What does a hot tub, a pergola or a screen room need from a new patio?

What does a hot tub need under it?

A slab thick enough and reinforced for the tub’s filled weight, a spot that sits dead level, and a power feed brought in before the pour. The filled weight is the whole question, and it varies a lot by model. Water and people in a small two-seater can come to a few thousand pounds, and a big family tub can be double that or more. The only number that counts is the one on your model’s own spec sheet.

That number decides the concrete. Many tub makers’ install guides accept a four-inch slab on a well-compacted base for a smaller model, and the guide for yours says which. A larger tub, or any tub going on the clay that runs under most of Henderson’s East End, is where the crew thickens that section to five or six inches and trades mesh for rebar under the footprint. Once the slab cures, nobody can make it thicker.

Level is the part people miss. A patio is built to fall away from the house so water leaves, and a tub wants the opposite, a flat bed so the water line sits even and the shell carries its weight evenly. The usual answer is a level panel formed inside the sloped patio, with the fall built in around it.

Then there is the wire. A tub needs its own feed, and the easy version is an electrician’s conduit laid in the base and stubbed up where the tub’s equipment side will sit, capped before the concrete arrives. That is the electrician’s work, not the concrete crew’s. Where the disconnect goes and how the circuit runs are decisions for the electrician too. The concrete side is making sure the stub exists before the screed goes over it.

Fill the tub after the slab has reached full strength at 28 days, not at the 7 days when a car could park on it. The difference is covered in how long before you can drive on new concrete. A car rolls off. A tub sits in one spot for fifteen years.

Can a pergola or a shade structure be anchored to a patio?

Yes, and the best time is while the concrete is wet. Post bases or anchor bolts set into the fresh pour on the builder’s layout grip far better than wedge anchors drilled in later. A light freestanding pergola can live on drilled anchors. Anything with a solid roof wants a real footing dug under the slab at each post, poured with the patio.

The reason is wind more than weight. A roofed pergola or a louvered cover catches a summer storm like a sail and pulls up on its posts. A wedge anchor in four inches of concrete, near the edge of a slab, is holding that pull with a small cone of concrete around the bolt. When it lets go, it takes a corner of the patio with it.

Henderson’s clay adds a second problem. The ground under a patio swells in a wet spring and shrinks through a dry August, and a slab rides that movement. A post anchored only to the slab rides it too, so the pergola racks a little every season. A footing that goes down below the slab and bears on its own gives the post something steadier than the patio to stand on.

A shade sail is the exception that asks the least of the slab. Its posts carry heavy tension and belong in their own deep holes off the edge of the patio, not in the slab at all. The concrete needs nothing from a sail except a gap where the post comes up beside it.

What changes if the patio might become a screened or roofed porch later?

The posts stop being decorations and become loads, so each post location wants a footing under the slab instead of a bolt in it. If screening it in or putting a roof over it is even a maybe, the day the patio is formed is the cheapest day that footing will ever be dug. Whether a roofed structure is allowed where you want it is a question for the county and your builder before it is framed.

Three more things get decided now, while they are still easy:

• Where the roof meets the house. A porch roof usually ties in below the eaves or gutters, and that sets how much headroom there is over the slab. A builder can tell you before the pour whether the slab height leaves enough.
• The back-door threshold. A screened porch wants the slab a step below the door sill so rain blowing through the screen does not run inside. If the door sits well above grade, the step or landing from the door is its own small pour, covered on the page for concrete steps, sidewalks and porches.
• The joint at the house stays an expansion joint. Putting a roof over the slab does not change why that joint is there, and the concrete patios page answers the foundation question in its FAQ.

A patio that might be a porch in five years looks almost exactly like one that will not. The difference is a few footings under the post line and a slab set at the right height.

Where does a fire pit go, and what does it do to the slab?

Off the slab is the easy answer. A wood fire set directly on concrete drives moisture out of the surface as steam, and the top pops off in flakes, called spalling. A gas pit on a proper base is gentler, but its gas line runs through a sleeve that has to go in before the pour. A wood pit usually lives best on its own pad or a gravel circle a few steps off the patio.

If the pit does go on the patio, it should sit up on its own base with a gap under it so the heat does not reach the concrete directly. Keep it well clear of the house and the eaves. A sealed or stamped finish is more sensitive to heat than plain broom finish, which matters if the patio is going to be stamped and colored under all this.

A gas pit means deciding its spot on the layout, because the sleeve under the slab is what the gas line runs through. Move the pit later and the sleeve stays where it was.

Does an outdoor kitchen or a grill station change the pour?

A rolling grill does not. A built-in counter does, because a block counter faced in stone is a heavy, continuous wall sitting on a four-inch slab. The crew thickens a strip under the counter’s footprint, much like the thickened edge under a garage wall, and lays sleeves through the base for any water line, drain or gas feed the counter will need.

Then look at the water. A patio sheds rain toward its low edge, away from the house, and that low edge is often where people want the counter so the cook faces the yard. A counter along the low side dams the water unless the slab is sloped to run past its ends or the counter sits on a raised curb.

What can be added later without cutting the concrete?

More than people fear. Anything that sits on the surface, bolts in lightly, or stands on its own footings beside the slab can come any year. What cannot come later is anything that has to run under the slab or bear down below it. That short list is where a saw comes in.

Fine to add later:

• Furniture, rugs, planters and a rolling grill.
• A portable plug-in tub, if the slab under it was poured thick enough for its filled weight in the first place.
• A freestanding pergola or shade sail on its own footings dug beside the patio.
• A small prefab fire bowl on a heat pad, kept off sealed surfaces.

Needs a saw, or a jackhammer:

• Conduit, gas or water lines that cross under the slab.
• A footing under a post in the middle of the patio.
• A thickened section for a big tub or a masonry counter.
• A level panel for a tub inside a sloped slab.

When the tub is going in next summer and the patio is going in now, a separate pad beside the patio is often cleaner than making the patio carry it. That is a standalone pour, the kind listed on the concrete slabs and pads page, where a 10 by 12 pad runs $1,100 - $1,700.

How do the slope and the joint layout change when something heavy sits on the patio?

The joints get laid out around the heavy thing instead of through it. A control joint is a planned crack, and a hot tub or a stone counter sitting across one sits on two panels that move on their own. So the tub pad or counter strip becomes its own panel, framed by joints, and the rest of the grid moves to fit.

On a plain four-inch patio the panels run about ten feet on a side, and the grid is usually drawn from the house outward. Put a tub in one corner and the grid shifts so a joint runs along the tub’s edge rather than under its middle. A counter along one side gets joints at its ends, and at any inside corner where the slab turns, because inside corners are where an uncut slab cracks first.

The fall does not go away under a heavy object or under a roof. The level tub panel sits inside a patio that still drains, so the slope is built into the base around it and the water gets steered past the tub rather than into its shell. A covered section still gets a slight fall too. Rain blows in under a porch roof, and a slab that gets hosed off should send that water out, not toward the door.

All of this goes on the layout at the site visit. The tub’s footprint and where its equipment side faces, the spot for a gas or power stub, a string line where the posts of a future roof would stand, the length of the counter. With those marked on the ground, the crew draws the joints, the thickened spots and the footings onto the quote for a concrete patio in Henderson, and the ranges for what a concrete patio costs in Henderson start at $1,500 - $2,200 for a plain 12 by 12 and $3,600 - $5,000 for a 20 by 20.