How to Bid Residential Plumbing: A GC's Complete Guide

Plumbing bids are where GCs lose the most money to scope gaps. A sub quotes $14K for "plumbing per plans" and you think you're covered — until rough-in day when they tell you gas line wasn't in their scope. Or the backflow preventer. Or testing. Or cleanup.

I've seen plumbing change orders eat $3,000–8,000 on residential jobs that should have been straightforward. The fix isn't hiring better plumbers — it's getting better bids upfront.

Here's exactly what a residential plumbing bid should include, what it typically costs in Southern California, and how to catch the gaps before they become change orders.

What a Complete Residential Plumbing Bid Should Include

Every residential plumbing bid should break down into these line items. If a sub gives you a lump sum with no breakdown, send it back.

Rough-in ($3,500–6,000)

This is the backbone — running supply and drain lines through walls and floors before drywall goes up. Includes copper or PEX supply lines, ABS or PVC drain lines, and all connections to the main. The price swings based on pipe routing complexity and how many fixtures you're feeding.

Watch for: Some subs quote rough-in but exclude stub-outs for future fixtures. If you're roughing in a laundry hookup or outdoor hose bib, make sure it's in the bid.

Fixtures supply and install ($2,000–8,000)

Toilets, sinks, faucets, shower valves, tub fillers — everything the homeowner touches. The range is huge because fixture quality varies wildly. A basic Kohler toilet is $200. A Toto Washlet is $1,200. Make sure the bid specifies whether fixtures are contractor-supplied or owner-supplied, and whether trim (handles, escutcheons, drain assemblies) is included.

Watch for: "Fixture installation only" bids that assume the GC or owner buys fixtures separately. That's fine if you know about it — but it's a $2,000–5,000 surprise if you don't.

Water heater ($1,200–3,500)

Supply, install, and connect. Tankless units run higher ($2,500–3,500 installed) vs. standard tank units ($1,200–2,000). The bid should specify the unit, capacity, and whether gas or electric. If it's gas, the gas line connection should be included or explicitly excluded.

Gas line ($800–2,500)

If the project has a gas water heater, cooktop, dryer, or fireplace, someone needs to run gas. Plumbing subs sometimes include this, sometimes don't. In California, gas line work requires specific licensing. Make sure the bid states whether gas is included and how many appliance connections.

Watch for: Gas line is the single most commonly excluded item in residential plumbing bids. Ask explicitly.

Drain/waste/vent — DWV ($2,000–4,500)

The drain and vent system. Includes all drain piping, vent piping through the roof, cleanouts, and connections to the sewer lateral. On remodels, this can get expensive if you're rerouting existing drains or dealing with cast iron that needs to be replaced.

Testing and inspection ($300–800)

Pressure testing (air or water test on supply lines), drain testing, and coordination with the building inspector. Some subs include this, some don't. If it's not in the bid, you'll get a change order when the inspector shows up and needs a test.

Permit ($200–600)

Plumbing permits in most California jurisdictions run $200–600 depending on scope. The sub should either include the permit fee or clearly exclude it. Don't assume.

Cleanup ($100–300)

Removing pipe scraps, cleaning up flux and solder residue, hauling out old fixtures. Minor cost but frequently excluded — and you end up having your laborers do it.

The 5 Most Common Plumbing Scope Gaps

These are the items that consistently get left out of plumbing bids and turn into change orders. Use a plumbing scope checklist to catch them before you award.

1. Backflow preventer

Required by code on most residential projects, especially irrigation connections. Costs $400–1,200 installed. Plumbing subs often assume it's in the irrigation contractor's scope.

2. Fixture trim and accessories

Supply stops, angle stops, escutcheons, drain assemblies — the small parts that connect fixtures to rough plumbing. A sub might price the faucet install but not the supply lines from the wall to the faucet. That's $50–150 per fixture in parts and labor.

3. Gas line work

As mentioned above, this is the #1 gap. If your project has any gas appliances, confirm gas is in the plumbing bid or in a separate gas contractor's scope.

4. Pressure testing

The inspector will require it. If it's not in the bid, you'll pay extra and potentially delay the inspection.

5. Cleanup and haul-off

Old fixtures, demo debris, pipe scraps. Sounds minor until your laborers spend half a day cleaning up after the plumber leaves.

These five gaps alone can add $2,000–5,000 to a plumbing scope on a typical residential project. That's the difference between your margin and break-even. For more on how scope gaps cost GCs thousands, we've documented the patterns across every trade.

Red Flags in Plumbing Bids

After reviewing hundreds of plumbing bids, these are the warning signs:

• Lump sum with no breakdown. "Plumbing: $14,500." What does that include? Everything? Nothing? You can't level a lump sum. Send it back and ask for line items.
• "Per plans and specs" language. This means the sub priced whatever they interpreted from the drawings. That interpretation might not match yours. Get specifics.
• Missing permit and testing. If these aren't line items, they're going to be change orders.
• 30%+ below other bids. A plumbing bid that's significantly cheaper isn't a deal — it's missing scope. Call and ask what they're excluding.
• No exclusions listed. A professional plumbing sub knows what's in and out of their scope. If they list zero exclusions, they either haven't read the plans carefully or they're planning to change-order you later.

How to Compare Plumbing Bids

Once you have 3+ bids with proper line items:

1. Normalize the scope. Make sure every bid covers the same items. If Sub A excludes gas and Sub B includes it, adjust before comparing totals.
2. Compare line items, not just totals. Two bids at $15K can look identical until you realize one has $3K in fixtures and the other has $6K. That's a quality difference.
3. Flag outliers. Any line item that's 20%+ above or below the group average needs a phone call.
4. Check fixture specs. "Toilet install" at $400 vs. $800 might be a Glacier Bay vs. a Kohler. Apples to apples.
5. Verify licensing. In California, plumbing work requires a C-36 license. Gas work may require additional certification.

Use our free bid comparison template to organize this process, or try ClearBids free to automate the comparison with outlier detection and scope gap analysis built in.

Sample Plumbing Bid Breakdown

Here's what a clean residential plumbing bid looks like for a 2-bath, 1-kitchen remodel in the 91362 area:

• Rough-in (2 bath + kitchen): $4,800
• Fixtures supply & install (5 fixtures): $3,200
• Water heater (40-gal tank, gas): $1,800
• Gas line (water heater + cooktop): $1,400
• DWV modifications: $2,800
• Testing & inspection: $500
• Permit: $350
• Cleanup: $150
• Total: $15,000
• Exclusions: backflow preventer, irrigation, fire sprinkler

If a sub comes in at $9,000 for the same scope, they're missing something. If they come in at $22,000, ask what's driving the premium. Either way, the line-item breakdown tells the story.

The Bottom Line

Residential plumbing bids are only as good as the detail they contain. A vague bid is a future change order. A detailed bid with clear inclusions, exclusions, and line-item pricing is a bid you can actually compare and award with confidence.

Get specific. Get line items. Get exclusions in writing. Your margin depends on it.