What Dana said. For one, the "A" in any UA determination is highly variable. A two-story house might have twice the wall surface as it does attic surface. A ranch might have equal parts.

Dana, the code types are doing blower door testing in Pa. In my corner of the state, the headache is sealing sprinkler-head penetrations in ceilings.To use mains pressure rather than pump and tank requires many, many heads.

Todd- it's good to hear that at least some code-enforcement bodies are actually starting  to measuring the air leakage!

Regarding powered attic ventilation see the discussion starting on p.60 (pdf pagination) of this document:

http://www.fsec.ucf.edu/en/publicat...496-05.pdf

If for whatever reason you're committed to going to power venting the attic, make the intake cross section large, and be DAMNED sure you've air-sealed between the attic and conditioned space well.   Most of the 1980s research was on existing stock, with low R and fairly leaky attic floors, although some of the post Y2K in-situ studies in FL were reasonably tight.

You can get a modest reduction in cooling power in a high-R roof going with one or more of the photovoltaic powered attic fans, but bang/buck, air sealing and going even higher R or steeper pitch and using a CRRC-rated  or CA Title 24 compiant cool-roof is still going to be more worthwhile.

OP here ... man of mystery, dropping clues ...   I'm afraid that the truth is much more mundane fellers.  I'm in and out of touch with this forum because I'm getting ready for surgery (giving great sums of money to various medical types ... I should have been an anesthesiologist) , and caring for elderly parents.

I grew up around San Marcos, near the river, as Lee and a couple others that know the area have 'surmised.'  I left in 1970 (army) and just returned this year.  I am considering building here ... if I remain in the area after my father passes.  I have no house plan as such ... other than small, 1000 to 1200 ft².  Budget will be limited/constrained.  Other than that I'm considering many options ... all driven by energy efficiency/conservation.  As an aid to explain my preferences/philosophies I will say that we (former wife) built our house in SC;  stick frame, off-grid solar PV system, rainwater catchment for all needs, wood heat ... obviously no AC given the PV/battery.  I suspect everyone on this list would be appalled at the poor, untrained construction of the house no doubt, but we attacked it with youthful enthusiasm; if, NO training/background. Age, arthritis, and general wear & tear dictate paying a builder in the future.

My various questions to the list have been to help narrow down my options.  A quick note about shading with big pecan and oak trees along the river ... the few lots available like that cost 5 to 10x my whole house/land budget!  So that's not an option, a nice fantasy yes ... (if only I could have bought one in the 50's but priorities at that time revolved around girls, getting on/to the river, and and talking girls into tubing, canoeing, fishing ....)  My shading options probably revolve more around mesquite, huisache, and mescal bean (Texas Laural) trees or, perhaps wrap-around porches.  Given my age and life circumstances re-sale value is not a major concern.  I have considered straw bale but that's really a do-it yourself option.  Windows probably can be minimized compared to "typical"  as I prefer to be outside and this area lends itself to that.  Yesterday, 16 Nov., the coeds (Texas State) were out sunbathing along the river when I was walking ... bathing suits seem a bit smaller than when I was growing up?  I'm rambling and being nostalgic ... let me try a list approach to hold the BS down:

- limited windows but, large covered and open patio areas well integrated into design for ease of use
- one level, NO steps, due to stainless steel knees!  Perhaps handicap accessible? ...
- +/- 5 Kw grid tied PV system
- rainwater catchment, and perhaps a barn/workshop for additional roof surface for catchment
- probably a 2 bedroom, one bath design
- a water core area (bath, utility, kitchen) to minimize water-line length, especially hot water
- gray water recovery
- probably slab on grade ... with acid etched concrete for floor finish
- probably rural location (3 - 5 miles out of town), and able to place house for optimum orientation
- have considered ICF with flat concrete roof (hacienda style) for storm proofing, quite, secure ... but most likely beyond my budget
- if not flat, white metal roof for reflectance and water quality (assuming no HOA)
- Will NOT place HVAC in attic, if not a Minisplit, then exposed ducts in house ... allergies would prefer excellent filtration
- there is a SIP manufacturer in Kerrville, NW of San Antonio, 'bout 100 miles away ... I know very little about SIPs ... but doing homework
- aspire to net-zero ... at least my billfold does
- house could easily be a plain rectangle, FUNCTION over form in most cases
- will have the house blower tested IF budget allows

I have a few other thoughts but don't want my post to become too cumbersome.  I do appreciate any and all thoughts, recommendation, considerations.

Dana1 ... I was over at TAMU also ... about a decade before you it seems

Thanks again for all the thoughts.  Y'all take care ...

Edit to add:  I consider "code" a bare-ass minimum ...

To clarify- I didn't attend TAMU, but I've read a lot of good work & papers on energy related stuff on attics & cooling loads (attic insulation, radiant barrier efficacy, attic ventilation)that came out of there in the 1980s (many of which are available on the searchable archives.) I accept their work at face value, but note that there may have been factors not in evidence on some aspect. Many of those papers are cited by subsequent building-science studies- I've read some of the most-cited papers, but haven't tapped even the frost on the tip of the iceberg of the relevant material that is available on the TAMU site. The 1980s was something of a post-oil-shock renaissance on many building-science issues, and cooling power was a key topic of study (and continues to be, but now with more knowledge, better tools.)

SIPs are pretty low mass, and there is significant benefit to higher-mass construction in that climate, but the mass need not all be incorporated into the wall. SIPs are generally easier to air-seal than other low-mass walls. (Slab on grade is good, and at your subsoil temps insulating the slab-edge but not center slab will probably be cost-effective.)

For rough guidance on where the long-term economics on going high-R with net-zero on your mind, assuming you're cooling & heating with moderately high-efficiency equipment such as mini-splits going with the whole-assembly Rs found here will likely work:

http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

See Table2, p. 10. Note that the R values are "whole assembly", not center-cavity values. A cellulose or high-density fiberglass (or open cell foam) filled 2x4 studwall is ~ R10 after the thermal bridging of framing is factored in. A 2x6 studwall is ~R14. I'm assuming you're probably on the cooler edge of zone 2 or warmer edge of zone 3 if you're 100 miles from Kerville, so you're looking the values at the second or third row.

But getting to net-zero is more than just high-R, the site and building orientation are huge design factors.

If going with a flat roof note that flat roofs won't convection cool to the exterior, nor would it convection cool below the roof deck if vented- you need at least a 3:12 (or better yet 4:12) pitch to get much exterior convection cooling, but if you use a highly reflective moderate emissivity roofing material it'll radiation-cool reasonably well. A mass-roof with high-emissivity radiation cools pretty well too- the thermal mass delays and reduces the peak temp of the underside of the roofing. Ceramic roofs might be out of the question on cost, but there may still be a concrete mass-roof solution even if you use something other than ICF for the wall structures. To get to an honest R40-R50 with a cheap cellulose fill you'd have to use ~15" deep trusses or TGIs underneath a thin-slab roof, but with the dynamic benefit of the exterior thermal mass R35 might be just fine. With a low mass FLAT roof R45+ is probably always going to be cost effective.

A 2x6 blown-cellulose studwall with 1" of foil-faced rigid iso over the exterior sheathing hits an honest R20 in that climate, and it's relatively easy to use the combination of sealing the structural sheathing as the primary air barrier, lapping the seams of the iso with that of the sheathing by a foot, and FSK taping the iso facer as a secondary air barrier. With ~1/2-3/4" gap between the exterior foil and wire lath for stucco siding you'd have a fairly high performance wall. The mass of the stucco + the radiant-barrier effect of the exterior facer would give it better-than-steady-state-R performance during the cooling season. Alternatively, fiber-cement siding on 1x furring (through-screwed to the studs 24" o.c.) to maintain the gap also adds some exterior mass and a radiant barrier effect.

Going with a flat roof means you'd probably be using ground-mounted PV(?) One advantage to going with a pitched roof and a rack-mounted PV array covering most of the roof is that the PV shades the roof, lowering the direct solar gain, making it something of a 2-fer deal during the cooling season. With at least 3" between the panels and roofing you get pretty much the same convective cooling, but at a lower temp due to the lower solar gain.

As for what sunbathing coeds along the river walk wear these days, I've recently heard it referred to as "bathing floss". :-)

Posted By Lee Dodge on 17 Nov 2011 11:08 AM
Obviously bpnkrtn is a mystery writer, giving brief clues in various posts that must be assembled to answer his questions. For example, Dana1 has paraphrased bpnkrtn's opening question in this thread as:

So following these clues given by bpnkrtn, let's focus on new construction. Let us assume that bpnkrtn will at least build to current code, which is IECC 2009 in the area and requires R-30 ceiling, R-13 walls, and R-13 floors. When I put my generic 1600 sq ft house in Martindale overlooking the Martindale Dam so that I can check on those good-looking Texas State U. coeds sunning by the dam, and run REScheck, I get UA factors (thermal conductivity times area) of 51 for the ceiling, and 95 for the walls. This means the conduction heat losses through the ceiling and the wall are predicted to be in the ratio of 51:95 respectively. Now I don't believe REScheck properly accounts for the fact that attics in that area can get hot as he--, so that fact runs the ceiling heat loss up some. But I should not assume that I can build a energy-efficient house without also doing something about the wall thickness/insulation.

Lee ... Howdy.  My 'man of mystery' post was primarily aimed at/to you ... and just to make sure the written word carries my intent ... it was meant to be in good fun.  I appreciate your information and have perused your site several times ... good stuff.  I find it quite interesting that a man sitting in the rarefied atmosphere of Salida, CO knows about the Martindale damn.

Thanks again for taking the time to post and assist in my education.

Dana1 said: "Power venting attics in the gulf states is more likely to increase total power use..."

I could believe that, but I would consider power venting for two other reasons: (1) to avoid having the replace a $9000 or so roof every 12 years, and (2) for safety and convenience when you do have to do anything in the attic. Once or twice I have had to repair holes purposely made in attic A/C ducts after the cable installer purposely poked them to stay alive while running cables. Of course, if you can keep the ducting out of the attic, you can avoid the second problem. The roof issue is harder to overcome with conventional roofing materials. Of course, if money is no object, get a tile roof and it lasts forever if you don't break them. Unfortunately, money is ususally a consideration.

Posted By Lee Dodge on 17 Nov 2011 07:14 PM
The roof issue is harder to overcome with conventional roofing materials. Of course, if money is no object, get a tile roof and it lasts forever if you don't break them. Unfortunately, money is ususally a consideration.

When I hear tile I'm reminded of the Oklahoma State campus in 1950 when a hail storm hit.  Most of the buildings had tile roofs, orange tile of course.  After the storm there were piles of tile all over the ground.  This area also gets serious hail storms so I think I'll stick to metal roofs, preferably 26 gauge ... because I can't afford 24 gauge :-)

Posted By Dana1 on 17 Nov 2011 05:40 PM
Going with a flat roof means you'd probably be using ground-mounted PV(?) One advantage to going with a pitched roof and a rack-mounted PV array covering most of the roof is that the PV shades the roof, lowering the direct solar gain, making it something of a 2-fer deal during the cooling season. With at least 3" between the panels and roofing you get pretty much the same convective cooling, but at a lower temp due to the lower solar gain.

As for what sunbathing coeds along the river walk wear these days, I've recently heard it referred to as "bathing floss". :-)

My experience with PV panels indicate they really need to be washed, at least once a year.  I'm past the age of carrying a mop and bucket up on a 4:12 roof ... ground mounted offers serious advantages!  If I thought I could pay for PV maintenance, and get it done right, roof mounting does offer the advantages you mention plus greater protection from possible future shading problems with other buildings and/or vegetation growth.

... "bathing floss" I will remember ...

bptkrtn-

I appreciated your response, and it helped everyone understand your goals better. Yes, the lot along the river would be a fantasy for me for sure, but you had me dreaming about it anyway. I understand your frustration with trying to build a low-energy-consumption house in that area. Darn A/C's really chew up the electricity.

I lived in San Antonio for quite a while, and paddled the San Marcos River down through Martindale many times. Also paddled the upper Blanco, way upstream of the confluence with the San Marcos, in flood a few times -- more exciting than the San Marcos.

I was interested in constructing an ICF home here in Salida, but there was a $25K increment in cost for my modest size home, and there did not seem to be much experience with them here. Alternatively, for an extra $5K I could cover a 2x6 frame house with 2" of XPS and get a better R-value wall than the standard "$25K increment" ICF. The lower cost for a frame house allowed me to spend money on more insulation elsewhere, and the solar stuff. One fundamental reason for the higher costs of ICFs and SIPs compared to stick frame houses is the higher cost per unit R-value for the EPS compared to cellulose or fiberglass. I still thought an ICF might be nice for protection against tornadoes, but my builder said that they did not get tornadoes or forest fires here.

You'll never make a perfect decision on a house, so chose a path and take it. Having built a house yourself, you should have a good starting point.

Greetings,

You're a perfect candidate for a geodesic home. Goes up fast, does not have shingles, is earthquake and tornado resistant and if you have some free help you can turn key for about $30.00 sf or less.

A 30' with 2 to 3 bedrooms should cost about $42,000.00 plus a second 30' for 2 car garage and 700sf storage on second floor. I believe the longest framing strut is about 4.5 foot long. Unit comes as a precut kit. Best home value there is.

See: econodome.com

Geodesics (an foam-domes, concrete domes) have high scrap rates when timber framed, no straight walls making interior cabinets & closets a real PITA. Air-sealing a timber-framed dome also takes some real doing.

They're really only for Buckminster Fuller devotees.

Lee: Concrete roofs (not concrete tiles) aren't always a pocketbook breaker in the same way that tiles are, and can have similar or better performance & longevity. It's fairly common in Mediterranean countries and in the hurricane-prone Caribean. On a flat(ter) roof where the aesthetic issue are less prominent it can be relatively cheap compared to tile, if more expensive (but also far more durable) than membranes, etc.

Greetings,

QUOTE>Geodesics (an foam-domes, concrete domes) have high scrap rates when timber framed, no straight walls making interior cabinets & closets a real PITA. Air-sealing a timber-framed dome also takes some real doing.

You might want to ck the econodome.com site to see if maybe some of those problems have been resolved.

Dana1, Lee, and others ... thanks again for the input.

rbisys1 ... I do have interest in Domes.  I hope to drive to Italy (Texas, south of Dallas) next week in fact and look these over,  Monolithic Domes. 

Again ... thanks ... y'all have a great Thanksgiving.

A friend of mine lives in a concrete molded-dome house insulated with 3" of 2lb foam over the exteirior. It's very comfortable from a heating/cooling point of view, but the cupboard & closet thing is totally awkward.

Air sealing the concrete dome would be 1000x easier than any bucky-ball stick built dome.

Greetings,

Thanks for the link.
The econodome is very resistant to projectiles too. They use a DENS sheathing and the then coat it with a rubberized coating. You could also use a polyurea coating.

Econodome has a direct link to Bucky. They inherited all of Bucky's paraphernalia when he went to Bucky heaven.

Their design overcomes the 1st floor curved wall problem and windows and doors do not require special framing. Another good feature is that they do not use hubs, but it is still a single strut design.
This dome is strong enough that it can be used for an underground project, and has been. It was featured in a Pop Sc mag several years ago. At about $30.00 dollars / sf, turn key, on crawl space or slab, plus land, this has to be one of the best buys out there.
By the way this is a kit and the window/door framing is cost included.

A vertical ICF sys for the 1st floor wall is an option.

Be careful about the amount of glass you have and southern exposures. It is very easy to over heat a dome even with small amounts of glass area.

Whatever sys you choose I think you'll really enjoy your dome. We have been wanting to build a dome for over 30 yrs but it never happened. Guess we'll have to wait for our next life time.

Keep those Bucky balls bouncing.

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