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Improving the drying efficiency of timber frame walls in cold climates, by using exterior insulation

Ojanen, T.
1998
Thermal Performance of the Exterior Envelopes of Buildings VII, Clear water Beach, Florida, pp. 155 - 164
OSB, exterior sheathing

Ojanen, T., (1998), "Improving the drying efficiency of timber frame walls in cold climates, by using exterior insulation", Thermal Performance of the Exterior Envelopes of Buildings VII, Clear water Beach, Florida, pp. 155 - 164.
Abstract:
Safe moisture performance of a structure requires high drying efficiency. Even if a structure has acceptable moisture performance under normal design conditions, long exposure to moist conditions due to high initial moisture content or accidental moisture loads may start biological deterioration. Timber frame walls with rigid exterior sheathing, such as oriented strand board (OSB) or plywood, have relatively low vapor permeance. Use of exterior insulatior made of vapor permeable, open porous material and installed at the cold side of the sheathing, is an effective method to improve the drying efficiency of a wall

Three objective of this study was to present how the moisture performance of timber frame walls can be improved with vapor permeable exterior insulation. Numerical simulations and laboratory-scale experiments were used in the analysis. Both moisture content levels and a numerically solved mold growth index were used as criteria in the analyses.

Experiments with wall structures having initial moisture loads and temperature gradients were used to study the drying efficiency through sheathing boards with and without exterior insulation. The conditions corresponded to those typical for cold climates experiencing drying: condensation with below and above freezing temperatures at the exterior sheathing. In some conditions, exterior insulation could improve the drying efficiency by nearly a factor of 8. Numerical simulation results show the effect of climate, thickness of exterior insulation, and moisture loads caused by diffusion and initial moisture content on the drying efficiency and moisture performance of timber frame walls.
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Author Information and Other Publications Notes
Ojanen, T.
Tiiomo Ojanen Senior research scientist VTT Building Technology, Finland.
  1. Drying capabilities of wood frame walls with wood siding
  2. Effect of exfiltration on the hygrothermal behaviour of a residential wall assembly: results from calculations and computer simulations
  3. Heat and mass transfer between indoor air and a permeable and hygroscopic building envelope: part I -- field measurements
  4. Heat and mass transfer between indoor air and a permeable and hygroscopic building envelope: part II --verification and numerical studies
  5. Improving indoor climate and comfort with wooden structures
  6. Integration of simplified drying tests and numerical simulation in moisture performance analysis of the building envelope
  7. Measuring and modeling vapor boundary layer growth during transient diffusion heat and moisture transfer in cellulose insulation
  8. Modeling heat, air and moisture transport through building materials and components
  9. Moisture and bio-deterioration risk of building materials and structuresL?hdesm?ki
  10. Moisture buffer value of building materials
  11. Moisture Buffer Value of Materials in Buildings
  12. Moisture performance of an airtight, vapor-permeable building envelope in a cold climate
  13. Moisture transport coefficient of pine from gamma ray absorption measurements
  14. Numerical simulation of mould growth in timber frame walls
  15. Thermal and moisture performance of a sealed cold-roof system with a vapor-permeable underlay
  16. Towards modelling of decay risk of wooden materials  


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