Twinsprings Research Institute

I asked the Asbestos test engineer, Rick Luce, for a recommendation for a soils engineer, as he had mentioned that he worked with several and would give me a recommendation when the time came. He recommended Alan Lisowy at HP Geotech.

The original engineer who reported on the status of the slab turned out to be a rather famous guy in Arvada, Joe Jehn of Jehn Engineering. He has not continued with the project as it is not a typical Jehn project, however, he has been generous in response to emails and also recommended HPGeotech.

Alan works out of the Parker, Colorado office and we emailed back and forth until it was decided what tests needed to be done and when they could get a drill truck out to the site to take the test samples. I didn’t get out to the site in time to take photos of their work, but Alan said they got all that they needed and we will be getting the report now in just a matter of days!

The Waffle Mat system uses 19 1/2″ X 19 1/2″ X 8 1/2″ recycled plastic boxes. The boxes have a rim on two sides and can be used in sets of 4 or individually depending on the design. I decided on the individual boxes, even though they cannot be tied with the plastic ties that come with them, because there will be more rigid cross beams, and concrete is somewhat cheaper than the boxes. I paid almost $3000 for the 216 boxes plus delivery. But I was thrilled when Greg, the engineer, and Claudia Puertos, also an engineer and the regional sales director, decided to deliver the boxes to me directly. This personal attention showed that both of them are members of the project team of experts in their fields who helped with the design and implementation of this renovation.

They were able to speak with the structural engineer and to tell me about the system as well as take pictures. There are not many customers in Colorado (although I am not the first) and there are not many retrofit projects as most are new homes with slab on grade foundations. I hope my project makes it to their website.

They arrived with the boxes on Nov. 2nd. Greg and Alberto’s crew unloaded them into the garage, about 2 pallets full along with the boxes of ties. We walked the house site, with Greg giving Mark Benjamin and Alberto detailed instructions about the installation and design parameters, while Claudia and I discussed the foundation issues that the WaffleMat solution has been able to fix when big money was spent first on other types of solutions that did NOT fix the issues. I think it is pretty obvious that this is a sensible solution for expansive soils in Colorado, but Greg also strongly recommended accurate soils testing at the site, so that was the next step.

These photos are from the websites that illustrate the use of Waffle Mat.

Wafflemat Foundation – Monserrat Detail

Smithville, Texas – Similar angles to our house.

Texas.Ribbed Wafflemat.Layout

Waffle Mat with plumbing rough in and post tensioned cables.

Waffle Mat being setup.

Waffle Mat in sets on diagonal

At Greg’s strong recommendation, I decided to seek out a structural engineer who would be willing to take care of the specific design using WaffleMat for our installation. The person I chose had presented at a USGBC event as a certified Passive House engineer. I thought if anyone would be willing to consider an alternative solution, it would be someone in the green building industry interested in the most highly efficient systems. Mark Benjamin is the principal of his company, Crown Jade Engineering located in Bellevue, Colorado, and his son Daniel works with him using the highly technical software tools to create the designs. The first thing they discovered, using the technology instead of my poor math, was that I had figured 1200 square feet of slab and it is actually 1600 square feet. Good that the house is a little bigger in this area than I thought I guess but bad in that Mile High Contracting was taking longer than they expected! When I told Alberto he just laughed–saying that it was great to work with me since issues always seem to work themselves out naturally. So we did a deal to make up the difference and we are both happy to have a better sense of the actual job that is getting done! Thanks to Crown Jade!

The slab was the major issue that made this house virtually unsellable. Like most foreclosures, the house suffered from years of delayed maintenance, like peeling paint on the windowsills, and broken glass in some of the windows. Once it was determined, however, that the cracked slab had heaved over 3″, a structural engineer was called in to tell the sellers (the bank) that the house had to have major repairs. We had several estimates and ideas of what the repairs would cost and what solutions were available, but we bought the house already knowing that we were going to tear out the slab.

The bank reasoned that one of the lowest bids was likely to be the cost of the repair so the house price was reduced by that amount. We were willing to take the chance, because the rest of the foundation system seemed to be without any visible cracks and we loved the earth-bermed, south-facing “bones” of the house as well as the agricultural zoning and almost 2 acres of land in the city. SO I had to set about finding a solution for a slab on expansive soils.

Much of Colorado has expansive soils and there is a great deal of information about the problems associated with them and building on them. Slab technology has changed over the years and this house was built in the early 1980’s. There was a theory then that the slab should not have an underlayment of rock or plastic as it might retain and draw in moisture. The compromised slab was laid directly on the soil. and although a french drain was laid all around the perimeter of the house, there was moisture that got under the slab and the ground heaved and sank over time until there were deep cracks at the kitchen, at both the south and north corners, and along the back wall. The engineer said that the canal behind the house also “leaked” moisture throughout the area and was probably also responsible for the problems.

This Missouri State University report (will open DAMAGE TO FOUNDATIONS FROM EXPANSIVE SOILS.pdf) is a nice explanation of the issues with expansive soils and foundations. Professional organizations often have good technical articles regarding their subjects. I found several short articles on Concrete in Practice (National Ready Mix Concrete Assoication) and the American Concrete Institute’s Standard. Other sources were commercial sites like Prospections in Texas that had a couple of great articles about this common problem in that state and also lead to the author’s personal site with even more articles and links.

Somewhere in all this research I started reading about Mat Foundations as a structural solution to expansive soils which finally led to Waffle Mat, the solution I chose for this project.