Looking for the Wednesday Wandering? Page back one and hear about Adara the Puppy, contests, and offer a few thoughts on short stories. Then join me and Alan as we world-build our way into the question of flat roofs.
JANE: Last time I promised to unravel the mysteries of flat roofs. Between my husband, Jim, being an archeologist and our good friend, Chip, being a roofing estimator, I know more about flat roofs old and new than I ever thought possible. To really understand the phenomenon of the flat roof – at least in the American Southwest – you need to know a bit about the region.
Unravelling the mystery involves distinct similarities to the sort of world-building one does when writing SF or Fantasy.
ALAN: That sounds fascinating. Tell me more.
JANE: All right, here goes. First, you need to understand that the original southwestern flat roofs were built in areas that lacked two things: rain and long pieces of timber. The long, hot summers and the fact that, even in mid-winter, days can be pleasant and sunny (if not overly warm) also played a role.
Sloping roofs need beams to create the slope. To make beams, you need large pieces of timber. In many parts of the southwest, large pieces of timber simply aren’t there. The nearest trees are small and scrubby. Cottonwoods are notoriously soft (and explosive, but that’s another matter entirely). If you want roof beams, you need to go up in the mountains, cut the trees, then haul the logs all the way back to where you live.
This was done but these beams then became highly valuable items. Are you familiar with the “old wood problem”?
ALAN: No – I’ve never heard of it.
JANE: This is a problem archeologists out here encounter when they try to date a structure (actually, anything at all) by wood or wood residue. Wood can be dated in several ways, including C14 dating and dendrochronology.
ALAN: Ah yes! I know all about that. C14 dating measures the concentration of radioactive Carbon-14 in organic material such as wood. Since it decays at a known rate, the concentration gives a measure of the age of the material.
Dendrochronology is where you cut a Beatle in half and count the rings in order to calculate the age of the drummer. Hmmm… That doesn’t sound quite right…
JANE: Ouch! But, you’re almost right. Dendrochronology is also known as “tree ring dating.” And since I anticipate jokes about dating services for trees, I’m not going to ask you if you know how that works. I’m going to be grim and serious and focus on roofs.
The old wood problem arises for a number of reasons, but I’m going to stick to the one that has to do with roofing beams. Since the beams took a lot of labor to acquire, when a group left an area, they’d let the houses go back to mud and stone, but they’d often take the beams with them. This means that archeologists can’t assume that the date they get from testing the wood is the same as the date for the structure. The beams might, in fact, be the equivalent of family heirlooms, handed down for generations.
ALAN: That must have made the reading of the will rather tense. Which child will get which bit of the roof? And think of the bargaining afterwards! “I’ll swap you three joists for a gable truss…”
JANE: Actually, I suspect there would have been discussions quite like that – even if the terms were different.
Now, back to flat roofs… Out here the main types of beams are usually referred to by their Spanish names. Vigas are tree trunks, usually stripped of their bark and smoothed. Latillas are slimmer, either cut from saplings or from long branches. None are cut into planks or joists. They’re just pieces of wood, valued for their length and hardness as much as anything else.
Now, imagine you’re a Pueblo Indian. You’ve carefully constructed your house either from adobe (a blending of mud with straw) or from mud mortared stone or some combination of the two. If you used adobe, you coated the exterior with various forms of mud plaster.
The time has come for the roof. First you lay down vigas, then crosswise you put a dense layer of lattias. Then you layer on other materials: brush, smaller branches, dry grass, and suchlike. When this is in place, you start layering on mud. Techniques varied, but the end result was a very thick roof – one or two feet thick was not uncommon.
ALAN: That sounds rather like thatching – though thatched roofs do slope because they are built on joists, and there isn’t a final covering of mud. But the layering of other organic material is typical of the type.
JANE: Good comparison – but thatching wasn’t done here, probably because there wasn’t sufficient timber to build the joists necessary to support the roof so that it would properly drain.
The southwestern style flat roofs not only kept out the worst of the rain and snow, they provided extra living space. The evidence is that – except in the worst extremes of weather – the rooms were used more for storage than as living space. Additionally, the thick walls and roofs provided excellent insulation, making for rooms that were cool in the summer and would retain heat in the winter.
When the Spanish came to the area, they adopted similar building techniques. I believe they were the first to introduce “canales” – channels or canals that encouraged runoff into gutters that jutted over the side of the structure so as not to erode the mud walls. This rain was often caught in rain barrels and stored for later use.
Until the railroads made transportation of building materials practical, variations on this type of structure continued. Re-plastering and otherwise repairing the houses was an annual event.
ALAN: We do have some houses here that are built to look like that. They are known as “Spanish Style” houses.
JANE: Yes… And that ties into my next point. In modern times, various architects admired the appearance of both “pueblo” and “territorial” style architecture and sought to emulate it for modern structures. However, since they were no longer designing roofs at least a foot thick and made of absorbent materials, all the problems you listed last time occurred – without the advantage of creating trout fishing ponds.
Often these modern flat roofs were covered in tar and gravel. This would seal the roof for a while but, eventually, hollows would appear, creating weak spots, which, in turn would create leaks.
Nonetheless, architects and home owners persisted in wanting the look of “traditional” southwestern architecture and that demanded flat roofs (or a combination of flat and peaked roofs).
These days, advances in building materials make flat roofs possible to construct with fewer leaks. In new construction, a parapet running around the edge of the roof often conceals the fact that the roof is actually not completely flat, but is pitched to encourage runoff. This, in turn, is channeled into the modern version of canales.
ALAN: So the flat roofs are actually optical illusions? How clever.
JANE: That’s it! And, as I mentioned all those years ago when I visited New Zealand, New Mexico remains stuck on brown as the only acceptable color for houses. Even though modern frame stucco construction is no long constrained by the color of mud, the majority of houses are some shade of brown with color reserved for trim.
ALAN (to the tune of “The Hippopotamus Song” by Flanders and Swann): Mud, mud, glorious mud…
JANE (singing along): …nothing quite like it for cooling the blood.
And the house.
ALAN: (sung to the tune of “Food, Glorious Food,” from Oliver!”) Mud, glorious mud…
JANE: (singing along) “Hot Tar and Gravel!”
And while we’re talking about roofs, I have a few questions about how the climate in your part of the world influences construction. After all, there’s not only world-building – the world influences buildings!