At Davis Frame Co., we have learned through over 28 years of experience what works the best to ensure long-lasting performance of your Structural Insulated wall & roof system. The key to best performance is ventilation. No matter how well-constructed a home is, there is always going to be moisture at some point in time attacking the exterior shell of the home. This article will review briefly some methods to help keep the moisture from damaging one of your biggest investments, your home.
Structural Insulated Panels are different than conventionally framed walls and roofs, as they are basically an insulated foam core, sandwiched between two layers of structural sheathing, usually 7/16” OSB. Because SIPs have no wood framing in their main structure, there is a minimal amount of heat loss and moisture that gets behind the siding or roofing does not have any extra help from heat loss to evaporate. So it is important to provide a way for this moisture to dry out, and the best way to do this is through ventilation.
For the wall assembly, one of the best methods to ventilate the exterior sheathing is to create a gap between the siding and the sheathing. This gap can be achieved using a variety of materials, from a manufactured product such as Home Slicker, to installing wood furring strips. Experience has also shown that one of the best materials to use for an underlayment over the sheathing is #15 or #30 felt paper. Felt paper has a proven track record and allows trapped moisture to evaporate away from the sheathing.
For the roof assembly, a similar approach is used, where wood furring strips/strapping is installed over the SIPs to create an air space, with a top layer of sheathing installed over the strapping. Again, it is a good idea to use felt paper directly over the SIPs, which is added insurance that any moisture that gets to that level of the assembly will be trapped and then allowed to evaporate.
At Davis Frame Co., we are always looking for ways to promote the best building practices available to us. When it comes to SIP construction, we highly recommend the above methods to ensure that your timber frame and SIP home lasts for as long as possible. For more information on our design methods and material options, check out our website or give us a call (800.636.0993). We would love to hear from you!