Question 1

Do I need a structural engineer to install bifold or sliding doors?

Accepted Answer

If you're widening an existing opening or creating a new one, yes. The wall above will need new support, and Building Control will need calculations showing it has been designed correctly. A like-for-like replacement in an opening of the same size usually doesn't need an engineer.

Question 2

Do I need Building Regulations approval?

Accepted Answer

Yes, if the opening is being made wider or a new one is being formed. This is a structural alteration and needs approval from Building Control.

Question 3

Do I need planning permission for bifold or sliding doors?

Accepted Answer

Often not. Many rear openings count as permitted development. However, you may need permission if your property is listed, in a conservation area, a flat or maisonette, or covered by an Article 4 direction. Check with your local planning authority if you're unsure.

Question 4

Why does the support above bifold doors need special design?

Accepted Answer

Bifold and sliding doors are sensitive to movement. If the structure above bends too much, the doors can stick, drag or stop sliding smoothly. Many door manufacturers set strict limits on how much the support can deflect, and we design to meet those limits.

Question 5

Can I use my existing lintel if I'm making the opening wider?

Accepted Answer

Usually not. A wider opening means a longer span, and the existing lintel is unlikely to be long enough or strong enough. We'll assess what's there and design the right solution.

Question 6

Is there a limit to how wide the opening can be?

Accepted Answer

Wide openings are often possible, but the structure above, the wall on each side and the foundations all need to be checked. Very wide openings or corner openings may need a more substantial structure, which we can design for you.

Question 7

Should I choose my doors before getting the structural design?

Accepted Answer

Ideally, yes. Knowing the door system and its opening size helps us design the support to suit the manufacturer's requirements. It also avoids problems at installation.

Question 8

How long does the structural design take?

Accepted Answer

Most residential door opening designs are completed within a few days of the site visit. That means your builder and Building Control have everything they need without delaying the project.

Bifold & Sliding Door Structural Calculations

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