The use of structural insulated panel (SIP) technology makes for a high-performance “overcoat” for a serious home energy retrofit
Ted Clifton has been building and remodeling homes for more than 45 years. But he continues to recognize good innovations as they come along. That’s why he decided to use nailbase insulation panels on a recent green remodeling project for Bob and Tobie Johnson of Oak Harbor, WA.
What is nailbase insulation?
Nailbase insulation panels are essentially SIPs without the interior OSB skin. The panels keep the exterior OSB skin as the nailbase for the new cladding. Many SIP manufacturers, including Premier Building Systems, which manufactured the panels used by Clifton, are now making nailbase insulation panels.
“What is great about nailbase is that you get air sealing as well as insulation,” said Clifton. “We were able to cover the rim joist, which is typically a major source of air leakage in older homes.”
The nailbase insulation panels are fastened directly to the existing structural sheathing of the home, after the existing cladding has been stripped off. The same high performance screws used in conventional SIPs are used with the nailbase panels.
Clifton has also used the nailbase insulation panels to retrofit roof assemblies, although with the conditioning boundary on this home remaining at the ceiling plane, raised heel trusses were used on this project.
Air sealing details
In addition to using spray foam sealant at all panel joints and caulking every bucked window and door opening to the nailbase insulation panels, Clifton custom-routed each panel on site. “We do it all on-site for this type of work. We need to fit existing openings precisely, and we would never be assured enough of the accuracy of the existing framing to have the openings fabricated at the factory,” said Clifton. “In addition, at the top corners of the walls, we used 2x2 steel angle flashing under the drywall, to provide a better seal at the plate line.”
The other detail that looks challenging is the triple-window bump-out in the guest room. Clifton weighs in on this detail: “The whole bump-out is SIP panels; this is a ‘trick’ we have been using for some time. We simply cut the opening 13 in. bigger than the window rough opening all the way around, then install the top SIP full width of the opening, then the two sides all the way to the bottom, then the bottom panel in between. The sides hold up the top and the bottom, they have plenty of leverage along the sides to extend a goodly ways... We do add a few square feet of surface area, but it is all R-25 SIP panels.”
Drainage plane details (for a mason)
A portion of the new wall cladding is a veneer called Thinstone. When I asked Clifton about the best way to do this type of stone veneer cladding, here is what he had to say: “There is a double WRB [water-resistive barrier]; first we used a layer of Tyvek, then the mason (it was his house) installed a layer of 30 lb. felt, then expanded metal lath, scratch-coat, and stone, in that order. All the stone veneer is on the west side of the house, where we do not experience any direct rainfall, and it is under substantial overhangs, so it is not likely to have any moisture problems.” But that double layer of materials with all types of masonry claddings is critical, with one acting as the bond break and the other acting as the dedicated drainage plane or WRB.
What about bugs and EPS panels?
GBA hears quite a bit about carpenter ants and termites in exposed rigid foam. Clifton is right on top of that: “Every inch of the foam is covered with wood. The bottom edge of all the panels is capped with a pressure-treated 2 by 4, the window and door openings and corners are capped with two-bys, and at the top we install the Hardi-Soffit first, then adhere the angled top edge of the panel to the soffit. We are tight! No venting, no bugs.”
Clifton’s approach to mechanical ventilation
For this project, Clifton used a 240 cfm powered supply fan with a HEPA filter to bring fresh air in, while using the remote-mounted 230 cfm kitchen exhaust fan to move stale air out. Both are on a speed control, with the lowest setting at around 30 cfm. If the range fan is turned on by itself, it uses a 3-way switch to select full power, and the HEPA fanr continues at its lower rate, which is resumed also by the kitchen fan when the switch is turned "off." When any of the bath fans are running, or when the kitchen fan is on full, the 8-in. inlet duct through the HEPA filter is providing the makeup air.
Clifton continues: “Because our outdoor temperatures are so mild in the spring, summer, and fall, HRVs are not particularly useful here. One of the beauties of this system is that on a hot day, with no wind blowing, our owners can turn up the speed control, and exchange all the air in the house in less than one hour. If they do this in the early morning hours, before it gets hot outside, they have a house full of nice cool fresh, filtered air, at about 65 degrees at 8:00 a.m. or so. Then the air-conditioning never needs to come on during the day, even on a 90 degree day, because of the tightness of the house, and the insulation values we used.”
The biggest surprise to Clifton on this project was the crawl space: “The foundation under this house was a crawl space, with unfilled concrete block walls. It was one of the cleanest and driest crawl spaces I have ever seen, so we did the math on whether or not to close it up, or keep it as a vented crawl space. This is the first time in years I have had one come up as more cost-effective to leave as a vented crawl space, partly I think because it had joists deep enough to insulate to R-38. We added the layer of 1/2-in. OSB (3/4 in. in places due to different floor covering thicknesses) to air-seal the existing shiplap board subfloor.”
The other big lesson learned was on the issue of tearing the whole thing down, given that they essentially rebuilt this home from both the inside and the outside. The homeowners first thought that it made more sense to start from scratch, given all of the changes a remodel would entail, but Clifton calculated that he could complete the gut rehab of the home for a fraction of the cost, if, among other things, he used the nailbase insulation panels on the project.
Finally, this from Ted Clifton: "It is very difficult to work around existing masonry fireplaces. Our mason-owners, Bob and Tobie Johnson (Ward-Johnson Masonry & Tile) had a very hard time plugging up all the water leaks and air leaks, but did an excellent job of it in the end."