Thermal Bridging – designing structurally and energy efficient buildings
Thermal bridging – having uninsulated or thermally inefficient elements in your building’s structure – can kill the insulation value of your building. These problems are often found at the foundation/wall intersection, at the parapet/wall/roof detail & at any structural projection in the building (balcony, overhang, cantilever, brick ledge, building offset, etc).
Here is a great article (along with thermal calculator tool) on this subject.
http://www.healthyheating.com/Definitions/Mean%20Radiant_pg5.htm#.Uve4VvldVjY
here is the spreadsheet / calculator / tool:
http://www.healthyheating.com/Definitions/Spreadsheets/Area-weighted-avg-insulation-web-version.xlsx
Another brief article by Jim D’Aloisio on this topic:
a U-value to R-value calculator:
http://www.ecowho.com/tools/r_value_to_u_value_calculator.php
Common u values of building materials:
http://www.combustionresearch.com/Infra-Spec/infra-spec/uvalue.html