Help solve the mystery of the T-door

Here in the southwestern US and northern Mexico, ancient civilizations created entry ways shaped like a "T". Archeologists, such as the expert in the video below, call these doors an “enigma.” Knowing that many natural builders using stone, adobe, cob, wattle and daub have come up with ingenious approaches to keeping subterranean spaces warm in winter and cool in summer, it seems that our hands-on experts could help solve the T-door mystery.
As you can see from the photos in the slide show, the T-door has a narrow entry at the bottom, a wide opening on top, and the threshold to the T-door is slightly raised (like a submarine door). Thinking about laminar flow and cold heavy ground air rushing into a space to feed a fire, blocking that small low opening with something like a rolled up blanket seems like a good way to keep warm air in. Deflectors inside the buildings were used to keep the heavy cold air off occupants. Let’s put our heads together regarding this mystery: how cold the T-door keep occupants warmer in winter and cooler in summer?

Seems to me the least amount of cold air can come in low, and the most amount of hot air can flow out in summer and it provides great ventilation. Put a split door so you can open either half, you have a very versatile opening.
Think double hung windows and dutch doors.

Evidently, one person's theory was that the door would allow only one person to go in.

The doors are shaped like a tau so as to allow only one person to go through (Lúxan 1602, 73-74). The pueblo with T-shaped doors that Lúxan described

https://www.academia.edu/44957771/Ik_WAY_The_Mayan_Origin_of_T_Shaped_Doors_in_the_North_American_Southwest

Sounds good to me.

I also like the idea that cold air came in at the bottom and hot air went out at the top.

It could just be the most minimal opening practical. Any door\covering would have been made by hand, and such materials were more precious back then.

It could prevent many larger animals from entering.

It could force a person to enter slowly, giving a disadvantage to any enemy attacker.

Defense was my first thought.

I was reading a book which suggested that the many "tribes" in North America often had cultural differences that seemed to specifically set them apart from their neighbors, "we're us, and they're them" concept. It's how I always felt about religious dietary restrictions - some of them had at least a vague basis in food safety, but mostly it seemed like one way to define them. I realize that when working with adobe - even adobe bricks - the "T" wouldn't be that much more difficult to make, but the  idea that it was more a symbol than something practical fits what the images in the video. That said, it's possible he only showed images that supported his opinion rather than a full spectrum of variations.

Reminds me of the gateless fences where a person can step through, but animals will not because off the odd arrangement for their hooves/paws/etc.

As others have said, pretty hard to enter that door with a weapon in your hand on a deadly charge too.

Speaking as a father though, what a great way to have your twelve children living in the house and not have to yell at them for slamming the door!

Wonderful brainstorming so far!
By imagining living back in time a thousand or more years, some archeologists have theorized that the door shape is like the silhouette of a person carrying an oversized basket on their back: skinny legs and a large bundle. Imagining “the other” leads to all kinds of research papers about “them.”  
Yet, there is another approach to research that is a permies specialty: actually making something and studying it. Would anyone consider making a T-door to address a current, real-life, off-grid (or non-powered) problem? How could a raised T-door be an advantage to a room heated only by wood stove, fireplace, or rocket stove? In addition to the heat-ventilation-cooling example, someone here might be struggling with pests or would like to funnel certain animals into a trap for food or pelts. Does the T-door style offer solution to an actual challenge that anyone is experiencing now? How could the T-door be useful to you?

I don't know.  I like the cold air/hot air hypothesis.  But I'm seeing that it also allows the legs in at the bottom, but enough room for the torso to also carry objects in and out.  Kind of a human Tetris thing.

:)

Nissa Gadbois wrote:I don't know.  I like the cold air/hot air hypothesis.  But I'm seeing that it also allows the legs in at the bottom, but enough room for the torso to also carry objects in and out.  Kind of a human Tetris thing.

:)

That was my thinking.  It would be very hard to carry an armload of fire wood through a slot that size, but open it into a T and it would be much easier.

The issue I have with the cold\hot air hypothesis is that in order for any amount of air to enter, an equal amount must leave. This would be regardless of the shape of the door. I do wonder if the narrow bottom would possible create a narrow beam of cold air when it's cold out and send it straight to the fire instead of creating a cold draft all over the floor of the room. The radiant heat from the fire and the smallest possible door would help keep people warm. The wider top would let smoke out without it pooling up too much at the ceiling, but then it would be necessary anyway for a person to fit through. However, all this could be done by simply incorporating it into a removable door in a standard rectangular or arched doorway. That makes me think there's something else at play.

Judging by the size in the screenshot, I cannot imagine a person walking through the doorway with a large, especially heavy, basket on their back. It looks like a person would have to be doubled over to enter, unless they were a race of pygmies. And we once again arrive back at the point that a person could carry a basket through a full sized door even more easily, and with more options than these T doors. I think it's not about the wide top; it's something about the narrow bottom.

I can however guarantee something they did not do. They definitely did not carry a refrigerator, couch, table, etc. through them!

Jordan Holland wrote:
It could prevent many larger animals from entering.

I think this may be at least a part of the reason for the shape. It reminds me of squeeze stiles in dry stone walls of Northern England:

source
Sometimes these have steps up as well which would help keep smaller animals out as well as larger ones.

Great photo Nancy! That looks like actual usage of the lower part of the T to me.
The doorways to buildings vary in size. For more photos, skim the slide show in the first post. The T-doors can be very large, as in this photo by Russ Bodnar at Casa Rinconada in Chaco Canyon:

This room can accommodate hundreds of people. There is evidence that the space was warmed with fires inside the building and that the structure had some kind of roof.
For more information about Casa Rinconada, this Wikipedia entry with external photo links is helpful:
https://en.wikipedia.org/wiki/Casa_Rinconada

Hmm, Wow! that's definitely a bit big to keep out cows! I'll have to think again.

Amy Gardener wrote:Casa Rinconada in Chaco Canyon:

This room can accommodate hundreds of people. [...]

My first thought was the same as Anne, but the animal idea sounded plausible as well.  This seems to discourage both of those.

Though just going by the pic it may be an "evolution of design" thing.  From that pic it seems like the window to the right is very similar to the top of the T.  Possibly in early days all they had were windows to climb through.  Then somebody noticed, "hey, this would be a lot more comfortable if there was someplace for your legs to go."

In light of the range of scales, it seems highly probable that it acquired some symbolic importance beyond whatever functional benefits it might provide in the one person scale.
Knowing the timeline could help us know whether the small T openings were reflections of the large T openings and also symbolic rather than a primarily functional design.

Without knowing lots more about internal design, actual location details, orientation, it’s not possible for me to offer any possibilities based on anything but blind speculation.

Great point about needing more information, Peter! Check out the Crow Canyon Archeological Center
video lecture noted in the original post for this thread. Location maps, timeline, photographs and extra info is in the 50 minute lecture. Additional details about "internal design, actual location details, orientation" are available by checking out each site on Wikipedia (more info by following the external links provided on Wikipedia). Weather patterns for the specific locations are available by searching The National Weather Service.
However, what makes this inquiry relevant to permies is that someone may consider conducting primary research about the door. By making an actual T-door opening for a real building, we may learn first hand if the doorway actually offers some benefit to a fire-heated living space. We won't arrive at the answer by speculation.

Form follows function.



In the 60's and 70's, there is a travelling hawker selling rice and side dishes.
His wares were carried in two baskets supported by a flexible pole. He used
an unusual gait which allowed him to carry such loads further before tiring.
The bouncing load and some kind of harmonics made this possible. The art
is lost since most have gravitated into permanent premises that have bright
lights and several flat screens showing Qatar 2022 matches.



This picture is posted below. I haven't found out how to fix any picture
at the desired spot within this text.

The next two pictures show what I did to my front door. Most of the time
you don't have your house-keys at hand when you are burden with parcels.
Those hooks allow me to free my hands for this. I believe those ledges
at the doorway serve a similar purpose prior to the invention of S-hooks and
metal brackets, hinges and fold-down trays.

I wasted 59 minutes watching that video. There should be close-ups of
the aperture. I want to see the wear marks, scrapes and bumps.
I want to see a human traversing the door. I want to see what the
inhabitants were wearing what might require such an odd shape for
a doorway. I want to to see the ceiling. Fires will leave soot marks.
I want to see hieroglyphics that might indicate the use of those T-doors.

I found nothing helpful in that video. It almost seems like they are
hiding this from further scrutiny.

Thus, based on available evidence and existing contemporary events
like this,



The inhabitants must be some form of long lost bipedal hominid
mentioned in ancient texts as Spongia lascivius quadra braccas.

I wasted 59 minutes watching that video. There should be close-ups of the aperture. I want to see the wear marks, scrapes and bumps. I want to see a human traversing the door. I want to see what the inhabitants were wearing what might require such an odd shape for a doorway. I want to to see the ceiling. Fires will leave soot marks. I want to see hieroglyphics that might indicate the use of those T-doors.
I found nothing helpful in that video. It almost seems like they are hiding this from further scrutiny.

Thank you for wrestling with this “enigma,” Edward! I was similarly underwhelmed with the lecture. If as you keenly note, “form follows function,” how can we figure out what the function actually is?
There are many post-doctoral thesis’s that explore the symbolism of the doorway (function is to  tell people approaching from afar that we’re the T-clan). But I can not find anything about why people made the T-doorway from an improved shelter or comfort perspective. Many of the external signs that you want to see are lost to erosion. What is known is that these doorways are the entryways to multiple once-enclosed-spaces heated with indoor fires. The ruins exist.
While watching lectures and reading academic papers, I kept thinking, “why doesn’t someone just make a model of the door, live in the space for a period of time then submit their practical, hands-on, in-the-field findings?” The apparent absence of real-life experimentation with the T-doorway leaves an opportunity for discovery for anyone who is motivated to actually do a contemporary hands-on exploration by modifying the entryway to a hand-made earthen shelter.
Naturally, I am considering making the T-door unless some other permie has already done so.

Having known virtually nothing about this area and culture, I now know a very little more having spent (rather too much) time online today , and came independently to agree with this paper that concluded that there was a connection between Mayan culture and the T shaped doors. A t shape like this is a Mayan Glyph signifiying a god of wind and rain, which for an agricultural people in a fairly arid region would have been particularly important.

It is important for grasping the significance of the 'Ik’ to understand the wind and rain -- and, by extension, the connection between rain, the god of rain, Chaak (also Romanized “Chac”, and known as Tlaloc to the Aztecs) and wind. For example, in the traditional religion of the modern Yucatec Maya people, which has strong roots in the religion of the ancient Maya, a  prayer intended to summon rain states this inexorable connection explicitly:
"I also commend this food to the winds who come for the first time and for the wind that spies from behind the stones, without forgetting the great winds that emerge from caves. Lord, Chaak [sic], we call on all the rain gods, the lords of these winds. I offer this food to you. I also ask that the lords of the wind move the clouds so that they may water the milpas [i.e., cornfields] of their children" (Cámara and Preuss 1990, 130-144)

source
The Aztec god Tlāloc often seems to have the 'ik'symbol as earings for example:

https://en.wikipedia.org/wiki/Tl%C4%81loc#Representations

The speaker in the above lecture thinks that the reason the t doors were particularly in exterior walls were symbolic rather than practical (there appear to be separate high window vents for smoke outlets for example). It is likely that we will never know without more well researched artifacts after all this time though.

I did wonder whether there may have been a practical function in the doorway - whether for example a lack of door hinges may have made the shape better for a two piece door - solid at the bottom and a curtain at the top, but that is pure speculation. If it worked that way, you'd have thought that the style would be common elsewhere in the world, and I can't find much in drier areas of Africa for example. The only contemporary-rish features I can find are the front doors flanked by windows you sometimes find in 'between the wars' semi=detatched houses in the UK

(source)
Although, as can be seen in the above image, these tend to be archways which are stronger (and subjectively more attractive) than the wide t openings of the true t doors. I think these have their origins in prtacticality since these houses typically would not have had another window in the hallway, being typically very close to the neighbour they are nbot attached to, so having additional windows by the door lets in more light.

Peter Ellis wrote:Knowing the timeline could help us know whether the small T openings were reflections of the large T openings and also symbolic rather than a primarily functional design.

The canyon was occupied between 850 AD and 1250 AD.

The ruins were discovered in 1896.

Steve Zoma wrote:Reminds me of the gateless fences where a person can step through, but animals will not because off the odd arrangement for their hooves/paws/etc.

As others have said, pretty hard to enter that door with a weapon in your hand on a deadly charge too.

Speaking as a father though, what a great way to have your twelve children living in the house and not have to yell at them for slamming the door!

I don't know if they had dogs or goats, but both can go literally anywhere, from my past and current experiences... (no more goats but one dog that climbs on any and all furniture in storms!).
We know so little about their religions, as any libraries were destroyed, by us, or rather our ancestors.
I reckon that like most beliefs (i.e. no pork in desserts. It goes rotten and toxic in the heat, etc)that they may be a religious idea based on healthy air circulation.
Or for easier conservation of food in cellars?

Just been watching this which also has a T-Shaped door (and led me to this thread).

My thought are that a T-shaped door is the minimal size. If you didn't have a door but it was cold at night you'd hang a 'curtain' in front of it.  The smaller the door, the better and the T-shape is arguably the minimum practical.  If my theory were true I'd also expect a step at the bottom and a lintel so that the curtain could seal  on all 4 sides.

Amy Gardener wrote:..... What is known is that these doorways are the entryways to multiple once-enclosed-spaces heated with indoor fires. The ruins exist.
While watching lectures and reading academic papers, I kept thinking, “why doesn’t someone just make a model of the door, live in the space for a period of time then submit their practical, hands-on, in-the-field findings?” The apparent absence of real-life experimentation with the T-doorway leaves an opportunity for discovery for anyone who is motivated to actually do a contemporary hands-on exploration by modifying the entryway to a hand-made earthen shelter.
Naturally, I am considering making the T-door unless some other permie has already done so.

 
Amy, did you ever build one of these to assuage your curiosity?  It may have been mentioned already, but in addition to other suggestions and taking into account both their prevalence in exterior walls and wall thickness, I could completely relate to the added benefit of the 'shoulders' of the T being a place to rest baskets/gathered goods when entering and exiting the door.  We live in a way that all sorts of domestic and wild animals could enter our doors and have as a consequence several (yet still inadequate in number) railings and side-tables for placing garden goods, tools, firewood, etc....all which would be vulnerable to animal curiosity if not raised.  The shoulders of the T of those doors would allow temporary storage while moving through the narrow walkway after a gathering expedition. ....Maybe?  And if such rooms often held large gatherings, all of the long-coats and mink stoles could be piled up on these shoulders as a sort of ancient "coat check" function... ;-)

It would allow a skin, cloth, or wicker door to be draped over that area by itself without being hung or need support. I'd always thought that with them in the cliff dwellings and the lower door blocked it would help to keep small children out of trouble...falling off the cliff, but still allow for visual into the room.

Very interesting. This is my take: the speaker said the first “doors” at Chaco were the raised rectangular ones and the later ones were the “T” shape. That makes it easy for me to think that it began as a purely practical way to make it easier to move your feet through, instead of over. They still had the ability to seal the wide opening to trap heat in the winter and, if needed, for defensive reasons.
It seemed to me the opening that started off as just an easier way to move through a wall became symbolic. As the people who became known as the ones that used the “T” shaped doors moved into different areas and took this idea with them the symbology became more important than the practicality. The basic “T” became oversized and it was less about getting in or out of a building and more about advertising either who was there or what they believed. IMHO it was kind of like their flag.

Yes, I did experiment with the T-door and here are my experiential observations without using temperature and air movement measuring tools.

My fascination with the T-door was practical not aesthetic. Considering the basic physics of hot air rising and cold air sinking, my goal was to find a way to keep my adobe dwelling warmer with less fuel (we don’t have much wood). The 6 foot tall door to the cob and mud brick building reaches down about 3 feet below ground level and about 3 feet above ground level. The cold air sinks into the space and the fire continues to draw cold air. The adobe does warm up with the fire and the thermal mass hold the heat. However, no matter how much wood is piled on the fire, the space never really warms up beyond the 60 degree underground temperature.

When I block the lower two feet in winter, the air intake to feed the fire comes from a higher, warmer, point. Allowing only a small point of air intake at the top of the doorway causes more subtle air movement in the room as the warm air cools and sinks on its way to feed the fire; this could be a convection* effect. Naturally, the earthen room is far more comfortable when air intake comes from the top of the 6 foot opening as opposed to the ground level opening.

Practically speaking, a narrow or slot-style opening is much easier to block at ground level than a wide door opening. It is also easier to close quickly using light-weight materials (I used bundles of rags and rugs). I started by blocking the wider door at its base without creating a narrow slot. The bundles to close the wider door required triple the quantity of material compared to the narrow opening. In a small dwelling, storing the fiber bundles took up living space: very problematic in a small structure. Removing the bundles to exit was difficult and even dangerous when trying to exit. Narrowing the walls at the base of the doorway effectively produced the T-door shape.

*On a smaller scale, I see that my wood fired oven draws cool air from the bottom of the oven door. Since there is no chimney for the oven, the smokey hot air exits, (after swirling around thus producing convection heat) from the top of the oven door.

I live near ancestral puebloan country and have spent quite a bit of time backpacking there and reading about their cultures (as best as you can since they moved away and their culture was impacted in big ways by other tribes and Spanish/American colonization after that). The first thing of note that is that they did not have any large domesticated animals. Turkeys are all that you hear about but surely dogs were also there. Large wildlife was also surely not a problem because man was one of their bigger predators.

One interesting thing to note is the puebloan art style depicts people with these big torsos, broad shoulders, and stick figure legs (see link below). Nearly everyone, which I think is fascinating. I obviously don't think that was how they were built but it is interesting that it matches up with how their doors were shaped. Was that the unrealistic body image that their culture idealized? Did that somehow impact their architecture? Doubtful, but an interesting thought.

Another thing that you'll notice in this region is the high prevalence of granaries and their meticulous construction to keep rodents out. Minimizing the entrance at ground level may have helped slightly with keeping mice out of their rooms. Similarly, it would reduce the amount of snow blown inside during winter.

Mostly though, I bet it just made sense with air intake/venting combined with passive solar heating. Maximize the venting of smoke while reducing the drafting of colder air at floor level as others have said. With regard to solar, these homes are almost exclusively built on south facing rock alcoves. The summers are very hot and winters can be brutally cold. During th winter months, the sun is low enough to shine under the alcove and radiate the homes while in summer they stay mostly shaded. For those that aren't far enough recessed, greater shade at floor level would help with that since it would be the first to get sun.

Hi Dave,

Welcome to Permies.

I wonder if I make a T shaped panel for my greenhouse door could the heat exchange  be measured?  With the  structure that has such a heat differential  cutting a t in a sheet of plywood is a simple thing. If that is the purpose of the door a simple experiment to put in place. Is it as simple as a planar venturi?

If the T-shaped door was purely functional it is unlikely that it would have been memorialized in items such as mugs and altars at Páquime. I agree with Dr. Lekson, who has studied these, that they symbolize something and possibly indicate spaces used by a particular group of people.

Medieval wooden houses here in Norway usually have nearly square doors - wider than strictly necessary for ordinary use, but also lower than what we today would consider comfortable. The door sill (? or threshold?) would also be quite high, so you would have to consciously step over it at the same time as bending down to get in. The "folk interpretation" is that this is a defensive feature, but it definitely changes the air and temperature exchange between outside and inside. Even when you open the door some warm air will be trapped above the level of the door opening, and cold air from outside can not as easily "flood" the floor. I realise this does not really solve the mystery of the T-door, I just wanted to mention an example of a building feature that likely has a practical purpose, but still lends itself to other perhaps less likely (although possible) interpretations.

The T-shape does seem strange. If the lower part is very narrow, it would force you to mind your feet when using the door, which would be inconvenient in daily life - on the other hand, a wider than necessary top would be a structural weakness that would have to be compensated. So both parts of the T shape seem illogical, but depending on the way they were used, what people took in and out of the buildings, whether they went in and out many times a day, what the weather and climate was like - the inconveniences could be outweighed by, I don't know, less draft along the floor, more light when the door was open? Maybe you could sit on the little ledges under the arms of the T, doing some sort of chore in the daylight, while conveniently close to small children inside, pots on the fire, safely stored supplies of whatever? Being easily able to block the lower half does seem to be the most obvious practical advantage, keeping small children in, and to some extent drafts, dogs and turkeys out (if you keep half an eye on it at least).