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How Gazebo Construction Resists Wind Uplift in Kansas City
A house has walls that block the wind. A gazebo doesn't, so air moves over its roof and under it at the same time. ASCE 7, the wind-load standard that building codes reference, classifies a building whose walls are each at least 80 percent open as an open building and treats its roof as a free roof, with wind loads calculated from the combined pressure on the top and the underside. The practical result is that the roof can be pushed upward with more force than the gazebo's own weight resists.
That uplift has to travel down a continuous path. The rafters are tied to the beams, the beams to the posts, and the posts to post bases that are anchored into the foundation. A strong footing with a weak connection above it, such as a post that is only toenailed to its base, still leaves the structure free to lift at that joint.
Gazebos are usually anchored in one of two ways. Individual footings at each post put concrete below the surface, where its weight and the soil around it resist lifting, and the post base is fastened into each one. A slab can serve as both the floor and the foundation, with posts anchored into it, provided the slab is thick enough at the anchor points and the anchors sit far enough from its edges to hold. Precast pier blocks set on the ground, stakes and anchors driven into pavers offer far less resistance to uplift than either.
Frost is the other consideration. Overland Park's accessory structure guidelines require foundations to reach 36 inches below grade but exempt freestanding light-frame accessory structures under 600 square feet with eaves no higher than 10 feet, an exception that follows the International Residential Code. Exemption from frost depth doesn't remove the need for anchorage, though, and a shallow footing that heaves more than its neighbors can push one post up and pull the frame out of square.
Framing a Gazebo: Posts, Beams and Rafters
The posts carry the entire roof to the foundation, because there are no walls to share the load. Lumber in contact with the ground has to be preservative-treated for ground contact or be the heartwood of a naturally durable species, and fasteners and connectors in treated wood need to be hot-dip galvanized or stainless steel.
On an octagonal or hexagonal gazebo, beams run from post to post to form a ring around the top. Hip rafters rise from each corner of that ring and meet at the center, usually at a hub or king post that holds their upper ends together. Rafters pushed down by the weight of the roof also push outward at their lower ends, and on a gazebo there are no ceiling joists running across to stop that spread. The beam ring does that job. Its corner joints act in tension, so they are fastened with hardware designed to hold them together rather than with nails alone. When those joints loosen, the ring spreads, the rafters drop and the roof sags at the peak, a failure covered on our gazebo repair page.
Open sides also mean nothing stops the frame from swaying sideways. Knee braces between posts and beams, rigid connections at the post tops or a combination of both keep the frame square when wind pushes on the roof. A rectangular gazebo with a gable roof works the same way, except that its rafters bear on a ridge rather than a center hub, and ties across the frame keep the beams from spreading apart.
Gazebo Roof Options: Shape, Pitch and Covering
A hip roof, often called a pyramid roof on a square plan, slopes down on every side and sheds water in all directions, which is why it is the usual roof on octagonal and hexagonal gazebos. A gable roof has two slopes and open triangular ends, and it suits rectangular plans. A tiered roof or cupola raises a smaller roof section above the peak. It can let warm air escape at the top, but it adds framing and more places where flashing has to keep water out.
Pitch limits the covering. The International Residential Code, which Kansas City, Missouri and Olathe have adopted in its 2018 edition, permits asphalt shingles only on slopes of 2 in 12 or steeper, and requires a double layer of underlayment on slopes between 2 in 12 and 4 in 12. Common gazebo roof coverings include asphalt shingles chosen to match the house and metal roofing panels.
The underside of the roof is visible from inside an open gazebo, so the sheathing is part of the finished look. Tongue-and-groove boards can be left exposed between the rafters, while plain sheathing is usually covered with a finished ceiling.
Gazebo Setbacks and Permits in Overland Park, Olathe and Kansas City
- Permit
- required for an accessory structure larger than 200 square feet, with a plot plan showing setbacks and construction drawings that include foundation and roof framing plans
- Location
- at least 5 feet from the house, outside the required front and side yards, and no closer than 3 feet to the rear property line
- Height
- no taller than the house or 20 feet, measured from grade to the peak, and any accessory structure taller than 10 feet must sit at least one-third of its height from side and rear property lines
- Number and area
- no more than two detached accessory structures on a lot, together covering no more than 30 percent of the required rear yard
The height rule matters for gazebos in particular, because a steeper roof raises the peak and pushes the structure farther from the lot lines. Overland Park also advises against building over utility easements.
Olathe lists canopies, gazebos, pergolas and pavilions as exterior roof structures that need a roof structure permit, with plans and a site plan among the common documents. Kansas City, Missouri's list of building permit exempt work names sheds, playhouses, garages and carports among exempt accessory buildings and doesn't mention gazebos, and it states that exempt work still has to meet zoning requirements such as setbacks. Other cities in our service area apply their own codes.
Building a Gazebo on an Existing Deck or on the Ground
On the ground, a gazebo stands on its own foundation, and the floor is either framed and raised like a small deck or built as a surface at grade.
A gazebo on an existing deck is a different structural problem. Deck framing is designed for floor loads spread across many joists. A gazebo concentrates its roof weight onto a few posts, and in wind it pulls up on those same points. The American Wood Council's prescriptive deck guide places decks that support large concentrated loads, such as hot tubs, outside its scope, and a roof landing on a few posts is also a load the deck's original design didn't account for.
For a deck to carry a gazebo, each gazebo post needs a continuous path down to a footing, either by landing directly over a beam and post that bear on a footing, or by adding new footings and posts under the deck. The gazebo posts are tied into the deck framing, not fastened to the decking boards, and the deck itself has to be anchored well enough to resist the uplift the gazebo passes into it. Overland Park's deck guidelines, for example, require a roof plan and a footing inspection for covered decks, which reflects how a roof changes what a deck's foundation has to do. A roof built over a whole deck is a covered deck, a related project with its own design questions.
What Affects the Cost of Gazebo Construction in Kansas City
Most of the cost is in the structure rather than the footprint, which is also where a built gazebo differs most from a kit. The main factors are:
- Size and shape
- octagonal and hexagonal plans need more angled cuts, hip rafters and joints than a square plan of similar area
- Roof
- a steeper pitch, a tier or cupola, and the choice of covering all add material and labor
- Foundation
- the number and depth of footings, a slab instead of footings, and soil or rock conditions at the site
- Floor
- a raised framed floor with decking takes more work than a surface at grade
- Deck placement
- reinforcing an existing deck to carry a gazebo adds framing and often footings
- Site
- slope and how materials reach the backyard
- Permits
- where the city requires one, drawings, fees and inspections are part of the project
Get a gazebo construction estimate
Gazebo Construction Questions
Does a gazebo need a railing?
Guards are required where a walking surface is more than 30 inches above the ground, so a gazebo with a high floor needs them on its open sides. A gazebo with a floor near grade can be left open or railed by choice. Guard heights and railing options are covered on our deck railing page.
Do cities regulate how a gazebo looks?
Some do. Overland Park's accessory structure guidelines require an exterior appearance compatible with residential construction and state that pre-engineered metal buildings are not generally considered compatible.
Can a gazebo be built from composite?
Composite decking can form a gazebo's floor, but composite isn't a structural framing material, so the posts, beams and rafters are wood. The choice between wood species and treated lumber for the visible structure is covered on our wood deck page.