Is it the kitchen pipes that freeze or second floor above kitchen as well? I get frozen pipes in my basement bathroom and have found a space heater and running the fan/vent eliminates the problem - pushes warm air into the subfloor area just enough as my plumbing comes in from the ceiling. -- so if you can get heating in the basement above the kitchen on that wall - maybe close up the 20" overhang and insulate well

Assuming both hot and cold water lines in that wall, maybe a hot water recirculating system would help.

Look outside the box: where can you move the pipes so that they will be warm enough?

Some people just let the faucet drip when it is predicted to get that cold.

Another trick is to leave the cabinet door open so that the inside heat gets to the pipes.

Can you put insulation between pipes and outside wall? We keep our vanity door open on very cold nights..

Insulate the pipes and the cavity over the pipe, whats the problem? Done all the time.

You need an HVAC/local guy. On site. Failing that, for the few 10 degree days, open all the cabinets and make certain the house itself is warm enough.....and leave a tiny drip running.: ).

Hey,

I live where it gets -15 at times. The first thing is to avoid running pipes on outside walls altogether if possible. Moving the pipes out of the wall so they come out of the floor of the base cabinet is common.

Assuming you have moved them as best you can already, the other answer is to put insulation between the outside wall and the pipe and leave the area between the pipe and the warm interior un-insulated. See crude diagram

Use RMax (highest R value per inch) and layer it if you need to between the outside wall and the pipe. Also insulate the walls of the studs.

Alternately - you can use spray foam to make the same insulated channel for the pipes, but you need to remove the pipes first to do a decent job. Using spray foam has the advantage of sealing any air leaks.

Thank you all for your comments. Some clarification: Though I realize the ideal solution is to relocate the pipes (would require remodeling the whole kitchen) - that scale of effort is beyond my resources. I'm looking for the safest way to redirect heat to the portions of the pipe that I can already get to, without ripping apart walls. I've already added insulation where I could get at it. I already leave the cabinet doors open on those coldest days - and it still froze.

Where do the pipes go? Is it just the supplies for the kitchen or are they travelling up to the second floor?

What about creating an opening in the back of the cabinets so that the pipes are exposed there? Then the heat from the house can get into that cavity better.

The pipes only go to the kitchen sink. I am indeed considering opening the back of the cabinets to expose the pipes, in addition to adding heat cables to the exposed pipes, and converting the channel between the floor joists into a heating duct. I've not probed inside the wall to determine the fidelity of insulation. Where the floor juts out beyond the foundation block wall, there was only wood. I added what insulation I could wedge in between that wood and pipes.

I've made a crude (not to scale) sketch.

What Greg shows is exactly what I was saying about routing through the bottom of the sink base instead of the wall. Doing that in PEX will be easy to route and if PEX freezes it will be less likely to crack.

That cantilever can be spray foamed as well. There are small spray foam kits sold online.

I'm not endorsing the company or product - just saying that it's there.