I am planning on building a southwestern style home in Arizona. Can anyone give suggestions on the best way to design / build a traditional flat roof? I know that there will need to be a slight pitch to shed rain. My question is regarding the type of material options for the roof. I saw an article in FH using a neoprene material but that is a very costly option. Any other options you know of that have been successful? Also, what is the lowest recommended pitch that could be used on the high desert (is 1/12 OK?). Thanks for any & all suggestions.
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My bias is obvious with my tag line. My experience, however, includes 20 yrs on the (low) desert there. The sun is not your friend, nor the friend of your roofing, unless it's metal and has a lot of ventilation underneath it. Galvanized standing seam will last about forever when there's no rust. Seeyou's the go-to guy for metal roofing, and he's side-stepping. The most successful almost level roofs I knew were hot tar with gravel (white) thrown on top. The sun killed them too, but lasted longer than asphalt shingles.
Were I to build there (or about anywhere) it would definitely be with a dirt roof, carrying the native small plants to prevent wind erosion. 1 in 12 will work fine. Ours is steeper, and steeper than we needed. We use cheap 6 mil plastic here for water-shedding. Keep it out of the sun and it works great in multiple layers with insulation between.
With a dirt roof you have to watch loading and spans. Untraditional, but we use steel bar joists to effect 40' spans with ease and small cost, while supporting 300 psf. Short spans you can do with wood. Do you have your walls decided? If you find neoprene costly, you're not likely thinking adobe.
PAHS Designer/Builder- Bury it!
I hestitate to answer when I see the word, "traditional".
See, traditional is not that great and very intensive maintaniance-wise.
So I am supposing you really mean something that looks like the traditional adobe styule structure.
Add to that, you mention high desrt, which to me means that you will see some snow build-up, like around Flagstaff. That calls for a bit more pitch than , say, Tuscson.
I'm feeling wordy today, since I've been off-line for a few days, so I'll walk throguh some of the history of these things. I lived in Lubbock, Tx, Taos, NM, and western Colorado for many years and did lots of roofing in those placves....
The origianl Adobes were built with vegas ( long straight, clean lodgepole pine) for structural support spaced at anywhere from 16" OC to four feet, depending on pole size, spans covered, and loads applied.
These would be sheathed in with smaller poles or boards which weere then covered with a layeer os straw grass to insulate and catch dirt. Then the top was pounded adobe clay. Since the desert doesn't see much rain, this was a good thermal heat sink and repelled most of the water, but it needed to be replastered every year - the miantainance deal.
older places eventually got skinned over with either corrugated metal roofing or 90# rool roofing. The roll roofing still needed to be replaced about every 5-10 years. Some were done with hot-mopped smooth surface BUR roofing and coated with AL paint to reflect solar UV rays which dry and crack the asphalt, and heat up the interior. The tie-ins to the parrapet walls would always need attention after hail storms too.
jump to today. If you want it to look like traditional but have some goodness of modern technology and materials - do the structural frame with vegas still , but with help from an engineer to size them. Then skin them over with a nice 1x8 T&G. Before insstalling any of this, peel the vetgaas first, and oil or polyurethene both them and the sheathing. This is so much easier done on sawhorses at wiast level than up over your head!
Then place SIPs - structural insulated panels - to add better strength, and insulation integrity.
For the top, their is not gioiung to be anythiung better than an EPDM roof membrane. it will glue down with contact cement and is flexiable enough to be easy to tie to the parapet walls. You can order it in white to reflect the sun.
And as a bonus, if you wanted to add an adobe clay over it like Vatom suggests, for added insulation and heat sink, the EPDM can handle that. but you need to be engineeered for the weight of that earth when you design the structure. Also, it the desrt, if you were to use vegetation like he suggests, you will have to figure out how to water it to keep it alive. I'd skip that myself.
have fun
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Good synsopsis.
Regarding required engineering for earth cover, there's a huge swath of E. Arizona where inspections are minimal. The only engineering (easily found on the internet) required is that necessary to assure the builder of success. Even in our chichi Virginia county with strict inspections, the only "engineering" they require is a downloaded bar joist chart. Couldn't be much simpler, or cheaper. The exact how-to-assemble comes with the bar joists, from the steel company, not that the inspectors know enough to check.
Had work done on the family place near Nutrioso (Apache county) this yr. They still aren't very fussy. Which I understand is common when you get away from the cities.
I am curious why you'd think irrigation of native plants would be necessary? The houses I know of there don't. PAHS Designer/Builder- Bury it!
first, because I was thinking you were in Indiana which has different native plants than Arizonabut also, because a lot of desert vegetation is cyclical./ If you plant to prevent erosion and use cyclical vegetation that only grows and blooms after the rain falls, there is little prevention happening. And again, because a good adobe clay packed tight as the traditional metod dictated is extremely resistant to growth of plants. The vey fact that the plant exists, means the surface is penetrated
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
We're in Virginia, still have some Arizona land. I sure wouldn't recommend Indiana or Virginia indigenous plants for an Arizona roof. OK, we do have some yucca on ours. But the small high desert plants that do a decent job of erosion control on the open ground will do the same thing on a roof. The roots remain there even if the plants aren't doing much other than serving as windbreaks.
You're right about the clay roof. Anybody counting on it shedding water certainly wouldn't want plant growth. But as you already mentioned, clay ain't much of a roof unless you put it over a sheet of something impervious, making the clay moot. PAHS Designer/Builder- Bury it!
I have used this system in New Mexico with great success:
http://www.conklin.com/pg.asp?p=74
I'm sorry, I don't have current pricing for this system, see if someone in your area is a conklin certified installer, you might look under 'Conklin Roofs'
The heck, you say?
The advice you've received so far is pretty good, but much of it is outdated by anywhere from 15 to 150 years. <G>
As you've surmised, the style of the roof is described as flat, but it must drain reliably. A 1/12 pitch is perfectly adequate. Less is acceptable down to about a half inch per foot.
It's important to get crickets in at corners, skylights, and some changes in elevation. That is an oft-ignored detail.
If you are using sawn beams, the roof is pretty easy to build. If you are using round beams (vigas -- "viga" simply means beam in Spanish. "Vega" as previously posted refers to a grassy meadow, field, or plain used for grazing.)
If you are using vigas, it's worth having them "crowned". This is different than what carpenters ordinarily mean by the term. In this case, you're shaving one part of the beam flat for a width of about 2 inches. This shaved or planed surface goes up. It makes nailing the T&G much easier, faster, cheaper, and stronger.
Your pitch can be achieved by over-framing or with tapered foam. Over-framing is often as simple as ripping tapers from dimensional lumber. Either works, the over-framing is stronger and resists uplift better. In any case, you will want to insulate your roof.
Stay away from spray foam roofs, no matter what you are told, they are trouble. Just go with me on this one, I have repaired many, they are a heartache waiting to happen.
A recent development in roofing not mentioned here is thermoplastic polyolefin. Excellent UV resistance, light, easy to repair, inexpensive, and comes with an excellent warranty.
Check it out here;
http://www.jpselastomerics.com/
Reflectivity, resistance to UV, and tolerance of extremes in temperature are key.
Right after that, foolproof application and ease of repair is crucial. The best and the brightest do not end up roofers in Arizona. I know, because I was one. <G>
Drainage off of the roof is also critical. Make sure the design will not allow for leaks at the roof drains or for drains to become plugged up. This should be common sense, architects still screw it up, and the roofers screw up whatever the archtects don't.
One last caution, be sure your designer understands the spans you are working with. Those roofs made from round beams are usually not as strong as sawn (and graded) lumber. The Southwest is covered with houses that have sagging roofs that now pond in the middle of the roof. The more it ponds, the more it sags, and the worse it gets.
Another reason to build in as much pitch as you can hide behind a parapet.
Good luck!
Thank you Catskinner. This is great advice & very much appreciated. MarilynJ