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Timber Frame Enclosure

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 complete.

A timber frame home makes a statement about your identity that conventional buildings don't make. You have opted to spend more per square foot than conventional construction would have cost. You have decided to make the structure of your home not only visible, but fully displayed. You have decided to build one of the strongest, longest-lasting structures that can be built.

Often, the professional that erects the timber frame is only interested in getting the frame up and the general contractor is not as familiar with options for the next phase of construction, enclosure, as you would like him to be. The timbers that you paid so much for are out in the weather, and panic sets in about how to get them covered before the sealing process gets too cumbersome.

There are basically three choices for enclosure: Stick frame, Wrap and strap, or 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 were just another stud. 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 timberframe 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

A few 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  Problems include:

Most contractors are not familiar with the process, so the timber framer must build the wrap and strap enclosure (usually against his will) and you end up paying artisan wages for basic construction to get the enclosure built.
Time-consuming and costly.
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.

Enclosure Panels

More and more timber framers (2001- 95% estimated by the Timber Frame Business Council) are recommending the use of enclosure panels to finish the enclosure. Panels are made by laminating rigid foam to osb and other building materials to form a sandwich panel. Various panels used are structural insulated panels (engineered with osb on both sides- when roof or floor spans are over 12'), stress skin panels (also osb on both sides but not engineered- for spans up to 12'), osb/gyp panels (spans of 16" to 48"), and nailbase panels (osb on one side only- used over structural decks like T&G ceilings) for insulation and a nailing surface. Other specialty panels are also available. Panels come in sizes from 4' by 8' by 4" thick up to 8' by 24' by 12 1/4" thick.

Panels have a number of advantages over other enclosure methods.

They're faster to install
They do not need lumber (osb splines are used to connect them to each other and the timberframe structure handles the roof load)
They're stronger in shear and racking than stick frame or wrap and strap
Often panels are less expensive as an enclosure due to reduced labor
They are the most-energy efficient alternative available. Often energy bills can be reduced 40% or more by switching to panel enclosures
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. Often timber framers and contractors are unaware of this option, so it may be wise to bring it up.