Our foundation was constructed using Insulated Concrete Forms, which are large blocks that interlock together like Lego bricks and then filled with concrete. ICF foundations provide a number of advantages over their block and poured counterparts, but their insulating properties are typically their most attractive benefit. Made of expanded polystyrene, the blocks have an R-value of about 22.4, however the thermal mass provided by the concrete increases the 'effective R-value' to somewhere between 30 and 50. Hopefully that'll make for a toasty basement.

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More 360 Winnett posts:

+ The 360 Winnett Project
+ 360 Winnett: Demolition