UA Alternative

[Bama dav]

Can anyone explain to me what this means?(n1102.1.4 2012 irc). I have read the commentary and actually got more confused. Thanks for any help.

 

[jeffc]

The Energy Code allows a couple of methods to show compliance. One method is the prescriptive method that gives all of the required R and U values. N1102.1.4 gives the applicant a means to under insulate in some areas, say R-19 floor, and add more insulation in other areas so in the end, the house meets the energy code. Going through the calculation manually could take lots of time and compromise your sanity. He is the form we in Washington State use: http://www.energy.wsu.edu/Documents/CP_Worksheet_070110.xlsx. If your energy code differs from ours, this form may not be helpful but shows how the process works. In the end, the results give you numerical heat loss value for a code compliance house and the numerical value for the proposed house must be less than the code house. Lower UA means more energy efficient.

 

[rogerpa]

What N1102.1.4 says is that you can have areas of the envelope that don't meet the R-values specified in Table R301.1 as long as you have offsetting areas that are above the R-values in the table.

You can calculate this using this formula. Area-weighted average: (A1 x U1 + A2 x U2 + ... + An x Un ) ÷ 0.35(A 1 + A 2 + ... + A n ) ≤ 1 where A equals the various areas and U equals 1 divided by the R-value. 0.35 is the code specified U-value for fenestration in Zone 3 (from Table N1102.1.3).

 

[Bama dav]

Thanks for the reply, I called the code congress and had someone explain it to me.Do you think they could have made it harder to figure insulation requirements. I think it will get worse.

 

[TheCommish]

you could use ResCheck if you juristiction allows it, seems to be the simplest way to achieve compliance if you dont want to use prescriptive method

REScheck | Building Energy Codes Program

 

[globe trekker]

Bama dav,

Rather than state that you "must use" specific types of assemblies in achieving energy efficiency,

this section and Table gives the minimum levels of achieving energy efficiency when using other

types of materials & products.

The new energy efficiency requirements are here to stay, and "yes", they are difficult to understand

at first. It's like a lot of things in the codes, ..it's different and will require some different ways of

thinking. IMO, they are not unfounded though! The United States is the largest consumer of

energy in the world, and that amount is projected to grow over the coming years.

I thing that the "intent" behind the energy efficiency movement was well intended. The actual

letter of applying that intent is lacking in a lot of areas.

As a suggestion, it will behoove us all to become familiar with the language and application of

the various energy codes.

.