Covered Decks & Pergolas in Boise, ID

Why does a small patio cover need a permit in Boise?

Because it hangs part of its weight on the house. Boise's residential construction guide requires a permit for any attached patio cover, regardless of size. The reason is structural: the wall a cover ledgers onto was framed to carry the house, and the cover adds snow, wind and its own weight at that one line of fasteners. Freestanding pergolas and gazebos are treated differently: no permit up to 200 square feet, and a permit beyond that, usually reviewed as pole construction that needs an Idaho-licensed engineer.

What does Boise's patio cover policy allow without an engineer?

Boise's Building Division adopted a Residential Patio Cover Construction Policy, effective May 17, 2022, that offers pre-engineered drawings for wood-framed patio covers and pergolas attached to a single-family home or accessory building. A cover that meets every provision skips project-specific structural engineering unless the building official requires it:

• The longest side of the structure is fully attached to the house or accessory building.
• Spans from the house to the posts, and from post to post, are 12 feet or less, with overhangs of 2 feet or less.
• Height at the post line is 10 feet or less, and roof pitch is under 10/12 (40 degrees).
• Footings go to frost depth, 24 inches in Boise, and are at least the size shown on the pre-engineered drawings.
• Framing materials and connections match the drawings or an equivalent.
• Lateral loads are carried by wood structural sheathing on top or by knee braces built to the drawings.

Anything outside those limits needs an engineered design. In practice that catches covers deeper than 12 feet off a family room, wide covers with long post-to-post spans, and tall covers over second-story decks. We design to the policy where the layout allows, because it removes a consultant and a round of review from the schedule.

How much snow and wind does a Boise cover have to carry?

Boise's adopted design criteria set a 20 psf ground snow load with a 25 psf minimum roof snow load, and a 90 mph design wind. Average snowfall is modest, 17.6 inches a year with about 6 days of an inch or more, but a solid cover is designed for the code load, not the average winter. Snow also slides. A pitched cover can drop its load onto the deck boards, a stair or a walkway, so we place the low edge where that does no harm. Open pergolas shed most snow through the rafters, though a pergola with a fabric or polycarbonate top collects it like a solid cover.

Wind matters on covers more than on decks, because a cover is a sail. Uplift ties at every rafter and post connection, and knee braces or sheathing for lateral load, keep a 90 mph gust from racking the frame. More on load paths is in deck snow loads in Boise.

Solid cover or open pergola for Boise afternoons?

It depends on which way the deck faces and what is behind it. Boise averages a 92.7°F July high and about 55 days a year at 90°F or more, and the afternoon sun is what makes west- and south-facing decks unusable. A solid cover gives full shade and rain protection, but it also darkens the rooms behind it. An open pergola with rafters at a tight spacing cuts the harshest light while keeping the house bright, and it is the lighter structure.

Many decks in Southeast Boise subdivisions and West Boise face west across open lots with little mature shade, and that is where covers pay off most. For layouts that combine a cover with an open section, our covered deck ideas show the common Treasure Valley arrangements.

Do fans, heaters and lights under a Boise cover need a permit?

Line-voltage ones do. Boise's residential construction guide says low-voltage outdoor lighting needs no electrical permit, while 110-volt work does. Ceiling fans, outlets and most electric heaters run on line voltage, so they need an electrical permit and an Idaho-licensed electrician; Boise's owner-builder allowance covers a homeowner doing their own work, not trades hired to help. We frame blocking and conduit paths into the cover so the electrician is not cutting into finished beams later.

Can you add a cover in a historic district, the Foothills or Harris Ranch?

Yes, with an extra review in each. Inside Boise's historic districts the Certificate of Appropriateness list names constructing an addition, porch or deck, and the residential design guidelines prefer new porch-like structures on rear or side elevations, which are less critical to the home's appearance. In the Foothills IR1 wildfire zone a cover is an appendage to the house, so materials and the space beneath get the same fire scrutiny as the deck. In Harris Ranch the specific plan's design guidelines and review board come first; the Harris Ranch and Barber Valley guide explains who reviews which lots.

Cost and planning

Cover and pergola pricing depends on span, height, top material and whether engineering is needed, so it is priced after a site visit rather than by formula. The Boise covered deck cost guide lays out the published ranges. If the deck under the cover is due for new boards anyway, plan both together; composite decking in Boise covers board choice, and the Boise deck permit guide covers how a deck and cover share one submittal.

1. Sun study: note where shade is needed at 4 p.m. in July, not noon.
2. Check the lot for historic, WUI, hillside and HOA reviews.
3. Fit the design to Boise's patio cover policy where possible; engineer it where not.
4. Permit, then footings to 24 inches with an inspection before concrete.
5. Frame, sheath or brace, add the top, and route any electrical with its own permit.