Should window security bars and grilles be installed inside or outside?

Window security bars and grilles can be installed either inside or outside a property. There is no single position that is right for every window. The best location depends on the type of window, how it opens, the property layout, the available fixing points, access, security requirements, appearance and maintenance.

Where the property allows both options, at IKS Locksmiths we generally prefer installing window security bars or grilles internally. Internal grilles are protected from the weather, their fixings are less accessible from outside and they are usually easier to operate and maintain.

External installation may be the better option where window opening direction, limited internal space, access or the construction around the opening prevents an internal installation.

For this reason, the decision between window security bars inside or outside should be made after assessing the individual window rather than choosing a position in isolation.

A professional property survey can establish which arrangement provides the best combination of security, everyday use and appearance.

How professionals decide whether security bars should be installed inside or outside

When installing window security bars or security grilles, we assess the property before deciding where they should be positioned.

Every installation is different. Two neighbouring properties can require different solutions because of variations in their windows, walls or internal layout.

The main points we assess are:

• Property type: A modern house, period property, flat, shop or commercial building can present different installation conditions.
• Window style: Casement, sash, sliding and other window designs provide different amounts of space for a grille.
• Opening direction: The security grille must not prevent the window or door from operating correctly.
• Surrounding walls: There needs to be a suitable structure into which the bars or grille can be securely fixed.
• Internal space: Curtains, shutters, radiators, furniture or architectural features can affect where a grille can be positioned.
• External obstructions: Pipes, guttering, window sills and other features can restrict external fixing positions.
• Floor level and access: External installation on upper floors may require scaffolding.
• Intended use: Fixed bars and retractable grilles work differently, so the way the opening needs to be used is part of the assessment.
• Appearance: The grille needs to work with the style of the property, particularly when considering window security for period properties.
• Emergency escape: Where a window forms part of an escape route, the proposed security arrangement must not obstruct the required means of escape.
• Planning and property restrictions: Listed buildings, conservation considerations and leasehold restrictions may affect what can be fitted and where.

The aim is to find the safest practical fixing position while allowing the window and the security product to work as intended.

How window opening direction influences installation

One of the first questions we ask when visiting prospective clients is simple: which way does the window open?

Opening direction can immediately rule out some installation positions.

Outward-opening windows

For an outward-opening window, installing security grilles inside is often the most practical arrangement.

The window can continue to open outwards without being obstructed by the grille, while the security barrier remains on the internal side of the opening.

Where the surrounding structure provides suitable fixing points, this also gives many of the maintenance and security benefits associated with internal installation.

Inward-opening windows

If a window opens inwards, internal fixed bars positioned directly across its opening could stop it from opening properly.

In this situation, external window security bars or grilles may make more sense.

The exact arrangement still depends on the window design. A survey is needed to identify whether the grille can be positioned internally without restricting movement or whether an external fixing is preferable.

Sliding windows

Sliding windows do not swing inwards or outwards, so there can be more flexibility.

The position depends on the available fixing space, the direction in which the panels slide and whether access to handles or locks needs to be maintained.

Internal security grilles are often possible, but the complete opening needs to be assessed first.

French doors

French doors require enough room for both leaves to open and for handles and locks to remain accessible.

Depending on whether the doors open in or out, security may be provided by internal or external fixed bars or by a retractable grille that can be opened when access is required.

Patio doors

Patio doors frequently suit retractable security grilles because the grille can protect a wide glazed opening while still allowing access when it is unlocked and folded back.

Some of the IKS Locksmiths installation examples we have done include patio doors combining external burglar bars on adjacent windows with an internal retractable grille across the doors (as shown in the image above). The correct arrangement depends on the configuration of the complete opening rather than applying one solution to every glazed section.

When internal security bars are the better choice

Where the configuration allows it, internal security grilles for windows are often our preferred option.

There are several practical reasons.

The bars and fixings are less accessible from outside

With internal window security bars, an intruder first has the window itself between them and the security barrier.

The fixings are also less directly accessible than those used for an external grille.

External installations can still provide a high level of protection, but their bars and fixings need to be specified for their more exposed position.

Internal bars are protected from the weather

Rain, moisture, dirt and changing weather conditions all affect externally installed metalwork.

Internal security grilles are sheltered within the property, so they are generally easier to keep clean and in good condition.

This can reduce ongoing maintenance and helps preserve the finish of the grille.

They can be easier to operate

This is particularly relevant to retractable grilles.

An internal retractable grille can normally be opened and closed from inside the property without needing external access.

That is especially useful on upper floors or where reaching the outside of the window would be difficult.

Decorating and maintenance can be simpler

Internal bars can be more accessible if work is required around the window.

Depending on their fixing method, they may also be simpler to remove temporarily when decorating or carrying out maintenance.

Internal installation can cost less

The existing IKS installation guidance identifies several reasons why internal bars can cost less than an equivalent external installation.

For example, external bars may require heavier sections, weather protection such as galvanising and more specialist security fixings because the bars and fixings are directly accessible from outside.

For example some installations can use 12 mm square bars internally compared with 16 mm or 20 mm bars externally. Specifications vary according to the opening and required design, so the final bar size and fixing system should always be selected for the individual installation.

External installations on upper floors can also involve scaffolding, adding another cost that may not apply when the grille can be installed internally.

For a wider explanation of the factors affecting price, see our guide to how much security grilles cost.

When external security bars make more sense

Although internal installation is often preferable, external security grilles and bars are the right solution for some properties.

Inward-opening windows

As explained above, an internal fixed grille may obstruct a window that needs to swing into the room.

An external installation can allow the window to retain its normal movement.

Limited internal space

There may not be enough space around the inside of a window for suitable fixings.

Shutters, window furniture, architectural features or other obstructions can also make internal installation impractical.

Basement and lower-ground-floor windows

Basement windows can have unusual reveals, restricted internal access or external light wells.

Depending on their construction and opening style, an external grille may provide the best fixing position.

Structural limitations

A secure installation depends on the quality and position of the available fixing points.

If the internal construction does not provide a suitable fixing depth or there are obstructions around the opening, the external structure may offer the better solution.

Pipes, cables, guttering and other features also have to be taken into account.

Period and listed properties

With period properties, the position of security bars needs particularly careful consideration because original windows, decorative surrounds and other architectural features may need to be preserved.

For listed buildings, changes to the exterior or historic fabric may also be subject to restrictions or consent requirements.

The decision between internal and external installation should therefore be based on the individual building, its window design and any applicable restrictions rather than assuming one position is suitable for every period property.

Where internal access is difficult

Some windows are simply difficult to reach from inside because of their location or the internal layout.

In these cases, an external installation can be the more practical option.

When bars are installed externally, the specification needs to reflect the fact that both the bars and their fixings are more accessible. Depending on the installation, this can mean heavier bars, specialist security fixings or additional protection against the weather.

What about security grilles on upper-floor windows?

Floor level has a major influence on installation.

On upper floors, we generally prefer installing fixed or retractable grilles internally where the property allows it. This avoids the practical difficulties involved in installing and operating a grille from outside.

External installation at height is possible, but safe access may require suitable scaffolding.

A heavy security grille cannot simply be carried up a ladder as an alternative. Installation can require more than one person, accurate positioning and secure fixing into the surrounding structure.

External retractable grilles can also be impractical at height because the occupier needs safe access to open and close them. Exceptions may include openings such as patio doors with a Juliet balcony where suitable access is available.

Where external protection is required on an upper floor, fixed bars may therefore be more practical than a retractable system.

Internal vs external security bars: a practical comparison

The following table summarises the main differences between internal vs external window security bars. The individual property can alter the recommendation.

Factor	Internal security bars or grilles	External security bars or grilles
Security	Bars and fixings are less accessible from outside	Can provide high security but exposed fixings may require a stronger specification
Appearance	Can often be integrated with the interior and window design	More visible on the exterior of the property
Maintenance	Easier to access and protected from the weather	More exposed to rain, dirt and weathering
Cost	Often less expensive where straightforward internal fixing is possible	Can cost more due to specification, external fixings, weather protection and access requirements
Ease of use	Usually easier for retractable grilles that need regular opening and closing	Operation can be less convenient, particularly above ground level
Lifespan and finish	Protected indoor environment can help preserve the finish	Weather exposure needs to be taken into account when specifying and maintaining the grille
Installation complexity	Often simpler where suitable internal fixing points are available	May require specialist fixings, external access or scaffolding
Best suited to	Often outward-opening windows and properties with suitable internal space	Often inward-opening windows or openings where internal fixing is not practical

In simple terms, internal security bars are usually preferable when the window design and fixing points allow them. External bars become the better option when the opening direction, available space, building structure or access requirements make internal installation unsuitable.

Does the installation position depend on the type of security grille?

Yes. Whether a grille is fixed or retractable changes the way it needs to be positioned and used.

Retractable security grilles

Retractable security grilles need to be opened and closed, so convenient access is particularly important.

Internal installation is often preferable because the grille can be operated from inside the property.

External retractable grilles can be fitted where the window configuration requires them, but practical access must be considered. This becomes particularly important on upper floors.

Fixed security grilles

Fixed security grilles do not need to be opened during everyday use, giving greater flexibility over their position.

They can be installed internally or externally depending on the window, available fixing points and required appearance.

External fixed bars can be particularly useful where inward-opening windows prevent internal installation.

Invisible window security bars

Invisible window security bars are designed to provide physical protection with a less visually dominant appearance.

Internal installation can allow the bars to be colour matched and aligned with the existing window framework, helping them blend with the interior and original glazing pattern.

The existing IKS installations include internal bars colour matched to dark window frames, demonstrating how security can be incorporated without dominating the appearance of the room.

You can also read our guide to the different types of security grilles for more information about the available designs.

Questions we assess during a property survey

The position of a security grille should follow the characteristics of the property rather than being decided from photographs or measurements alone.

During a security grille survey, questions can include:

• Which way do the windows or doors open?
• Does the opening need to remain available for emergency escape?
• Is there sufficient fixing depth around the window?
• Which part of the surrounding structure provides the strongest fixing position?
• Are there pipes, cables, guttering or other obstructions nearby?
• Is there enough internal space for the proposed grille?
• Can a retractable grille be opened and closed conveniently?
• What floor is the window on?
• Would external installation require scaffolding?
• Is the property listed or subject to other restrictions?
• Are there original architectural features that need to be retained?
• How visible does the customer want the security bars to be?
• Will the installation interfere with curtains, shutters, handles or other window fittings?
• Is a fixed, retractable or more discreet bar design best suited to the opening?

The answers allow the installation to be designed around the actual window rather than adapting the window to a predetermined grille position.

Frequently asked questions

Can security bars be fitted inside windows?

Yes. Security bars can be fitted inside windows and internal installation is often preferable where the window design allows it. Internal bars have less exposed fixings, are protected from the weather and are generally easier to maintain.

Whether internal installation is possible depends largely on how the window opens and whether suitable fixing points are available.

Are outside security bars more secure?

Not automatically.

Both internal and external window security bars can provide a high level of security when they are correctly specified and professionally installed.

Internal bars have the advantage that the bars and fixings are less accessible from outside. External bars are more exposed, so their design and fixing system may need to compensate for this.

Can retractable grilles be installed outside?

Yes, retractable grilles can be installed outside when the property configuration requires it.

However, the grille needs to remain practical to open and close. External retractable grilles are therefore less convenient on upper floors unless there is safe external access, such as a suitable balcony.

Do external security bars rust?

Metal bars exposed to the weather require an appropriate finish and maintenance.

External bars can be galvanised or otherwise protected to reduce the effects of moisture and weathering. The exact finish should be selected according to the product and installation environment.

Internal security bars are less exposed to these conditions and are generally easier to maintain.

Can window security bars be removed for decorating?

Some internal window bars can be removed more easily than externally installed bars, depending on the fixing system.

External security bars may use specialist security fixings designed to make them more difficult to tamper with from outside, so removal can be more involved.

If future access for decorating or maintenance is important, this can be discussed when the system is designed.

Will internal security bars affect ventilation?

Not necessarily.

Fixed internal bars normally allow air to pass through the opening, while retractable grilles can be opened when appropriate.

The more important consideration is whether the grille interferes with the operation of the window. Its position should allow the window to open as intended while still providing the required security when the grille is in use.

Need advice on choosing between internal and external security bars?

Choosing between internal and external window security bars starts with the window itself.

At IKS Locksmiths, we survey each property before recommending the position, grille type and fixing method. We work with fixed bars, retractable grilles and discreet security solutions for homes and commercial properties across London and Hertfordshire.

Our experience includes modern properties, period homes, bay windows, basement windows, French doors, patio doors and openings where standard security grille configurations are not suitable.

A survey allows us to assess the opening direction, fixing points, access, appearance and how the window needs to be used before recommending whether the security grille should be installed inside or outside.

For advice on your property, contact our security grilles specialists in North London and Hertfordshire to arrange a security survey.