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> For example, how many houses have a cupola? They're common on older homes, but non-existent on modern ones. What the roof does is accelerate the wind moving over the roof, then the air vents in the cupola let the wind through, which sucks the heat out of the attic.

This one is genuinely obsolete. With modern techniques, it’s straightforward to build a reliable unvented attic, and there are few if any climates where a vented attic makes sense. There are plenty of climates where a vented attic, even a nice one with a cupola, is massively inferior to an unvented, conditioned attic.

Seal and condition your attic. Put on a decorative cupola if you like. If you live in a place with heavy snow load, you vent a small gap between the top of your attic and your roof surface to help keep the actual roof surface cold enough to avoid melting the snow.

I've been in an attic many times on a sunny day. The heat in the attic is well above what it is outside. I'm highly skeptical that an unvented attic is going to keep a house cool in summer.

Me too. But have you been in a competently built insulated and unvented attic? The insulation on top makes an enormous difference, to the point that the attic can usually maintain a very pleasant temperature.

While it’s true that the top side of above-attic insulation will be rather warmer than a vented attic on a hot sunny day, insulation on top of your attic also tends to work rather better than ceiling insulation. And there are plenty of other benefits to an unvented, insulated attic.

Interesting! But having a sealed attic makes me concerned about mildew. Ventilation is needed to keep the moisture out.

Au contraire.

If you live in a climate where the outdoor air is generally fairly dry and also sufficiently warm that it spends most of its time above the interior dewpoint, then fine. You can vent our attic and it stays dry. This covers rather little of the world.

If you do not insulate at all and you heat your house when it’s cold or wet and you do not experience hot and humid weather, then there will be enough heat flow to keep your attic dry. This is generally an awful idea, but old insulated houses did work in many climates.

If you live somewhere cold and put fluffy stuff on your ceiling and you vent your attic and you have air leaks in your ceiling (hint: this is basically unavoidable) and it’s very cold in your attic, you may get condensation in the ceiling insulation or the attic. Mold time.

If you live somewhere hot and humid and you vent your attic, then you are are filling your attic with hot, humid air. Your dehumidifier or A/C will not control your attic humidity. But your A/C may cool parts of your attic, leading to additional condensation.

If you have nasty severe blowing rain, it may blow into your attic, leading to damage. This is a problem in hurricanes.

Wildfire embers can ignite the inside of your attic. You can try to use fancy supposedly ember resistant vents to mitigate this, or you can omit vents entirely.

If you seal your attic and control moisture in the living spaces well enough to avoid moisture problems and you have adequate conditioning in your attic, your attic will be about the same temperature and humidity as your living spaces, and you’ll be fine.

You can geek out at buildingscience.com. The author appears to have become increasingly convinced that vented attics are basically never the answer.

All I can say is my attic is vented, and is dry and free of mold.

Ridge vent is the modern approach, with vents and wind baffles in the eaves so air is evenly distributed.

1.5' overhang is good, 2' is ideal. Cheap builders will go 1' or even less.

Good architects still pay attention to the sun. It's often builders who are the culprits because they want to save money.

Around Seattle, modern houses are square boxes with a flat roof, and zero eaves. I watch these homes get built all the time. A few years later, I see all the water damage to the siding.

You're right about ridge vents, they behave much like a cupola, but the holes in them are too small for much airflow, and are easily blocked by debris, insects and moss.

> easily blocked

That's a concern. It may be a good idea to put a connected thermometer and hygrometer in the attic. If it is ventilating properly, the temperature and humidity should be close to outdoor values.

Forced ventilation of the attic creates negative pressure in the attic, which pulls conditioned air from the house. The additional air movement (which you should minimize with air sealing) costs more than the additional loses by the mildly increased temperature differential through the insulation.

If you aren't using A/C and have the windows open, then it only helps, of course.

The idea includes gaps where the roof meets the ceiling, so air is drawn from outside.

> If you aren't using A/C and have the windows open, then it only helps, of course.

I make use of the "stack effect" to cool the house down in the evening. Not even a fan is necessary.

One mistake I made was to not have the A/C pull from the basement, which is always 10 degrees cooler than the rest of the house.

> The idea includes gaps where the roof meets the ceiling, so air is drawn from outside.

Of course you should have soffit venting, but forced ventilation results in negative pressure, regardless of whether that venting is a cupola harnessing the wind or a motorized fan. That negative pressure will pull conditioned air out and building science research shows higher attic temperatures are better than forced ventilation.

Even better is larger amounts of passive ventilation, but if the only thing you change is adding forced ventilation, then you're creating negative pressure and this is worse if using A/C.

Unless you have really good insulation, in hotter areas, your roof will absorb a lot of heat and that gets transferred to the attic and then to the rest of the house. One of the cheapest and best upgrades in hotter areas is to have an attic fan and vents to send the hot attic air outside.

> attic fan

The cupola does that using the "stack effect" and the acceleration of the wind as it hits the sloping roof, at zero cost!

That said, I do have an attic fan connected to a thermostat. I'd rather have a cupola, though.

Building science shows this is not true if you use A/C and have appropriate amount of ceiling insulation. Inadequate ceiling insulation is helped by this.