meeting residential energy requirements with wood-frame ...air film 0.25 x x path r-value sum...

Copyright © 2018 American Wood Council. All rights reserved. 1

Meeting Residential Energy Requirements with Wood-Frame ConstructionLoren Ross, P.E.Manager, Engineering ResearchAmerican Wood Council

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This presentation is protected by US and International Copyright laws. Reproduction,

distribution, display and use of the presentation without written permission of the speaker is

prohibited.

© American Wood Council 2018

Copyright Materials


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• The American Wood Council is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider # 50111237.

• Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.

• This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner ofhandling, using, distributing, or dealing in any material or product.

• Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

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Polling QuestionWhat is your profession?

a) Architect

b) Engineer

c) Code Official

d) Building Designer

e) Other

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• As compliance with modern energy codes becomes more complex, designers, builders and code officials are looking to more thoroughly understand requirements, especially those that offer flexibility in design. This presentation will focus on the prescriptive compliance paths for meeting the energy requirements of the 2012 International Residential Code (IRC)and the 2012 International Energy Conservation Code (IECC). Included will be a discussion on the flexibility offered in the codes and what design aids are available to make compliance easier, including DCA 7 – Meeting Residential Energy Requirements with Wood-Frame Construction – 2012 IECC Version and a complementary Energy UA calculator.

* Updated 10/18

Course Description

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• Describe and evaluate R-values and U-factors related to wood construction and understand how to calculate them.

• Recognize and evaluate the three prescriptive compliance energy paths. recognized by the code and understand how to use them in single-family design.

• Research and utilize the allowable trade-offs for residential energy requirements related to wood construction in the IRC and IECC.

• Describe the free design aids that are available from AWC and utilize them for designing residential wood

* Updated 10/18

Objectives

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Outline

• R-values and U-factors• Compliance Paths• Trade-offs• Example Problems• Design Aids• Questions?

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R-Value versus U-Factor• R-Value

• Measure of resistance of heat flow

• Material Specific

• Labeled on Product or ASHRAE Handbook of Fundamentals• Can be Summed

• U-Factor• Measure of heat flow

• Assembly Specific

• Derived from sum of R-Values

• Area Weighted


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R-values to U-Factors: Parallel Path MethodItem R-Value Stud

PathCavity Path

Air Film 0.68 X X2 Gyp. 1/2” 0.45 X X1 Stud 2x4 4.375 X4 Insulation 13 X3 OSB 7/16” 0.62 X X5 Vinyl Siding 0.62 X X

Air Film 0.25 X X

Path R-Value Sum U-Factor of PathStud 6.995 0.143

Cavity 15.62 0.064

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R-values to U-Factors: Framing Factors

Framing FactorHeaders 3-4%

Studs 16” o.c. 21-22%Studs 24” o.c. 18-19%

Projected Area of wood / Total Projected opaque wall area = Framing Factor


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Polling QuestionWhat is the definition of framing factor?

a) Projected wood area / projected opaque wall area

b) Projected wood area / total wall area

c) 25% for all buildings

d) Other

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R-values to U-Factors: Parallel Path Method

Path Sum U-FactorStud 6.995 0.143

Cavity 15.62 0.064@ 25% Framing Factor - 0.084

0.25(0.1430)+0.75(0.064) = 0.084

25%75%


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R-Values to U-Factors: Table Method

The same value can be found in DCA 7 Appendix A

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Compliance Paths• Same options for the IRC and IECC

• IRC Part IV – Energy Conservation• N1101.1 through N1105.6.3

• IECC – Residential Provisions• Chapters 1 through 5


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Compliance Paths• R-Value [R402.1.2]

• Simple

• Cavity or Cavity and Continuous Only

• Least Flexible

• U-Factor [R402.1.3]• Similar to R-value, only Assembly based

• Trade-offs only within the Assembly

• Total UA Method [R402.1.4]• Most Complex of Prescriptive

• Trade-offs between Assembly Types

• Method of DCA 7, REScheck

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Compliance Path: R-Value2012 IECC


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Compliance Path: U-Factor2012 IECC

=U-Factor

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Compliance Path: U-Factor2012 IECC

Path Sum U-FactorStud 6.995 0.1430

Cavity 15.62 0.064@ 25%

Framing Factor - 0.084

0.084 > 0.082 NG


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Polling QuestionIs a 2x4, R‐13 wall compliant with the 2012 IECC?

a) Yes, but only using the R‐value path

b) No, its U‐factor is too high

c) Whatever REScheck says

d) All of the above

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Compliance Path: Total UA Alternative2012 IECC

=UA

assemblyactassemblyref AUAU


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Trade-offs: Total UA Alternative2012 IECC

Energystar.gov

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Trade-offs: Window and WallFor a 30’ by 40’, two-story, house with 16% window area:

Window Wall Area: 2240 ft2 x (0.16) = 358.4 ft2Opaque Wall Area: 2240 ft2 x (0.84) = 1881.6 ft2

Reference UA of Proposed Home:

Total UA: 125.44 + 107.25 = 232.69

Window UA: 358.4 ft2 x (0.35) = 125.44Opaque UA: 1881.6 ft2 x (0.057) = 107.25

Proposed Home:Window UA: 358.4 ft2 x (0.30) = 107.52Proposed Opaque UA: 232.69 – 107.52 = 125.17Proposed Opaque U: 125.17/1881.6= 0.0665

Total Wall Area: (30’)(8’)(2)(2) + (40’)(8’)(2)(2) = 2240 ft2

0.057 0.0665


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Trade-offs: Window and Wall

0.057 0.0665

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Trade-offs: Window and Wall


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DCA 7

• Background on compliance paths• U-Factor Calculation • U-Factors for various assemblies (Appendix A)

• OSB, Plywood, Fiberboard• 16” o.c. & 24” o.c.• 2x4 & 2x6• R-13 through R-24 cavity insulation

• Tables for UA trade-offs for fenestrations and walls for 2012 IECC(Appendix B)

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DCA 7 – Appendix A


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Framing Factor vs. U-Factor

Framing FactorU-Factor

2x4 w/ R-13 2x4 w/ R-13+5 2x6 w/ R-2025% 0.084 0.060 0.06024% 0.084 0.059 0.05923% 0.083 0.059 0.05922% 0.082 0.059 0.05821% 0.081 0.058 0.05720% 0.080 0.058 0.05719% 0.080 0.057 0.05618% 0.079 0.057 0.055

Max. Difference 0.005 0.003 0.005

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DCA 7 – Appendix B


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DCA 7 – Calculator For iOS, Android, and Silverlight

www.awc.org

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Polling QuestionHow familiar are you with AWC’s website?

a) Never been there

b) Only go there for education

c) Familiar with publications and calculators

d) It’s my homepage

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DCA 7 – Calculator, Silverlight

Insert state specific values!

R-values show in the calculator are the performance needed after compression of the insulation!

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DCA 7 – Calculator, Silverlight


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Future Plans/Desires for the Calculator• 2015 IECC Reference Values• State Specific Reference Values• U-Factor Calculator• Moisture Criteria

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Take Home Messages...

• R-values and U-factors are related but require calculation to go from one to the other

• There are three prescriptive compliance paths in the IRC and IECC• The paths trade-off between simplicity and flexibility

• Modern energy codes have tightened opaque envelope requirements• Leveraging the UA Alternative method can alleviate requirements• AWC has online aids for determining U-factors and using the UA

Alternative method at www.awc.org


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• This concludes The American Institute of Architects Continuing Education Systems Course

Questions?

[email protected]

meeting residential energy requirements with wood-frame ...air film 0.25 x x path r-value sum...

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