Does a Metal Roof Make a House Hotter in a North Carolina Summer?

A metal roof will not make your house hotter when it is installed the way residential roofs are, over a solid deck with underlayment and an insulated attic below. In many cases the opposite happens, especially with a light or cool-rated color. The U.S. Department of Energy says conventional roofs can reach 150°F or more on a sunny summer afternoon, while a reflective roof can stay more than 50°F cooler under the same conditions.

Roofing material is only one layer in a stack. Heat that reaches your bedrooms has to pass through the roof covering, the underlayment, the deck, the attic air and the insulation on the attic floor. On most North Carolina homes, the attic and its insulation do far more to control indoor temperature than the roof surface does.

That is why two neighbors with identical roofs can have very different upstairs comfort. One has deep insulation and good ventilation; the other has a thin, compressed layer and a crowded, unvented attic. The rest of this article explains where the heat comes from, why the myth persists and what makes the real difference, so you can judge a roofing bid on facts rather than on what the barn down the road feels like.

The idea comes from buildings where metal really does make the space hot: barns, sheds, carports, workshops and old farm buildings with bare corrugated metal fastened straight to open purlins. There is no deck, no underlayment, no insulation and no ceiling, so the hot metal sits a few feet above your head and radiates heat downward. Stand in a pole barn in Johnston County on a July afternoon and the myth makes sense.

Old unpainted roofs added to the problem. DOE notes that unpainted metal reflects sunlight well but emits heat poorly, so bare metal holds onto absorbed heat. Modern residential metal roofs are painted with finishes that have high thermal emittance, which means they release heat readily instead of trapping it.

A residential metal roof is a different assembly entirely. The panels sit on a plywood or OSB deck covered with underlayment. Below that is an attic with ventilation and, on the attic floor, insulation. The house is separated from the roof by several layers and an air space. The hot tin roof of the barn never comes into it, and neither does the drumming noise people associate with it.

Roof heat reaches the rooms below mainly through the attic. During the day, the sun heats the roof surface. Some of that heat passes through the deck and radiates into the attic, warming the air and everything in it. From there, heat moves down through the attic floor into the ceilings of the rooms below, and it soaks into any ductwork running through the attic.

That last point matters in North Carolina, where many houses have their air handler and supply ducts in the attic. If the attic reaches very high temperatures, cool air loses some of its cooling on the way to the vents, and the system runs longer to keep up. Leaky duct joints make it worse by pulling hot attic air in or pushing cooled air out.

So the questions that matter most are how hot the attic gets and how well the ceiling and ducts are protected from it. The roof surface affects the first; insulation, air sealing and duct sealing affect the second. Our guide to attic ventilation in NC heat and humidity goes into the ventilation side in more depth.

A metal roof stays cooler when it reflects more sunlight and sheds the heat it absorbs quickly. Three things help:

• Color. Lighter colors reflect more sunlight. Cool-rated darker colors reflect more infrared than older dark paints. Compare solar reflectance and thermal emittance values in the Cool Roof Rating Council directory; see metal roof colors for NC heat.
• A high-emittance finish. Painted finishes release absorbed heat as infrared radiation. Interlock aluminum panels use the Alunar 70% PVDF coating, built to the AAMA 2605 standard.
• Low heat storage. Thin metal panels hold little heat. After sunset they cool quickly, unlike heavier materials that keep releasing stored heat into the attic well into the evening.

The Cool Roof Rating Council's directory is the place to compare products now that, as the Council reports, the ENERGY STAR roof program ended on June 1, 2022. DOE also notes that cool roofs can help older or undersized air conditioners keep up and improve comfort in spaces without air conditioning, such as a bonus room over the garage.

The attic matters more than the roofing material. If upstairs rooms are hot in summer, check these before blaming the roof:

• Insulation depth. ENERGY STAR recommends attic insulation levels by climate zone, from R38 to R60 across climate zones 3 through 5, depending on how much is already there. Many older North Carolina homes fall short.
• Air sealing. Gaps around recessed lights, attic hatches, plumbing and wiring let hot attic air and humid air move into the house. Sealing them helps comfort and humidity control.
• Ductwork. Seal duct joints and insulate ducts that run through the attic, or ask an HVAC contractor about moving equipment into conditioned space.
• Ventilation. Balanced intake at the soffits and exhaust at the ridge carries hot, moist air out of the attic.

A roof replacement is the natural time to deal with ventilation, because the crew is already working at the eaves and ridge. Insulation and duct work are usually separate trades, but scheduling them around the roof job can save a second disruption.

A metal roof will not make a house noticeably colder in a North Carolina winter. DOE notes that reflective cool roofs can carry a winter heating penalty in cold climates, because they reflect sun that would otherwise add a little warmth. In hot climates, the summer cooling savings outweigh that penalty, and North Carolina's Piedmont and coastal winters are moderately cold rather than severe, as NOAA's state climate summary describes them.

The winter sun is lower and weaker, and much of a roof's winter heat loss is controlled by the attic insulation, not by the roof color. A house that is well insulated and sealed for summer is also better protected in winter.

Winter does bring one metal-roof-specific question in the Piedmont and mountains: snow and ice slide off metal more readily than off asphalt. Ice storms, such as the February 2014 event NOAA describes with up to half an inch of freezing rain, can shed ice in sheets. Plan ahead for walkways and entries under the eaves; see ice storm roof damage in NC.

Ask for the roof, the ventilation and the attic to be looked at together. A short list for the estimate:

• Which color and finish, and what are its Cool Roof Rating Council values?
• How is the attic ventilated now, and will intake and exhaust be balanced after the new roof goes on?
• Is any decking soft or delaminated from past heat and moisture?
• Are there signs of moisture, mold or rusted nails in the attic that point to ventilation problems?
• Would added insulation or duct sealing help, and who would do it?

Metal Roof NC, an authorized Interlock aluminum roofing dealer, gives a project-specific estimate before work begins and can point out ventilation issues while the roof is open. See aluminum roofing and our roof replacement page for more on the process.