Doug Tarry Homes
After investigating concerns about water build up on the poly that could indicate leaking in the basement, the Doug Tarry Homes team recognized that this issue was not a leaking basement, but a condensation issue due to the performance of the basement wall and that this was not an uncommon problem. In fact it is quite common, happening in many new homes across the province due to similar wall assemblies that meet and, at times, exceed code.
A great deal of research and field testing was conducted by the company to learn about the challenges of controlling vapor diffusion in a basement wall assembly and about how the basement wall needs to work differently during the summer than it does during the winter. Doug Tarry Homes engaged with leading building science educators including Gord Cooke, Dr. John Straube and John Godden to develop the Better Basement Wall, and ultimately the Optimum Basement Wall.
ROXUL insulation was chosen to be included in the Better Basement Wall, and ultimately the Optimum Basement Wall, because of its performance and ability to address the issues of slumping, thermal bridging and mould growth in the wall assembly.
Based on the performance review of the Better Basement Wall,
another aspect of the Optimum Basement Wall was to bring the air
barrier to the warm side of the wall and use the poly as a
combination Air/Vapor Barrier. The other step was to change out the
top portion of the poly with a breathable Smart Membrane to permit
the summer vapor migration to dry through the wall into the
conditioned basement. After consulting with our Chief Building
Official Leon Bach, he permitted us to try a new wall design as an
Alternative Compliance to the Building Code. The concept of the
Optimum Basement Wall was to create a more
forgiving wall system which has four basic principles.
4 Principles of the Optimum Basement Wall
1. Limit the ability for water to enter the wall
2. Use of materials that won't trap moisture.
3. Change the location of the Air Barrier.
4. Allow drying paths for moisture migration.
The materials within the wall assembly were evaluated, performance tested, re-evaluated, removed, changed and reassembled. Along the way performance issues were identified:
In early October 2013, Doug Tarry Homes opened their latest Discovery Home in St. Thomas, Ontario. This home features two major pilot projects, one of which is the Optimum Basement Wall. This wall was constructed and closed in during the July heat wave while the drywall was being installed upstairs, adding a large volume of additional moisture into the home at the same time as there was no dehumidification or air conditioning running in the home and the wall performed beyond expectations.
In order to prove the performance of the Optimum Basement Wall, Doug Tarry Homes partnered with ROXUL Insulation and George Brown College to study the home as part of the Argile Project through one full heating and cooling season. In addition, a renovation detail was designed to modify the Better Basement Wall for clients that were having vapor build up on the poly during the summer. This detail was completed by Doug Tarry Homes for more than a dozen customers who saw immediate results in the performance of their basement.
Moving forward, Doug Tarry Homes and ROXUL are partnering with leading building science experts to educate builders, renovators, building officials, warranty programs, and code planners about the need to rethink the design of basement wall systems. Optimum Basement Wall system details have been created for builders, as well as renovators, for both R14 and R20 basement walls so that homeowners can have basements that meet their expectations.