IECC standards

[dobanion]

To bring this discussion back up, and pertaining to what I'd like to accomplish...…

I still want to build a thin shell concrete structure, and do so WITHOUT using any insulation. Plans are also for a very reflective surface (90%+). I think I have a path forward, which could very well apply to others.

Structurally, the county has recently approved a dome, in April 2018. However, this was just before they started enforcing IECC requirements. The dome in question does not contain any insulation of any kind. It's 5" thick of concrete with steel rebar.

For IECC, read up on "Simulated Performance Alternative." On first reading you will be intimidated by it a bit, but keep going. The gist is simple, compare your proposed home to their "reference design," and have a engineering firm do the calculations that show your design will not use any more electricity in a year than the reference design.

You need to compare fairly. If your proposed design has AC (or heat), so should the reference design. So, if you do NOT desire any climate control beyond opening the windows, the R-value doesn't really play into energy usage at all, does it?

Stay tuned, work in progress.

[dobanion]

FYI, I found a engineering outfit that can do the comparison rather affordably, once you have construction drawings for the proposed design. Moving that way now. Shape is about finalized, structural engineering is gonna start soon.

[Thronester]

What engineering firm did you use?

[dobanion]

I haven't used them YET, just got a quote from them.

I still need to get structural engineering done, then architect, which will give me construction drawings. That's what they need to be able to run the numbers.

The name of the outfit I found was JKP Energy. They are in Arizona. They state they can do the comparison and issue me a certificate comparing energy usage of my proposed structure vs the reference design.

[dobanion]

Well, I learned a lot from last time I posted here, and I'd like to share, hopefully help someone out.

There's this fantastic and FREE software from the National Research Laboratory, that allows you to model the energy usage for a proposed home. It was fairly straight forward to learn as well:

https://beopt.nrel.gov/

What I found after messing around was quite surprising. Pleasantly so. The "reference design" calls for a moderately absorbing surface for the walls and roof, and R-30 in the ceiling. My proposed design used reflective surfaces for wall and roof, and uninsulated ceiling. Calculated AC costs (you are required to model it) were consistently lower every time for the reflective approach.

Gist is, if you don't want to insulate, get a white metal roof and paint the walls a light color, and you can probably do it.

[kalakoa]

You will probably still have to hire an engineer to explain the concept of IECC compliance to the County Building Department.

[Thronester]

Has there been any word on if Hawai’i county has amended the IECC yet? The last bit I heard was in regards to the portable window installed AC units being exempt from permitting

[dobanion]

Original IECC 2015 (start with reading this): https://codes.iccsafe.org/content/IECC2015

Hawaii county started enforcing IECC 2015 compliance (without amendments) on August 15, 2019. Then, as of Feb 4, 2020, they published their official amendments. Follow the link below to the page and you can read through their amendments.

https://energy.hawaii.gov/wp-content/upl...gyCode.pdf

IECC compliance sheet is here:

http://records.hawaiicounty.gov/weblink/...ronic.aspx

In further discussion, I'm just calling Simulated Performance Alternative as SPA, getting tired of typing it out.

To expand on what I stated above, it would seem that my initial assumptions were wrong. Usually are. The fine print in the original 2015 IECC for the table for how to model the SPA basically says you need to include a basic air conditioner and heater in the model, even if you aren't going to use one. I see now the purpose of this. Without those, anything would go. It would always compare out as similar energy use. But they want to see that the house as modeled is as or more efficient than whatever they are calling for, and to do that, you need to model how much energy a AC unit would use on a annual basis, were you to stick one in a window. Makes sense.

So in my model, I had AC and heat. I entered in the climate model for Hilo (they have one for Kona too). When I ran the simulation, with the AC set to 73F, and the heat set to 68F, I got AC usage, but zero heat usage. If you were to install a electric furnace in a house in Hilo with the thermostat set to 68F, it would in all probability NEVER turn on. Model makes sense.

For the reference design you essentially do all the things that they have in the "prescriptive" approach. The big stuff:

Walls and roof have .75 absorption (means 75% of the energy that falls on them is absorbed). Most colors are in this range.
Ceiling or roof has R-30
Framed walls have R-13
"Mass" walls (ie concrete, be it block or otherwise) has R-4. This is not additional R-4, rather the wall itself must be R-4. According to the NREL software, a cinderblock wall is already R-5.
Floors do not need insulation, be it slab or post and pier. This is from the amended code, the original IECC 2015 did call for floor insulation on above grade floors (not slab). So, kudos to Hawaii county for that.

Now, for the house I'm designing, I use mass walls. So, I don't have to call for insulation in the walls of either my reference or my design.

When I switch from .75 to .3 absorption exterior surfaces (ie white metal roof and a bright exterior color), and I eliminate the R-30 in the roof, I end up with about 30% LOWER cooling energy usage on a annual basis. As it turns out, keeping the surface from absorbing the heat in the first place is a better approach than trying to keep the heat out with insulation.

This is the approach I plan to take in my permit application. I will also note this model is bound to stink if I needed to use a heater. This house wouldn't work in Volcano, for instance.

I tried this with a wood framed house as well. Now things change, because I'm required to use R-13 in my reference design walls. Now, it's a wash. The uninsulated/reflective house and the insulated/non-reflective house are nearly the same. It's so close I doubt you could convince anyone to approve it. But, if you either use some mylar in the attic, OR switch to the best roof paint I could find (Henry 887 Tropi-Cool at .15 absorption), that gives you a 8-10% margin. I didn't run the numbers with the super bright stuff on the walls, I know nobody is gonna do that.

[Thronester]

Great explanation and thanks for posting your results. I didn’t see that the county amended it in February. I’ve got some reading to do.

[dobanion]

Another item, which may apply specifically to the house I'm planning to build. I am still moving forward on a monolithic concrete dome, built in the Eco-shell style.

Well on page 19 of Hawaii's amendments:

R402.2.5 Mass walls. Mass walls for the purposes of this chapter shall be considered above- grade walls of concrete block, concrete, insulated concrete form ICF), masonry cavity, brick (other than brick veneer), earth ( adobe, compressed earth block, rammed earth) and solid timber/logs, or any other walls having a heat capacity greater than or equal to 6 Btu/ft2 x °F ( 123 kJ/ m2 x K).

Exception: Insulation or R- value for mass walls, indicated in Table R402.1.2, is not required when at least one of the following conditions is met:
1. Walls have a covering with a reflectance of> 0.64.
2. Walls have overhangs with a projection factor equal to or greater than 0. 3. The projection factor is the horizontal distance from the surface of the wall to the farthest most point of the overhang divided by the vertical distance from the first floor level to the bottom most point of the overhang.
3. Concrete, CMU, and similar mass walls are 6 inches or greater in thickness.

So, my feeling is if the county lets me classify the entire shell of the dome as a "mass wall," that greatly simplifies things, for my project.

For every home style, after plugging away at simulations, I still contend that reflective surfaces are much more effective than insulation for interior comfort on hot sunny days.