To ensure an airtight enclosure, acoustical sealant is used extensively to seal every wood-to-wood connection through the interior wall’s connection points.


A careful insulating barrier at the home’s eaves makes certain that for ventilated roofs, outdoor air is isolated when entering the baffles. Another option is to build an unvented attic, a technique that you can learn more about from case studies by Building America (www.buildingscience.com).


 


Dow’s STYROFOAM SIS Brand structural insulated sheathing is actually a neat solution because it offers structural, water resistance and thermal insulation all in one product.


“We were an early adopter of this Dow product and have been very happy with it this far,” reports Raymond Pruban, chief manager, Amaris Custom Homes, Minneapolis. “This product is an exterior sheathing. Because it wraps 100% of the exterior structure, there is no thermal bridging, and it provides a minimum of R-5.5 at the stud locations.”


This is actually key as the studs and framing typically make up about 25% of the wall area, according to Dale Winger, marketing manager, Dow Building Solutions, Saginaw, Mich.


At the same time, even though a number of sheathing products have been tested for strength, Pruban prefers to use metal strapping from the footings to the roof, along with metal lateral bracing for reinforcement.


Another issue is protecting the above-grade insulation from ultraviolet rays and physical abuse. For this, “various materials can be used such as fiberglass reinforced panels, stucco, coatings, pressure-treated plywood, aluminum or vinyl coil stock and pre-coated insulated panels,” says Winger.


Moving on to the floor, the codes require around R-30, while Energy Star mandates R-38.


“In the practical world, what works best is to use a minimum of a 10” joist depth for floor framing and to fill the joist bay completely with insulation,” advises Tom Reid, owner, Green Home Construction, Hood River, Ore.


For example, Dow’s STYROFOAM’s Tongue and Groove insulation can be used under the basement slab, and if the boards are taped at the seams, then a vapor barrier isn’t required.


When it comes to wall insulation, a number of options are available, such as insulated concrete forms (ICF) and structural insulated panels (SIP)—making other cladding systems thicker with foam by using a double stud configuration or an alternate stud wall.


While Reid is in favor of all these options, he points out, “the double stud is a simple solution and allows for lots of flexibility and maximum potential for insulation.”


“We’ve used SIP panels which have benefits in easy, fast erection as well as in the large scale—which helps in preventing the air infiltration,” says Jovanović. “We have also used high-density blow in cellulose, which does have a lesser R-value than the rigid expanded polystyrene board of the SIP panel, but is more pervious and has less embodied energy.”


Lastly, to combat rising heat, the ceiling and attic require a high level of insulation. Because space can sometimes be an issue, Reid recommends raised-heel trusses, so that the full depth of the attic insulation can extend all the way to the exterior wall, where the truss lands on top of the wall.


Another approach, as was used in the InVision Zero Home, a demonstration net-zero house in Midland, Mich., built by Cobblestone Homes and Dow, is to layer spray polyurethane foam in the wood framing cavity, for both insulation and air sealing, with spray cellulose insulation for a continuous layer.

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