How to Build a Hoop House (Low Tunnel)

A hoop house is the cheapest, fastest way to add weeks or even months to your growing season. At its simplest it’s a row of bent pipes pushed into the ground and covered with plastic, a structure you can build in an afternoon for the price of a few dinners out. The term covers a whole range, from knee-high low tunnels stretched over a single garden bed to walk-in caterpillar tunnels you can stand inside. This guide shows you how to build both, because they share the same logic: pick a pipe to bend into hoops, anchor those hoops in a straight row, stretch a cover over them, and, most importantly, give yourself a way to vent the heat. Skip that last part and you’ll bake your crops on the first sunny day, so ventilation gets real attention here.

What a Hoop House Is and What It Does

A hoop house, sometimes called a polytunnel or high tunnel, is an unheated greenhouse: hoops of pipe covered in plastic, relying entirely on the sun for warmth. Because there’s no glazing system or foundation, it costs a fraction of a true greenhouse. What it buys you is a warmer, sheltered microclimate. In spring it lets you transplant tomatoes and start seeds several weeks early; in fall it holds off the first frosts; and through winter it keeps hardy greens like spinach, kale, mâche, and carrots alive and harvestable in much colder zones than they’d survive outdoors.

It helps to know the family of structures so you build the right one. A low tunnel is knee- to waist-high, covers one or two beds, and you tend it by lifting the cover, this is the simplest and cheapest. A caterpillar tunnel is a tall, narrow walk-in version, typically 6 to 12 feet wide, covered with a single sheet held down by ropes zig-zagged over the top. A full high tunnel is a permanent walk-in structure with roll-up sides and a door. Decide which fits your space and ambitions before buying materials; the rest of this guide scales across all three.

Choose Your Materials

The hoops are the heart of the build, and the right pipe depends on size. Here are the workable options from lightest to sturdiest.

• 9-gauge galvanized wire or fiberglass rod makes excellent low-tunnel hoops over a single bed. Cheap, rustproof, and you just push the ends into the soil. Best for covers under about 18 inches tall.
• 1/2-inch PVC pipe is the classic beginner low-tunnel material: a 10-foot length bends into a hoop spanning a standard 4-foot bed with comfortable height. Inexpensive and tool-free to bend, but it degrades in UV over a couple of seasons and can crack in cold, so paint it or replace it periodically.
• 3/4-inch or 1-inch PVC steps up the strength for slightly larger tunnels, though it still sags under snow.
• 1/2-inch or 3/4-inch metal electrical conduit (EMT) bent with an inexpensive hoop-bending jig is the gold standard for walk-in tunnels. It’s strong, sheds snow, and lasts for years. The jig pays for itself if you’re making more than a handful of hoops.

You’ll also need anchors, lengths of rebar (½-inch, cut to 18-24 inches) driven into the ground that PVC hoops slide over, or ground stakes for conduit; a ridgepole (a length of pipe or a taut wire running the peak) to tie the hoops together and stop them racking in wind; and a cover. For the cover, use 6-mil UV-stabilized greenhouse polyethylene for maximum warmth and a multi-year life, or a spun floating row cover (such as Agribon) when you want frost protection with breathability and don’t need to trap as much heat. Round out the list with snap clamps or clips to hold the cover, sandbags or stakes to weight the edges, and zip ties or screws to fix the ridgepole.

Size and Site the Tunnel

Match the tunnel width to your beds. A single 4-foot raised bed takes a 10-foot pipe bent into a hoop with roughly 2 to 3 feet of peak height, plenty for greens and low crops. For a walk-in, plan a width of 6 to 12 feet and a peak of at least 6 to 7 feet so you can stand. Length is flexible, just add more hoops; space them 3 to 4 feet apart for light covers and snowless climates, and tighten to 2 to 3 feet where snow load or strong wind is a factor.

Site it like a greenhouse: full sun, especially in winter, and level, well-drained ground. Run the long axis east-west so the broad south side collects low-angle winter light. Pay attention to your prevailing wind and orient an anchored, closeable end into it rather than letting wind hit the long flank, which turns the whole tunnel into a sail. Keep it clear of trees that shade it or drop limbs. A tunnel close to the house and a water source is one you’ll actually use in cold weather.

Step-by-Step: Building a Low Tunnel

This is the weekend build, ideal over an existing 4-foot bed.

• 1. Set the anchors. Drive 18- to 24-inch rebar stakes into the ground a foot or so on each side of the bed, directly across from each other, leaving 8 to 10 inches exposed. Space the pairs 3 to 4 feet apart down the bed’s length.
• 2. Bend and set the hoops. Slide one end of a 10-foot 1/2-inch PVC pipe over a rebar stake, arc it over the bed, and slide the other end onto the opposite stake. Repeat down the row. Wire or fiberglass hoops simply push into the soil on each side instead.
• 3. Add a ridgepole. Run a length of PVC or a taut wire along the peak and fasten each hoop to it with a zip tie or a tee fitting. This single step stops the hoops from leaning over and dramatically stiffens the tunnel.
• 4. Cover it. On a calm day, drape greenhouse film or row cover over the hoops, leaving extra material at both ends. Pull it snug.
• 5. Secure the edges. Hold the cover to each hoop with snap clamps. Weight the long edges with sandbags, lengths of lumber, or soil-filled trenches, and gather and tie off the ends so they can be opened. Tight edges are what stop wind from peeling the whole cover off.

Step-by-Step: Building a Walk-In Hoop House

The walk-in version follows the same logic at larger scale, with metal hoops.

• 1. Bend the hoops. Run lengths of EMT conduit through a hoop-bending jig to form uniform arches sized to your width. Consistency matters here, so bend them all against the same jig.
• 2. Drive ground posts. Pound 2- to 3-foot sections of rebar or larger ground stakes into the soil in two parallel rows, spaced 2 to 4 feet apart, marking your tunnel’s footprint. Keep the two rows perfectly parallel and the posts square.
• 3. Mount the hoops. Slide each conduit hoop over a pair of opposing ground posts. Work down the rows until all hoops stand.
• 4. Add a ridge and purlins. Fasten a horizontal ridgepole along the peak and, on bigger tunnels, side purlins partway up each side, connecting every hoop with cross-clamps or self-tapping screws. This bracing is what carries snow and wind load.
• 5. Frame the ends. Build simple end walls from 2×4 lumber framing a doorway, and attach them to the end hoops. The ends take most of the wind, so anchor them well.
• 6. Cover and clamp. Stretch greenhouse film over the frame on a windless day, fasten it along the baseboards or with a wiggle-wire channel, and secure the ends around the door frames.

Covering and Ventilation

Choosing the cover is half the decision. Greenhouse polyethylene traps the most heat and is what you want for true season extension and winter growing; floating row cover breathes, prevents overheating, and gives a few degrees of frost protection while letting rain and light through, ideal when your main goal is pest exclusion or light frost insurance. Many growers run row cover in fall and switch to poly for deep winter.

Now the part people skip and regret: ventilation. A sealed tunnel is a solar oven. On a sunny day in the 40s or 50s, the interior can rocket past 90°F and cook tender plants in an hour, even while it’s cold outside. Build venting into the design. On a low tunnel, simply open or roll back one or both ends, and lift the side cover, every warm day, then close at night. On a walk-in, the standard solution is roll-up sides: attach the bottom edge of the cover to a length of pipe you can roll up to open a gap along each long wall, plus openable doors at each end for cross-flow. Vent in the morning before the sun loads the tunnel, and don’t trust yourself to remember on a busy day, an inexpensive max-min thermometer inside tells you whether your venting is keeping up. These same heat-management habits apply to any backyard greenhouse build.

Anchoring, Snow, and What to Grow

Wind is the number-one destroyer of hoop houses, far more than cold. The defenses are tight covers (a loose cover flaps, fatigues, and tears), well-driven ground anchors rather than pipe stuck in soft dirt, a ridgepole tying the hoops together, and braced end walls facing the prevailing wind. In snow country, tighten hoop spacing to 2 to 3 feet, use metal conduit rather than PVC so the roof doesn’t collapse under load, and keep the cover taut and the pitch steep enough to shed snow; brush off heavy accumulations before they build.

For what to grow, lean into cold-hardy crops that thrive in the cool, bright tunnel environment: spinach, kale, Swiss chard, mâche, claytonia, arugula, lettuce, and overwintered carrots and scallions all hold and even sweeten in winter tunnels. In spring, use the warmth to get a jump on tomatoes, peppers, cucumbers, and basil weeks ahead of the open garden. A hoop house pairs naturally with raised beds and other small-space and season-extension techniques, letting a modest yard produce far longer into the cold months.