I have a 2nd floor full bath in a detached garage. I need to increase my water pressure in this building only, as water pressure in the house is great. This bath is rarely used. I am guessing when the garage was built and full bath added after the fact, and uphill from the house, there is too much elevation gain to run the garage water properly. There is 1/2 inch pvc plumbing in the garage. I have 1gpm flow and 35 lbs of pressure. I am assuming I should add some type of booster pump with a pressure tank?

Your pipe is undersized. It should be at least 1" to the garage, 3/4" throughout garage with 1/2" branching off to each plumbing fixture.

Last time we plumbed a house with 35psi, we ran 2" copper main all the way throughout the house to assure full volume delivery to each plumbing fixture.

Yes, you can install booster pump or upgrade your pipes.

Milo,
Thanks for the answer. From looking at what I can see, there is a 1" line going from the outside of the house footing, 75 feet to the garage, probably a 15 foot elevation gain, can't tell what size pipe is in the wall, but 1/2" pipe is attached to sink and toilet. Since bathroom is on 2nd floor, there's another 12 foot elevation gain there. Lastly, looks like a 15 foot 1/2" pipe feeds that one inch underground line from inside my basement. Probably the only pipe that can be changed is the 1/2" in my house basement which feeds the 1" from my footing to the garage.

What's the house pressure? It should be around 50 PSI which with a line loss of about 6'5 PSi due to the 15 foot elevation should give you about 43.5 PSI at the garage.
If your house pressure's up there you shouldn't have a problem with a 15 foot lift. Again, what's the house PSI? Back to you, Tom

Tom, the house pressure is 35psi with 1gln/m flow...

1/2" pipe diameter at the fixture is fine. Before you do anything, do some exploration of existing water line. See if it is 1" all the way to the garage and is not reduced along the way. If it is, replace it with new section of pipe maintaining same size throughout.

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Originally Posted by speedball1

What's the house pressure? It should be around 50 PSI which with a line loss of about 6'5 PSi due to the 15 foot elevation should give you about 43.5 PSI at the garage.
If your house pressure's up there you shouldn't have a problem with a 15 foot lift. Again, what's the house PSI? Back to you, Tom

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House is on a 40-60 pressure switch. Overall elevation gain is probably closer to 30 feet when considering going from the house basement then up to the 2nd floor of the garage 75 feet away and uphill.

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Originally Posted by Milo Dolezal

Tom, the house pressure is 35psi with 1gln/m flow...

1/2" pipe diameter at the fixture is fine. Before you do anything, do some exploration of existing water line. See if it is 1" all the way to the garage and is not reduced along the way. If it is, replace it with new section of pipe maintaining same size throughout.

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I dug down the edge of the house and garage footings, same 1" pipe at both ends, 75 feet of distance, covered in asphalt so that can't be replaced. About all that can be gotten to is a 1/2" pvc line the feeds the 1" in the house basement. In the house I have a 40-60 pressure switch on a 55gpm well. In the garage I have 1 gpm and 35 lbs pressure. Total elevation gain going from house basement to topfloor garage bath over a 75 foot distance is closer to 30 feet.

Any valves installed on this pipe ?

If the water leaves your house at around 60PSI and arrives at the garage at 35 PSI where's the pressure loss. A head of 30 feet,(are you sure it isn't more?) will drop the pressure to almost 47 PSI Somehow I don't figure the friction line loss at 75 feet in a 1" line would be 12 pounds. So where's the loss?
Perhaps your best bet would be a booster pump at the house with a check valve and bladder tank at the garage. Good luck, Tom

There is an on/off valve where the 1/2" hits the house footing and another one on the inside of the garage footing.

If it is valve with yoke, chances are the yoke is stuck inside in half-closed position. Handle will still turn left and right - but will not engage the yoke.