What are casement windows? How do they compare with sash windows?

what are casement windows? how do they compare with sash windows?

Casement windows are a type of window that is hinged on one side and opens outward, typically with a crank or lever mechanism. 

They are often used in homes and buildings to provide ventilation and natural light while offering a clear view of the outside. Casement windows can be made from various materials, including wood, metal, and uPVC (unplasticized polyvinyl chloride).

Historical Background of Casement Windows

The use of casement windows dates back to medieval times, but they became particularly popular during the Renaissance period and onwards. 

During the medieval era in Britain, windows were smaller and often made of small panes of glass held together by lead or iron bars. Casement windows began to gain popularity during the Tudor period (1485-1603) in Britain. 

During this time, windows started to feature larger glass panes held in wooden frames hinged on one side. These windows were usually divided into smaller sections with mullions and transoms, giving rise to the distinctive “diamond” or “leadlight” pattern.

With advancements in window technology and materials, casement windows have continued to evolve. While sash windows became more prevalent in larger urban buildings, casement windows remained popular in rural and suburban settings due to their practicality, ease of use, and versatility.

The working mechanism of Casement Windows

Casement windows open using a hinged mechanism that allows the window sash (the framed portion that holds the glass) to swing outward or inward like a door. The mechanism used to open and close casement windows can vary, but the most common mechanism involves the use of a crank or lever.

Here’s how the typical mechanism works

Crank or Lever Handle: Casement windows are equipped with a crank or lever handle usually located at the bottom of the window frame. This handle is used to control the opening and closing of the window.

Hinges: Casement windows are hinged on one side, either on the left or the right. The hinges are usually positioned vertically along the window frame. When the handle is turned, it activates the hinges and allows the window sash to pivot outward.

Crank Operation: When you turn the crank handle in one direction (often clockwise), it causes the window sash to swing open. Turning the handle in the opposite direction (counterclockwise) will close the window by pulling the sash back into its closed position.

Stay or Latch: Casement windows often have a stay or latch mechanism to hold the window in an open position. This prevents the window from swinging shut due to wind or other external forces. The stay or latch can be released when you want to close the window.

Seal and Lock: When the casement window is closed, a sealing mechanism around the frame helps create a tight seal to prevent drafts and moisture from entering. Some casement windows also come with locking mechanisms to enhance security.

How do casement windows open?

Casement windows open by swinging outward or inward on a hinge, similar to how a door opens.

Casement windows will have a handle, crank, or lever usually positioned at the bottom of the window frame. This handle is used to operate the window and initiate the opening process.

To open the window, turn the handle or crank in the appropriate direction. This action engages the window’s hinge mechanism.

As you turn the handle, the hinged side of the window sash will start to pivot. 

If the window swings outward, the hinged side will move away from the frame and open into the outdoor space. If the window swings inward, the hinged side will move toward the interior of the room.

To close the window, simply turn the handle in the opposite direction until the window sash is back in its closed position against the frame.

Sash Windows

Sash windows

Sash windows are a type of window that consists of one or more movable panels or “sashes” that slide vertically or horizontally within a frame. 

They are a classic and traditional window design that has been used in architecture for centuries. Sash windows are known for their elegant and timeless appearance, as well as their practicality and functionality.

There are two main types of sash windows:

Vertical Sash Windows (Single-Hung and Double-Hung): In vertical sash windows, the sashes slide up and down within the frame. There are two common variations of vertical sash windows:

  • Single-Hung: In a single-hung window, only the bottom sash is movable, while the top sash remains fixed.
  • Double-Hung: In a double-hung window, both the top and bottom sashes are movable. This allows for greater control over ventilation, as you can open either the top or bottom sash, or both.

Horizontal Sash Windows (Slider Windows): In horizontal sash windows, the sashes slide horizontally within the frame. These windows are also known as slider windows. They can have one or more movable sashes that slide side to side.

Casement windows compared to sash windows


Casement windows and sash windows offer different types of ventilation, each with its own advantages and considerations. 

Here’s a comparison of the ventilation characteristics of these two window types:

Casement windows and sash windows offer different approaches to ventilation. Casement windows provide effective and versatile ventilation by fully opening outward, allowing unrestricted airflow. 

They can catch breezes from various angles, making them suitable for cross-ventilation. 

On the other hand, sash windows, particularly double-hung ones, allow controlled ventilation through sliding sashes. 

While they may not fully open like casement windows, their dual sashes enable adjustable top and bottom openings for regulating airflow.

Both window types contribute to ventilation, with casement windows favoring maximum air circulation and sash windows providing adjustable and balanced airflow options.


Casement windows and sash windows differ in the way they allow light into a space. Casement windows, with their unobstructed single pane of glass, offer a wide and clear view that maximizes natural light intake. 

When fully opened, casement windows expose the entire window area to sunlight, enhancing brightness. 

Sash windows, while also permitting ample light, may be divided by muntins into smaller panes, potentially dispersing light differently. 

The vertical alignment of sashes in double-hung windows can create a segmented view, affecting the overall amount of light. 

Nonetheless, both window types facilitate illumination, with casement windows emphasizing expansive views and unblocked light, while sash windows offer a more structured and potentially ornate aesthetic.

Energy efficiency

Casement windows and sash windows exhibit distinct characteristics in terms of energy efficiency. 

Casement windows tend to offer better sealing when closed due to their design, resulting in reduced air leakage and potential energy savings. 

The sash’s tight seal against the frame minimizes drafts and heat loss. However, when fully open, casement windows may disrupt airflow more significantly than sash windows, which can limit ventilation while maintaining energy efficiency.

Sash windows, particularly double-hung ones, can have more potential points of air infiltration due to their sliding operation. 

Proper maintenance and weatherstripping are crucial for maintaining their energy efficiency. The division of sash windows into multiple panes may contribute to some heat loss and air leakage, especially if the seals between panes degrade.

Both window types can be enhanced with modern materials and glazing options to improve energy efficiency, but casement windows generally offer a slightly better sealing when closed, potentially contributing to higher energy efficiency compared to sash windows, especially when taking into account the ease of maintaining a secure seal.

How to  calculate energy efficiency of casement windows?

Calculating the energy efficiency of casement windows involves considering various factors that contribute to their overall thermal performance, including heat flow and energy-efficiency.

Here’s a basic guide on how to assess the energy efficiency of casement windows:

U-Factor and R-Value

The U-factor measures the rate of heat transfer through a window, with lower values indicating better insulation. It basically measures heat transfer (whether lost or obtained) through the window glass.

The R-value is the inverse of the U-factor and represents the window’s resistance to heat flow. Look for casement windows with lower U-factors and higher R-values, as these indicate better energy efficiency.

The R-value is the reciprocal of the U-factor and represents the thermal resistance of a material or assembly. A higher R-value indicates better insulation. It is commonly expressed in units of ft²·°F·hr/BTU or m²·K/W.

The formula to calculate the R-value (thermal resistance) of a window’s energy efficiency is straightforward and involves using the reciprocal of the U-factor (rate of heat transfer):

R-value = 1 / U-factor

In this formula:

  • R-value is the thermal resistance of the window assembly, expressed in units of ft²·°F·hr/BTU or m²·K/W.
  • U-factor is the rate of heat transfer through the window assembly, expressed in units of BTU/(hr·ft²·°F) or W/(m²·K).

To calculate the R-value, simply divide 1 by the U-factor of the window. Keep in mind the R-value of a window assembly is not always prominently provided, as the U-factor is a more common measure for windows.

Glazing Options

Choose windows with energy-efficient glazing, such as double or triple glazing, low-emissivity (low-e) coatings, and gas fills (like argon or krypton) between the glass panes. These features enhance insulation and reduce heat transfer.

Sealing and Weatherstripping

Well-sealed casement windows minimize air leakage, which can significantly impact energy efficiency. Check for effective weatherstripping and proper installation to ensure a tight seal.

Solar Heat Gain Coefficient (SHGC) 

The SHGC measures the amount of solar radiation that enters a window and contributes to heat gain. Consider windows with lower SHGC values for better energy efficiency, especially in hot climates.

Energy Labels and Ratings

Look for energy performance labels or ratings, such as Energy Star® certification, which indicate that the window meets specific energy efficiency criteria.

Where are casement and sash windows mostly installed?

Casement and sash windows are installed in a variety of architectural settings based on their design, functionality, and aesthetic appeal.

Casement Windows

  • Casement windows are often installed in locations where unobstructed views, effective ventilation, and ease of operation are priorities.
  • They are commonly seen in residential settings, including bedrooms, living rooms, and kitchens, where they can be opened to catch breezes and provide ample natural light.
  • Casement windows are also used in modern and contemporary architectural designs due to their sleek, minimalist appearance and compatibility with clean lines.
  • In regions with milder climates, casement windows can be a popular choice because of their ability to catch prevailing winds and allow for cross-ventilation.

Sash Windows:

  • Sash windows have a traditional and timeless aesthetic, making them a common choice for historical and period-style homes, such as Georgian, Victorian, and Colonial Revival architecture.
  • They are frequently installed in residential buildings where maintaining a classic or vintage look is desired.
  • Sash windows are often used in bedrooms, dining rooms, and formal living areas to preserve the historical character of the space.
  • In regions with colder climates, sash windows can be equipped with double-glazing and weatherstripping to improve energy efficiency and insulation.

Ultimately, the choice between casement and sash windows depends on architectural style, design preferences, functional requirements (ventilation, light, energy efficiency), and the overall ambiance that the homeowner or designer aims to achieve. Both window types have their unique strengths and are adaptable to a range of settings.

The cost difference between casement windows and sash windows

The cost of casement windows and sash windows can vary widely based on several factors, including the material, size, design, glazing options, and installation requirements. 

Additionally, local labor and material costs, as well as the specific manufacturer or supplier, can influence the final price. 

Casement windows cost

  • Casement windows are typically more affordable than some other window types due to their simpler design and operation.
  • Basic casement windows made from materials like vinyl or uPVC (unplasticized polyvinyl chloride) tend to be more budget-friendly.
  • Casement windows cost can range from $00 to $1500 or more per window, depending on factors like size, material, and additional features.

Sash Windows

  • Sash windows, especially those with traditional designs or made from high-quality materials, can be more expensive than casement windows.
  • Wood sash windows are often considered premium options and can have a higher cost due to the craftsmanship involved.
  • The cost of sash windows can range from $400 to $1,500 or more per window, depending on factors like material, size, and design intricacy.

Which window type is better: Casement windows or Sash windows?

Both window types have their own advantages and considerations, so it’s important to evaluate these factors based on your specific circumstances. Here’s a balanced overview to help you make an informed decision:

Casement Windows


  • Better ventilation: Casement windows can open fully outward, maximizing airflow and cross-ventilation.
  • Unobstructed views: They offer a clear and unobstructed view when fully open.
  • Energy efficiency: When closed and sealed properly, casement windows can provide excellent insulation and energy efficiency.
  • Modern aesthetics: Casement windows often align well with contemporary or modern architectural styles.


  • Wind resistance: Fully open casement windows can catch wind and act like sails, potentially stressing the hinges or hardware.
  • Limited window covering options: The outward swing may limit the types of window treatments that can be used.
  • Cleaning: Exterior cleaning may be more challenging due to the outward-opening design.

Sash Windows


  • Classic aesthetics: Sash windows have a timeless and traditional appearance that suits historic and period-style homes.
  • Controlled ventilation: Double-hung sash windows allow for adjustable top and bottom openings, offering controlled ventilation.
  • Versatile window treatments: Sash windows can accommodate a wider range of window treatments.
  • Historical accuracy: They maintain the authenticity and charm of older homes.


  • Limited full opening: Sash windows do not fully open like casement windows, which may affect airflow.
  • Potential air leakage: Sliding sashes can have more potential points of air infiltration, affecting energy efficiency if not properly maintained.
  • View obstruction: Divided muntins may affect the clarity of the view compared to large, uninterrupted glass panes.

Ultimately, the “better” choice between casement windows and sash windows depends on your specific priorities. If you value maximum ventilation, modern aesthetics, and unobstructed views, casement windows might be preferable. 

On the other hand, if you prioritize classic charm, historical accuracy, and controlled ventilation, sash windows may be more suitable. 

Considering your specific needs, consulting with a professional window installation company and weighing the pros and cons will help you make the best decision for your home or project.