Three-season Porch - Part 1 of 4

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Three-season porches add living space to your home. Typically, they are wired with lights and electrical service, but they are not hooked into your heating and cooling system.


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A three-season porch blends indoor comfort with an outdoor atmosphere. It is a transition space between your home and yard. Windows with self-storing screens line each wall to provide plenty of fresh air and an enjoyable view of your landscape, while keeping insects and inclement weather at bay.
Building a three-season porch is an ambitious project, but like any large-scale project, it can be divided into simple, manageable steps, making the construction process less daunting. Because each building situation is different, you’ll need to create your own plans and plan drawings to reflect the specific details and dimensions of your home and yard. For example, the distance from the ground to your home’s entrance will vary, affecting the height of the deck frame posts and the steps and landing. Make sure all plans comply with your local building codes and zoning laws. You will need to submit complete plan drawings, including an elevation drawing and a floor plan, along with an estimated cost of materials in order to be issued a building permit.

What You'll Need


Circular saw
Caulk gun
Power auger or clamshell digger
Reciprocating saw
Hand tamper
Power miter saw
Hammer drill


2 x 2s
2 x 4s
Lag screws
Joist hangers
Post anchors
Angle brackets
Hurricane ties
Common nails
Joist-hanger nails
Box nails
Siding nails
Roofing nails
Finish nails
Deck screws
Masonry screws
2 x 4 trusses (8-in-12 pitch)
Silicone caulk
Construction adhesive
Roofing cement
15# building paper
Compactible gravel
12"-dia. concrete footing forms
Asphalt shingles
Windows with self-storing screens
Combination storm door and threshold
12 x 12" aluminum louvered


Step 1

How to Build a Three-season Porch

Attach the ledger. Measure and mark the center of your entrance, then measure out from that centerpoint in both directions and mark for the ends of the ledger outline. Draw an outline 2" below the door threshold to lay out the ledger position. Remove the siding within the outlined area and position the ledger in the cutout. Brace the ledger with 2 x 4s and tack it in place with 10d common nails. Fasten the ledger to the rim joist with counterbored 3⁄8 x 4" lag screws and washers. Cover the heads of the lag screws with silicone caulk.

Step 2

How to Build a Three-season Porch

Locate the footings. Build and set up batterboards that are aligned with the post locations. Run mason’s strings from one set of batterboards to the ledger and between the other set of batterboards and level them using a line level. Make sure the strings are perpendicular and mark the centerpoints of the footings on the strings. Transfer the centerpoints of the footings to the ground, using a plumb bob. Mark each point with a stake.

Step 3

How to Build a Three-season Porch

Pour the footings. Remove the mason’s strings and dig holes for 12"-dia. footings using a power auger or a clamshell digger. Pour 2 to 3" of compactible gravel into each hole for drainage. Cut 12"-dia. concrete tube forms to length and set them into the footing holes so the tops are level and 2" above ground. Make sure the tops of the forms are level, then pack soil around them for support. Mix concrete and fill each form. Set 6" J-bolts in the centers of the footings before the concrete sets. Let the concrete cure for two to three days.

Step 4

How to Build a Three-season Porch

Set the posts. Fasten a 6 x 6 metal post anchor on each footing, centered over the J-bolt. Cut 6 x 6 posts at least 6" longer than the required post height and set the posts in the anchors. Tack each post with a nail and brace with 1 x 4s and stakes. Run a level mason’s line from the bottom of the ledger to one end post, and run another level string across all the posts at the bottom of ledger height. Mark cutting lines at the string height and then move and cut the posts to length. Replace the posts, check for plumb, and fasten with 16d galvanized nails.

Step 5

How to Build a Three-season Porch

Build the floor frame. Cut the doubled rim joist boards to length and bind them together with construction adhesive and 10d nails. Lay out matching joist hanger locations on the ledger and the inside face of the rim joist. Attach joist hangers with 10d galvanized nails. Then, position the rim joist on the posts and tack with nails. Cut the joists to length and make double joists for the ends and the middle, leaving the inner board of each doubled end joist 11⁄2" shorter than the outer board at the ledger end only. Install the end joists by facenailing to the end of the ledger at the house and nailing through the rim joist and into the joist ends at the posts.

Step 6

How to Build a Three-season Porch

Check for square and reinforce the corners at the posts with metal corner braces. Cut and hang the joists, fastening with 10d joist-hanger nails.

Step 7

How to Build a Three-season Porch

Install the joist blocking. From the ledger, measure along the top of both end joists and mark a reference at the midpoint. Connect the reference lines with a chalk line between the marks and then measure and cut 2 x 10 blocking to fit in each bay between the joists. End nail the blocks to the joists with 16d galvanized common nails, staggering the pattern along the chalk line.

Step 8

How to Build a Three-season Porch

Remove the siding. Outline the porch walls (but not the roof) onto the house siding. Set your circular saw blade to the depth equal to the thickness of the house siding, and cut along the outline. Finish the cuts in the corners with a handsaw. Remove the siding pieces using a pry bar.

Step 9

How to Build a Three-season Porch

Option: If the end studs of the porch walls will not be located at a house wall stud location, install 2 x 4 blocking in the stud bay where the porch walls tie in. In each stud bay that will contain blocking, mark for blocking against the bottom plate, then measure up and mark the studs every 24" up to the top plate. Also mark for blocking at the top plate. Cut 2 x 4s to size and install them in pairs using 16d common nails.

Step 10

How to Build a Three-season Porch

Install the subfloor. Beginning next to the house, install a full sheet of 5⁄8 or 3⁄4" exterior-grade, tongue-and-groove subflooring. Apply a bead of construction adhesive to the joist tops first, and nail the subfloor with 8d box nails spaced every 6" along the edges and 12" in the field. (You can use 21⁄2" deck screws instead.) If necessary, trim the sheet so the edges fall on the center of a joist. Cut the next piece to size and install, leaving a 1⁄8" gap. Install the next row, beginning with a half sheet so the joints are staggered.



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