A wooden frame receives its insulation on the outside. One approach is to wrap the frame in structural insulation panels. Another is to frame exterior walls conventionally with dimensional wood. Timber frame construction design does not lend itself to meeting the heat wrap standards of contemporary housing and building codes.
Fortunately, modern insulation technology offers several high-quality insulation options. Owners of timber-framed buildings can choose between stressed skin paneling options or use a technique we call the inside-out method. Often wooden frames are insulated with SIP (structural insulation panels), which can be fixed to the outside of the frame. A SIP wall would offer seamless insulation wrap, and if you glue the joints properly (see our page on how to make an air barrier properly), it can also be airtight.
The foam inside the core of a SIP acts as a vapor barrier. You can also do it with straw bales, and if the time comes, you can even stick the frame between the posts for easy insulation and wiring. What have you come up with to date as a wall mount?. It focuses on cases where timbers are exposed externally, which are usually the most problematic, but also considers wooden frames that are hidden behind the siding (either from the same period or later).
There is no reason why a timber-framed house cannot be as well insulated and airtight as a stick-framed house. If you are working on a timber framing project and would like us to take a look at your plans, send them to us. Typically, the woods were left exposed externally and internally and the spaces between the frame were filled with clay-based stains, often finished with lime. Systems such as these may work better in theory than under the varying conditions found on site, where quality control can be difficult, especially when the wooden structure is not straight or in perfect condition.
If the wooden structure is to remain exposed, the first essential step in improving thermal performance is to ensure that the frame and surrounding fabric are in good condition and consist of materials that allow the wall to breathe. In a surprising number of cases, what appears to be a wooden structure is actually an agglomeration of paint, putty and cementitious plaster repair that hides a severely degraded and structurally compromised structure. It is for this reason that this type of insulation is now more commonly found on the top of beams or on the outside of wooden frames. However, it is quite common to find widespread active attack by the Deathwatch beetle on woods immediately behind lime renderings, but it is rare to find it in exposed external woods, suggesting that sometimes the moisture content of a frame rendered with lime may be high enough to withstand the attack of fungi and beetles.
When the wooden structure requires repair involving removal of infill, there is an opportunity to introduce more comprehensive and better performing infill. Vermont Timber Works custom designs and manufactures beautiful timber-framed homes, post and beam barns, heavy-wood churches, cathedral ceilings and more. When insulating between timbers, you need to be able to cut the insulation easily and quickly so that it fits tightly to the wooden frame and also to the inner surface of the frame, whether it is OSB or a membrane. The crucial point is that modern, waterproof finishes and sealants not only cause significant and ongoing damage to the wooden structure and other historic fabrics, but also greatly diminish the thermal performance of the wall.
Simply put, wood fiber insulation, such as the Unger-Diffutherm range, is one of the simplest and most effective ways to insulate a wood-framed building. If the wooden structure and infill are in good enough condition and are robust enough to cope with continuous exposure with limited interventions, the insulation can be placed on the inside face, either directly on the wall or with an air gap. . .