DW Timber Frame Design



Sheathing Methods

   If you are building a timber frame home or are considering building
one, you should consider your choices for enclosing the frame once it's
                    There are basically three choices for enclosure

                                                         Stick frame

                                                      Wrap and strap

                                              Structural Insulated Panels 

                                        Conventional enclosure (Stick frame)

  Generally contractors will only be familiar with stick frame as an enclosure option. In stick frame enclosures, the walls are built as if the timberframe posts were just studs. The walls are built with studs between the posts or bents and the timberframe holds up the roof.

  There are three problems with this method

  The timber frame has already used enough first growth timber for one house, studs are excessive, especially since they are not necessary to hold up the roof conventional construction is energy inefficient it takes too long to build the structure twice, which is what you're doing if you use conventional stick frame for the enclosure. 

                                                         Wrap and strap

  Many timber framers use a system called wrap and strap, which is a better system than stick frame in that it uses less lumber and is more energy efficient. but it is also has substantial problems. 
Problems include:

  1.    Most contractors are not familiar with the process. 
  2.   Time consuming and costly.
  3.    If rigid foam is not used as the insulation material, the energy efficiency of the structure is only slightly better than stick frame and if rigid foam is used, there are enough gaps between foam and wrap and strap materials to allow air spaces which can cause problems over time. 

                                                 Structural Insulated Panels 

  I prefer to use stress skin panels to finish the enclosure. Panels are made by laminating rigid foam to OSB board to form a sandwich panel. Panels can be engineered for longer spans (Structural Insulated Panels- SIPs).   Stress Skin Panels, which are built to SIP standards, but unstamped, can be used for enclosure walls, floors, and shorter roof/ceiling spans (up to 12').  OSB/GYP Panels can be used in some circumstances (spans of 16" to 48" or wall areas supported at 8' o.c. each way) if drywall walls are desired and budgets are tight.   Nailbase Panels (osb on one side only) can be used over structural decks like T&G ceilings for insulation and a nailing surface.  Panels come in sizes from 4' by 8' by 4 1/2" thick up to 8' by 24' by 12 1/4" thick.  In most circumstances, panels in excess of 4' x 16' are too cumbersome to use- the handling cost exceeds the time savings.  This is especially true for jobsites where access is challenging- which, in my experience, has been most timber frame sites.

  Panels have a number of advantages over other enclosure methods

  1.   They're faster to install.
  2.   They do not need lumber (osb splines are used to connect them to each other and the timberframe structure handles the roof load).
  3.   They're stronger in shear and racking than stick frame or wrap and strap.
  4.   Cathedral ceilings are much easier to install using panels.
  5.   Sometimes panels are less expensive as an enclosure due to reduced labor.
  6.   They are the most-energy efficient alternative available. Often energy bills can be reduced 40% - 50% or more by switching to panel enclosures
  7.   Many homeowners also report significant noise and draft reduction as well as less heat convection in panel enclosed homes. 

  Structural Insulated Panels (SIPs) are an excellent option for hybrid timber frame homes, homes where part of the structure is timber frame and part is not. Most timber framers and contractors are unaware of this option, seek it out if it is appropriate to you.