Lintels for Patio Doors

If you are installing lintels for patio doors, the lintel you need is determined primarily by the wall construction, the width of the opening, and whether the door sits in a loadbearing wall.
In most modern UK homes with cavity walls, that will usually mean a steel cavity lintel designed to support both the outer brick leaf and the inner block leaf. In some extensions or older properties, it may involve a concrete lintel or a steel beam specified by an engineer.

As a rule of thumb, if you are replacing like-for-like within an existing opening, you follow the existing structural arrangement unless Building Control advises otherwise. If you are forming a new opening or increasing the width, you should expect Building Control involvement and, in many cases, input from a structural engineer.

If you are unsure how lintel choice fits into the wider picture, it’s worth reading our main guide on Which Lintel Do I Need?, which explains the core principles.

When This Applies

This guidance applies when you are:

• Installing new sliding or bi-fold patio doors in an external wall
• Enlarging an existing window opening to form a door
• Replacing existing patio doors but altering the structural opening
• Building an extension with large glazed openings

It particularly applies to cavity wall construction, which is standard across most low-rise housing in England. That means an outer brick leaf, an inner block leaf, and a cavity in between. In that scenario, you normally require a lintel that supports both leaves, not just one.

If the wall is solid masonry, timber frame, or steel frame construction, the approach differs and may move beyond standard lintel solutions.

How to Approach the Decision

1. Is the wall loadbearing?

First establish whether the wall is carrying load. In most two-storey houses, the rear elevation wall will be loadbearing. If there is masonry, floor structure, or roof structure above, assume it is structural until confirmed otherwise.

2. What type of wall are you dealing with?

In modern cavity construction, you will usually be looking at:

• Steel cavity lintels, designed to support both leaves and maintain the cavity
• Insulated cavity lintels, which help reduce thermal bridging
• Separate lintels for each leaf in some specific designs

Concrete lintels are more common in solid walls or for internal loadbearing walls. They are robust and familiar, but they are not typically used to span across a cavity in standard modern construction.

For wider patio openings, standard off-the-shelf lintels may not always be appropriate. This is where engineered steel solutions sometimes come into play.

3. Consider the width and door type

Patio doors often span a significant width, particularly bi-fold systems. The structural demand increases as the opening widens. You must consider not only the brickwork above, but also any floor loads, roof loads, or point loads bearing onto that section of wall.

4. Think about insulation and damp control

Patio doors sit at ground level, which makes damp proofing and thermal performance important. The lintel should be compatible with:

• Cavity insulation
• Damp proof courses
• Cavity trays and weep vents

Ignoring these elements can lead to cold bridging or moisture problems around the head of the door opening.

Common Mistakes to Avoid

Assuming wider simply means “heavier duty”

Many installers assume that choosing the strongest available stock lintel solves the problem. In reality, structural suitability depends on loading conditions, not just span width. Over-specifying can create installation and bearing issues, while under-specifying is obviously unacceptable.

Forgetting bearing requirements

Lintels must have adequate end bearing onto sound masonry. Reducing bearing length to “make it fit” is not acceptable practice. If the design does not allow proper bearing, the structural solution needs to change.

Treating patio doors like standard windows

A standard window opening and a wide bi-fold opening are not equivalent scenarios. The structural consequences are very different. Larger openings often need more than a simple like-for-like replacement.

Ignoring Building Control

Any new structural opening in a loadbearing wall requires Building Regulations approval. This is not optional. Even in domestic projects, compliance is required and documentation may be needed later for property sale.

When You Must Involve a Structural Engineer

You should involve a structural engineer when:

• You are creating a new opening in a loadbearing wall
• You are significantly widening an existing opening
• The opening is unusually wide
• There are multiple storeys or heavy loads above
• The property is older and construction is unclear

In these cases, the engineer will assess loads and specify an appropriate structural solution. That may still be a proprietary lintel, or it may be a steel beam integrated into the wall construction.

Building Control will expect structural justification for these scenarios. As suppliers, we can guide you through product types, but we cannot provide structural approval for your specific project.

Practical Buying Considerations

Once the structural route is clear, practical considerations come into play.

Cavity width

Ensure the lintel matches your cavity size. Modern cavities vary, and older properties may differ again. A mismatch can cause alignment problems and poor support to one leaf.

Insulation compatibility

Many modern steel cavity lintels include insulation to reduce thermal bridging. This is worth considering for patio doors, as large glazed areas already affect overall thermal performance.

Lead times and handling

Longer lintels can be awkward to transport and manoeuvre on site. Plan delivery and lifting arrangements accordingly. Some larger structural sections may be made to order.

Manufacturer guidance

Always follow the manufacturer’s published guidance for installation, bearing, and associated components such as cavity trays. Deviating from this can invalidate warranties and raise compliance issues.

Clear Summary

For most UK cavity wall houses, lintels for patio doors will be steel cavity lintels designed to support both leaves of masonry. The wider the opening, the more likely it is that structural input will be required.

If you are forming or altering a structural opening, involve Building Control and, where necessary, a structural engineer. Once the structural solution is defined, selecting the correct lintel becomes a matter of matching wall type, cavity width, and practical installation requirements.

If you would like a broader overview of how lintel choice works across different scenarios, see our main guide on Which Lintel Do I Need?, which sets out the principles behind making the right decision.