Interior design for humans

Today, I wanted to quickly explore a fascinating and often forgotten aspect of interior design: how things are scaled according to the human body. Let me present some quick (but fascinating in my opinion) insights this entails.

First, inside environments must be comfortable. Yes, this means we should probably focus on comfortable furniture but it goes a lot farther than this. For a start, the temperature should be in a specific range judged acceptable. According to designer superstars Henry Dreyfuss and Nino Repetto (my two sources for all information to follow), this range is 65 to 75 degrees Fahrenheit. Other atmospheric ranges include 30% to 70% humidity, pressures between 10 and 20 PSIA, and gas concentrations. CO should be limited to 100 ppm, CO2 to 1700 ppm and oxygen should be around 15% to 60% of air volume. But that‘s not all, Dreyfuss also proposes ranges for ventilation (13 to 20 cubic ft/min), noise (a maximum of 85 dB which is A LOT), heat loss (330 to 1450 BTU/h) and even light (20 to 100 foot candle - not a very common unit nowadays). These are all elements Dreyfuss paid attention to in his work. Just showed how meticulous he was.

But that‘s only the start.

Dreyfuss also includes standard furniture sizes all made to accommodate adults up to 97.5% (this means that the 2.5% smallest and 2.5% biggest adults are outside the range). In his “The Measure of Man“, he also included sketches for the standard measurement he used for the 2.5% percentile of men, the 50% percentile and the 97.5% percentile. Of course, he did the same for women. I found these sketches pretty interesting. You might want to go look them up.

Ok: he took into account human proportions, but what does that entail in practice? Well, here are a few general pointers you could use:

For men, the highest shelves should be no more than 5 feet 8 high. For women, 5 feet 5 inches.
Mirrors should be no more than 5 feet high.
Workbenches should be about 3 feet high.
Lavatories can be a bit lower (31 inches) and tables even lower than that (about 28 inches).
4 inches should be the minimal toe space
The optimal stair angle is 35 degrees. Stairs should be spaced by 10 inches from each other and 51 inches wide (to allow two people side by side).
Doorways should always have a 3-foot circle of free space around them.
For some reason, Dreyfuss felt he needed to specify that we need about 25-30 inches to crawl through a pipe. It gives me some bad ideas…

On that note, I have to say that I LOVE Nino Repetto‘s drawings on the subject. They are clear, informative and frankly quite charming. I highly recommend looking them up.

But that‘s not all yet. Dreyfuss also describes the typical comfortable movement ranges of the human body. Notably:

Head movement back and forth: 30 degrees on both sides.
Head movement left and right: 60 degrees on both sides.
Knees: 45 degrees to 135 degrees.
Feet: 30 degrees between both feet while standing, but only 15 degrees while walking or running.

There are even visual angular limits. Here they are for a horizontal axis:

The standard line of sight is only 2 degrees from the center.
Word recognition is possible for about 10 degrees on both sides.
Symbol recognition is possible for 5 to 30 degrees on both sides.
Colour discrimination is the next to go at about 30 to 60 degrees on both sides.
Binocular vision (vision with both eyes) is possible for 62 degrees on both sides.
But, MONOcular vision is possible for 94 degrees on both sides. That‘s right, more than 90 degrees!

Hopefully, you like this lightning round of facts. I was quite surprised at just how much I loved peering through Dreyfuss‘s and Repetto‘s work.

See you next time,

References

The Measure of Man - Human factors in design, Henry Dreyfuss, 1959.
Anatomy for the interior designers and how to talk to a client, Nino Repetto, Withney Publication, 1948.