Triple glazed bifold doors
Triple glazed bifold doors have glass with a Ug of 0.6 W/m²K, against 1.1 for double glazing. The glass is only part of it: with bifold doors the frame and the number of leaves count more than with a window.
Bifold doors triple glazed or double
Triple glazing has three panes and two cavities and loses nearly half as much heat through the glass as double. It is also heavier, and a leaf may weigh up to 120 kg, so on large leaves the weight can set the size. Which glass the profile you chose takes, the configurator tells you.
Aluminium bi-fold doors U-value
For the Reynaers ConceptFolding 77 the manufacturer gives a frame Uf of 1.66 W/m²K. For the Aluprof MB-86 Fold Line HD the brochure gives no Uf; it does give a thermal break of 24 mm in the frame and 34 mm in the leaf. The Uf is the frame alone, the Ug the glass alone; the U-value of your whole door is in your quote.
Energy efficient bifold doors: fewer leaves
Every leaf brings two profiles, so more leaves means more profile and less glass. For the same opening, fewer and wider leaves with triple glazing give the best result.
The threshold
A surface-mounted threshold with a rebate seal closes tightest against wind and rain. The low threshold is easier to walk over; the choice decides how much water and wind the threshold keeps out, not the Uf.
Part L for a replacement bifold door
In England, Approved Document L sets a U-value of 1.4 W/m²K or DSER band C for a replacement door that is more than 60% glass. That is the U-value of the whole door, not the Uf or the Ug. A replacement may not perform worse than what it replaces. Scotland and Northern Ireland have their own rules.
Uf, Ug and Uw: three different figures
Uf is the heat lost through the frame and leaf profiles, Ug through the centre of the glass, and Uw through the complete unit. All three are in W/m²K, and a lower number means less heat escapes. The Uw is not the average of the other two: it depends on how much of the door is aluminium and how much is glass.
That is why the same glass can give two doors a different U-value. On a bifold, with two profiles per leaf and a hinge joint between every pair, the aluminium takes a bigger share of the surface than on a fixed window of the same size.
Triple glazing on a bifold: weight and thickness
Triple glazing is 12 to 16 mm thicker than HR++ double glazing and weighs 30 to 36 kg per m², against 20 to 24 kg. Take a leaf of 1,000 × 2,300 mm and count all of it as glass: that comes to at most about 83 kg in triple and 55 kg in double, before the aluminium is added. At the largest leaf the manufacturers allow, 1,200 × 3,000 mm, triple glass alone gets close to the 120 kg a leaf may weigh in total.
The thicker unit also has to fit in the leaf. The configurator only offers the glass a profile can take, and it refuses a combination that doesn't exist.
The glass you can choose
Our catalogue has six glass types: HR++ double glazing (Ug 1.1), triple glazing (Ug 0.6), obscure glass as double or triple, and P4A laminated safety glass, Ug 1.0 as double and 0.6 as triple. Laminated glass has a plastic interlayer that holds the fragments in place if the pane breaks.
In a bifold the glass starts close to the floor in every leaf. Whether that means it has to be safety glass is set by the building regulations where you live; your installer or building control can tell you which panes it applies to.
Quieter is a different question
A third pane doesn't make a door quieter on its own. Sound is held back by panes of different thickness and by laminated glass. If your garden side faces a road and noise matters to you as much as heat, mention it in the comments of your request.
The Fold Line HD without a Uf
Aluprof's brochure for the MB-86 Fold Line HD gives no Uf, and we don't fill the gap with an estimate. What it does give is the width of the thermal break, the insulating strips between the outer and inner aluminium: 24 mm in the frame and 34 mm in the leaf. It also says the system uses the technology of the MB-86N. Neither is a U-value, so for this profile the figure to go on is the one in your quote.
Frequently asked questions
Are bifold doors energy efficient?
They can be, with triple glazing and as few leaves as your opening allows. Because each leaf joint needs its own hinge point and seal, the Uf of a bifold is higher than that of a window.
How do I insulate bifold doors?
On a new door you decide it when ordering: triple glazing, fewer wider leaves and a surface-mounted threshold. We only supply glass in a new door, not for an existing one.
Which of your bifold doors insulates best?
We can only compare where the figure is known: the ConceptFolding 77 has a Uf of 1.66 W/m²K, and for the Fold Line HD the manufacturer gives no Uf yet.
Is double glazing enough for a bifold door?
The glass alone doesn't answer that. HR++ double glazing has a Ug of 1.1, but whether the whole door reaches the 1.4 W/m²K Part L asks for depends on the frame and the number of leaves as well. Compare the U-value in your quote with that limit.
What if my bifold door is less than 60% glass?
Then Approved Document L treats it as another door: in England, a U-value of 1.4 W/m²K or DSER band D. The rule that a replacement may not be worse than the old door still applies.
Who tells building control about the new door?
Not us: we supply, we don't install. In England and Wales an installer registered with a competent person scheme, such as FENSA or Certass, notifies the work, or you notify building control yourself before it starts. Agree which it will be before you order.
Is there a grant for energy-efficient bifold doors?
We can't name one, and we don't give grant advice. Base your choice on the U-value in your quote.
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