Dummy sash uPVC windows are fixed uPVC windows designed to look like traditional sliding sash windows, without any opening function. They are widely used in UK homes where ventilation is provided elsewhere, or where opening sashes are unnecessary, impractical, or restricted.
This guide explains what dummy sash uPVC windows are, how they differ from opening sash windows, whether they are cheaper, and when they are the right choice.
Quick Answer
Dummy sash uPVC windows are non-opening uPVC sash windows that replicate the appearance of traditional sliding sash windows. They are commonly used in UK properties where ventilation is not required and offer lower cost, improved airtightness, and high security.
What Are Dummy Sash uPVC Windows?
A dummy sash uPVC window is a fixed window where the sash or sashes do not move, but the proportions, glazing bars, and detailing match a working sash window.
Typically:
- Both the top and bottom sashes are fixed
- Or one sash is visually separated but permanently secured
From inside and outside the property, dummy sash uPVC windows are almost indistinguishable from opening sash windows.
What Is a Dummy Sash on a Window?
A dummy sash is a fixed sash that looks like a traditional sliding sash window but does not open. In uPVC sash windows, dummy sashes are permanently fixed in place to provide the sash appearance without ventilation or movement.
Why Choose Dummy Sash uPVC Windows?
Dummy sash uPVC windows are chosen for practical, cost, and performance reasons.
Lower Cost
Because there are no balances, springs, or locking mechanisms, dummy sash uPVC windows are simpler to manufacture and install.
Improved Energy Efficiency
Fixed windows generally provide:
- Better airtightness
- Reduced draughts
- Improved thermal performance compared to opening sashes
High Security
With no opening parts, dummy sash uPVC windows:
- Cannot be forced open
- Do not rely on locks for security
- Are ideal for ground floors and side elevations
Planning and Design Flexibility
They are often used where a sash appearance is required but opening windows are restricted, for example in stairwells or on façades where symmetry matters.
Are Mock Sash Windows Cheaper?
Yes, mock sash windows are usually cheaper than opening sash windows. They do not require balances, springs, locks, or moving components, which reduces manufacturing complexity and installation time while maintaining the same visual style.
Need Help Choosing Between Dummy and Opening Sash Windows?
The right mix affects ventilation, energy efficiency, and your total project cost.
We help you design layouts that meet UK Building Regulations while maintaining that flawless, traditional appearance your home deserves.
Dummy Sash uPVC Windows vs Opening uPVC Sash Windows
| Feature | Dummy Sash | Opening Sash |
|---|---|---|
| Opens | ✘ No | ✔ Yes |
| Ventilation | None | Natural |
| Airtightness | Excellent | Good |
| Cost | Lower | Higher |
| Maintenance | Minimal | Moderate |
| Appearance | Traditional Sash | Traditional Sash |
Do Dummy Sash uPVC Windows Meet UK Building Regulations?
Yes, dummy sash uPVC windows comply with UK Building Regulations as long as they are not relied upon for:
- Emergency escape under Part B
- Mandatory background ventilation under Part F
They are typically installed alongside opening windows elsewhere in the property.
Are Dummy Sash uPVC Windows Double Glazed?
Yes. Dummy sash uPVC windows can be supplied with:
- Standard double glazing
- Acoustic laminated glass
- Slimline heritage-style units
Because the window does not open, heavier sealed units can often be used without issue.
How Do You Child Proof Sash Windows?
Sash windows can be child-proofed by fitting sash restrictors, key-lockable sash stops, or child safety locks.
Alternatively, dummy sash uPVC windows are naturally child-safe, as they do not open at all and remove the risk of falls from open windows.
What Are Mock Sash Windows?
Mock sash windows are non-opening windows designed to look like traditional sash windows. They are also known as dummy sash windows and are commonly manufactured in uPVC for UK homes where the sash appearance is required without opening functionality.
Where Are Dummy Sash uPVC Windows Commonly Used?
They are frequently installed in:
- Stairwells and landings
- Hallways
- Bathrooms with extractor fans
- Side and rear elevations
- Period-style new builds
- Upper floors where ventilation is not required
Can You Mix Dummy and Opening uPVC Sash Windows?
Yes, this is very common in UK homes.
A typical layout includes:
- One opening uPVC sash window for ventilation
- One or more dummy sash uPVC windows to maintain symmetry and reduce cost
Visually, the windows appear identical.
Advantages and Disadvantages
Advantages
- Lower cost than opening sash windows
- Excellent thermal performance
- High security
- Minimal maintenance
- Traditional sash appearance
Disadvantages
- No ventilation through the window
- Cannot be used as a fire escape
- Must be paired with other ventilation methods
Summary
Dummy sash uPVC windows provide the classic sash window look without the complexity, cost, or maintenance of opening sashes. They are widely used across the UK where ventilation is handled elsewhere or where fixed windows make more practical sense.
When combined with opening sash windows in the same property, dummy sash uPVC windows offer a well-balanced solution for appearance, performance, and budget control.
Need Help Choosing Between Dummy and Opening Sash Windows?
The right mix affects ventilation, energy efficiency, and your total project cost.
We help you design layouts that meet UK Building Regulations while maintaining that flawless, traditional appearance your home deserves.
