Planning to build a new home, we love the ultra modern steel beam, glass type. We have seen some multi-stories LEED certifified building with mostly glass exterior. But aren't windows or glass has lower insulation value than dry walls? How can one build a flat roofed mostly glass walled building and yet still provide superior insulation?

FYI, Douple pane low e insulated glass is around R3.5. Triple pane glass can be as high as R5.

Still far cry from insulated drywalls though. Aren't the well insulated dry walls in 20-23 range? Wondering what was specifiied in LEED on wall R values?

Posted By toffee on 25 May 2012 03:45 PM
Still far cry from insulated drywalls though. Aren't the well insulated dry walls in 20-23 range? Wondering what was specifiied in LEED on wall R values?

They have triple pane windows that are now sitting around R-11 but they are very expensive. Typically one can get R-5 through R-8 for a reasonable cost. The triple pane windows I am looking to get are around R-7.

With solid walls you are looking at R-20 or higher.

The only way all that glass would work is if you are in a cold climate and the SHGC overrides all the energy loss you would experience at night with that glass. In the summer, you need to position the home and overhang so that you don't turn that home into an oven. One can easily overheat the home during summer with that much glass. Spring and fall can also be problematic depending on outdoor temperatures.


Where are you located at?

It's in Monterey California, average temperature: http://www.weather.com/weather/wxclimatology/monthly/graph/93940 Very mild summer, winter can dip into 20s but mostly average in the mid 40s.

Posted By toffee on 25 May 2012 04:51 PM
It's in Monterey California, average temperature: http://www.weather.com/weather/wxclimatology/monthly/graph/93940 Very mild summer, winter can dip into 20s but mostly average in the mid 40s.

So you do have more of a heating load than a cooling load.

What are contemplating to do can be done but it will be a lot harder and a lot more expensive than a simple drab and boring looking rectangular home with a few holes poked into it for windows. I admire your passion for an architecturally pleasing home but still have it be energy efficient. Like you, I am not a fan of boring looking homes.

What you will need is a really good architect who is energy savvy, come up with a design and go from there. Remember, a good architect will cost you over $15k.

With a flat roof you will need to get in at least R-40 or better up there. Depending on code and what you want.

Posted By toffee on 25 May 2012 03:45 PM
Still far cry from insulated drywalls though. Aren't the well insulated dry walls in 20-23 range? Wondering what was specifiied in LEED on wall R values?

To hit R23 average on a 2x6 timber-framed wall with R20 fiber cavity insulation and a 25% framing fraction takes about 2" of exterior foam. To hit R20 takes ~1.5" of exterior foam.

To hit R20 on a 2x4 timber framed wall with R13 cavity insulation takes 2" of exterior foam, R23 takes 2.5".

Prescriptive minimum R values for LEED have traditionally followed IECC/IRC for climate-specific minimum values, and you get extra points for exceeding that. As I understand it they still are using the IRC 2004 as the baseline values, but in places where the IRC 2009 or IRC 2012 have been enshrined in local code, a building built to IRC 2004 wouldn't meet code- you'd get some LEED points for merely making current code-min(!).

The other method for getting LEED points for the thermal envelope performance-based- you need to simulate/model the performance of the building as-sited & oriented using standardized methods, and you get points for beating their prescribed baseline number, independently of the R & U values of any individual element of the design.  In most locations it would be tough to hit the performance numbers in a mostly glass & steel house.  On high-rise construction you might get there with sufficiently high performance glazing under just the right circumstances, but probably not in a detached house design.

[edited to add]

This is because in high-rise the exterior surface area is smaller than the total conditioned floor area, whereas in 1-2 story houses the exterior surface of the building exceeds the floor area of the conditioned space.  High-rise construction tends to be a heat-trap, and the heating/cooling balance point is well below the ~65F typical for standard detached home construction.  In a mostly-glass high-rise controlling the solar gains to keep the air conditioning loads down is often a bigger problem than moderating the heating loads.

The mean winter temp in Monterrey is closer to ~50F than mid-40s- mid 40s is the typical overnight LOW.  (see http://weatherspark.com/#!dashboard;a=USA/CA/Monterey )  The 99% heating design temp is ~38F, with a 1% cooling design temps in the mid-70s by the shore, (but ~90F inland, if you're not right on the peninsula.)

You may be able to hit LEED performance using a performance based modeling method with a high glazing fraction if you go with high performance low solar gain triple-pane throughout, with some exterior east & west shading and south-side overhangs to optimize winter gains.  This is an extremely temperate climate.

From an aesthetic point of view you may find that the cool blue-tint of high-perf triples takes a bit more away from the view than going with a somewhat lower-performance window, but less glazed area.

Key to getting the performance will be figuring out how to thermally-break the steel framing at the exterior, since the thermal conductivity of steel is quite high relative to windows or wood.  Typical residential architects may not have that in their standard methods, but commercial building designers in cold climates probably have a clue.

This is an extremely temperate climate

The thing that is so screwy about Monterey is that coastal foggy, misty thing they have. It's special. You would want to look very carefully at your modelling software to see if it was doing the right thing with those foggy Summer days.

My site is one mile directly south of Monterey fisherman's wharf, about 270ft above sea level, in a small canyon. So not quite as cold or foggy as ocean front but still quite chilly. You guys are right, the need for cooling is a lot less than the need for heating. That being said, it doesn't get that cold either, Monterey is windy, foggy but in the end of the day, not freezing or icy.

Not quite sure where to find that one architect that is passionate and knowledgeable about high efficiency ultra contemporary designs.

Posted By Lbear on 25 May 2012 04:59 PM

Posted By toffee on 25 May 2012 04:51 PM
It's in Monterey California, average temperature: http://www.weather.com/weather/wxclimatology/monthly/graph/93940 Very mild summer, winter can dip into 20s but mostly average in the mid 40s.

So you do have more of a heating load than a cooling load.

What are contemplating to do can be done but it will be a lot harder and a lot more expensive than a simple drab and boring looking rectangular home with a few holes poked into it for windows. I admire your passion for an architecturally pleasing home but still have it be energy efficient. Like you, I am not a fan of boring looking homes.

What you will need is a really good architect who is energy savvy, come up with a design and go from there. Remember, a good architect will cost you over $15k.

With a flat roof you will need to get in at least R-40 or better up there. Depending on code and what you want.

Not quite sure where to find that one architect that is passionate and knowledgeable about high efficiency ultra contemporary designs.

You have to look at previous work. Contact the local AIA chapter, look at local architect's web sites.

Look up www.zeroenergydesign.com in Boston. Passive House architects; both traditional & contemporary work

Or go to the Passive House US website & look up architects in your area who have taken the Passive House course & become certified.

Posted By Bob I on 28 May 2012 06:20 PM
Or go to the Passive House US website & look up architects in your area who have taken the Passive House course & become certified.

Thx Bob, may I have link to the passive house's US website?

This 'might' be what Bob1 is talking about.

http://phaus.org/home-page

It's getting confusing - below are the links to PH-US. the PH Alliance is another group with dues & a separate membership list. There is also a PH Boston group not tied to the PHAUS. Point is that everyone in these groups is either learning about or understands superinsulation and the need to get US builders and homes upgraded.


http://www.passivehouse.us/passiveHouse/PHIUSHome.html

http://www.passivehouse.us/consultants.php