I'd like to deepen my existing window wells to accomodate larger windows. I've read that 'If the bottom of the window well is less than 1,800 mm (6 ft) above the footing, consult a geotechnical engineer about protecting the footing from frost action.' and (this refers to stairs, but I think it would apply to window wells as well): 'When an exterior basement stairwell is added, the stairwell opening effectively lowers the exterior grade level, and also lowers the depth to which frost can penetrate. After the stairwell is in place, the frost can theoretically go down as much as four feet below the bottom of the stairwell opening. This can lead to localized frost heaving of the footings and the foundations.' What would I need to do to avoid these type of problems? 2" of exterior foam on the whole wall? I live in upstate NY.