My wife and I bought a new construction house in NJ 5 years ago, last year and this year the PEX pipe(s) under the kitchen sink froze. The sink cabinet is against an outside wall and rest on a concrete slab. I looked under the sink with an endoscope and saw that the pipes are not wrapped with any insulation, lay against the slab and run under another cabinet toward, I believe, the attached garage. Should the pipes have been wrapped when the house was built. It seems like a common sense thing, since we live in the northeast and temps can go below freezing.

I grew up in the north east... though I live in the mid-Atlanitc now. Interior pipes are never wrapped, not in any house I have lived in or ever visited... and under the kitchen sink is indoors and would not be exposed to subfreezing tempratures as long as the house remains heated. Most kitchens have sinks on outside walls under a window. If the house was not heated no amount of wrapping would prevent a pipe from freezing. Example that my exterior walls in my 50 year old house are uninsulated.....it's been in the single digits here and they aren't even cold to the touch much less cold enough for pipes to freeze.

The slab of the house is heated by the inside air... so that slab under the kitchen sink should never get anywhere near freezing... or you would have significant ice buildup during the winter, from the moisture in the air.

I think you may have descibed this incorrectly...or perhaps you have a situation with air infiltration for some reason.

Never saw interior piping wrapped. Basement perhaps.

How did you determine where the frozen section of pipe(s) are located? Maybe the main service line is not deep enough in the ground. Make sure you know where the shutoff is located because you may have a leak when it thaws.

Thanks for you answers, but The pipes lay on the slab about and about 6 inches from the exterior wall I don't see how the heat from the house can keep the pipes from freezing. They froze even with the cabinet doors open and left water dripping from the faucet.

smearcase: I assumes they were frozen under the sink, because that is the only place I could see getting cold enough. All my other pipes are ran in interior walls. I used a space heater blowing under the sink and the pipe unfroze in about an hour.

If anything the pipes probably froze where they go intto the garage. Many kitchen cabinets havd a heat vent in the toekick. If you don't have one cut one in and room temp air will get in under the cabinet.

The slab is a heat mass... it soaks up the heat and hangs onto it releasing it slowly (works so well its a major part in passive solar heating)... and the heat from the rest of the house will carry more than enough heat the slab under the sink will never get that cold... if it did... you would have ice under the sink... a LOT of it... ever leave a freezer door up just a tiny bit... notice how much ice formed when you did? It would be even more significant than that.

Since it's a slab there is no crawlspace under it... and the ground under your house will not get as cold as that in your yard.

Like I said... YOUR exterir walls WILL be insulated... mine are not, I don't have the ventilation mention by ballengerb1... and my outside wall UNDER my sink isn't even cold to the touch. I also believe your point of freezing is not where you thought it was... but in a different area closer to the outside or maybe even outside.

If it got cold enough to freeze under that cabinet... ALL the moisture in the air in your house will be condensing there and forming significant ice that would be VERY visible.

lay against the slab and run under another cabinet toward, I believe, the attached garage
That implies that you possibly have pipes in the wall between the house and the garage. If so and the pipes are on the garage side of the insulation they would be subject to freezing in extreme conditions. The only way pipes under the cabinets would freeze would be if there is some air movement under the cabinets from the outside (garage).

Thanks guys, but if the possible freezing point is the garage wall, why would heat blowing from a space heater into the sink cabinet thaw out the frozen pipe?

Add to clarify, when I typed "wrapped" I meant with any insulation, not wrapped in heat tape. Sorry if I confused anyone.

why would heat blowing from a space heater into the sink cabinet thaw out the frozen pipe?
Well, you have a point there. Assuming that you are blowing heat into the sink cabinet and not in the cabinet between it and the garage wall. Of course it is always possible that the thawing resulted from rising temperatures in the garage not from the heat you applied.
It is contrary to logic that you could have 40 to 45 degree difference between the kitchen floor and the floor under the cabinets unless there is air movement. In other words air coming in from the outside.

Do the pipes to the sink come up through the bottom of the cabinet or do they come out from the wall in the rear?
Most kitchen cabinets today are individual units with a false front on the toe kick. If the toe kick material you see is continuous across all the cabinets it is a false front. It will be 1/4 thick and held in place with a few finish nails. You can probably remove that with out damage. You would then be able to remove any toe kick material behind that and see what is going on under the cabinet.

hkstroud, thanks the pipes come up from the bottom of the cabinet and make a 90 degree bend and travel along the slab toward the wall connecting the attached garage.

Add to clarify, when I typed "wrapped" I meant with any insulation, not wrapped in heat tape. Sorry if I confused anyone.

Insulation is what I had assumed you meant. The most likely place one would encounter heat wrap tape would be in a crawlspace... and not in a fairly new construction.

Where is water heater located?

I suggest going to garage side of the common wall, measure carefully and cut a small opening so you can see where the pipes go. Even if the garage side of the wall is finished, repairs should be an easy task.

Harold, thanks for the advice. I was thinking the same thing, along with removing the toe kick to see the entire pipe and where it is coming from.

Let us know what you find. We always like to know the end of the story.

Right now I'm thinking,
PEX piping, bet they go into the wall and turn, up, down or horizontal. Because they are curved around the turn, not fitting, just curved pipe, they are right next to the drywall of the garage, outside the insulation. That would be the freezing point.

Thanks, going open up the drywall in the garage this weekend to see what it uncovers. Thanks everyone for you comments and suggestions.

My suggestion, would be, and notice that I am just full of suggestions.

Try to accurately locate from the garage side, where the pipe would be. Cut a small hole, say about 2 x3". Look and feel for the pipes. As previously stated they are probably bent around the turn and are on the garage or outside of the insulation. This may also be true even if a fitting was used to make a sharp turn.

If that is correct I would get a 2 gang low voltage electrical mounting frame and a blank cover plate. Enlarge the hole, mount the frame and install the cover plate. Call the problem solved.

Because you have PEX piping you do not have to be concerned about pipes bursting. That's the important part. You said earlier that you have been in your home five years and I presume that this is the first time you have had pipes freeze. I don't know where you are located, but I think it would be safe to say that the present weather condition are not the normal. We probably won't see these kind of low temperatures again in another 10 years.

So, 10 years from now, you can contend with the temporary inconvenience of the frozen pipes. Or you can remove the cover plate and thaw the frozen pipes with a hairdrier. Probably in about 15 minutes.

Just my thoughts.

UPDATE: Hi all. I have come to the conclusion that the slab did cause the pipes to freeze. I borrowed an IR thermometer from my father-in-law and measured the temperature of the slab through cabinet pipes cutout. I got readings as low as 24 degrees when the outside temperature was around 15 degrees.

I was not able to cut into the drywall in the garage, as it's a fire wall with two sheets of dry wall with 3/4 plywood between them. Instead we cut a hole into the corner cabinet to see the pipes better and added blown insulation as there a 1 foot space behind the corner cabinet. I think that hole has really helped the space heat's heat circulate under the cabinets.

Thanks for the update.