The garage in July sits somewhere around 100 degrees by mid-afternoon and stays warm most of the night. The bedroom on the other side of that wall is the one that never quite cools down, and the air handler runs and runs.
The insulated garage door is the obvious purchase and it is often the right one. It is also sold on the wrong argument down here, and there is a second effect that matters more in this climate than the temperature does.
The sticker is measuring the wrong thing for this climate
R-value is a resistance to conducted heat, and the figure quoted on a garage door describes the panel construction. That is a real measurement of a real property.
It is not, however, the property that dominates a Broward garage. Conduction through a panel is a slow, steady process. What actually loads that space is bulk air movement around the door, and air arrives warm, arrives fast, and arrives carrying water. No panel figure describes any of that.
Which is why two doors with identical stickers can produce very different garages, and why the order of spending matters more here than the specification does.
Air first, then the panel
In this climate the bigger effect is usually air exchange rather than conduction, and air carries something conduction does not: moisture.
An old door with a hardened bottom seal, perished stop moulding on the jambs and daylight at the top corners is exchanging outside air with the garage continuously. In Broward that air is warm and it is wet. So the garage is not only hot, it is humid, and humid is what causes the problems people actually notice.
The order that gets the best result per unit spent:
- The bottom seal. The least expensive thermal improvement available, and it is also what keeps water, dust and insects out. A U-shaped astragal in its retainer, replaced when it goes hard, which in this sun is sooner than people expect.
- The perimeter stop moulding. The vinyl strip on the jambs and header the door closes against. It shrinks and hardens in the sun and stops touching the door.
- Then the panel.
Doing the third without the first two is the most common way to be disappointed by an expensive door.
The humidity argument, which is the real one
Here is the effect that matters in South Florida and that nobody mentions in the brochure.
Warm humid air meeting a cool surface produces condensation. In a garage that is exchanging air freely with the outside, the cool surfaces are whatever the house is cooling on the other side of that shared wall, and any metal that has been sitting in the air conditioning’s influence.
Reduce the air exchange and you reduce the moisture load in the garage. That does several things at once: less condensation on the springs and hardware overnight, less corrosion, less of the musty smell that gets into anything stored out there, and less humid air being dragged into the house every time the connecting door opens.
So the case for sealing a garage door here is a durability and comfort case as much as an energy one, and it is stronger than the R-value conversation on its own.
Why the construction matters more than the number
There are three ways a garage door panel is built, and in Broward the differences between them are only half about temperature.
An uninsulated panel is a single sheet of steel with air behind it. It has almost no thermal resistance, it drums in wind, and it dents if a coconut hits it.
A foam-board-filled panel has cut polystyrene pressed into the back. It insulates meaningfully. The board is not bonded across its full face, so the panel is still a sheet with something behind it rather than a single structural item.
An injected polyurethane panel has foam expanded in place between the two skins, chemically bonded to both. Thermally it is the best of the three per inch. Structurally it is a different object: the two skins and the core act together, which makes the panel far stiffer than either skin alone.
That stiffness is the part worth paying attention to down here. A stiffer panel deflects less under wind pressure and takes debris impact better. It is not a wind rating and it does not substitute for one, but it is a genuine property that the R-value conversation obscures.
The consequence that gets missed
Foam has mass, and the springs above your opening were wound to counterbalance a particular door. That calculation is the central specification of the whole assembly, not a tolerance.
When a door and its springs are supplied together for each other, this never comes up. It comes up when somebody adds a retrofit insulation kit to a door that is already hanging. The kit is inexpensive and takes an afternoon, and nothing about it prompts anyone to redo the spring arithmetic.
What follows is a door that is heavier than the springs are holding. In a coastal garage that has a second consequence beyond the strain: the opener has to be turned up to cope, and turning it up is what removes the reversal that stops the door closing on something. So a comfort improvement quietly costs you a safety system, and nobody connects the two.
If your garage door was insulated after it was installed, the balance test is worth doing this week rather than eventually.
The money question
No prices. Construction sets the number first, size second, glazing third. Polyurethane costs more than polystyrene, which costs more than nothing, at every size. Windows cost more and reduce the thermal performance you were buying.
What is genuinely inexpensive is the seal and the stop moulding, and in this climate they should be done first regardless of what else happens.
What not to buy
- Do not buy R-value for a detached garage you do not cool. The seals still make sense, because moisture and insects do not care whether the space is conditioned. The panel insulation does not.
- Do not buy a retrofit insulation kit without a spring recalculation. The kit is cheap and the consequence is not.
- Do not buy insulation instead of a wind rating. They are unrelated properties and only one of them is on a permit.
- Do not buy glazing and expect the brochure’s thermal figure. Glass is the weakest part of any door. Worth it for light, not for heat.
The short version
Seal the perimeter, then insulate the panel, and make sure whoever hangs a heavier door has redone the spring arithmetic. In Broward the moisture you keep out matters as much as the heat.
The first item on that list is a strip of rubber and a short visit, which is not the sale anybody comes to us hoping to make. It is still where the money goes furthest.
M&M Garage Door Service · (954) 787-3756 · mnmgaragedoorrepair.com
Serving Plantation, Fort Lauderdale and Broward County.