Quote Originally Posted by waynehapp View Post
I recently bought an old Victorian. There's a half bath on the first floor which was an addition before me.

After 3 days or so off a deep freeze in the NE where I live. The water stopped flowing into the half bath. I surmise that it had frozen somewhere since when it warmed up a bit the water started up again.

Since the bath is well inside the house, I have no idea where it cold be freezing.

Any ideas on how to prevent the freezing?

I know that eventually I have to crawl around the house and find the place where it needs insulation. But I'm not keen on doing that when it's 10 degrees out. Any backup ideas?
Although just about any home with any significant age on it in the NE could probably use a little more insulation somewhere, it might not be the main issue. For example it could be an issue of air/wind infiltration and needing to seal gaps (caulk, etc.) or isolating something from transmitting the cold temps inside - such as a thermal break (like a gasket).

If the addition bathroom is between the main house plumbing and an outside wall and plumbing brought to a hose bib on the addition cold water supply plumbing might be a contributing factor. If the hose bib still has a hose attached (oh no!) or hasn't been protected from extreme temps (like an insulated cover, even for those frost proof hose bibs) could be freezing up there and the ice expanding/obstructing flow to the bathroom. Some homes have an interior shut off for the supply to a hose bib that should also be shut off and the line between it and the hose bib drained for the winter, might want to check that. Even if all is as it should be, metal pipe can transmit cold into the house to the plumbing - keeping that junction warm on the cold side of the inside shutoff valve might be the ticket (sometimes with sub zero sustained freezes issues pop up - plumbing, weaknesses in insulation, air infiltration, etc. that during many years of "normal" winters don't reveal as any sort of a problem, especially with sustained subzero temps plus sustained winds).

If nearby crawl vent or basement window below near supply may also be source of increased cold affecting water lines - also crawl or basement sill ridge board may not be too well insulated and even if ceiling below cold air could be coming in like a chute and freezing water lines further interior of home.

Ed21 makes an excellent suggestion about keeping plumbing open to the heated areas such as under a cabinet keeping the doors open. A dribbling faucet keepiing water moving also helpful, Toilet water supply line tough to keep "dripping" and sometimes overlooked for anti-freezing protection. Sometimes using a fan to circulate and draw warmer air from HEATED areas and directing the blow on to the problem plumbing area will also help to keep pipes from freezing. (sometimes your only option besides space heater or heat tape for the toilet supply plumbing).

Could be a chute of cold air in wall channel from original house or in transition area from old to addition, the old vics often balloon construction. Cast Iron plumbing vents to the roof, old original masonry wall or chimney now sandwiched between original house foot print and addition also possible transmitters of the deep cold down into house plumbing area.

They are forecasting a long cold hard winter and its only just begun, you might want to get on tracking down the problem areas sooner rather than later one burst pipe can cause tens of thousands of dollars worth of damage.

Good luck with your investigations.