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Cost per Sq. Foot

by Stacey Dash last modified Aug 18, 2005 11:31 AM
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Cost per Sq. Foot

Posted by Stacey Dash at June 24. 2005


My husband and I are planning to move back to Austin from San Francisco. The cost and over bidding on houses in the Bay Area has made us realize what we had in Austin 10 years ago!!!

Can anyone tell me what the cost per square foot will be to build a modern home in the Austin area? We are looking to build on a one acre plot of flat land. A courtyard home (pool in the middle) with 3 bedrooms and 2 1/2 baths, +study/media room. I also want to use the best quality materials. A medium size house (2,200 - 2,500 sq feet), preferably using rammed earth contruction. Any pointers to architects/contractors will also be highly appreciated.



Re: Cost per Sq. Foot

Posted by Mark Meyer at June 25. 2005


I'd love to talk to you about your project, especially in the regards of doing something out of rammed earth. So you have a plot of land yet? If you are really considering rammed earth I think you'll find the cost to be around $150/s.f. upwards to $200/s.f.

If you take a look at my livemodern homepage (link in my signature) you'll see that I'm as enamored of courtyard houses as you are, and while the courtyards in the courtHOUSE variants aren't quite big enough for a pool, the idea is very intriguing to me.

I can totally see a really nice composition of heavy rammed- earth walls playing off large expanses of glass and sliding patio doors, with exposed wooden beams that cantilever out supporting a highly insulated SIP panel roof structure. It could all be kept very simple and clean (think Rick Joy's work in Arizona).

Feel free to contact me at the number below should you want to talk some more about this idea.

Mark Meyer

Re: Cost per Sq. Foot

Posted by Chris Czichos at July 24. 2005


I just read your inquiry about building cost and specifically rammed earth construction. You might want to look at some alternative construction material. Unfortunately this climate (hot/humid with small temperature changes day to night) is one of the few situations that insulating with mass is extremely inefficient. In fact, it is arguably a determent to overcome.

Even with large overhangs the ambient temperature outside will heat the rammed earth walls while your air conditioning is fighting to cool the large mass. In dryer climates the diurnal temperature change is enough to cool the building at night the mass of the building acts as a heat sink during the day and assist in cooling the interior of the house.

In Austin the summer night remain fairly warm and don not allow the building to cool it’s self adequately. This means that even in the evening as the outside temperature drops the interior temperature will remain high.

I appreciate rammed earth construction and given the right climate would love to incorporate it into a design, however, it doesn’t make since in this area.

An alternative with a somewhat similar aesthetic is straw bail construction. I don’t believe that it has the crisp lines that make rammed earth so appealing but it cools quicker.

Better yet, look at the vernacular architecture of Central Texas to give you inspiration. Where as the desert southwest has a tradition of adobe and rammed earth, this area has a traditional building type of Dog Trout style homes. They had very large overhangs they were designed and situated to allow air to flow in, around, and through the building. This means that the direct sun cannot heat the building during the day and it cools quickly at night.

Good luck with your project and if you have additional questions about cost etc. I work with KRDB a local design/build firm and I can give you a good idea about what you budget needs to be,

Chris Czichos
O 512.374.0946
C 512.293.8003
F 512.374.0736

Re: Cost per Sq. Foot

Posted by Mark Meyer at July 28. 2005

While the technical aspects of what Chris is saying are indeed true, I've been in rammed earth houses in Austin, during the summer, and without the AC on (they were still under construction) and they are remarkably cooler than the outside temps. I think the key is that there was a LOT of rammed earth mass as INTERIOR walls and not just exterior walls. If the mass is interior and is always in the conditioned space then it will naturally act as a temperature ballast and keep the interior temps close to at what the thermostat is set.

I think what might be appropriate to look into is Autoclaved Aerated Concrete blocks for exterior walls and rammed earth accent walls at approporiate places. AAC gives you a fairly large thermal mass (and thick walls) but it is compesed of a lot of air cells as well and so has decent insulative properties. It is then finished with whatever exterior and interior finish you choose, but does take stucco and plaster extremely well, and can be made to look incredibly crisp and modern.

I imagine there would also be a way to insulate a rammed earth wall within its thickness. If it can be done with cast in place concrete I don't see why it wouldn't work in rammed earth.

We do live n a tricky climate, in terms of passive systems. Hot and Humid is the most difficult to deal with, as the ONLY thing (other than de-humidifying) that will get the percieved comfort level right is air-flow, and as the temps rise, and the humidity jumps, it takes a hell of a breeze to amke one feel comfortable.

Mark Meyer

Re: Cost per Sq. Foot

Posted by KT Hernandez at July 28. 2005

The idea of thermal mass on the *interior* to act as a kind of regulator is new to me, as is autoclaved aerated concrete block. Cool, literally. :cool:

I thought I would throw in a couple of ideas I've actually used to retrofit my home which might also be useful in new design and construction depending on needs and aesthetics.

The first is using external solar screening to block the sun from heating the thermal mass to begin with. I used this along the western exposure, which receives full sun, reflected and magnified off the lake, all afternoon. To keep from permanently blocking a lovely view, I used fabric solar screening (sold in garden centers) made into roll up blinds so I can enjoy my view when I want to, usually in the morning when it's cool and the sun is on the other side of the house. If the view had not been an issue, I've seen materials of various types implemented cleverly in static panels to add privacy and architectural interest as well as to block direct sun. The solar screening has worked so well, the resulting energy savings has already recouped the entire cost of materials in only two months!

Another option is to use the ice chest model -- build the wall to be a radiant barrier, a thermal break, and a thermal mass. Ideally, the thermal mass should be to the interior, the barrier to the exterior, and the break in between, but any arrangement of these three elements will result in very significant savings. This is easier to do during construction, but can be done as a retrofit.

Here's how I did it: my house is made of reinforced cinderblock -- which is purely a thermal mass -- and this was very problematic, radiating heat bi-directionally so the house was never warm in the winter, and turning the house into an oven in the summer. As I can afford to buy materials, I am lining the inside surfaces of the exterior walls with a false studwall (which is actually structural; it's made to support shelves and cabinets like any other interior wall). The purpose of this interior studwall is twofold: to hold insulation and new wiring (the old wiring is buried in the concrete and is failing). The insulation is a sandwich of foil backed foam (foil facing the exterior), high-R value batting, and foil backed foam (foil facing the interior), overlayed with real wood paneling. The result provides a radiant barrier both directions and a thermal break between the radiant barriers. Yes, I lost some square footage, but my house was actually *warm* this winter, for the first time since I bought it.

Something else to consider when insulating a wall is humidity and mold. Any system that incorporates both a thermal mass (particularly one that can absorb moisure from the air) and materials like plastic housewrap or plastic faced insulation, mylar, foil, or foamboard runs the risk of creating a zone in which condensation can form. The materials I selected were chosen for resistance to moisture, and were installed so that the wall breathes to the interior space, where humidity is controlled, so moisture can't get trapped in there and grow mold.

Hope that helps.

Re: Cost per Sq. Foot

Posted by pk at August 07. 2005

Hi Chris:

Wow...interesting comments about use of rammed earth in the austin area. Makes complete sense. I wonder why the greenbuilder site is promoting rammed earth const as a viable method for this area? Your comments about looking to the vernacular architecture for ideas for sustainable buildings is also completely logical.

We have property on Hwy 71 west on a naturally terraced hillside overlooking the Pedernales river valley. The building site is spectacular, flat, breezy ....but, unfortunately the best part of the view is due west! We're struggling with whether to be practical and give up on that view ...or...what?...a 20' overhang?

I was exploring the idea of rammed earth. Glad to read your post. Will definately rethink that idea! Maybe that's why you don't see Lake/Flato using rammed earth!

So do you think SIPs are the single best way to build in Austin?


Re: Cost per Sq. Foot

Posted by pk at August 07. 2005


Is there a source for additional ingormation for the ice chest model that you mention in your post?


Re: Cost per Sq. Foot

Posted by Mark Meyer at August 07. 2005

There is no single best way to build in Austin. SIPs are great however. If you click on my logo at the botom of this post you can take a look at the Deep Eddy West project. It is a SIP based solution a few miles from Hamilton's Pool, out your way. It is very much a modern solution that looks to the Texas vernacular for ideas about how to inhabit the landscape. SIPs worked well in that application (as they do in most applications), but there are other ways. I mentioned AAC (autoclaved aerated concrete) as another alternative. It gives you the solid mass of wall you'd get with rammed earth but it also has built in insulation.

Your West facing property/view is a tricky one, but is very typical of the Pedernales riverside lots. You do need a large overhang to the west, but it could also be a completely seperate porch structure. But it will only get you so far trough the day. Once the sun slips down past the shading structure of your porch you have to combat it with a shade structure that hangs vertically. I would recommend sliding wooden slat screens (or the like) that you manually move into place when the sun gets completely blinding, and then move out of the way when the sun is shaded by the overhang/porch. That way you have the best of both worlds, the view when you can have it earlier in the day and later at dusk, and then a cozy shaded space when the sun is at its blinding lowest (which only happens a few hours during the evening until it slips down past the hilltops.)

Since you have a breezy spot out on the river, you WILL want to take advantage of as much exterior living/entertaining space as possible, some of which would want to be screened in, and other of which would want to just be covered deck, and even more deck that would be uncovered for wintertime sun soaking. This is great though as it means you can shrink your actual conditioned space into a gracious but modest amount of interior living space. Country living at its best.

For something like that (SIP or AAC based construction) built out near the Pedernales I'd expect you to need to spend between $120/s.f. and $150/s.f. which isn't bad, epecially assuming what you'd be forced to spend in SF.

I'd love to speak with you further about your project. I for one LOVE working on projects that are in the Hill Country and can take advantage of passive cooling, rainwater collection, solar, and other green building techniques. It sounds like you have a lovely spot of land as well.

Mark Meyer

Re: Cost per Sq. Foot

Posted by pk at August 09. 2005

Nice work, Mark! You might want to add some interior shots as well...

My hubby is loath to let go of the idea of rammed earth. He was enamored with the look and the idea that you wouldn't need to put another treatment on the exterior like stucco, stone, or hardiplank. My understanding is that you can even forgo interior walls in some places. Seems like a very economic way to build...

So, is there any other material like that that would be appropriate for austin's climate...something that is both structural and finished exterior/exterior walls all in one? Can the AACs/ICFs be left exposed? How do they look if left uncovered?

Re: Cost per Sq. Foot

Posted by Mark Meyer at August 09. 2005
Rammed earth isn't as "affordable" as it would seem if you take everything into account. "Supposedly" the materials are quite cheap, but in reality you have to truck in TONS of various types of dirt, as most of the soils around these parts aren't truly the correct mix of clay and loams required.(this may or may not be the case with your site) Then there is the labor for constructing the formworks (which are quite immense) as there is a significant amount of pressure involved in lifting the earth up into the height of a wall, as well as tamping the earth back down. Then there is the labor (and machinery) involved in mixing the dirt, placing the dirt in the forms and tamping it back down, then repeating the process. Even though labor in Central Texas isn't super expensive like it is in California, it is still a MAJOR portion of any construction project. While it is true that once the forms are erected you could essentially DIY the mixing and placing and the ramming of the dirt, it would take FOREVER (and it takes a long time anyway), and in construction TIME = $$. True, you end up with a wall that only requires a finish coat of sealer (especialy in our humid and inevitably rainy climate) and can be left exposed to the interior and exterior, but at what cost in time and labor (and lack of insulation)? This is NOT to say that I don't think that rammed earth is a viable option. It is what it is (beautiful) and I for one would LOVE to design a house around it. Rammed Earth homes are not without precedent in Austin and Central Texas, although the two that I know of are pretty chi-chi and fall into the trap of "desert southwest" style. The two houses I know of also don't fall into the category of affordable...

ICF's require that you apply a "finish" material over the foam as the foam needs a minimum protection from flame spread. There are some other products (FasWall etc) that are quasi-ICF that use different materials than foam, but they are pretty ugly in and of themselves. AAC on the other hand could be left exposed on the interior, although its inherent porosity would require an exterior finish. It is however not a readily flammable product like ICF, so the interiors could be sanded smooth and left exposed. It is however a relatively delicate surface and is very easy to scratch and gouge (which makes it ideal for carving) so an application of plaster is usually advised to toughen up the walls. The nice thing about AAC is that it takes plaster and stucco readily without the need for lath, which can't be said of many materials.

I'm still of the opinion that one could devise a rammed earth wall that had insulation integral to the structure much like the Structural Concrete Insulated Panel idea.

I imagine one could even use the Dow T-Mass idea (and their proprietary connectors) within a site formed rammed-earth wall. It would take a thicker wall to pull this off but it is possible. I imagine you'd need at least a 6" mass of wall on the exterior side of the insulation, and then a 12" mass to the interior side of the insualtion, which would give you a roughly 20" deep wall (assuming 2" of rigid XPS at an R-12 insulation value). Even though R-12 is only slightly better than the standard R-11 required of stick built construction in Central Texas, coupling that insulation value with the isolated rammed-earth mass to the interior should provide for a very efficient wall system, as the isolated thermal mass would keep the interior temp swings to a minimum (even when you had the windows and doors open on those fabulous fall and spring days.

Mark Meyer

Re: Cost per Sq. Foot

Posted by pk at August 09. 2005

Eeek...chi-chi...what could be worse! So, not only is it expensive and time consuming, you have to go through all sorts of machinations to make the stuff viable. There is a home (Degobah) on Pilgrim Builder's website that combines rammed earth and SIP....not too chi-chi and more vernacular than desert sw in style...the rammed earth looks more decorative than structural, however...

You mentioned Structural Concrete Insulated Panels. What do you know about them? There is next to nothing about them on the web...

Re: Cost per Sq. Foot

Posted by Mark Meyer at August 09. 2005
SCIPs are something I've been looking into recently for a project I'm designing right now. I think they make a LOT of sense. You get a structural/insulated shell, and an exterior and interior finish all in one go. Add to that the fact that you can get the panels pre-cast at a local pre-cast plant (of which there are many in our general vicinity) and you start talking about a really economically viable product. They seem to lend themselves handily to modern spaces, as they are perfectly suited to dovetail with structural steel beams and columns. The window and door openings would be cast inplace at the factory, as would be the electrical conduits. I imagine the erection of the panels would only take a few days (but would require a crane), thus saving on the TIME=$$ eqaution.

I don't know of anyone that has actually done this sort of thing in Central Texas, but I do know that we have a great pre-cast concrete infrastructure here, so it would just be a matter of getting in touch with the right people.

I am awaiting contact from DOW right now to see if they already have a working relationship with any of the local pre-cast plants. Like I said I'm very excited by the technology and look forward to working with it.

Mark Meyer

Re: Cost per Sq. Foot

Posted by pk at August 11. 2005

The SCIPs do sound promising, Mark. Have they been used in industrial/commercial applications? Or are they pretty much untested at this point? Would you pair them with a standing seam roof steel framing a-la Dietrich

Re: Cost per Sq. Foot

Posted by Mark Meyer at August 11. 2005
I'm not too sure how long the technology has been around, but there are a few manufacturers of the technology out there. As posted above DOW has their T-Mass system which is simply licensed out to pre-cast concrete shops. If DOW is behind it I'm sure they've spent some time and effort making sure everything works well.

As you can see from the pic everything seems to be well figured out. Conduit is in place for running electrical, the windows are blocked out, and welding plates are in place for connecting beams and other structural connections.

Green Sandwich Technologies has a very interesting system and everything seems to be recycled content. Pugh+Scarpa are using this system to build their Vail Grant Residence in SilverLake.

I can envision exposed concrete SCIPS with exposed steel framing or even better with exposed glu-lam timbers and beams. Interior walls and floors could definitely be framed with Dietrich framing. I've looked into the Dietrich stuff and I really like the system and the price-point. For a Texas application metal roofing is probably best


Posted by paul schuster at August 17. 2005

I like those concrete sips.


Posted by Mark Meyer at August 18. 2005

I thought you might!

Re: Cost per Sq. Foot

Posted by pk at August 18. 2005

What about Rastra? Is anyone still using it? A dude I chatted with last night said you could put stucco directly on without lathe inside and out. He built his office with Rastra and the stucco was something impregnated with some sort of fiber he said....

Is there enough polystyrene in the rastra mix (85% I think is what they say) to be insulative rather than conductive?

Re: Cost per Sq. Foot

Posted by Mark Meyer at August 18. 2005
Rastra seemed to have been used extensively a few years ago, but I see less and less of it now. I think it is an OK product, and you can put stucco/plaster directly onto it as it has a fairly rough structure. It seems however that all of the project I know of that used it have a decidedly Southwest Santa Fe aesthetic. Some of this is due to the fragility of the rastra matrix, which keeps it from having sharp crisp corners. Most of the time I see it used the corners have been rasped off into a more organic rounded feel. Rastra panels are aslo fairly heavy and cumbersome (they don't require a crane, but they do require some additional man-power to negotiate). For these reasons I like AAC blocks rather than RASTRA. The AAC blocks are smaller, easier to handle, don't require a LOT of extra concrete and rebar to complete the system, and have nice crisp corners and edges, but yet is still soft enough to be carved into whatever form you like.

The AAC companies like ConTec also have a pretty broad selection of differnt products, from large panels, to standard blocks,a nd a significant amoun of products in between. Rastra is pretty much just two differnt panlels, which means there is a LOT of site modifications to be made when you start building a wall.
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