The Myth Of The R-Value

  • The Door Works Amarr Garage Doors

The Myth Of The R-Value

We are often asked about what the R-value is on new Garage Doors.  Often building plans and specs require a particular R-value.

Some of these specifications are nearly impossible to meet such as in aluminum glazed doors because aluminum and glass conduct heat and cold so well.

This got me thinking about what R-value is all about and what it means in the world of Garage Doors.

I looked up R-Value on Wikipedia to see how it was determined, it said:

“The R-value is a measure of thermal resistance

[1] used in the building and construction industry. Under uniform conditions [italics added] it is the ratio of the temperature difference across an insulator and the heat flux (heat transfer per unit area per unit time, ) through it or . The R-value being discussed is the unit thermal resistance.

This is used for a unit value of any particular material. It is expressed as the thickness of the material divided by the thermal conductivity. For the thermal resistance of an entire section of material, instead of the unit resistance, divide the unit thermal resistance by the area of the material.

For example, if you have the unit thermal resistance of a wall, divide by the cross-sectional area of the depth of the wall to compute the thermal resistance. The unit thermal conductance of a material is denoted as C and is the reciprocal of the unit thermal resistance. This can also be called the unit surface conductance, commonly denoted by h.[2] The higher the number, the better the building insulation‘s effectiveness. R-value is the reciprocal of U-value.”

Did you get all that?

Well, I can sort of follow what they are saying but I also know there is some game playing going on when it comes to the way they measure the R-value of Garage Doors.

Different Door Manufactures use different methods of measuring R-Value.  This results in some inconsistancies in being able to compare “apples to apples”.

One Garage Door Company recently sent us a chart showing the difference between R-values.  They called it the R-Value Reality Check.

R Value

Very Interesting!

So, it appears that R-values are like the percentage rating in milk. Whole milk contains usually between 3.25% and 4.0% fat, where as 2% obviously contains 2% fat.  It’s not as if whole milk is 100% fat!

An R-value of 16 is not twice as good as an R-value of 8.  It does not offer twice as much thermal resistance or twice the energy savings.

A value of R-16 offers a 5% reduction in heat flow and a 5% improvement in energy efficiency over an R-value of 8.

Should you be concerned about R-value in choosing your Garage Door?

I think so but the reasons may be a little surprising.  If you were living in an extremely cold climate and never intended to open your garage door it could be very significant, but the R-value of an open Door immediately becomes zero.

A Door that is never opened is called a wall.  A well insulated door can really be nice when the Garage is used as a workshop but there are other advantages of an insulated Garage Door.

Most insulated steel and wood Garage Doors are insulated with polystyrene (styrafoam) layers.  Some improve their R-values by using high density polystyrene or HD.

Some of the highest rated insulated doors are those that are ‘foam injected’ doors that use polyurethane.  Polystyrene insulation is either attached to the back of steel door panels with a vinyl backing or sandwithced between layers of steel.

To increase insulation you either use a higher density foam or make a thicker door.  Some manufactures have even started making a three inch thick door.

It looks pretty impressive but it still can’t match the R-value in a two inch thick polyurethane door. Polyurethane is like the foam insulation in a can that can be sprayed or injected to seal around doors and windows.

Urethane injected doors and laminated polystyrene sandwich doors make good solid and sturdy sections and are both reasonably priced.

But, then we add windows for light and style and that is the end of reasonably priced; by this I mean insulated glass is lots more expensive and a fraction of the R-value.

Even double pane glass with one half inch space between panes has an R-value slightly above 2.

Unfortunately, Sectional Garage Doors can’t be installed air tight, there needs to be room for the door to slide up and down against the jambs.  These little spaces let cold air draft in and negate much of the insulating that was done in door construction.

Some of the drafts can be stopped with a vinyl weather seal around the door and bottom seal, or astrigal, can fill in the space along the bottom of the door depending on how level and even the floor is.

We’ve now come back to why, in the moderate climate of the Northwest do we need an insulated Garage Door.

  1. More insulation of course.
  2. A stronger, more rigid door.  Both polystyrene sandwitch doors and polyurethane doors are bonded to the steel to make them stronger.  They hold up to better to moderate abuse.  We still haven’t found the door that will hold up to a car bumper.
  3. They are much quieter.  The bonding eliminates most of the rattling that comes with pan Doors or as I recently heard them referred to as ‘Beer Can Doors”.   Combine a good quality insulated door with high quality rollers and one of the new DC motor, Belt Drive Garage Door Openers, you have a door that will make you smile each time you don’t hear it go up and down.

If you have questions regarding any of this, please give us a call! Call today at 1-800-478-8428 or Contact Us Here


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