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Green Homes

A Deep Energy Retrofit Using Nailbase Insulation Panels

View Gallery 12 images
This photo shows the original front side of the house, which in part faces south to the stunning views of Skagit Bay in Washington state.
Image Credit: Ted Clifton
This photo shows the original home from the back of the house, which faces Skagit Bay.
Image Credit: Ted Clifton
This photo shows the original front side of the house, which in part faces south to the stunning views of Skagit Bay in Washington state.
Image Credit: Ted Clifton
This is the view from the southeast of the remodeled home. Note the mini-split heat pump, which now provides all the space conditioning needs of the renovated home.
Image Credit: Ted Clifton
The panoramic view of Skagit Bay from the new living room. Although large, the new windows have a respectable U-factor of 0.28.
Image Credit: Ted Clifton
The inside of the Skagit Bay home was completely gutted. While the SIP nailbase insulation is a great way to improve the thermal performance of a home without touching the inside of the home, it is also a fast and efficient approach for a gut rehab.
Image Credit: Ted Clifton
The window buck is caulked and ready to receive the nailbase insulation panel.
Image Credit: Ted Clifton
Two carpenters can easily place each 4' by 8' or 4' by 9' nailbase panel. After the panels are installed, each butt joint is foamed in place for a continuous exterior air barrier.
Image Credit: Ted Clifton
The original or existing floor plan of the Johnson residence. Note the 3-bedroom configuration with formal dining room adjacent to the small kitchen.
Image Credit: Ted Clifton
The new floor plan, showing nearly complete reconfiguration of interior spaces to suit the needs of the new owners.
Image Credit: Ted Clifton
Cross sections of the renovated home. Note that the exterior nailbase insulation panels extend down over the original bottom-of-wall/top-of-foundation transition and the crawlspace remains unvented and unconditioned.
Image Credit: Ted Clifton
This is the summary performance page of the HERS rating on the Clifton - Johnson project. Note that the predicted space heating load represents about an 80% reduction in energy use. The homeowners are reporting actual utility bills pretty close to the modeled results.
Image Credit: Ted Clifton

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 2×2 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.”

Lessons Learned

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."

General Specs and Team

Location: Oak Harbor, WA
Bedrooms: 2
Bathrooms: 2.5
Living Space: 2900
Cost: 100
Additional Notes: Although this per square foot cost does not include the masonry work (done by owner), the cost is well below the "going rate" for new construction in this neighborhood, about $200 per square foot.

HVAC: Barron Heating & Air Conditioning Energy/Rating Consultant: Pinnacle Inspections Masonry/Tile: Ward-Johnson Masonry & Tile


- Foundation: block wall crawl space
- Above-grade wall: 2x4 wood-framed wall
- Roof assembly: Raised-heel truss

Energy Specs

- Foundation: 1st floor, R-38 batt insulation; air barrier sealed floor sheathing
- Above-grade walls: R-29 (4-inch EPS nailbase + high-density fiberglass batts in wall cavity)
- Ceiling: R-38 blown-in fiberglass with 14" raised-heel roof truss
- Windows: Atrium U = 0.28, SHGC = 0.44, VT = 0.46 - 0.56

Water Efficiency

- Low-flow faucets
- Dual-flush toilet (powder room)

Indoor Air Quality

- HEPA filter system
- Rodda zero-VOC paints
- Exhaust fan in garage coupled to door opener and light timer

Green Materials and Resource Efficiency

- 90% recycle rate (commingled off-site recovery)
- Extensive reuse of interior doors
- Extensive continued use of all kitchen cabinets
- Some cabinets reused in garage



  1. RemBKgKYVs | | #1

    exterior insulation
    2/3 of my house is 8" block sized and colored to look like oversized brick.
    Would this method work for insulationg the block wall? Am I asking for humidity problems such as occurred with the EPS retrofits?
    I intend to replace the old single pane plus storm windows in any case so replacing door jambs and window frames for a thicker wall doesn't add too much work to the job.

  2. Expert Member
    Peter Yost | | #2

    Exterior insulation on block wall
    Exterior insulation retrofits can work on any building, any climate. Exterior insulation makes everything to the interior of the insulation experience conditions more like the building's interior, or what the occupants are experiencing. Having said that, you need to make sure that:

    1. you are managing moisture well, particularly in terms of bulk water and air-transported moisture.

    2. you have drying potential in at least one direction so that if a wall assembly gets wet, it can dry. See the GBA blog on vapor profiles.

    With nailbase panels like the ones for this project that have an exterior layer of OSB, most of your drying potential will need to be to the interior. Check your assembly and the vapor permeability of all layers to the interior of the nailbase.

    In terms of your reference to humidity problems with EPA retrofits, I am not sure what you mean so I am not sure how that bears on your question or on the use of nailbase panels.

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