How do you build a rooftop deck, and how much does one cost?
Short answer. A rooftop deck is built over a structurally rated, fully waterproofed low-slope roof, usually with a membrane underneath and a walking surface set on sleepers or pedestals so nothing punctures the waterproofing. It needs an engineer's review, a building permit, code-compliant guards, and safe access, which is why it costs much more than a ground-level deck of the same size.
The key pieces
- Structure: the roof framing must carry deck loads, people, furniture, and planters, which are far heavier than a normal roof is designed for. An engineer usually has to evaluate or redesign it.
- Waterproofing: a continuous membrane roof system, turned up walls and sealed at every penetration and door threshold. This is the part that protects the house below.
- Drainage: the membrane must slope to drains or scuppers so water does not pond under the decking during Georgia downpours.
- Walking surface: pavers on pedestals or wood or composite decking on sleepers that float on the membrane instead of being screwed through it.
- Guards: the residential code requires guards on open sides more than 30 inches above the surface below, generally at least 36 inches tall. Guard posts are a common leak point, so their attachment needs careful detailing.
- Access: stairs or a door from an upper floor; roof hatches are less practical for daily use.
Permits and approvals
A rooftop deck is a structural addition and requires a building permit in Georgia jurisdictions; HOAs and zoning may also limit height and visibility. See roofing permits in Georgia.
What drives the cost
Engineering, reinforcement, the membrane system, guards, and access are the big costs, and they apply even to a small deck. Expect a price closer to a room renovation than a backyard deck, and get detailed bids from contractors with flat roof and structural experience.
Leaks under rooftop decks are hard to find once the deck is down, so the waterproofing has to be right the first time. See common causes of roof leaks.