A pop-top is one of the best ways to get more room out of a Denver bungalow without giving up the lot or the neighborhood. Folks in Washington Park, the Highlands and Berkeley do it all the time, and most of them want at least one full bathroom up there, sometimes two. The catch is that the house underneath was plumbed for one bath and a kitchen sink. The new floor has to live on that old system, or the system has to change. Deciding which one before anybody frames a wall is the difference between a second story you love and one that makes the downstairs gurgle every time somebody showers.
The house underneath was never plumbed for this
Walk down to the basement of most early bungalows and follow the drain. You will usually find one main stack, often cast iron, running from a vent through the roof down to where the sewer leaves the house. Everything ties into it: the bathroom, the kitchen, maybe a laundry tub someone added decades later. The supply side looks similar. A single line comes in from the street, and the branches were sized for the handful of fixtures the house had when it was built.
Stack a new bathroom on top of that and you are asking old pipe to carry a shower, a toilet and a vanity from a floor that did not exist when it went in. Sometimes the existing stack can take it. Sometimes it is corroded, too small for the added load, or sitting in the wrong spot for where the architect drew the new bath. The only way to know is to look at it with the whole plan in hand, fixture by fixture, and be honest about what the old pipe can handle. Better to hear that before the drywall goes up.
Venting is the part people forget
A drain needs air to flow. Every fixture pushes water down the pipe, and air has to come in behind it or the moving water drags the seal right out of the nearest trap. That is the gurgle. You run the new upstairs tub, and the downstairs sink burps and smells like sewer for a second because its trap just got siphoned dry.
In an old house the vent is often a single pipe through the roof, sized for what was there. When a pop-top goes on, the roofline changes, the old vent may get cut or shoved aside by the framers, and the new fixtures need their own path to open air. If the plumbing layout is not ready when the roof comes off, the vent tends to get handled however is fastest that afternoon.
We lay out the vents alongside the drains, at the same time, so the new roof gets its penetrations in the right places and every fixture on both floors has the air it needs.
Checking the water main before adding fixtures
The supply side gets less attention because it does not smell when it is wrong. It just underperforms. Add a second full bath upstairs, and suddenly two people cannot shower at once without one of them standing under a trickle. The water is also climbing a full floor higher than it used to, so every bit of pressure the house has matters more.
Older Denver houses in neighborhoods like Congress Park and Park Hill can still have original galvanized pipe somewhere between the meter and the fixtures. Galvanized closes up from the inside, so a line that looks fine from the basement may be carrying a fraction of what it should. Hang a new bathroom off that and the upstairs will be disappointing from the first morning.
So before the design is final, we look at the service line coming in, what it is made of, what size it is, and how the branches run. Sometimes the answer is a new line up to the second floor in PEX or copper while the rest stays. Sometimes the whole house is due, and a pop-top is the easiest time it will ever be to handle it, with walls and ceilings already open.
Why the plumbing plan comes before the framing
A framer’s job is to build a strong, square floor quickly. A plumber’s job is to get a three-inch drain from the new toilet to the stack with the right slope and without cutting a joist in half. Those two goals run straight into each other when the plumbing gets figured out after the floor system is already in.
The usual result is a drain that takes the long way around, a bulkhead dropped into the downstairs ceiling to hide it, or joists notched deeper than anyone should allow. None of that is necessary if the bathroom layout, the joist direction and the drain route get settled together on paper first. Moving a toilet a foot on the drawing is free. Moving it after the subfloor is glued down is a very different conversation.
The shower works the same way. Where the drain lands, where the valve sits, and where the supply comes up through the floor all get decided early, so the tile setter is working over a layout that already makes sense instead of around a compromise somebody made in a hurry.
One person owning both sides of the job
Most pop-tops involve a general contractor, a plumber and a pile of other trades, and the plumbing often gets bid as a line item once the structure is drawn. That is how stacks get skipped and vents get improvised. Everyone does their piece, and nobody owns how the whole system performs once the family moves back in.
Wes carries a master plumber license and a GC license, and that pairing fits this kind of project well. He looks at the drainage and the framing as one problem. If the stack has to move, he knows what that does to the walls around it. If a beam is going in, he knows where the drain cannot go. Nobody gets to point at anybody else when something does not line up, because one person made both calls.
The downstairs gets treated as part of the project too. If a tired section of old drain in the basement is the weak link between your new bathroom and the sewer, it gets dealt with while everything is open, instead of waiting until it announces itself on a holiday weekend.
Thinking about going up on a Denver bungalow? Call Wes at (303) 883-9075 before the drawings are final, or tell us about the project. We will walk the basement, look at the stack and the main, and give you a straight quote on what the new bathroom really needs. Our bathroom remodel work in Denver covers the plumbing and the build-back together, and the project gallery shows finished rooms.
Can my existing drain stack handle a new upstairs bathroom?
Sometimes it can. It depends on the pipe’s condition, its size, where it runs and how many fixtures already tie into it. An old cast iron stack that is corroded or in the wrong place for the new layout usually gets replaced or rerouted. We look at it against the full plan before anyone commits to a design.
Why do my downstairs drains gurgle since the addition went on?
Gurgling usually means a trap is being siphoned because a fixture does not have enough air behind it. That points to venting that was cut, undersized or left out when the new floor went on. It can also mean the drain is too small for what now empties into it. A look at the vent and drain layout finds the cause.
Will a second bathroom upstairs lower my water pressure?
It can if the service line or branches are old or small. Water has to climb another floor, and two showers at once pull more than a house built for one bath was meant to deliver. Galvanized supply pipe makes it worse. Checking the main before the design is final lets you fix it while the walls are open.
When should the plumber get involved in a pop-top project?
Before framing, ideally while the drawings are still being adjusted. That is when the bathroom layout, joist direction, drain route and vents can be settled together. Wes holds both a master plumber license and a GC license, so he can look at the structure and the plumbing as one plan.