Prescriptive Compliance failing COMcheck

[ryan81]

Hello All.

From a compliance path standpoint, my understanding of the IECC is that three options are available - ASHRAE 90.1, Prescriptive, and Performance. Over the last several years, it seems that more and more AHJ's are requiring compliance "verification" through software such as COMcheck.

The problem that we've encountered, is that commonly COMcheck will spit out a "failing" score when inputting the values which adhere to the minimum prescriptive requirements requiring us to make adjustments to those variables (such that they now exceed the prescriptive requirements) so that we can pass and get approval from the building building department.

My question is this: If the City is requiring a compliance verification report (such as a COMcheck), AND that compliance verification software doesn't necessarily provide a passing score with minimum prescriptive values, aren't those jurisdictions...in effect saying that they don't allow the prescriptive approach?

Much confusion.

Thanks everyone.

 

[Mr. Inspector]

Ask the plan reviewer what section of the code or what local ordinance requires a COMcheck. We don't.

 

[ryan81]

To add to this....

My understanding is that compliance verification software such as COMcheck would fall under the "performance" approach in the energy code. If this is correct, it appears that those jurisdictions requiring a COMcheck are essentially forcing designers to use the performance method. Prescriptive is either valid or it isn't and if a COMcheck shows a failing score with those prescriptive values, it shouldn't negate that code allows the prescriptive values.

Thanks again!

Ask the plan reviewer what section of the code or what local ordinance requires a COMcheck. We don't.

Thanks for your response. I will definitely ask that question. Regarding my original post, does my line of thinking make sense? Does it track to you, or is there a key failure in my logic:

Simply - If a jurisdiction is requiring a Compliance verification report like COMcheck, aren't they effectively mandating the "performance" method and ignoring that the code allows other pathways to compliance...namely prescriptive?

 

[Paul Sweet]

IECC C407 covers the performance method. Basically you have to show that the proposed building costs less to heat, cool, and light than an "equivalent" building meeting certain standards (generally the same as prescriptive requirements). The calculation software has to calculate energy usage & cost for every hour in a year.

I believe that COMcheck is basically the prescriptive method, but allowing for improvements in some parts of the envelope to compensate for shortfalls in other areas.

 

[Sifu]

I look at it similarly to Rick and Paul. COM/REScheck is a compliance material option within the prescriptive method that allows trade-offs. I know of many an AHJ that includes them as a requirement but I don't. However, some time ago ran a report with straight prescriptive values to see what happened and it did not spit out a failure. Maybe I didn't do it right, but it seems pretty ridiculous if you are correct.

FWIW, when I review the COM/RESchecks, HERS reports, manual J's, I have NEVER come up with the same data that the submitter has. How anything more than a squared box is measured is subjective, and a deviation can make a big difference. And I would say nobody ever makes purposeful deviations to get a passing score......

 

[Mech]

ryan81 - Contact COMCheck support. By the way the software does not permit the default IECC glass U-values to be used. Would you like to mention that also?

When I contacted COMCheck support in 2010 because I could not get a building to pass using the 2006 IECC prescriptive values, they told me COMCheck determined compliance by the "trade-off" method, not the "prescriptive" method. As a result of my inquiry, they also then altered the COMCheck software to correct for some faults (in the energy code, I think).

Here is the string of emails. I have not wrapped my head around it completely, but I think it says the IECC was screwed up. (I changed this text to green.) It is very possible that it is messed up again. I replaced my name with "Mech" and the support personnel names with "COMCheck Support." I changed the text to Bold to show where COMCheck support mentions the trade-off method and also where they said they would alter the software.


Notification of Issue Change

Issue:	[On-Line Form] IECC minimum values used, COMCheck fails design
Issue Number:	xxxxx

Description:
Entered on 12/27/2010 at 09:50:21 PST (GMT-0800) by COMCheck Support:
Mech,

Please note that I modified COMcheck to deal the the issue described in this email
thread.
You should now be able to enter the 'prescriptive' values for your project and get a
passing compliance.

You will need to download and install COMcheck 3.8.1 again. The build version with
the fix for this issue is "3.8.1.3".
The build version you are using is found by clicking Help->About COMcheck and looking
in the top right pane of that screen.

Let me know if there are any ongoing issues.

COMCheck Support
COMcheck Software Support

Entered on 12/16/2010 at 11:43:57 PST (GMT-0800) by COMCheck Support:
Mech,

I've had another conversation with one of our energy code engineers about this problem.
We decided to resolve it (hopefully once and for all) by calculating the required
U-factor using the prescriptive R-values for cavity and continuous insulation instead
of fetching the required U-factor from a table directly.
This is inconsistent methodology that we have tried to avoid but it is so obviously
wrong in the code language that we feel justified in taking this approach.

I will notify you when I have a new release of COMcheck out on the website.

COMCheck Support
COMcheck Software Support

Entered on 12/15/2010 at 13:25:46 PST (GMT-0800) by COMCheck Support:
Mech,

First off, you should note that COMcheck does not show compliance by the
'prescriptive' method. It determines compliance by the 'trade-off' method.
And COMcheck applies the "U-factor" requirements set forth by the energy code.
Regrettably, and I mean that seriously, the IECC code committees, for metal building
roofs, assigned requirement U-factors that couldn't be matched with the proposed
U-factor table values. You'd have to look closely at the code language of 2006 IECC
and ASHRAE 90.1-1999 and 2004 to see how this plays out.

More specifically, your project fails using the 'prescriptive' values because the
roof requirement U-0.041 is based on the "Filled Cavity with Thermal Space Blocks"
criteria (see Description and Reference columns in 2006 IECC, page 31, Table
502.2(2), Roof = R-19+R-10). But the proposed U-factor is based on the ASHRAE 90.1
criteria called "Standing Seam Roofs with Thermal Spacer Blocks, Double-Layer,
R-10+R-19", and in the ASHRAE Table A2.3 (page 81), a R-29 (R-10 + R-19) proposed
insulation is equivalent to U-0.052. So on this basis alone the proposed U-factor is
not meeting the required U-factor. And if you look at that ASHRAE table you'll also
note that you never can get the Double Layer criteria to convert to U-0.041. This is
a serious fault in the 2006 IECC energy code.

So in order to make this project pass you have to add wall and roof insulation above
and beyond the code 'prescriptive' requirements to an extent that the walls make-up
(i.e., trade-off) for the roof shortfall. One example of this is to enter R-30 walls
and R-35 roof insulation values.

Alternatively, you could visit with your code official to explain the problem and
hopefully obtain a clearance from him/her.
Or don't use COMcheck but instead find a prescriptive compliance tool/worksheet to
show compliance.
Or, change your metal building roof to a "Other Metal Building Roof" then enter a
U-factor that you and your code official recognize as an acceptable U-factor for your
building. The 'prescriptive' U-factor would be 0.041. When I tested this last option
I noticed that there is a bug in COMcheck when specifying Other Metal Building Roof
while the energy code is 2006 IECC and the climate zone is '7'. The bug was that the
software would revert the "Other Metal Building Roof" to a metal building standing
seam type roof. This bug didn't affect the requirement you would face but it does
prevent you from simply entering a U-factor for the Other Metal Building assembly.
So I fixed this bug and recompiled COMcheck and have posted the fixed version out on
our website for you to download. The fixed version will have a 'build version' number
3.8.1.2. You can find the build version you are currently working with by clicking
the Help-About COMcheck menu option then look in the upper right hand pane. Note that
he main version number will remain as 3.8.1.

Sorry, that's the best explanation I give.

COMCheck Support

Entered on 12/07/2010 at 14:51:40 PST (GMT-0800) by Mech:
I was curious if anyone was able to determine the answer to my
questions?

Thanks,
Mech

Entered on 11/12/2010 at 09:17:26 PST (GMT-0800) by Mech:
Attached is the data file.

On a side note, the building fails by 3% with perimeter insulation.
Without the perimeter insulation, it only fails by 2%.

Sincerely,
Mech

Entered on 11/12/2010 at 08:57:51 PST (GMT-0800) by COMCheck Support:
Mech

Can you forward me your data file to review further.

Entered on 11/10/2010 at 14:46:12 PST (GMT-0800) by Mech:
Priority=3

Status=Open

COMCheck 3.8.0
Project is located in Superior, WI, Zone 7 per the 2006 IECC.

I input values for a metal building with a 1,738 sqft standing seam metal roof with R29 cavity insulation, 3,248 sqft of wall area with R26 cavity insulation, 149 ft slab perimeter insulated to R15, and no doors. I used the minimum values required by the Energy Code, but the building fails by 2%. Why does COMCheck fail the building with minimum Energy Code values? Did I enter something incorrectly?

Thank you for your assistance.

Attachments: ProcessBldg#2.cck

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