developing durable wood-frame building envelope...

Developing Durable Wood-frame Building Envelope Systems

Dr. John Straube Dr. Hua Ge Michael Fox

Trevor Trainor

For net-zero energy ready buildings

Introduction

Buildings for Tomorrow Conference – Toronto Canada - October 28-30, 2014

2 14th Canadian Conference on Building Science and Technology

( Straube and Smegal, 2009)

Background Objective: To obtain measured data to evaluate the

hygrothermal performance of highly insulated wall systems Approach: Natural exposure field testing with additional

(controlled) moisture exposure Scope: Interpretation of measured data from six types of high-R walls on two exposures in the Waterloo, Ontario climate. This information can provide validation and calibration data for future testing and for hygrothermal models.





Test Walls: Framing pattern



Datum Wall (vertical cross-section)



Layers •  Fibre-cement lap siding •  ¾ “ (19 mm) strapping •  SBPO WRB and air barrier •  7/16” (11 mm) OSB sheathing •  2” X 6” SPF framing- 24” O.C. •  6 mil poly vapour barrier •  ½ “ (12.7 mm) gypsum wall board

Datum Wall (exploded cross-section) R-24 (installed)



Rockwool XPS PIC

Exterior Insulated Walls

R-35 (installed) R-35 (installed) R-34 (installed)



Deep Cavity Walls I-Joist Double Stud

R-33 (installed) R-39 (installed)



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•  North and south elevations were used for testing •  Natural weather exposure (Waterloo, Ontario) •  Interior Conditions- 21 °C, 40% RH (winter)

Instrumentation



2- Temperature Sensors 2- Relative Humidity/ Temperature Sensors 5- Moisture Content/ Temperature Sensors Wetting Mat Air Injection Port

Wetting Mechanisms



Air Injection System Wetting Mat System

Air Injection Testing



•  Energy Star air leakage limit = .02 l/s/m2 at 50 Pa

•  Power Law: Q = C * (delta P)n (n=0.65, delta P = 4 Pa) this was converted to an in-service air leakage rate of 0.2 l/s/m2

•  Applying this to the area of the center bay (1.3 m2), results in a leakage rate of .26 l/s/m2 per test wall

•  30 CFH (.24 l/s/m2) was used

Testing Protocol

Phase 1- Baseline (as-built condition)

October 2012 to February 18th, 2012

Phase 2- Air Injection testing

February 19th to April 9th

Phase 3- Drying

April 10th to June 4th

Phase 4- Wetting mat water injection

June 3rd to July 5th

Phase 5 – Drying

July 6th to October



Sheathing Moisture Content : Deep Cavity-North


Double Stud

I-Joist

Sheathing Moisture Content: Exterior Insulated-North


PIC

XPS

Rockwool

Change in Sheathing Moisture Content: Due to Air Injection Wetting


Results: The Warming Effects of Air Leakage


-‐10.0

-‐5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

1/5 1/12 1/19 1/26 2/2 2/9 2/16 2/23 3/2 3/9 3/16 3/23 3/30 4/6 4/13 4/20 4/27 5/4 5/11

Temperature (D

eg. C)

Date (D/M)

The Warming Effect of Exfiltrating Air

Actual Sheathing Temp.

Predicted Sheathing Temp. Air Injection Phase

Sheathing Moisture Content: Drying Analysis


Drying Analysis: Moisture Content Hours




Conclusions- Deep Cavity Walls

• Elevated M.C. in air-sealed (baseline) condition •  Upper sheathing up to 17% and upper plate up to 24%

• Susceptible to air leakage condensation •  Lower sheathing up to 30% and lower plate up to 50%

• Drying from exterior wetting was as good as Datum wall



Conclusions- Exterior Insulated Walls

• All performed well under air-sealed condition

• All provided good resistance to air leakage condensation

• Polyiso and XPS walls dried much slower from exterior wetting than Datum wall

• Rockwool walls dried nearly as fast from exterior wetting as Datum wall

NEWBuildS – NSERC strategic research Network for Engineered Wood-based Building Systems

Project T4-7-C10



Acknowledgements

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