Do Metal Roofs Make Your House Hotter? Tucson Answer

No. A light coloured metal roof will generally make a Tucson house cooler than the asphalt roof it replaced, not hotter.

That answer surprises people, because it contradicts the most intuitive thing in the world: metal gets hot in the sun, therefore a metal roof must push that heat into the house. The intuition is reasonable and it is wrong, and the reason it is wrong is worth understanding before you spend five figures on a roof.

Why the intuition misleads you

Put your hand on a metal panel in July and it will burn you. Put your hand on an asphalt shingle in July and it will also burn you, and in fact the shingle is very often the hotter of the two.

What you are feeling is conductivity, not temperature alone. Metal moves heat into your hand quickly, so it feels hotter than something at the same temperature that conducts poorly. That tells you about the metal. It tells you nothing about what is happening to the air in your house.

The two things that actually determine how much roof heat reaches your living space are how much sunlight the surface reflects rather than absorbs, and what happens to the heat that does get absorbed before it reaches your ceiling.

Reflectivity is where metal wins

A dark asphalt shingle is close to an ideal solar absorber. It is dark, it is textured, and it soaks up a large share of the sunlight landing on it. All that absorbed energy becomes heat in the roof.

A light coloured coated metal panel reflects a large share of that same sunlight straight back off the building. Energy that is reflected never becomes heat at all, so it never has to be dealt with by your insulation or your air conditioner.

The colour and the coating are doing that work, not the fact that it is metal. A dark metal roof reflects far less than a light one. If cooling is your priority, that choice matters more than almost anything else on the estimate.

What happens to the heat that is absorbed

Some heat gets absorbed regardless. What matters then is whether it can get away before it reaches your ceiling.

Metal has very low thermal mass. It heats up fast, and it sheds that heat fast the moment the sun comes off it. An asphalt roof holds heat, which is why a shingle roof keeps radiating warmth downward into the evening long after sunset, right through the hours you are trying to cool the house to sleep.

The assembly underneath matters more than the roofing material. A vented air gap between the panel and the deck lets absorbed heat move out rather than down. Insulation at the ceiling plane does the rest. A metal roof over a well vented, well insulated assembly is a genuinely cool roof. A metal roof laid straight over an old, badly insulated, unvented assembly will disappoint you, and so would anything else in that position.

This is the part worth pressing your roofer on, and it is the part most quotes are silent about.

What we are not going to tell you

We are not going to put a percentage on your cooling bill.

Plenty of roofing companies will. The number depends on your insulation, your ventilation, your ductwork, your windows, your equipment, its age, and what you set the thermostat to. Anybody quoting you a specific saving without knowing all of that is making it up, and you should treat the rest of their estimate with the same suspicion.

What we will say is that the mechanism is real, the direction is favourable, and a light coloured metal roof over a properly vented assembly is one of the better things you can do to a Tucson house.

If you want to look at incentives, Tucson Electric Power is the place to start, and you should confirm anything current directly with them rather than trusting a figure on a contractor’s website, including ours. These programmes change and the amounts go stale quietly.

The one honest caveat

If you have a dark metal roof laid directly onto an unvented deck over a poorly insulated ceiling, you will not enjoy the result. That is a real failure case and it is worth naming.

It is also avoidable, and it is avoided by specification rather than by choosing a different material. Light finish, vented assembly, insulation at the ceiling plane. Get those three right and the roof performs.

When this is worth a conversation

Upstairs rooms or the west side of the house are noticeably hotter than the rest
The house stays warm well into the evening after a hot day
You are already replacing the roof and want the cooling side considered rather than ignored
You have a metal roof whose finish has chalked out and stopped reflecting
Somebody has quoted you a specific percentage saving and you want a second opinion on it

Worth reading next: what we actually do on a roof is set out across our services, and the surface renewal side of this is covered on metal roof coating and restoration. If you would rather just ask, get in touch.

02Questions

Heat questions

Do metal roofs make your home hot?

No. A light coloured metal roof generally results in less heat entering the house than the asphalt roof it replaced, because it reflects more sunlight and holds less heat once the sun goes off it. It feels hot to touch because metal conducts well, which is a different thing entirely.

Is metal roofing hotter than shingles?

The surface of a dark metal roof and the surface of a dark shingle roof reach broadly similar temperatures in full sun. The differences that matter are that metal has far less thermal mass, so it stops radiating heat downward much sooner in the evening, and that light coloured metal reflects considerably more sunlight than shingles do in the first place.

Is it harder to cool a house with a metal roof?

Generally the opposite, provided the roof is a light colour and the assembly under it is vented and insulated. If those things are not true, the roof will underperform, and that is a specification problem rather than a property of metal.

How to reduce heat from a metal roof?

Choose a light coloured, high reflectance coating. Make sure there is a vented air gap between the panel and the deck rather than laying it straight down. Get the ceiling insulation right, since that is your last line of defence. And keep the surface clean, because a chalked, dust filmed roof reflects a lot less than it did when it was new.

Are metal roofs a good idea in Arizona?

Yes, and the heat is one of the reasons rather than an argument against. Metal does not go brittle under ultraviolet the way asphalt does, and a reflective finish rejects heat the house would otherwise have to deal with. The details need to be right, because desert heat is hard on fasteners and sealant, but the material itself is well suited to this climate.

Does a reflective roof coating actually work?

The mechanism is sound: a cleaner, lighter, more reflective surface absorbs less solar energy than a dark chalked one. It is also why restoring an old metal roof has a practical benefit and not just a cosmetic one. We will not attach a savings figure to it, for the same reasons set out above.

Next step