How can I add valves to supply lines when the lines are soldered to the faucet?

Question

I am trying to replace an old faucet that my 3 yo child is unable to use because of its design. I'm new to plumbing but actively reading. I haven't seen these supply lines w/o valves before. This looks like the pipes are going straight into the faucet. This is an '86 built property in Canada. I tried to look through the vanity base but didn't find a valve.

Its a fatter pipe which gets slimmer as it enters the faucet.

1. Ideally I would like to add valves and then modern braided pipes into a new simple faucet. Is this doable and wise?
2. What tools will I need to achieve this - I have a wrench, channel locks and the basics. I think I'll need a pipe cutter and something to smooth out the freshly cut pipe. Any solution/paste?
3. What hardware will I need to purchase - if it's a 1/2" pipe, can I use any straight 1/2" valve?
4. Is a modern faucet built to the same standard that modern valves and pipes are built to?
5. How can I make a secure seal w/o using a soldering solution? I read this is where compression valves come in.

Pic of work area:

Pic of faucet inside:

Pic of view from under sink:

Answer 1

This isn't a very difficult job for a new diyer to tackle. You'll only need some basic tools in addition to a pipe cutter and deburring tool. Here is what needs to be done:

Installing the Shutoff Valves
I suggest that after you turn off the water at your main, make sure the water is off by opening the hot and cold faucets at the sink. Use a pipe cutter to cut both of the standpipe supply lines coming up through the bottom of the cabinet. Keep as much height as you can by cutting them directly below the soldered connection before the connection to the narrower tubes. Remove the old faucet. From the pics looks like a wrench will do it from under the cabinet.
Use a copper deburring tool to remove any copper burrs in the cut area. Use some fine steel wool to clean the exterior of the top two inches of copper.
Purchase two 1/4 turn straight shutoff valves with a 1/2" compression fitting on the inlet side and a 3/8" compression fitting on the outlet side as shown.

Follow the directions by sliding the 1/2" nut over the standpipe followed by the compression ring provided. Then slide the 1/2" end of the valve over the cleaned copper pipe. Make sure the valve is fully seated down onto the pipe. Thread the nut up onto the bottom of the valve by hand and then tighten it with an adjustable wrench. Use a second wrench on the body of the valve to stabilize it so you don't torque the copper pipe while you tighten the nut. It needs to be tightened enough to compress the brass compression ring - so good and tight.
Perform the same procedure on the other stand pipe. Make sure that both valves are closed with the valve handle pointing 90 degrees away from the pipe.
Turn on the main slowly and check for any leaks/seepage around the fitting.

You should be fine but as a novice you might want to have another person at the main in cell phone contact with you in case you need them to shut down the main quickly.

Installing the Supply lines and Faucet
Your sink has three holes precut. Make sure that the faucet you buy will accomodate that setup. Most faucets will have braided supply lines with the faucet. You'll want to measure to make sure the length will reach from the shutoffs you installed to the faucet connections.
Install the faucet according to the instructions attaching the braided supply lines to the outlet side of the shutoff valves. When using braided lines you won't need the compression nut on the outlet side of the valve. The braided line coupling will thread directly onto the outlet.
You can also tune in to a YouTube video which might increase your comfort level but take your time and it shouldn't be a problem.
Good Luck!

Answer 2

HoneyDo has a great answer; I'm putting extended comments here with some photos of one of my bathroom sinks with a new faucet installed last year.

I would just note that I like to spend extra and buy quality shut-off valves with real metal construction, not e.g. plastic knob shafts that can snap off. The supply lines should be good quality stainless-steel braided, not plastic braided. In my area of the US, bathroom faucets often come without supply lines, and often have 2 combination supply/mounting outer threaded pipes coming down from the ends of the bottom. Outer nuts run up the threads to clamp the faucet to the underside of the sink surround, then the supply lines thread onto the bottom ends of the pipes with an O-ring seal.

Re: faucet connection. The faucet type will likely be "centerset" with the outer mounting/water supply pipes 4" apart. They will likely accept a 1/2" IPS (Iron Pipe Standard) connection to the braided supply line. Thus, the stainless steel braided supply lines should be 1/2" IPS to 3/8" compression, but the actual connectors will have rubber gaskets inside making the seal. I tighten them finger tight, then use a wrench to tighten an additional 2/3 turn. It's important not to overtighten, as that distorts the O-ring and causes leaks.

Real plumbers use "basin wrenches" to turn nuts on the underside of the mounting area, but I've found the cheap-looking plastic faucet installation "wrenches" sold at big box stores easier to use for me (see bottom photo for example only). You can slide the side opening over an attached supply line or protruding pipe and tighten plastic or metal nuts, depending on the tool/insert orientation.

Answer 3

Update 3/10. Adding here due to size.

I've completed both sinks and the faucets and drains are functioning fine.

1. I used Sharkbite fittings instead of a compression valve as thats all HD had at the time. Since this was time sensitive I went with a pair. Otherwise I followed HoneyDo's steps. I marked 0.95" to ensure the fittings were pushed all the way.

2. I made a very clean and careful cut using the pipe cutter. After running my fingers around it (inner and outer) I did not feel sharp edges. However I still used a deburring tool (1.5-2 turns) and it was smooth,

3. I cut the pipe at its smoothest point where there was no solder residue. Felt uncomfortable using a steel wool pad or Scotch Brite pad as I felt it would make the pipe "thinner" therefore increasing leak risk. But all guides advised to use it so I did sparingly.

4. Is this level of bend/flex in the supply pipes OK?

5. The faucet had soft copper pipes which were annoying to work with. I felt they would break any second but I was as careful as I could be.

Here is the 2nd faucet that I shared in the original post. This marks the project complete.

Answer 4

I always change the enamelled steel sink to an American Standard Colonial vitreous China before adding a Moen or Delta faucet. Then, I cut the 1/2” water distribution lines debur, sand, flux and solder Dahl 1/4 turn shutoff 1/2 - 3/8” valves. No more soldering after this point. Wind in a clockwise direction 3 layers of Teflon tape to the water connections and at the metal fixture outlet drain where it screws into the ABS P-Trap. Carefully remove the aerator without damaging its finish. Tighten all connections, turn on the supply and check for leaks. Re-tighten at the leak. Turn on the water supply. Re-check for leaks. Re-install the aerator.