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Roofs on Adobe Homes

Quentin Wilson and Associates, specializes in solar adobe design and construction. He grew up in the South Valley of Albuquerque, New Mexico where he watched adobe bricks being made. In the fifth grade, he made miniature adobes on cookie sheets in his mother’s oven in order to construct house models for a class assignment. By age thirteen he made full-sized adobes in the back yard and ruined the grass. Later, he traveled a bit, went through the Army, and graduated eventually from the University of New Mexico with a major in physics, minors in math, chemistry, and education in 1970. After teaching high school two years and community college math for three more, Quentin moved into professional solar adobe construction in 1976 as the Project Manager and Instructor for the Sundwellings Demonstration Project at Ghost Ranch, Abiquiu, NM. He became a licensed general contractor in the State of New Mexico in 1982. He has been building homes and teaching seminars and workshops ever since. In the fall of 1995 he established and taught the full-time Adobe Construction Program at Northern New Mexico Community College. His website, quentinwilson.com, lists the course schedule and many other resources related to working with adobe.

Q: We are considering purchasing an adobe-style, flat-roofed house in Steamboat Springs, Colorado, but are concerned about how the roof handles the snowfall. The exterior is dryvit stucco. Our realtor says that it just stays on the roof throughout the winter and provides extra insulation. It has drainage spouts at the flat part of the roof and looks to be very well-built, with no signs of leakage. It is 15 years old and appears to be in excellent shape. Could you advise us on what kinds of questions to ask about the roof materials/design, etc., to make sure it is built properly?

A: Hopefully the roof has some pitch to it so that water drains to the canales and does not puddle on the roof. A flat roof should not be a level roof. A minimum slope of 1/4" per foot is what is expected of flat roofs. A really good roof has crickets which are sloped sections of the roof that make sure that water runs to the canales. Crickets might be barely discernable on a low slope roof but they should be there or else water puddles long the parapet where the roof meets it. If the roof is well insulated then I would expect in the right climate that the snow would indeed persist throughout the winter and add to the insulating value.

It would be good if the canales are not on the north side of the house so that when water is discharged in transitional weather it does not refreeze when it hits the shaded ground and build up an ice dam.

As for the roof membrane itself, a well done hot mop - sometimes called a built up - roof should give about thirty years life before it needs significant attention. Brai or other torch down modified bitumen roofs might last a bit longer and a rubber or synthetic single membrane roof would be expected to last the longest at around fifty years.

It really might be worth the cost to have a local home inspector look over the house. He would have a realistic idea of the weather requirements and could see in person many details that it is hard to judge from a distance. There is the National Association of Home Inspectors and at least one other professional group of inspectors which list their certified inspectors by state.

Q: I am buying an adobe house in Velarde, NM that was constructed in the 1940's. The surface and insulation on the roof have been replaced recently with TPO membrane on top to cure a leakage problem. The vigas and the 1" boards on top of the vigas have a slight sag and the roof ponds a thin film of water in one corner. I have had the house inspected by a licensed NM inspector. He did not seem to think the sag was a major problem in an adobe house that old but he did have a problem with the ponding. The vigas span is a little over 20'. Would it be a good idea to support the vigas with a beam across the center of the span and possibly jack them up a bit, not as a cure to the roof ponding but for extra support and internal appearance?

A: I am not familiar with TPO. I do know about TC&I, Thermal Coatings and Insulation, who spray on a polyurethane insulation with a final ultraviolet protection layer. TC&I usually works hard to eliminate any puddling areas by varying the thickness of the insulation. Some membranes tolerate standing water well. In Industrial America, many flat roofed buildings are built to stand up to a thin layer of water that is sprayed on in the summer to turn the roof into a giant evaporative cooling device. Whether or not your membrane is this quality, I cannot say.

If your vigas are big enough, a 20-foot span is not a problem. But if there is indeed a noticeable sag, it might be worth thinking about. Lots of older houses had dirt roofs even as recently as the 1940's. If that were the case and the dirt has been removed that subtracts a very large load and over time the vigas might just straighten out a bit. We have seen this happen on structures in Velarde and Dixon that belonged to the Archdiocese of Santa Fe.

Q: I have built a pueblo style poured adobe home in Casas Grandes Chi MX. It has parapets and canales on the roofs. I tried Formflex 4000 on concrete roofs; it is expensive ($180 5 gal.) and has a problem adhering on one deck. Is aluminum fiber coating a viable option at $35 5 gal. and will tile stick with flex set on roof/deck?

A: I am not familiar with Formflex. Aluminum Fiber coating will adhere once the concrete is fully cured. If the concrete is at all green, it is very problematic. Tile will adhere to the roof in a thick set, cement based adhesive probably with a latex or acrylic admixture to give it extra waterproofing. I would consult a tile and/or adhesive manufacturer. I have been happiest with the C-Cure adhesives over the years for floors, walls and shower surrounds. I have no experience with tile on exterior roof systems and the added environmental intensity I would expect in Casas Grandes.

Q: I'm planning to build a small home in Mexico and would prefer to use nature-friendly techniques. As both adobe structure and palapa roofing appeal to me, I am wondering if it is practical to combine these? The plan is evolving as a "modified" A-frame with intent to use adobe exterior walls, plus as interior walls to support the loft area.

A: Perfect. That's as autochthonous (autocrono) as you can get. Just like the thatched roof Irish adobe cottages or Zapotec structures in Oaxaca.

A: (Kelly) I also live in Mexico, and have seen many adobe and palapa roofed structures, as these are completely indigenous to the area. I see no reason why you shouldn't combine these two fine examples of natural, sustainable arhcitecture. However, for an A-frame design, only vertical walls should be made with adobe, and these need a good roof.

Q: I have an adobe style house with parapets and canales to drain water off the roof. Do you know of any system that will funnel rainwater from the parapets without completely compromising the architectural integrity of the home?

A: There are some clever sheet metal folks around Santa Fe who drill a hole in the bottom of the canales just after they exit the parapet wall. They solder on a tube that connects to a standard gutter conductor pipe to the ground. If painted to match the color of the wall they are nearly invisible. In case of a heavy rain or ice, water can spill out the front of the canales as originally intended. If there are problems on the roof itself in getting the water to move to the canales, the answer is crickets. A competent roofer will know what this means.

Q: I am in the negotiating and inspection phase of a 1946 California adobe in the desert community of Apple Valley. I am noticing that some interior walls up near the ceiling appear to have water staining (only in the corners). Additionally, the coating is failing on the outside of the house. How can I tell what the coating is? How do I prepare the coating for application of a new coating without destroying the adobe. It is hard to tell but the coating that is peeling off in places is stretchy and I think it could be a latex paint. There is some failing paint up near the ceiling beams in the living room as well. The house has lovely character and it is possible that I can purchase it for the value of the land. However, I am wanting to be cautious as I will be spending cash as I go and would hate for it to turn into a money pit.

A: I have been singing the Money Pit   movie tunes lately. All homes are money pits so you just have to know when to quit. Sounds as if there may be some roof problems  if there are water stains up high. A good roofer would propose  to repair problems. Other roofers, equally good might suggest complete replacement. Always a tough decision. The outside stretchy coating may be a masonry paint or it may be an elastomeric plaster. A knowledgeable local stucco firm should be able to tell you. Standard cement based stucco does just fine on adobe walls. It should be applied directly over metal stucco netting with no paper barrier. It is the paper that introduces impermeability. Cement stucco has 5 or 6 perms which is all adobe needs to breath. If you can buy it for the value of the land, then you are most fortunate. Many times the old adobe is like an old Ford. It only needs one spark plug to get it going fine.

Q: I'm considering building a low pitch (2:12) adobe roof. I would like to use a waterproof mixture, at least for the outer layer, and was wondering what your thoughts were. The water would be collected for indoor use, though probably not for drinking water. Asphalt emulsion does not appeal to me and I am curious what you think about lime or cement's ability to hold up? Which would you prefer?

A: I think lime might be your best bet. It is used over dirt roofs in northern Mexico very successfully. I am no expert with lime. Northern New Mexico got by for a couple of centuries with just plain dirt roofs. One still exists in El Rito but the two older gentlemen who lived there are gone and without maintenance it won't last much longer. Where are you located? Your annual rainfall can have an impact on how you do your project.

I will be in Northern New Mexico so rainfall is light. More than anything I'm thinking about the snow piling up and wanting to have good protection against that. Lime sounds like a nice choice. I've read a bit about it--mostly in conjunction with wall plaster--and will see what more I can find.

Q: I want to build an adobe house in Mexico, but I really don't want a pile of dirt on my roof. I don't want future maintenance or problems. I don't care much for corrugated steel or tiles either. I am willing to give up some of the insulation factor on the roof - can I used a poured concrete roof over 10' adobe walls which are 20" thick? What kind of support will I need and how thick should the concrete roof be?

A: That's seventeen questions all at once. Personally, I think a concrete roof is about the last one to consider. There is a lot of new information emerging on lime plaster coated dirt and reeds. 20-inch adobe walls, 10-feet high will be powerful enough to support most anything. But we need to know the span to determine the size of the beams, joists, girders, or monolithic concrete beams/deck for the roof. Never skimp on roof insulation if you are in a warm climate and located where the sun might shine on the roof. Except for the best mixed and poured, most concrete slabs crack after a little thermal stress which goes along with day/night cycles. Consider the expansion joints in sidewalks and what happens if they are absent.

Q: We are thinking of buying a standard type historic Adobe home in Santa Fe (single story). However the ceilings can be a bit low. I know there are many variables with such a project. But as a ball park figure how much would it cost to raise (by 1.5ft), and replace the roof (flat) including all Viga beams on a 1000 ft property?

A: Holy potatochips! No one ever asked me a question like that. So thanks. First of all, how low are they? My own ceilings vary but in the living room the bottom of the beams are at most seven-feet, two inches high. In all ceilings except the back bedroom, I can grab the bottoms of the vigas or beams. It makes the house much easier to heat since the volumes of the rooms are reduced and in the end its the volume of the air and the area of the floor, wall and ceilings that have to be heated. In addition, the low beams and ceilings are like a well appointed yacht which would have hand-holds on all ceilings to provide safe movement in a heavy sea. Its a comfort to know that as I age further I have a home that will be easy to navigate. Right now, I routinely and instinctively reach up to the vigas/beams to steady myself when I step into my sandals and slippers.

About half my twenty-five year career of adobe homebuilding was spent conserving, preserving, modernizing, stabilizing, remodeling, re-purposing and renovating or replicating existing adobe structures. For the Really Big Question from owners about whether or not it made economic sense to rebuild compared to tear-down and new construction, my rule was that if a house was intact to the degree that the roof structure did not have to be replaced, then there was enough embodied value in the structure to make it worth fixing. Your concept while within the perimeter is outside the parameters: the roof/ceiling does not have to be replaced, merely raised. We sort of did that with "The Ruin" in El Rito. One-hundred ten linear feet of adobe wall was in precarious shape so we jacked up the roof system, knocked down the wall and rebuilt it with a concrete foundation back up to a code compliant wood bond beam to which we re-attached the roof. The house was repaired nicely and represented the best work I have ever done but I was ruined since it was a speculative renovation where I had purchased the property to sell after renovation. Speculative renovation is perhaps the most dangerous job for a contractor to attempt.

So the answer to your question begins to unfold. If the original viga/ceiling/roof system is built in a manner that allows it to be jacked up as a unit, at least room by room, then if the tops of the walls are in condition to take the additional 1.5 feet of adobe bricks including a concrete or better yet wood bond beam to which the roof can be attached and if you find a Santa Fe Contractor or one from a nearby village in a good state of humor, and the building officials in Santa Fe who are never in a state of good humor, then the job would cost on the order of $25,000. For the ill-humored contractors the price will only go up from there.

If, however, the project is to remove all vigas and structure above them and replace all with new materials, then the job will cost at the very least $55,000 if done by three men in a pickup truck. Via private communication, I can give you the names of three well-respected Santa Fe area contractors who will be happy to do the job for $140,000 with clauses for hidden conditions and change order forms in tablets on their clipboards.

Q: We have bought a 20 year old stucco adobe style home with a flat roof. The home is un-airconditioned and we do not plan to do so. Our roof is asphalt and we are interested in a roof system that will cool the house in the summer and keep it warm in the winter. Now the home reaches 90 degrees, or warmer, on the ground floor and temperatures are not going down in the near future. The home provides cross-ventilation but the house is a hot box mid day. Any suggestions?

A: There are several roof membranes available that have a white surface. One that has been used a lot at Los Alamos and in a few homes in the surrounding area is SinTech, Synteck, or other spelling, by Carlisle. They pioneered single membranes with rubber such as is found in aircraft inner tubes. Sintech - and I might not have the spelling correct - is synthetic and may come from a division separate from Carlisle Rubber. Hubba hubba Carisle Rubba was the song of the pilots in WWII who were happy knowing that their tires would blow out every third landing.

Under the SynTeck, you can add a couple inches or more of rigid insulation. The application of both insulation and membrane can only be done by certified roofing contractors. There are other membranes such as Hypalon; torch-down roll roofing such as Brai from Germany and equivalents from GAF and other USA companies; and several other systems for single membrane roofs. White and additional insulation will be the key.

You can also have the roof sprayed with foamed-in-place polyurethane insulation foam which is top coated with a skin that can be specified to be white. Personally, I prefer the spray on foam since it seals up all the little places that are problems for other roofing systems. There are two really good foamers in Santa Fe and two sorta good. I am not familiar with foamers in other locations. Adding insulation can cause problems assuming that you have parapets and canales to remove the rainwater. The good foamer will know just how to deal with this and will create positive drainage for the roof to the canales.

From Tucson to Denver, the summer sun pounds down on a roof, probably about 1600 BTU's per square foot per day. South wall will get around 450, north 450 and east and west each at least 1100. The message here is that once you have armored your roof, do what you can to keep sunlight off your east and west walls. A little eyebrow will keep south sunlight out of windows. North glazing is a bit harder to protect. Plant a line of trees on the east and west sides or park a semi trailer there to stop the sun. Or maybe Sail Shades. East and west are the killer solar gainers after the roof.

Q: My wife and I plan to move to New Mexico and I would like to build a small (760sqft) adobe house. We like the un-plastered look and flat roof. I know I have a lot of studying to do, but I was wondering if what I want to do will conflict with local codes in Grant County?

A: As far as I know, Grant County uses the New Mexico Adobe Code put forth by the state. Flat roofs are permitted and so is earth plaster even though the code says that it is "not recommended."

Q: My mother lives in an adobe house in Albuquerque, built in the 1950's. A few of the horizontal vigas - they are rectangular rather than round vigas - are cracked (and have been for 30 years) and in one room, they are sagging quite a bit. We are considering removing the 7" of dirt and two layers of tar and gravel roofing from the flat roof, and replacing it with board insulation and PVC roofing, thinking that the weight reduction will help the house. Is this a good or bad decision?

A: Generally, this is a good idea since it indeed reduces the load on the vigas/beams. I have done this on a number of structures. A side effect is that if the vigas/beams return close to their original straightness, little crescents of airspace will develop in the wall beneath them. Caulk or plaster fixes that. Another thing to consider is that the top of the insulation may be lower than the top of the dirt and it may require additional thought and work to ensure that water drains to the canales and away from the house.

I have also had spray foam contractors or specialty roofers spray the roof with polyethylene foam insulation and follow that with a weather-tight skin. It costs more but is my favorite solution.


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