Traditionally, it has been the the practice to have 2/3 of the insulation inside the structure and 1/3 outside. Following that logic, if you own an older home with 2x4 exterior wall framing with R-12 insulation, you could then add R-6 to the outside and have a total of R18. That's optimistic. Most older homes had less than R-12 insulation no vapour barrier (vp) or poorly installed vp.
Removing the exterior finish and adding R-6 then replacing with new exterior finish will result in a great deal of expense for a new facade but a poor insulation end result.
Alternately, you could remove all the interior drywall, fir out the walls an additional 2" and insulate with R-20 insulation or better if you use a spray foam insulation. This would be very intrusive and expensive. Also, very difficult to eliminate the thermal bridging of the wood framing.
The good news is IKO has come up with a solution called Ener-Air wall insulation. Ener-air is a breathable polyisocyanurate foam insulation constructed of closed cell foam bonded on each sided with fiberglass. The panels come in easy to install 4'x8' panels and come in a variety of thicknesses. Included in the installation is IKO's specialized tape. The fact that Ener-air is breathable allows it to be used in any thickness desired and does not need to conform to the 2/3 and 1/3 traditional rules.
The fear with adding additional styrofoam products to the exterior facade could create a double vapour barrier. Styrofoam products are often extruded polystyrene and are impermeable to air flow. They may often have a foil back even making them more impermeable. The installation is often done by taping the joints or face sealing the foam panels prior to installing the finish. This created a non-permeable air barrier and thus creating a double vp - one on the face of the styrofoam and one on the interior face of the framing/interior insulation called polyethylene sheeting (or commonly called poly). This double vapour barrier would trap moisture in the assembly and cause problems, including mould and wood rot.
IKO recognized this issue and their research and development teams came up with breathable Ener-Air which has great insulative values but still allows moisture to escape. There is no limit to the amount of out-solation that can be added. Outsolation can also eliminate or reduce thermal bridging.
Outsolation solutions are leading edge technology. Whether you are renovating an older home or building new, Zero45 Consulting can help formulate the best solution for you.
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