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9 min read

Window Caulking: A Guaranteed Seal


9 min read

Window Caulking: A Guaranteed Seal

InsulationWindow Caulking: A Guaranteed Seal

When contemplating about insulating a house or condo, window insulation is rarely at the forefront of our minds. However, every year, in Quebec, energy costs related to poorly insulated window joints are valued at $417 out of the $1,460 spent. 

That’s 30% of your energy budget that’s just gone out the window. However, all of that can change with properly insulated window joints. The above-mentioned financial losses are far from being the only ramification of poorly insulated windows

What Are the Ramifications of a Poorly Insulated Window?

Water condensation requiring an insulated window joint

Source: Canva

There are plenty, and Zein Chehadeh of MAG-MTL Projects Inc. best filled us in on some of these when he sat down with us and stated that “a poorly insulated window will have a lot of ramifications, including poor [thermal, Ed.] insulation and poor soundproofing.”

And it doesn’t end here. According to him, there are at least 5 ramifications: air leaks, weak thermal insulation, poor soundproofing, condensation buildup, and mould growth.

Air Leaks

When it comes to window thermal insulation, there are two elements that should be factored into the pressure drop between the inside and outside of our home:

  • Temperature difference;

  • Wind force.

Temperature Difference & Air Density

The temperature, to which humidity levels are combined, directly influences air density:

Temperature (measured in °C & °F)

Air mass at 100% humidity

Air mass at 1% humidity



















This difference in density between the indoor and outdoor air masses results in what is referred to as the "stack effect." The heavier air mass will move towards the lighter air mass, much like the way water flows from one container to another. 

As a result, if your house is kept at a toasty 20°C (68°F) during the winter, when it’s -10°C (14°F) outside, the cold outside air, which is heavier, will seep into your dwelling.

On the other hand, during the summer, the refreshing 20°C (68°F) temperature inside your house will flow outside if the temperature is higher, like 30°C (86°F) for example. It’s all about communicating vessels.

As such, for a 10-metre high house, and an inside-and-outside temperature difference of 10°C (14°F), the stack effect will be 4 Pa (pascal). This usually happens during summertime.

For the same reason, a temperature difference of 30°C (86°F) between the inside and the outside will result in a 13 Pa stack effect. This unit will increase based on the height of the building since warm air is lighting than cold air. 

Wind Force

The above-mentioned values failed to take into account the wind force, which can profoundly change the pressure value. Thus, for a wind speed of 18 km/h (11 mph), the pressure exerted on the building's façade exposed to wind is 15 Pa, while the unexposed areas are subjected to a low pressure of 5 to 10 Pa.

In other words, if your windows are poorly insulated, your house will rapidly become the centre focus of drafts. 

Poor Thermal Insulation

As you’ve gathered from our brief overview of air masses: During the winter, you’re warming up the exterior atmosphere, and during the summer, you’re cooling it. Might as well point out that you’re literally throwing cash out the window. 

The environmental and financial impacts are so important that our neighbours across the pond (France), have, for example, set up a so-called CEE (White Certificates), which have led to more than 3 million window replacements since 2011, including those of their Senate. 

This shows how pressing the topic of thermal insulation is nowadays, when energy consumption is the focal point of all concerns. 

Little Soundproofing

As Chehadeh mentioned, windows with faulty or no insulation joints have very weak soundproofing abilities. 

A substandard window will only reduce exterior sounds seeping into your house by 26 to 28 decibels. On a decibel scale, 30 dB is comparable to a quiet bedroom. With such windows, outside sounds are almost as loud as if they were in your house. 

A high-end, double-pane window with joint insulation reduces noise levels to 40 decibels, which amounts to the average noise a moviegoer might emit. 

More Condensation

This is another serious problem that results from poorly insulated windows. In Quebec, condensation is especially prevalent in homes with poorly insulated windows since it usually occurs during the winter.

And that’s why the Canadian government encourages its citizens to invest in Energy Star-certified windows, meaning windows that have the following:

  • Triple panes;

  • Fitted with an anti-condensation coating;

  • Inert gas between the glass panes;

  • Quality spacers;

  • Insulated frames and sashes;

  • Extensively waterproof.

The whole lot is designed to better fight against a serious problem that we’ve already broached in a previous article: mould.

Mould Growth

Chehadeh draws the perfect parallel between condensation and mould: 

“Substandard window insulation will result in more condensation, which will, in turn, facilitate mould growth.”

In fact, mould growth in homes can cause health problems such as asthma, or much more serious illnesses in cases involving individuals with an immune deficiency. Among other things, mycetoma is, in immunocompromised individuals, a disease caused by the presence of mould spores in the lungs.

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How to Calculate Window Insulation Value

window insulation joint methods

Source: Canva

Before going over the various features offered with window insulation joints, let’s clarify the constraints these face, and how they’re measured.

To understand window insulation levels, you first need to consider two things: the window joints and the window itself.

Joint Thermal Efficiency

Windows are naturally subject to air pressure, which will vary between 50 and 600 Pa, and amount to a 5 to 60 kg/m² pressure, or 11 Lb to 132 Lb/sq. ft. So, what’s the reason behind such a variation? Well, because it correlates to 32 to 111 km/h winds, which equals 20 to 69 mph. 

Like a structure’s façade, windows are exposed to severe constraints, which directly affect the joints. Therefore, the thermal permeability is measured in m³/(h x m x Pa2/3). This ratio shows the cubic metres of air that penetrate a joint per hour and per joint metre, according to a pressure difference of 1 Pa. It's then used to determine the heat loss value, measured in W/m²K.

If you’re unfamiliar with K-value, continue on to the section down below.

Window K-Value

It’s a window's thermal conductivity value, measured in W/(m²K). A window, made up of a sash, a glass pane, as well as a screen, has a good thermal conductivity value when it’s measured somewhere between 1.1 and 0.6 W/m²K. 

This value can take into account up to 12 different factors, which ultimately correspond to the window’s overall thermal conductivity value (glass pane, frame, screen, etc.) divided by their total surface area. 

As such, not all materials are the same, as depicted in the chart below:


Thermal conductivity [W/mk]

Standard K-value [W/m²K] for a window sash

Standard K-value [W/m²K] for a window



2.1 -3.1

1.5 - 2.8



5.0 - 6.6 (thermally insulated)

1.9 - 3.3

PVC plastic


2.3 - 3.9

1.7 - 2.9

Various Sealants & Their Features

Installation a sealing window joint

Source: Canva

There are at least 5 different types of window insulation materials, and each has its pros and cons. As such, we've outlined their characteristics to help you choose between silicone, polyurethane, acrylic, MS polymer, latex, and hybrid sealants.

Caulking Silicone

Silicone is a white sealant made of silicon and methyl chloride. It’s:

  • Stretchy;

  • Resistant to adverse weather;

  • Easy to apply;

  • Adhesive;

  • Cheap.

It’s available under three formulas: neutral, ascetic, and aqueous.

Ascetic formulations have a vinegar-like odour while curing. Like neutral formulations, they're ideal for glass surfaces. The aqueous formulation will work fine when applied to a damp or wet surface.

Silicone sealants have a shelf life of over 20 years and are virtually unaffected by temperature variations, which is ideal for sealing windows in Canada, where the temperature fluctuation varies greatly from one season to the next.

Silicone sealants also have downsides:

  • Have to be applied in dry temperatures above 0°C (32°F);

  • Rendered useless when submerged or in stagnant water;

  • Can’t be painted;

  • Can stain stone and mirrors;

  • Will yellow when lacking UV exposure.

Hence, never use silicone sealant on a stone surface. The oily nature of the sealant can seep into the stone and discolour it. However, you can use sealants that were specially designed for this type of material.

Polyurethane Sealants

Polyurethane sealants are found in three formats: putty, foam, and tape.

They have plenty of advantages over silicone. The following are listed below:

  • Water and submersion proof;

  • Flexible;

  • Can be applied to plastic, glass, stainless steel, soil, etc.;

  • UV ray resistant;

  • 20-year shelf life.

They also have downsides, most notably:

  • Temperature fluctuation sensitivity (hardens during winter, softens during summer);

  • Can harden and crack over time;

  • Toxic isocyanate-based.

Acrylic Sealant

It's a mix of acrylic resins designed to fill in expansion joints or cracks. These sealants have a lot of advantages: they can be painted, are odourless while curing, and are easy to smooth out when first applied.

However, compared to silicone, acrylic sealants have a lot more downsides:

  • Less flexible;

  • Not as adhesive;

  • Not as waterproof;

  • Also has to be applied during dry temperatures above 0°C (32°F);

  • Have to be painted if applied outside.

MS Polymer Sealants

Consists of polymer and silane compounds that are also intended to render joints waterproof, benefiting from the fact that they're: 

  • Supple;

  • Stretchy;

  • Compatible with water-based paints;

  • Devoid of isocyanates;

  • Can be applied to damp surfaces and all types of materials.

However, MS polymer sealants also have downsides. As such, this material doesn’t age well when exposed to UV rays and doesn’t usually adhere well to solvent-based paints. 

Latex Sealants

Latex-sealed window joints are made using a water-based compound, and it has a lot of advantages. This type of product is cheap, can be painted, and is ideal for an aesthetic finish. 

However, it isn't made for outdoor use. 

Hybrid Sealants

Hybrid sealants are compounds that combine both polyurethane and silicone. As such, it’s designed to blend the advantages of both types of caulking. However, it's still very new in the construction industry. Therefore, there’s yet to be any feedback regarding this type of sealant.

Waterproofing Membranes

If sealants have yet to convince you that they're effective window joint insulation materials, you can also turn to another solution: window membranes. 

Such material is an elastomeric covering that’s installed around the perimeter of the window, which acts as a thermal insulator. The membrane also acts as a water leak prevention tool. For this reason, it's always paired with the installation of flashing with a drip edge.

Price Range for Window Insulation Materials

Applying a window sealing joint

Source: Canva

Cost of Silicone Sealant

For a 2.7 oz (roughly 81 ml) tube of silicone sealant, expect to pay $20. Some retailers carry multi-pack kits, which can be purchased for as little as $12 apiece. 

Which amounts to $4.44/oz.

Cost of Polyurethane Sealant

As for polyurethane sealant tubes, these go for about $35 for 10.01 oz (about 300ml). They’re cheaper than silicone sealants. 

Which amounts to $3.46/oz. 

Cost of Acrylic Sealants

The cost of acrylic sealants varies between that of silicone and polyurethane sealants; for a 14.5 oz (about 435ml) tube, the price is around $55. 

Which amounts to $3.79/oz.

Cost of MS Polymer Sealant 

This is the most expensive window sealant product mentioned. For two 19.3 oz (580 ml) tubes, expect to pay a little under 120 dollars.

Which amounts to $6.22/oz.

Cost of Latex Sealant

Latex sealant is, by far, the cheapest option. 10 oz tubes (about 300 ml) go for less than $5 apiece.

Which amounts to $0.50/oz.

Cost of a Hydrid Covering

You can purchase hybrid coverings for less than a silicone or polyurethane sealant. In fact, you can buy 10.1 oz (304 ml) tubes for roughly $8. 

Which amounts to $1.26/oz.

Cost of a Window Waterproofing Membrane

Sold in roll form, you can find a 12-inch wide by 75 feet-long roll for less than $85. 

Cover photo source: Ozgu Ozden - Unsplash

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Last modified 2023-11-07

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