cold entering from the outside of the house. It stops temperature transfer in its tracks if you do this correctly, and choose the right sealant:

  • Caulk to seal the joint between the frame and the building wall outside.
  • Sealant to caulk the joint to the inside wall, and where components join.
  • Special caulk for humid spaces inside, and exterior masonry walls.

It’s important to choose the right caulking material for every job. For example, exterior sealant must be water-resistant, and caulking inside a shower room must be mould resistant.

Before You Caulk, Prepare Your Workplace

You could apply fresh caulk to a window in all the right places, and have it come off again in a few months. Therefore, you first need to understand this angle before you do the job right. Make sure you remove any old caulking before you start.

Where Not To Caulk A Window And Why It Matters

We recommend you use a caulking gun that’s clean and in good condition. This will help you apply a thin bead of material accurately, and avoid getting it in any of three places where caulk could do more damage than good. These spots are:

  • Window drainage weep holes
  • Trimmed out window frames
  • Any one of the moving parts

Keep Clear Of Window Drainage Weep Holes

A certain amount of condensation inevitably collects on the inside of windows during winter time. That’s because of the temperature difference in the air inside and outside the house. You can wipe it away all day long but it will still be there in the morning.

Window frame manufacturers leave small holes or slits at the bottom of frames on the sills where this moisture gathers. Identify these before you start your caulking job. They are the number one place not to caulk in any home.

If they are covered over, or blocked with mold or grime, we recommend you clear them right away. However if there are none, then you’ll find the maker saved a few pennies by sloping the sill to redirect the water elsewhere.

Weep holes generally drain away on the outside of a window at the bottom of the frame. Make sure they are not blocked there either. It follows that this is the number two place you keep your silicone gun away from.

Don’t Seal Around Trimmed Out Windows

View of an exterior window. Image: Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy

Returning to the first image you’ll notice the builder trimmed out the window on the exterior of the building to create a picture frame effect. This is a popular device to make windows appear more generous when viewed from a distance.

Insider Tip: Don’t ever try to caulk around window frames for the following reasons:

  • The installer will have caulked the window to the wall before they added the siding. The shadow will have protected the sealant from degrading.
  • The weep holes we mentioned earlier will drain out behind the lower frame and the last thing you want to do is obstruct that.
  • Moreover, it is almost impossible to cut a clean caulking line under these circumstances. You could spoil the overall appearance while achieving nothing!

Keep Your Caulk Away From The Moving Parts

Moving parts, including casements, side casements, and top casements come complete with neoprene rubber seals. If your windows are leaking air or moisture past these, replace the seals. Never stop the windows opening. Fresh air is a necessity not a luxury.

So, Where Should The Caulking Go?

This diagram shows how to rehabilitate an old window that is leaking. Image: Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy

The caulking should go around the window frame where it abuts against the inside wall. It can also go on the inside corners where the glazing fits inside the frame. In the latter instance you could also repeat the exercise outside. That’s about all you need to know about caulking windows correctly.

Rehabilitating an Old Window That’s Leaking

(Office of Energy Efficiency and Renewable Energy)

Conclusion: Your Takeaway To Remember

Do not block the weep holes, add seal around the trimming out frame, or obstruct the moving parts with caulk sealant. 

Only apply it around the frame inside the house, and places where air is leaking past joints. 

This should help reduce your energy bills, keep you and your family cooler in summer and warmer in winter too!

Richard Farrell

Richard spent two decades planning interiors of new office complexes. Being a practical person, he discussed his ideas with artisans touching on every construction trade. Then he put his tools aside to share his knowledge on the internet with others.

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