Log Home package manufacturers often send low cost insulation materials as part of their package, or leave roof insulation choices to the General Contractor on the job. The Contractor generally decides how to insulate based on his experience with conventional roof systems, subcontractor experience and availability, and his relative profit margins. This is unfortunate because it often leads to higher construction cost, substandard roof insulation and higher operating expenses to the homeowner.
Most Log Homes have energy efficient walls and significant interior volume by virtue of their design. This is an arrangement which calls for a closed roof insulation system - ceiling, insulation and roof as a single unit.
Typically, General Contractors either put fiberglass batts between ceiling and roof (which requires attic venting and, therefore insulation effectiveness reduction, or build up a rigid foam roof with sheets of rigid foam between firring strips and covered with sheathing. Although a rigid foam built up roof does insulate better than fiberglass (more R-vale per inch)- due to air spaces, thermal breaks, and venting, the insulation is still not up to the standards set by the rest of your structure. More significantly, these "built-up" systems have substantial risk for moisture problems, often leading to infestation and rot.
An alternative method has been used in the timber frame industry for years. It's called structural insulated panels. Structural panels are made of rigid foam (usually EPS- expanded polystyrene) laminated to OSB (oriented strand board). With OSB laminated to only one side, you have a nailbase panel, which is suitable for use over tongue and groove decking. With OSB on one side and drywall on the other you have a finished interior surface (except for taping and sanding) which can span up to 48" o.c. With OSB on both surfaces, spans can reach 16'.
These panels are closed systems- venting is not required, so none of the insulation benefit is lost to venting, nor is there a space available to trap moisture as the air cools. Since the panels are sealed and splined together with OSB, thermal breaks are minimized. Additionally, since the surfaces of the three elements of the roof- ceiling, insulation and roof nailing surface are either laminated or mechanically fastened, no space exists for pests to inhabit, a common complaint of homeowners with built-up roof insulation systems.
The panels are much stronger than other roof construction methods. Many log home owners that have used panels in their roof systems comment on how much quieter their homes are than neighbor's homes with other roof systems.
Surprisingly, panel roofs are usually less expensive to install than other roofing systems, primarily due to labor savings. Cathedral ceilings are ALWAYS less expensive when panels are used. Unfortunately, since most Contractors make their profit on labor, they are often unenthusiastic about panel use. Fortunately, many loghome manufacturers now offer panels and installation with their log packages.
If your manufacturer does not offer panel roofs, or for more information, contact me or visit my company's website at www.generalpanel.com .
My name is Butch Johnson and I work for General Panel Corp, a panel manufacturer with Plants in Johnson City, Tennessee and Union, MS. You can reach me by e-mail at email@example.com.