Structural and Hygrothermal Performance of Light Wood-Frame Walls with Insulated Sheathing

• Author / Creator

  Spasojevic, Marko

• In order to meet a higher standard of building energy efficiency, the thermal insulation of exterior walls is often increased. Adding a layer of continuous thermal insulation exterior to the cavity insulation, insulated sheathing, to reduce thermal bridging is getting more popular in practice. In some cases, the continuous insulation is put outer to the wood sheathing while in other cases the insulation is inserted between the sheathing and framing. The former configuration may limit the air-drying capability of wood sheathing due to the low permeability of commonly selected exterior insulation materials. On the other hand, the latter configuration compromises the racking resistance of the wall due to the soft foam layer inserted between lumber and wood-based panels. Clearly there are contradicting influences on thermal and structural performance of the wall when the insulation thickness changes. This study aims to investigate and compare the hygrothermal and structural performance of two proposed wood-frame exterior wall configurations. The impact of the intermediate insulation on shear wall resistance was investigated and the results show that adding insulation between the sheathing and framing greatly decreases the lateral capacity and stiffness of the wall. Additionally, the lateral capacity of the shear wall with intermediate insulation can be accurately predicted based on nail joint properties. A sensitivity analysis was conducted to investigate the hygrothermal performance of these two wall assemblies considering different air leakage rates and indoor relative humidity levels. The results show that these two wall assemblies show similar drying and wetting potentials when excessive moisture accumulation is prevented by placing enough insulation exterior to the wall cavity. The minimum ratio of outboard-to-inboard thermal resistance necessary to prevent the mould growth and excessive moisture accumulation within the wall is recommended for eight locations in Canada. Putting insulation between the sheathing and framing, instead of outboard to the sheathing, increases this ratio by approximately 0.07 and 0.04 for 2×4 and 2×6 stud cavity walls, respectively.

• Subjects / Keywords

  • lateral load resistance
  • hygrothermal performance
  • insulated sheathing
  • wood-frame walls
  • shear wall

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-jhba-0523

• License

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