After a few months of planning… It’s here – Groundbreaking day. Our team’s objective (myself, Max Strickland – Energy Consultant, & Dan Pohlman – Energy Auditor) on this project is to build the most energy efficient & affordable Habitat home in Grand Traverse Region to date. In addition, this project is a test model for our LEED ND Development scheduled to start in the spring of 2013.
The model we developed is a semi super-insulated home, R-30 sub slab, R-43 above grade walls, & an R-65 attic with an ACH goal of 1.0ACH @50pa or less. This model produced a HERS score in the high 30’s, reducing our heat load to 11,500 btuH before mechanical ventilation (16,500 btuH after). The benefit to this model allows us to use a non-traditional heating system – Mitsubishi 1.5 ton air-to-air ducted mini-split, reducing our upfront primary mechanical heating system costs by roughly $2500. More importantly, we’ve reduced the operational costs by 60+%… (heating costs are reduced to $260 annually alone!). – Over the life-cycle of a home, operating and maintenance costs contribute to more than 2/3 of the costs of the home over that span!…
Our challenges on this project started with soil conditions. Unfortunately, like most property we inherit, this one had complications, beginning with a very high water table forcing us to eliminate the option of a basement. What we are doing however is a FPSF (Frost Protected Shallow Foundation) out of 11″ ICF blocks (Reward ICF), compacted interior granular backfill, 6″ (R-30) of Dow XPS 250 HD foam board, & a 4″ slab. The slab itself, when poured, will be above exterior finished grade and completely eliminate any water table issues with this site.
In an effort to stabilize our foundation on the poor soils, we increased the width of our footings to 24″ helping to distribute the weight of the foundation more evenly over a larger surface area. To strengthen the footing we added 3 #4 continuous horizontal rebar through the footing and then 30″ #4 vertical rebar every 4’0″ to tie in the ICF block (per code and manufacturers recommendation).
One of the advantages of using the ICF foundation wall, was the ability for on-site volunteers to assemble and pour. If you have not tried an ICF foundation wall system in one of your project, do! They are very simple to install – we set this up in approximately 2 hours. Using only 2 courses of 16″h block, we are also able to eliminate the need for wall bracing, which really sped up the process. The biggest advantage for us using this system on this project is the the thermal break provided by the outside 2-1/2″ layers of EPS foam of the form (Reward ICF). Pouring our interior slab up against this form creates our thermal break in the slab, and with the 6″ of sub slab insulation, technically brings our slab ‘into condition space’ – NO COLD SLAB! Cold, non-thermally broken, slabs in our climate zone (6A) have had a bad reputation for lots of years, but installed properly and insulated well, they are a far superior option to a crawl space on a non basement foundation!