Frost lines

… like a tan line but for colder climates, probably…

So the frost line is how deep water will form ice crystals in the soil during periods of freezing and in this area of the Hudson Valley ice will form down to maybe three or four feet. Why this is important is because water expands when frozen and if your footings are above the frost line they will shift and cracks may appear in the above dwelling.

When our right hand wall collapsed it was replaced with a wall with shallow footings. This wasn’t a building error but due to the fact the architect didn’t want to destabilize the front right hand corner wall, which was still standing, by digging a trench in the very sandy soil next to it. To fix the issue of having the footings above the frost line we laid down foam insulation slabs which is part of the building code for Frost-Protected Shallow Foundations. 

From the last picture you can see that you lay down a vertical and horizontal insulation. The calculations for how tall and wide the insulation need to be are pretty complicated so in the end I guessed, one foot deep and two foot horizontally. I’m pretty sure that these should be deeper and wider, but considering the house had none of this for over a hundred years it will be better than nothing, plus next year we can fill in all the trenches, making the footings at least 2 – 4′ deep. We can’t fill them until Derrick applies a lime mortar parge to the walls which will happen next summer.

We cut the foam with our track saw, bonding the pieces with an extra strength Gorilla construction glue (based off this review) and now it seems a shame to bury them!!

Where there were gaps between the foam and the footings, due to irregularities in the footings, I sprayed in expanding foam. Once that sets I’ll run some flashing over the foam /concrete bond. Those spray cans of foam don’t go far, they last for about 30 seconds and I think I used 12 cans, still pretty handy.

As you can see by the following weekend the ditches had started to collapse on the insulation, but that’s fine as they will be underground anyway, main thing is that they are in place and sealed with the foam. It was wet today so the flashing will have to wait, possibly to next year.

I could of started this job a few weeks earlier, but I wasn’t sure how deep or wide the insulation had to be and whether digging too deep might destabilize the footings again etc., etc. so I like the fact that I was up against a deadline (winter), so I made some decisions and got on with it. Possibly similar to a scrum sprint.