R-value explained, polyurethane vs polystyrene, retrofit kits vs insulated doors, and what insulation is actually worth in Northern Colorado's climate.
Northern Colorado gives insulation a real job to do: sub-zero January nights, ninety-degree July afternoons, and forty-degree swings inside a single day. But the return depends entirely on whether the garage is attached, conditioned, or used.
Here is how R-value actually works, where the marketing numbers overstate things, and how to decide what your garage needs.
R-value measures resistance to heat flow — higher is better. An uninsulated single-skin steel door is effectively R-0 to R-2. Entry-level insulated doors run R-6 to R-9. Premium polyurethane doors reach R-12 to R-18.
The published number is measured at the thickest part of the panel, not across the whole door assembly, and it does not account for perimeter air leakage. A well-sealed R-12 door outperforms a poorly sealed R-18 door in practice. Seals matter as much as the core.
Polystyrene is a rigid foam board slipped between the skins. It is cheaper, delivers moderate R-value, and does not bond to the steel, so it adds little rigidity.
Polyurethane is injected as a liquid and expands to fill every void, bonding to both skins. It yields higher R-value per inch, makes the section dramatically stiffer and quieter, and resists dents better. For attached garages in NoCo, it is the upgrade we recommend most often.
Retrofit kits — foam panels adhered to the inside of an existing door — cost a few hundred dollars and do help. They also add weight the springs were not sized for, which can throw the door out of balance and shorten spring life. If you install one, have the balance checked afterward.
If the door is old, dented, or already due, buying an insulated door is the better spend: you get the R-value, the rigidity, the quiet, and a sealed perimeter as one package.
It pays when the garage is attached, has living space above, holds a water heater or plumbing, or doubles as a gym or shop. Homeowners routinely report a garage running 10 to 20 degrees warmer in winter after the swap, plus a noticeably quieter door.
It rarely pays on an unheated detached shop used for storage, or on a rental where the garage is never occupied. In those cases, spend the money on durable hardware instead.
R-12 to R-16 for an attached garage is the sweet spot. R-6 to R-9 is plenty for a detached shop, and uninsulated is defensible for pure storage.
Yes, for most attached garages. It bonds to the steel skins, delivers higher R-value per inch, and makes the door noticeably stiffer and quieter.
They provide a modest improvement for a few hundred dollars, but they add weight the springs were not sized for. Have the door balance checked after installing one.
If the garage is attached or has living space above, most homeowners see a modest monthly reduction. On a detached unheated garage, the savings are essentially zero.
Yes, noticeably — both from road noise outside and from the door's own operation, because the foam core damps panel vibration.