Following up on our earlier post celebrating our most recent award-winning project, Harvey and Kay’s “Pleasant Future Vision” PHIUS+ Zero certified passive house home, we continue to take you behind the scenes revealing some of the high performance assemblies employed on this amazing project. Bringing the building envelope down to the below grade condition in this post we are sharing the high-performance basement slab assembly and sub-slab preparation. The critical importance of thermal and water management in the sub-grade condition is emphasized by building science expert, Joe Lstiburek, when he shares, “The most risky thing we do is build a basement, the second most risky thing we do is try to finish it and turn it into living space!” The key to sub-grade water management is keeping the water away: no water = no water concerns. The best way to keep water away is to use gravity to drain it away- because gravity never sleeps. For this project where we were challenged with relatively high ground water we used an extensive redundant system of a 12″ pea stone layer combined with a 12″ 6A rock layer with geotec fabric. The basement elevation was set at a height that allowed any collected water to then gravity drain to the city storm sewer- nothing to power, nothing to fail! And the insulation was an aggregate value of R-17.5, as compared to the current code minimum of R-10. That is a high-performance basement slab! Learn more here: https://bit.ly/417rgRR