A Hygrothermal Analysis and Structural Performance of Wood-Frame Wall Systems with Low-Permeance Exterior Insulation
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A Hygrothermal Analysis and Structural Performance of Wood-Frame Wall Systems with Low-Permeance Exterior Insulation

Authors: Marko Spasojevic, Ying Hei Chui, Yuxiang Chen

Abstract:

Increasing the level of exterior insulation in residential buildings is a popular way for improving the thermal characteristic of building enclosure and reducing heat loss. However, the layout and properties of materials composing the wall have a great effect on moisture accumulation within the wall cavity, long-term durability of a wall as well as the structural performance. A one-dimensional hygrothermal modeling has been performed to investigate moisture condensation risks and the drying capacity of standard 2×4 and 2×6 light wood-frame wall assemblies including exterior low-permeance extruded polystyrene (XPS) insulation. The analysis considered two different wall configurations whereby the rigid insulation board was placed either between Oriented Strand Board (OSB) sheathing and the stud or outboard to the structural sheathing. The thickness of the insulation varied between 0 mm and 50 mm and the analysis has been conducted for eight different locations in Canada, covering climate zone 4 through zone 8. Results show that the wall configuration with low-permeance insulation inserted between the stud and OSB sheathing accumulates more moisture within the stud cavity, compared to the assembly with the same insulation placed exterior to the sheathing. On the other hand, OSB moisture contents of the latter configuration were markedly higher. Consequently, the analysis of hygrothermal performance investigated and compared moisture accumulation in both the OSB and stud cavity. To investigate the structural performance of the wall and the effect of soft insulation layer inserted between the sheathing and framing, forty nail connection specimens were tested. Results have shown that both the connection strength and stiffness experience a significant reduction as the insulation thickness increases. These results will be compared with results from a full-scale shear wall tests in order to investigate if the capacity of shear walls with insulated sheathing would experience a similar reduction in structural capacities.

Keywords: Hygrothermal analysis, insulated sheathing, moisture performance, nail joints, wood shear wall.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.3346736

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References:


[1] Karagiozis, A. N. and M. K. Kumaran. 1993. "Computer Model Calculation on the Performance of Vapor Barriers in Canadian Residential Buildings" ASHRAE Transactions 99(2):991-1003.
[2] ASHRAE. 2009a. Heat, air, and moisture control in building assemblies-Fundamentals. In: 2009 ASHRAE Handbook-Fundamentals. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Chapter 25.
[3] NRC. 2015a. National Building Code of Canada, National Research Council of Canada, Ottawa.
[4] Ojanen, T. & M. K. Kumaran. 1996. Effect of Exfiltration on the Hygrothermal Behaviour of a Residential Wall Assembly. Journal of Thermal Insulation and Building Envelopes, Volume 19, pp.215-227.
[5] Kumaran, M. K. & J. C. Haysom. 2002. Low-Permeance Materials in Building Envelopes. Construction Technology Update No. 41. National Research Council Canada.
[6] Chown, G. A. and P. Mukhopadhyaya. 2005. NBC 9.25.1.2.: The On-Going Development of Building Code Requirements to Address Low Air and Vapour Permeance Materials. Proceedings of the 10th Canadian Conference on Building Science and Technology. Ottawa, ON.
[7] Fraunhofer IBP. 2018. WUFI® Pro v. 6.2. Holzkirchen, Germany: Fraunhofer Institute for Building Physics.
[8] ASHRAE 160-2016 Standard - Criteria for Moisture-Control Design Analysis in Buildings (ANSI/ASHRAE Approved), ASHRAE 2016, Atlanta, GA, 16 p.
[9] Health Canada (2016) "Relative humidity indoors: Fact sheet." Government of Canada, Ottawa. Cat.: H144-33/2016E-PDF.
[10] Roppel, P. J., M. D. Lawton & W. C. Brown. 2007. Modelling of Uncontrolled Interior Humidity for HAM Simulations of Residential Buildings. Thermal Performance of Exterior Envelopes of Whole Buildings X, Proceedings of ASHRAE/DOE/BTECC Conference. Clearwater Beach, FL.
[11] Maref, W., Saber, H. H., Armstrong, M. M., Glazer, R., Ganapathy, G., Nicholls, M., Elmahdy, H., Swinton, M.C., Integration of Vacuum Insulation Panels into Canadian Wood Frame Walls, Report 1- Performance Assessment in the Laboratory, Client Report – B1253, Building Envelope Engineering Materials Program, Construction Portfolio, National Research Council of Canada, Ottawa, Canada, 2012.
[12] Elmahdy, H., Maref, M., Saber, H. H., Swinton, M. C, and Glazer, R. “Assessment of the Energy Rating of Insulated Wall Assemblies a Step Towards Building Energy Labelling”, 10th International Conference for Enhanced Building Operations (ICEBO2010), Kuwait, October 2010.
[13] Elmahdy, A. H., Maref, W., Swinton, M. C., Saber, H. H., and Glazer, R. “Development of energy ratings for insulated wall assemblies”, Building Envelope Symposium, San Diego, California, October 26, 2009, pp. 21-30.
[14] Saber, H. H., Maref, W., Elmahdy, H., Swinton, M. C., and Glazer, R. “3D Heat and Air Transport Model for Predicting the Thermal Resistances of Insulated Wall Assemblies”, International Journal of Building Performance Simulation, First published on: 24 January 2011 (iFirst), Vol. 5, No. 2, p. 75–91, March 2012.
[15] Saber, H. H., Maref, W., Elmahdy, A. H., Swinton, M. C., and Glazer, R. “3D Thermal Model for Predicting the Thermal Resistances of Spray Polyurethane Foam Wall Assemblies”, Building XI conference, Clearwater, Florida, 2010.
[16] Saber, H. H., Maref, W., Abdulghani K., “Report on Properties and Position of Materials in the Building Envelope for Housing and Small Buildings”, National Research Council Canada, December 2014.
[17] Carll, C. G.; Highley, T. L. 1999. Decay of wood and wood-based products above ground in buildings. Journal of Testing and Evaluation. 27(2):150–158.
[18] Ojanen, T., Viitanen, H. A., Peuhkuri, R, Lähdesmäki, K., Vinha, J., and Salminen, K., "Mold Growth Modeling of Building Structures Using Sensitivity Classes of Materials", 11th International Conference on Thermal Performance of the Exterior Envelopes of Whole Buildings XI (Clearwater, (FL), USA, December-05-10), 10 p., 2010
[19] CSA. 2014. Engineering design in wood. CSA O86-14. Canadian Standards Association, Toronto, ON.