|Foam Core Panel Enclosures
On most timber frames, the enclosure of the structure becomes part of the overall project and it is therefore included in our description of THE WORK and its pricing. We offer it as a service as the client will have the option to contract us or not.
We use a variety of panels, depending on the requirements for the project.
The following is an article on Stressed Skin Panels published in SOLPLAN Review, July 2001.
Stressed skin panels, also known as structural insulated panels (or SIP) systems, are a material and labour-saving alternative to traditional stick framing. The insulation within the panels is not interrupted by framing, so provides a thermally efficient envelope. Structural insulated panels have been used for more than 30 years, and offer an energy efficient building system that is simple to build and thus reduces on-site labour time.
Stressed-skin panel homes are very energy-efficient. When panels are used throughout, the whole building envelope is insulated. The insulation is virtually continuous and panels allow little air leakage, so a stressed-skin panel house is generally easier to make airtight than a conventional stick frame house.
A house built with SIPs could produce heating energy savings of 12% - 17% compared to a stud-frame house of equal size and R-value. This is largely due to the more efficient insulation approach that eliminates any potential for themosiphoning or wind washing which can be a problem with improperly installed batt insulation.
The panels themselves provide the required air and vapour barrier. However, to ensure a continuous air barrier, the joints at the panel to floor, panel to panel, panel to roof, and at penetrations must be sealed with long life sealants. It is important to be aware that some adhesives and caulks are incompatible with foam insulation, so care must be taken when selecting sealants.
Design & Engineering
Stressed-skin panels offer design flexibility. For example, if they replace conventional roof trusses, they can accommodate a living area under the pitched roof or where it would otherwise be necessary to use very large rafters. The BC Advanced House is one example of this. The roof structure encloses a large volume while creating interesting living spaces.
Because the panels do not have open cavities, they require different approaches to plumbing and electrical systems than conventional framing. Ideally, a designer should incorporate as much of the plumbing and electrical work as possible on interior (non-panel) walls. Where that is not possible, walls can be furred out for plumbing vent stacks and electrical runs.
Pre-cut electrical chases are standard in some systems, but must be specially requested in others. Often, wiring on outside walls is fed from the top or bottom, so a single saw cut is made to insert the wiring, and then refilled with foam, but each manufacturer will supply information on these kinds of details.
Most stressed-skin panels require 1/2" interior gypsum drywall.
Building officials, while not necessarily familiar with stressed-skin panels, have generally been receptive to their use, but will likely ask for a professional engineer to verify the structural performance. Suppliers may provide this.
Larger stressed-skin panels, often used in a floor and roofs, can be so heavy that they require cranes or other machinery for handling.
If stressed-skin panels become wet, they take a long time to dry out and may harbour mould growth. MDI resin offers greater water resistance than phenolic resins in OSB skins.
Carpenter ants have been found to nest in stressed-skin panels, as they do in conventional framing. Measures for protection against termites and rodents are the same as they are for conventional construction. Some manufacturers have developed relatively non-toxic borate foam treatments that seem effective at preventing infestations.
Environmental & Performance Factors
There are tradeoffs for each type of stressed-skin panel. None of these products is without environmental impact. Overall, stressed-skin panels are a resource-efficient building technology with significant energy-efficiency and forest-conservation benefits, and hold distinct advantages over stick framing.
The allowable roof or floor panel span will depend on the type of foam used in the core. Each manufacturer will provide that design information. Thicker panels reduce long-term deflection or deformation due to creep.
Reprinted with permission from Solplan Review, the independent journal of energy conservation, building science and construction practice (issue No. 99, July 2001). For subscription information: P.O. Box 86627, North Vancouver, BC V7L 4L2 or firstname.lastname@example.org
At Northern Timberhouse/Timberhouse Supply, we do not push for any one particular brand of panel and we like to inform our clients on the options, suggest a course of action and reach a joint decision.