CLT: Building Enclosure Design

Mass Timber Building Enclosure Design: Many Combinations Are Possible

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Exclusively Mass Timber: vertical exterior panels and horizontally laid or sloped panels at the roof

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Combination CLT building enclosure with structural concrete or steel core

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Mass timber structure with traditional framed wall enclosure

Environmental Loads

The building enclosure is subjected to environmental loads of water, air, heat, and water vapor, fire, smoke, light, sound, and insects.

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We will focus on controlling the water, air, heat, and water vapor

Material Assembly Required


CLT alone is not capable of adequately controlling air, water, heat, and water vapor; thus, CLT must rely on an assembly of materials and other components to meet the building’s performance expectations.


While performance can have a variety of meanings we will focus on the building enclosure to effectively manage:

  • Water – both liquid and vapor
  • Heat – reducing the need for heating and cooling energy
  • Air – unintentional exchange of air between the interior and exterior environments.

Moisture Sensitivity

Design and performance considerations for CLT enclosures differ from those of more traditional lightweight or mass concrete enclosures. CLT has unique physical properties such as its moisture sensitivity, relatively high capacity to store moisture, and relatively low vapor permeability.

Critical Load

Liquid water, predominately rainwater but also snow melt and runoff, is typically the most critical environmental load. Other environmental loads—air, heat, and water vapor—are caused by differences between the indoor and outdoor conditions.

VaproShield Membranes Offer Solutions

VaproShield’s sheet membranes are highly vapor permeable, simultaneously managing bulk water while allowing for some drying of underlying materials.



CLT Design Guide


Wall Details


Roof Details