I was insulating some pipes in my crawlspace (hot potable water lines and a big, long vent for the Jenn Air). In the process I had started to notice areas between the floor joists where they meet the outside wall, just on top of the foundation, where cold air could be felt and daylight was clearly visible after removing the fiberglass sqaures.

I don't know how common this is, but I found an area under my front door where the exterior wall hadn't been built down all the way to cover the ends of the joists. To 'close' the space between the joists, the builders had taken chunks of 2x6's and placed them in the spaces. This, of course, leaves huge gaps because floor joists are skinny in their center portion. To make it worse, the joists had been sistered for some reason. So a 2x6 sistered to a joist leaves a nice channel in the middle.

I managed to seal all these gaps with spray foam and then replaced the little squares of fiberglass that had been concealing it for the past 25 years. There's only one spot where the spray foam nozzle simply couldn't reach due to distance and a narrow gap for accessibility.

The pay off was nearly immediate! This morning I checked my entryway floor and it was clearly much warmer than it had ever been. I've always thought I'd paid enough attention to things like this, but I guess it pays to dig deeper. I'll have to climb under my front porch in the spring to seal up any more concealed holes, unless anyone out there wasn't to volunteer to dive under the snow and do it now? :-)