Why don’t I go into very hot attics?
Essentially, because I might not make it out alive. Yes, a hot attic can be fatal. We have all read about dogs and children being killed in hot cars, but your ATTIC can be just as bad, if not worse, because it has been cooking all day in hot sunshine.
Temperatures this high can be fatal.
I routinely see attic temperatures well above 140 degrees, and at those temperatures, even if there is a pull down stair and an adequate walkway, just entering it can be dangerous. Contact burns are very likely at those temperatures; touching wood will hurt, and touching a metal surface such as a bare pipe, truss-plate or nail will burn the skin within a few seconds.
Getting the Facts
When I went looking for information for this post, I called OSHA, NIOSH, CDC, the fire Department, ASHREA and many more agencies, and scoured the internet for rules, standards and recommendations. There were none; lots about the symptoms of heat stroke, and that it can kill, how to treat it, drinking water and more, but nothing about how hot and how long. Then I found a VERY good document published by, of all people, the Coast Guard. Wow… I like the internet.
The Coast Guard has the best documentation on exposure vs. temperature. Interestingly, their chart STOPS at 125 degrees F. Speaking with one of the authors of the document, the reasoning was that the Coast Guard would be unwilling to subject their people to temperatures higher than that. At 125 degrees, the working time appears to be about 7 minutes.
The chart below gives the accepted work times (Personnel Heat Exposure Limits) for three different levels of activity. The “A” times are for the least amount of activity (just standing in the room); the “C” time is heavy activity (such as lifting or constant motion). As a Home Inspector, I would follow the “B” curve — I’m moving around, but not doing heavy work.
Source: US Coast Guard
So, for a 125-degree attic, my maximum exposure time is about 15 minutes; after that, I’m in serious danger.
What About the Stuff?
People aren’t alone in suffering ill effects from attic heat. Furnaces and heat pumps installed in attics don’t last as long as units in basements. They wear out VERY Fast. Even if the unit has 3/4″ of insulation on the cabinet, if the attic is 146 degrees, and you are trying to cool air to 68 degrees, you are going to have issues including stress on the equipment, condensation, thermal deformation and more. Never mind trying to service it during a heat wave (or touching the metal cabinet). No technician should attempt a repair in such a brutal environment.
As for storing stuff up there: DON’T. Natural materials such as cotton, wool, silk, or leather, will usually tolerate temperature extremes. But synthetics such as polyester, nylon, plastic and other “modern” materials and fabrics can melt, deform, stick, release toxic fumes, and otherwise are heavily damaged by exposures to such temperatures.
Attic Fans
Attic Fans are a MUST if your roof has no shading from trees, and is highly recommended for any roof with significant southern exposure. Passive “ridge vents” are not enough; on stagnant, humid days they are pretty much ineffective, and that’s when you’d need the most ventilation help.
It’s important to choose the correct fan, and install it properly. This is an example of a correctly installed attic fan.
Properly installed attic fan
Here’s a very creative solution spotted during a past inspection. It’s really not wise to improvise when safety is at stake.
This is NOT an attic fan. At least, it shouldn't be.
Installing a fan isn’t enough; you need to run power to it as well!
Attic fans need electricity to work!
A excessively hot attic can degrade the shingles, the roof decking, any equipment in the attic, the wiring in the attic, affect your cooling bill (substantially) and more.
How hot is too hot?
It looks like about 120 degrees is the 1/2 hour limit, and that is also the maximum recommended temperature setting for water heaters, among other things. That is what MY attic fans are set for.
I carry a laser thermometer to check attic temperatures before venturing up the ladder. On hot summer days, I will inspect the attic space first, before it’s had the chance to heat up — but even then, it might still be too hot to enter.
Don’t take chances with a hot attic. You can be overcome by heat and find yourself unable to reach safety before succumbing.
