I need to run some plumbing for a basement kitchen, laundry room, and an upstairs 1/2 bathroom. There is a 1/2" line to the area already. Do I need to change it to a 3/4" line? Will it be worth the cost to change it?

Yes, you will need to upgrade to - at least 3/4" pipe hot & cold side. . However, I would suggest to go to 1" pipe on cold water side.

You likely have a 5/8" main. There is little gain to go to 1".

Layneb:

Your asking two questions. A 1/2" supply to a 1/2 bath isn't usually a problem. The toilet and the sink fill through a 3/8" tube.

If the kitchen has only a sink, the same argument holds. If it has a dishwasher, then you may have to re-think it.

Even the laundry doesn't require it either. You might have a laundry tub and a washer.

The actual piping layout and the total water use through that section of pipe matters.

3/4" pipe can buy you something if you intend to add a demand reciculating system or even a convection loop for hot water.

Forget the 1" stuff.

I agree with Milo it be great to upgrade it 3/4", Good luck.

Regards,
John

KeepItSimpleStupid is incorrect...

Main line supplying your house should be at least 3/4" for less-than-average house, like those built few decades ago. Today's houses are lot bigger with more bathrooms and plumbing fixtures that require rapid water delivery in less time.

If your main water service is 5/8" than it is a case of incorrect pipe sizing and I would suggest you seriously consider upgrade to 1".

You are not stating size of your house, number of bathrooms, and incoming water pressure. But I assume you have at least 2 bathrooms and primery kitchen. If you add your new basement laundry and another kitchen, than 3/4" main water service becomes highly undersized and you will be lacking needed water-flow (volume) when demand peaks. Moreover, if you connect basement plumbing fixtures to 5/8" pipe, you will hear hissing sound every time you run your washing machine or flush your toilet.

Some people compensate for undersized pipes by increasing incoming water pressure at the pressure regulator. This only magnifies water friction (noise) as water passes in pipes. While it may provide temporary fix, it is incorrect, putting unwanted stress on your house plumbing system.

Hello layneb, can you please give us more detail on you plumbing layout, how many bathrooms in your house and what size service is going into your house. More than likely your going to be undersized on your water pipes, but if your going to remodel, or add on to your house you might as well go the extra mile and upgrade you pipesizes. Good luck---Zeke

I need to run some plumbing for a basement kitchen, laundry room, and an upstairs 1/2 bathroom. There is a 1/2" line to the area already. Do I need to change it to a 3/4" line? Will it be worth the cost to change it?
My code calls for a 3/4" service,( One inch is better). A 3/4" house main and not more then three fixtures on a 1//2" inch branch. Good luck, Tom

It all depends on what kind of fixtures you have. You can have 3 hand sinks on 1/2" line at 1.6gln per minute water flow per spout. But 3 toilets, tubs, or presence of washing machine - 1/2" pipe becomes undersized and noisy. Size your hot and cold house piping with this helpful tool:

Plumbing Sizing Activity: Assigning WSFUs and Pipe Size to the Water Distribution System - Learning Activity (http://www.wisc-online.com/objects/index_tj.asp?objID=PLU407)

Milo:

I'd like to refer you to this thread.

https://www.askmehelpdesk.com/plumbing/commercial-toilet-leak-how-solve-184836.html?highlight=toilet+commercial+residentia l

You can't make a fixture designed for a 1" main work by upgrading the pipe bigger than the smallest supply size, whether it be a main, the meter or a branch.

Upgrading to 1" is nonsense, unless you do it from the street.

PS: When I said 5/8" meter, I actually meant a 7/8" meter with a 3/4" supply, but the concept is still valid.

My code calls for a 3/4" service,( One inch is better). A 3/4" house main and not more then three fixtures on a 1//2" inch branch. Good luck, Tom

Are you sure it doesn't say 'three fixture units'?

Exactly which code book are you referencing and what is the year of its publication, Tom?

I need to run some plumbing for a basement kitchen, laundry room, and an upstairs 1/2 bathroom. There is a 1/2" line to the area already. Do I need to change it to a 3/4" line? Will it be worth the cost to change it?

Yes, you will need to upgrade the size to at least 3/4", however, the 'doability' of this project depends on a number of other factors;

What size is the incoming service?

What is the pressure at the street?

How many other bathrooms are there in the house?

Do any of the bathrooms have showers or bath tubs with 3/4" tub or shower valves?

Is there a Roman Tub in any of the existing bathrooms?

Are there double lavatories in any of the bathrooms?

How many sinks/appliances are there in the kichen -- One sink and dishwasher, or is there also an island sink and a second dishwasher?

Are there already existing laundry facilities -- If so, is there a laundry tub in the existing laundry room?

Is the H/W supply also feeding a hydronic heating system?

I'm not trying to pee on your cornflakes, Layne, but we are going to need a great deal more information from you before we can tell you how to proceed.

Are you sure it doesn't say 'three fixture units'?

Exactly which code book are you referencing and what is the year of its publication, Tom?
Well growler, if I were installing a single bathtub, and that's all, in a bathroom I'd opt for the three fixture units that you mention. But since , down here, we don't hang over six fixture units for a three piece bathroom group. That's what our code allows. For years it was pipe the baths in 1/2 inch but take off a dedicated 1/2" branch for the toilet on our condos. And we piped hundreds. I ran a entire division called "The Meadows " down here. Five trucks working five sub-divisions in various stages pluss phase # 2 of a shopping center coming out of da ground. It was a 6 year project and then I was brought in as the shop trouble shooter and warranty man until I retired 20 years ago come November. Which , by the way is the age of my Standard Plumbing Code book, ( But I've tried to keep up over the years.)
So don't attempt to snow me with your code knowledge. I've paid my dues!
Besides, we worrk under different codes on the other side of the nation so our methods are bound to be different. Steve, you're a good plumber, but I think you're too ridged in your ways. It shows up here and I bet it shows up in Seattle. This is not necessarily a bad thing. But it's my wager that you'll never get red tagged for a code violation. Regards, Tom

Fixture units is right , and it depends what fixture units you have that will determine how many you can put on a 1/2" line. a 1/2" line will carry up to 8 fixture units, and 3/4 will carry up to 20 units,and 1" up to 36 units. On 50 to 60 pounds of pressure per U.P.C.

Milo:

I'd like to refer you to this thread.

https://www.askmehelpdesk.com/plumbing/commercial-toilet-leak-how-solve-184836.html?highlight=toilet+commercial+residentia l

You can't make a fixture designed for a 1" main work by upgrading the pipe bigger than the smallest supply size, whether it be a main, the meter or a branch.

Upgrading to 1" is nonsense, unless you do it from the street.

PS: When I said 5/8" meter, I actually meant a 7/8" meter with a 3/4" supply, but the concept is still valid.

KISS: Yes, thank you for referring me to this link. If I was present during this exchange, I would immediately recognized the problem: You cannot run 3/4" (Sloan or Zurn) flush valves off of 1/2" supply. The follow up posts have put a wide grin on my face...

You misread my original post #5. There, I suggest that main water service line should be upgraded to 1". It would make no sense to upgrade in the middle of the run with larger pipe without upgrading main water supply.

In conclusion: no house should have 1/2", 5/8" or 3/4" main water service connecting water meter and main house when it has 3 bathrooms, 2 kitchens and at least one laundry room. Water demand calculations are not "my" opinion. They are facts.

I think we misread each other's posts. Points well taken. I guess I can't count. My house has 2 kitchens, 1.5 baths, laundry and a 3/4 main with a 7/8 meter (I think). The second kitchen is rarely used and just consists of a sink for water using appliances.

It was primarily created to can and bake or when you need more space.