Movable Glass Walls > U Values – What You Need to Know

U Values – What You Need to Know

Movable Glass Walls Inc. is an ideal choice for homeowners, builders and renovators with a discerning mind for quality, innovation and design excellence. Movable glass walls will complement and enhance your preferred architectural style while providing comfort, efficiency and healthy living.  The U Value of your sliding glass wall system is critical in meeting these demands.  Over the last few years the introduction of LEED certification (Leadership in Energy and Environmental) in construction design has meant that Sliding Glass Door U Values have had to achieve better performance levels than ever before.

U value is a formula that measures the rate of heat transmission through building materials and is shown as W/m2.
The amount of heat lost in watts (W) per square metre (m2) of said building material.
 The lower the number the better the performance.

Slimline CF77 Sliding Glass Door with 44mm Triple Glazed 0.6 W/m2K

3 Different Measurements for Sliding Glass  Door U Values

When talking about U values it’s important to understand the 3 different measurements that you are likely to encounter when browsing for information.

  • Ug = thermal transmittance of the glazing itself (or the ‘centre-pane’ U-Value)
  • Uf = Thermal transmittance of the frame itself
  • Uw value = thermal transmittance of the whole window – including glazing and frame. (This is the key number unless you are buying separate frames or glass)
  • ‘Edge’ or PSI value is a calculation of the spacer/edge effect of a unit. It doesn’t improve the Ug, but does improve the Uw. (
  • Look out for Sliding Glass  Door companies that state U values in what could be described as misleading in an attempt to make their Sliding Glass  Doors Uw values appear better than they are.

When talking about Sliding Glass  Door U values please understand that there are multiple factors that go into calculating the Sliding Glass  Door System U value.

The factors that can change the U value of a Sliding Glass Door are:

  • Size of the Sliding Glass Door
  • • Number of panels in a Sliding Glass Door
  • Opening configuration of a Sliding Glass Door
  • Does the Sliding Glass  Doors open inwards or outwards (some systems use different profiles for each.)

So when you see an advertisement stating Sliding Glass Doors at a certain U value you should look for the actual size, number of panels and configuration to which it refers.

An example might look like this: * 4200mm x 2100mm, 4:3:1 Opening Out using 1.2 Ug value Glazing = Overall Frame and Glass Uw Value of 1.77 W/m2K

Lets break this down so that you clearly understand which part of the Sliding Glass Door is being measured

* 4200mm x 2100mm – width and height in mm

4:3:1 – Opening configuration (this means a total of 4 panels, 3 moving left, 1 moving right)

Opening Out – Opens away from the dwelling.

Using 1.2 Ug value Glazing – The actual U value of the glass unit only.

Uw Value of 1.77 W/m2K –  Overall Frame and Glass U value.

We can offer various ranges of products to suit your U Value requirements ranging from the base model that uses a 28mm Double Glazed Unit of Ug 1.2 W/m2K that easily surpasses both categories of document L building regulations.  Uw Value of 1.77 W/m2K

Next level is a 36mm Triple Glazed Unit of Ug 0.8 W/m2K that changes the above Sliding Glass  Doors Uw value to 1.39 W/m2K (when using our CF77 Slimline Vent)

Our Top of the range offering is a 44mm Triple Glazed Unit of Ug 0.6 W/m2K that changes the above Sliding Glass  Doors Uw value to 1.20 W/m2K (when using our CF77 Slimline Vent)

So hopefully now you can better understand all about Sliding Glass  Doors U Values and what can be achieved by increasing the performance of the Glass Unit.

Actual Output of a 44mm Triple Glazed Unit taken from glas

See red circle for Glass only U value reading