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Finding a natural solution

Building the NewenHouse Kit Home: Installing a Frost Skirt and Perimeter Insulation Around the Slab

Sonya NewenhouseSonya Newenhouse, Ph.D. is an eco-entrepreneur who enjoys providing practical and creative solutions to help individuals and organizations live and manage green. Her firm, Madison Environmental Group, provides LEED green building and sustainability consulting services. She is also founder and president of Community Car, a car sharing organization in Madison Wisconsin. Currently she is developing NewenHouse, a business that will provide super-insulated sustainable kit homes.

Today I received the January/February issue of Natural Home in the mail. I usually sit in our reading chair and flip slowly through all of the pages because I can’t wait to see what’s inside. The following weekend  I’ll read it cover to cover. In this issue, I was pleased to see a thorough article by Carol Venolia on Passive Houses which included a Passive House retrofit. It’s encouraging to see the momentum for super-insulated houses gain attention. This week my friend Beth Churchill, a sustainability consultant, also shared with me an article on Passive Houses by Martin LaMonica from Green Tech. Thanks Beth!

Today’s blog will provide you with more information about the insulation around the slab. When the house is complete these critical details will be hidden under groundcover so now I should show you what it looks like.

NewenHouse frost skirt 
Close-up of 12-inch perimeter insulation and eight-inch EPS foam frost skirt. Photo By Sonya Newenhouse. 

The Monday before Thanksgiving the concrete crew did not show up and I was nervous because the ground was frozen about four inches deep and I did not understand how they could dig around the slab to install the 12 inches of perimeter insulation and the eight-inch thick frost skirt in these conditions. Either the crew wass deer hunting—we’re building in rural Wisconsin after all—or they had to pour a slab for another customer before the snow fell, which would take priority. When I reached Henry (the concrete subcontractor) on Tuesday, he was calm and working hard to get his other slab work done before Thanksgiving. He informed me that it was no problem to dig in the frozen ground as he would use a skid loader. The following Monday Henry’s whole crew (four men) arrived and worked feverishly all morning to install the insulation. By 1:30 p.m., just as the freezing rain started, the crew completed installing the insulation and burying the 4-by-8 inch sheets of EPS frost skirt while Henry was finishing up site work with his skid loader.

The timing worked out perfectly. The perimeter slab insulation is 12 inches wide and two inches deep. The eight-inch thick (two layers of 4-inch EPS foam) frost skirt was then placed and taped perpendicular to the perimeter insulation and extends four feet away from the house. A frost skirt is recommended to install if you’re building in a cold climate with a floating slab. The skirt eliminates the potential for frost to heave the floating foundation. Most frost skirts are two inches thick; ours is eight inches thick.

This insulating system means that we will only be able to plant ground cover or shallow root perennials above the frost skirt around the home. This is good because ideally you shouldn’t plant shrubs and trees to close to your foundation. In the future we’ll need to be careful with the frost skirt placement as we may forget about it (or forget to tell a landscaper about it) and plant a shrub within 4 feet of the home and puncture the EPS foam. If that mistake happens the foam could be repaired or replaced, but that’s just more work and no fun.

After Henry’s crew left and in the freezing rain, I quickly tried to toss the mud clumps that landed on our driveway into the yard. My hands became numb and I foolishly kept on going.  The next day, I realized my wedding ring was missing. Tears and panic set in. Then I remembered that the day before my hands were so cold while cleaning the driveway that I lost all feeling in my fingers. Maybe the ring slipped off as my fingers constricted in the cold? I was two hours away from the job site and could not look for the ring. Two days later a friend used a metal detector and found the ring in a mud clump near the driveway. What a relief—big smile.  I’ve only been married three months and had become very attached to the ring from Finland, circa 1960, with a smoky quartz stone in a modern setting.  Now I understand why many construction workers don’t wear wedding rings.