How to build a porch

What you are really building

A porch is a floor, a roof and the posts between them, fastened to your house. That makes it closer to a small addition than to a deck: the roof brings snow and wind loads, the floor needs guards and stairs, and the connection to the house has to carry both. The code rules below come from Minnesota's state guidance and city handouts that apply the International Residential Code; your city's version may differ on numbers such as frost depth, so check its own handout.

Before you design, settle three things:

• Where it can go. Setbacks decide the depth of a front porch. Ann Arbor, Michigan, for example, lets an unenclosed roofed porch up to eight feet deep project into the front setback in several residential districts, but never within five feet of the front lot line^[6].
• What it sits on. Mound, Minnesota, does not let a porch hang from a cantilevered part of the house unless the joists or trusses are engineered for the extra load^[3].
• Where your meters, wells and septic are. Minnesota tells porch builders to take the existing outside meters, wells and septic systems into account^[1].

Materials

• Decay-resistant wood: Minnesota requires treated wood or naturally durable wood (cedar heartwood or redwood) for joists 18 inches or closer to grade, beams 12 inches or closer to grade, their supports and all exterior members, and pressure-treated wood for posts in contact with the ground or embedded in concrete^[1].
• Corrosion-resistant fasteners: in Mound, all fasteners must be corrosion resistant as the code requires, and ledger fasteners hot-dipped galvanized or stainless steel^[3].
• Concrete for the footings, post bases, joist hangers with the fasteners approved for them^[3], roof framing (rafters or engineered trusses), sheathing, an ice and water barrier^[1] and the roof covering.

Step by step

Lay out the porch and locate utilities

Stake the outline and measure from the lot lines to check it against your survey and setbacks. Before you dig, Mound tells builders to contact the state one-call service to locate buried utilities^[3].

Dig footings below the frost line

Footings must extend to frost depth: Minneapolis and Mound both state 42 inches below grade as the minimum, or deeper to reach adequate bearing soil^[2][3]. Then call the first inspection: footings are inspected after the forms and reinforcing are in place, before the concrete is poured^[3].

Attach the ledger to the house

If the porch is supported by the house wall, it must be positively anchored for both vertical and lateral loads. Mound's handout spells it out: a treated 2x8 ledger at minimum, fastened to the band joist; no ledger on stone or masonry; and lateral hold-down devices, either two of at least 1,500 pounds capacity within 24 inches of each end or four of at least 750 pounds^[3].

Set posts and beams

Set the posts on the footings with post bases that resist lateral displacement: every joist-to-beam, beam-to-post and post-to-footing connection needs a positive connection^[3]. Columns standing on a concrete floor exposed to the weather need piers or metal pedestals at least 1 inch above the floor and 6 inches above exposed earth unless the wood is treated or naturally durable^[2].

Frame and deck the floor

Hang the joists from the ledger and the beam, at the size and spacing on your plans. Floor boards depend on the joist spacing: in Mound, boards laid perpendicular to joists at 24 inches on center must be 2 inches nominal, and 5/4 inch boards need joists at 16 inches on center; diagonal decking is not allowed above 16 inches on center^[3].

Raise the roof

Frame the walls or beams that carry the roof and set the rafters or trusses. Minnesota asks for a ridge board at least 1 inch nominal and as deep as the cut end of the rafters, rafters framed directly opposite each other at the ridge, and engineer-signed truss plans if you use manufactured trusses^[1]. A porch that projects more than 8 feet from the house wall needs a braced wall plan in Mound^[3]. The roof must be designed for your local snow load^[1].

Roof it and keep the water out

Roofs over porches need an ice and water barrier, either two layers of 15-pound felt mopped together or an approved ice and water shield underlayment^[1]. Then install the roof covering and call the framing inspection before anything hides the structure. In Mound, it comes after the roof and all framing are done and before insulation or siding^[3].

Build the guards and stairs

Guards are required on porches more than 30 inches above grade or the floor below: at least 36 inches high, with openings that do not pass a 4-inch sphere^[1][3]. Stairs must be at least 36 inches wide, with risers of 7 3/4 inches at most and treads of 10 inches at least, uniform within 3/8 inch^[1]. A handrail is required on stairways with four or more risers, its top 34 to 38 inches above the tread nosing^[2]. Mound adds stair lighting, with a light source near the top landing^[3].

Pass the final inspection

The final comes when the porch is complete, including stairs, handrails, guards and any electrical work^[3]. Keep the signed card: it proves the porch was built under a permit.

Mistakes inspectors see

• Footings poured before the inspection, or not deep enough for the frost line^[2][3].
• A ledger on brick veneer or stone, or nailed instead of bolted with hold-downs^[3].
• A porch hung off a cantilevered floor without engineering^[3].
• Guards missing or too low once the floor is more than 30 inches up^[1].
• Uneven stair risers: the largest may not exceed the smallest by more than 3/8 inch^[1].
• Bedroom windows behind the porch. A bedroom's required escape window may open onto a roofed porch only if the porch ceiling is at least 7 feet high and the longer side is at least 65 percent open, in Minneapolis^[2]. Enclose it later and you can break that rule.

Do you need a permit to build a porch?

Yes, in every jurisdiction we checked. Minnesota's state guidance says permits are required for all porches^[1], Tukwila requires one for every attached porch cover regardless of size^[5], and Fairfax County lists porches among the common projects that need a building permit^[7]. Your application needs a site plan with the setbacks, floor and roof framing, footing details and elevations; Golden Valley also asks for a cross section with the footing size and depth, the post and beam sizes and the roof pitch^[4]. The porch permit page shows what each city asks for and what it costs.

How we can help

With the All-in offer, the paperwork side of your porch is done for your address: setback and porch rules with links, a scaled site plan, the floor plan, section and elevation for the permit application, the forms and the fee, then our team's review and follow-up until the permit is approved. You build.

Common questions