How to Build a Deck Over a Flat Roof: 9 Steps From Empty Roof to Finished Terrace

Got a flat roof on a building, apartment complex or home just sitting unused? A rooftop deck adds usable square footage and gives tenants or family somewhere to be outside.

Here is the order, from the first phone call to the last paver.

What a rooftop deck is

A rooftop deck is a floor that sits on top of the roof without being attached to it. Short pedestals rest on the roof membrane. Pavers or tiles rest on the pedestals. Nothing is screwed, glued or nailed through the roof. The waterproofing stays intact and rain still drains underneath.

The surface can be concrete pavers, porcelain pavers, ipe wood tiles or artificial turf. Most roofs use a mix: pavers for the main area, turf for a dog run, wood tiles near seating.

Step 1: Confirm the roof can carry it

A structural engineer checks the roof's load capacity before anything else. A pedestal deck is lighter than a framed deck, but it still adds weight. People, furniture and planters add more.

The surface you choose sets most of the weight. Concrete pavers run about 22 pounds per square foot, porcelain about 9, ipe tiles and turf lighter still. The weight capacity guide explains what the engineer will look for.

Roofs that cannot carry concrete can usually carry porcelain or wood tiles. That is the most common reason owners end up with porcelain.

Step 2: Get the roof itself right first

The deck goes on last. Anything the roof needs (a new membrane, repairs, insulation, drains) happens before a single pedestal goes down. Lifting a finished deck to fix a leak is possible, but nobody wants to do it in year one.

Two things to settle with the roofer:

• The membrane warranty. Most manufacturers allow pedestal decks and some want a protection pad under each pedestal. Get that in writing.
• The finished roof height. Measure for the deck after the membrane and any tapered insulation are in, not from the drawings.

Step 3: Permits, codes and access

Most cities treat a rooftop deck as occupied space. That usually means a permit and a guardrail, 42 inches on commercial buildings. Larger decks often need a second way off the roof. Guardrails mount to the parapet or a curb, not to the deck. Some jurisdictions want non-combustible surfaces near property lines or on high-rises; concrete and porcelain qualify.

Access decides a lot. A door at roof level is simple. A hatch or ladder rarely passes for an occupied roof.

The building codes guide goes deeper on what inspectors ask for.

Step 4: Pick the surface

Concrete pavers are the budget choice and take abuse. Porcelain is lighter, cleaner and comes in more looks. Ipe wood tiles are the warmest underfoot. Turf is the softest, for pets and kids.

Most roofs mix two or three. The flooring options guide sorts surfaces by how the space gets used. The porcelain vs concrete comparison goes deep on those two.

Pick now. The surface sets the paver thickness, and the thickness sets the pedestal heights in Step 5.

Step 5: Measure heights and count parts

Two numbers drive the order. How much height the pedestals make up, and how many pedestals and pavers the roof takes.

Height is the gap between the finished roof and the underside of the paver. Measure it at the door threshold and at the drains. The roof slopes, so the gap changes across it. The measuring guide covers single-slope and multi-drain roofs step by step.

Counts come from the area and the perimeter, not area alone, because every paver corner needs support. The pedestal calculator does it from width, area and perimeter, and the pedestals-per-paver guide explains the math.

Order about 5 percent extra pavers from the same batch. Colors shift between production runs.

Step 6: Lay out the grid

Installation starts at the door, not at a corner. Pull a string line from the threshold across the roof at the finished deck height. That line is the reference for everything.

Decide where the cut pavers go before the first full one goes down. Put full pavers along the door and the main sight lines; push the cuts to the far walls and behind equipment. Mark the drains. Each one gets a paver that can be lifted later.

Step 7: Set pedestals and pavers

1. Set the first pedestal at the threshold and adjust it so a paver sits just under the door sill.
2. Work outward along the string line: pedestal, paver, check against the line, adjust, move on.
3. Turn the pedestal head to raise or lower it until the paver sits level. Adjustable pedestals turn by hand; nothing is cut.
4. Where the roof slopes, the pedestals get taller toward the high side. Slope correctors under the base take out the pitch so the head sits flat.
5. Keep the spacer tabs on each pedestal head. They set the joint width, and the joints are what let water through.

Checking every third paver against the string line and the previous row is enough on a flat roof.

Step 8: Edges, wind and anything tall

• Cuts. Pavers along walls and around equipment get cut on a wet saw. Measure each one; parapet walls are rarely square.
• Edge support. A cut paver still needs support under every corner. Wall clips hold the perimeter pedestals tight to the wall so the last row cannot creep.
• Wind. On exposed or tall buildings the engineer may call for the pavers to be held down. A restraint system locks pavers to each other and to the pedestals so a gust cannot lift a corner. The wind uplift guide covers when that comes up.
• Height. Pedestals over 21 3/4 inches need bracing. Anything that tall is usually over insulation or a steep slope; plan it with the supplier, not on the roof.

Walk the whole deck before the furniture goes up. Any paver that rocks gets its pedestal a quarter turn.

Step 9: The first year

A pedestal deck needs very little, but not nothing.

• Twice a year, lift the paver over each drain and clear leaves and grit from underneath.
• Rinse and sweep. Porcelain shows pollen and footprints more than textured concrete; a neutral cleaner handles it.
• Wood tiles grey naturally. The ipe maintenance guide has the oiling schedule if you want the color back.
• After the first winter, walk the deck and re-level anything that moved.

DIY or hire it out?

A single-family roof with a door at roof level is a realistic DIY job. You need to be comfortable with a string line and a wet saw. The pedestals do the hard part.

A commercial roof is a different job. Permits, guardrails, engineer sign-off, crane time for the pallets, and a roofing contractor who will stand behind the membrane. Hire that one.

Either way, SkyDeck supplies takeoffs and shop drawings from your plans. Send the drawings through the inquiry form and the pedestal and paver counts come back to you.

Frequently Asked Questions About Building a Rooftop Deck

Do I need a permit to build a rooftop deck?

Almost always. Most cities treat an occupied roof as new occupied space. Check with the city before design.

Can any flat roof support a deck?

No. A structural engineer has to confirm the capacity. Lighter surfaces (porcelain, wood tiles, turf) open up roofs that cannot take concrete.

How much does it cost to build a rooftop deck?

Most projects land between $15,000 and $50,000 depending on size, surface and access. The rooftop patio cost guide breaks it down.

What is the best material for a rooftop deck?

Concrete for budget and durability, porcelain for weight and looks, ipe for warmth, turf for pets and kids. Many roofs use two or three.

Is a rooftop deck a good investment for a commercial property?

Usable outdoor space is one of the top tenant requests in multifamily and office buildings. It leases faster and supports higher rents.