Article #1449 - REScheck Webcast Questions - Log Walls
This article is based on questions asked during both the May 6, 2005
REScheck Training Webcast
and the July 28, 2005
as well as questions received through email following these events. The original language of the questions and answers has been modified to make them as generic as possible while retaining the applicable specific information.
Is there anything special to enter in RES check when using log structure wood walls?
RES check has a drop down list of log walls to choose from. The log choices are based on nominal thickness in inches ranging from 5" to 16". If one of the log wall choices does not match your log wall assembly, you can choose "other" as your assembly type from the drop down list and enter the overall u-factor of the log wall.
For log home packages do I take the R-value per inch of log times thickness? For instance cedar is 1.41 per inch x 5.5= 7.75 R-value.
In RES check the log wall choices in the drop down list assume a thermal resistance r-value per inch range of 1.1-1.3 plus 0.85 for film resistance. A wood density range of 1.7 lb/ft3 at 12% moisture content for west coast wood and cedar to 41.2 lb/ft3 for southern pine and a specific heat of 0.39 Btu/lb degree F at 12% moisture content. The log choices are based on nominal thickness in inches ranging from 5" to 16". If one of the log wall choices does not match your log wall assembly, you can choose "other" as your assembly type from the drop down list and enter the overall u-factor of the log wall.
Why does RES check not allow Mass Wall Credit for anything less than a 7 inch log wall?
The MEC and IECC include a mass wall credit for walls having a heat capacity greater than or equal to 6 Btu/ft2 degree F. The code states that, "Solid wood walls having a mass greater than or equal to 20 lb/ft2 have heat capacities equal to or exceeding 6 Btu/ft2 degree F." According to the data in Table A.20 of the document titled, "
Methodology for Developing the REScheck Software through Version 3.6
", 5 inch and 6 inch log walls do not meet these criteria, with the heat capacity given just at the lower boundary but the weight falling below 20 lb/ft2.
We are currently working on updating the log wall assembly options in RES check . The next release of RES check will address the mass wall credit below a 7" log wall. Determination of the log mass wall credit will be based on the new consensus process in the ICC for log wall thermal calculations. The next release of the software is expected in September 2005. An email will be sent to all registered users.