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Dean Johnson

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finished porch frame


The majority of work for a porch project is framing. It's important to familiarize yourself with what's involved before you start to order lumber. If you'd like more information on the framing terms and methods used here, see our How-To Framing section.

Once you get going, framing can be completed rather quickly and the porch will really begin to take shape. Chalklining layout marks and double-checking layout measurements are going to save you some time, lumber and aggravation. Again, go through the framing steps mentally before cutting any lumber.

Building The Porch Deck

Ledger BoardBuilding the floor of a porch will have a lot in common with building a low deck. So you might also want to consult the Decks section of our site.

Cut a 2x10 (or larger) ledger board the width of the deck. Nail joist hangers to the ledger on 16" centers. Set the ledger board the thickness of the decking (usually 1-1/2") below the entrance height and use carriage bolts or lag screws to secure it to the house's rim joist.

NOTE: Make sure the ledger is level, or this will throw off the floor joist heights and cause an uneven floor.

Side Rim JoistCut and nail side rim joists the length of the deck and nail them to each end of the ledger board. Support the outside ends on short posts that rest on the footings. Check with your local building department to find out what connectors are required between the footing and the posts and between the posts and the rim joists.

Cut a front rim joist and nail on joist hangers to line up with the ledger board hangers. Fasten the front rim joist to the side joists to complete the perimeter of the deck.

NOTE: A center beam, with joist hangers on each side, may be needed to support the span of the floor joists.

Set the floor joists in their hangers, crown (or bow) side up.

DeckingLay out the first decking board perpendicular to the joists. Cut its ends to be flush with the side rims and fasten it down. This first board (butted to the house) will later serve as a chalkline guide for the rest of the decking.

In the process of installing the deck, you may want to include electrical outlets in the walls, so run those lines while there's still easy access.

Set the next decking boards flush with one side rim joist end and let the other side run longer (i.e. run wild). Don't fasten the deck board ends to the other side rim joist, yet.


Snap a chalkline even with the outside edge of the rim joist under the wild ends of the deck boards and cut them off with a circular saw.

NOTE: Be sure your circular saw depth is set to the precise thickness of the deck boards, or saw marks may be visible on the rim joist. Often, this is calculated into a plan with the addition of skirt boards that cap the rims and hide any saw marks.

Flush the side rim joist with the cut decking ends using a board or pry bar and fasten the deck board ends as you go. This will make your deck sides look straight.


Erecting Porch Walls

walking up a completed wall frameFraming out porch walls is fairly straightforward -- with a few exceptions like adding builder's felt to the exposed house sheathing and tying into the house.

NOTE: Your porch may have posts or columns instead of walls. The posts support the roof's weight and should have concrete footings under them. Beams set on the tops of the posts and serve as top plates for the roof trusses.

cutting back the roof eaveIn order to set the porch walls up to the house, the roof eave needs to be cut back.

Remove shingles, roof soffit, and cut back the rafter tails flush with the house wall as needed. After removing that section of roof, the walls can be butted up next to the house and fastened to it.

Cut and lay out the top and bottom plates on the subfloor. Locate the center of each wall's rough opening. Measure and mark half the opening's width on each side. Nail a trimmer stud on the outside edge of each mark. Scab on king studs to the outside of the trimmers.


center of wall's rough openingMeasure between the king studs to determine the header length. Porch walls usually have to accommodate several windows, so large headers are often needed. Fit cripple studs (if any) on 16" centers above the headers.

NOTE: Insulate the corner post cavity before tying wall corners together; because it gets covered when forming the corner joint.

installing the wall frame

After raising the wall, nail the bottom plate to the decking and nail the end stud to the house framing and/or the next porch wall.


Forming The Porch Roof

Building a study roof and tying the porch roof into the existing roof line is probably most complicated part of a porch building project. Prefabricated scissor trusses are one way to handle the majority of the roof framing.

Set the end (gable) truss flush with the end wall's top plate. Plumb and brace the truss. Working back toward the house, set the trusses (usually on 24" centers) and brace them together.

ridge boardAfter the truss nearest the house is set, run a string line level from its peak to the roof line peak. This is where the ridge board is nailed to the roof. It's mitered cut on the house end to match the roof pitch. The other end is nailed to the truss peak.

On each side, run a valley rafter from the ridge board at the house roof point down to the porch truss.

Nail jack rafters perpendicular to the ridge board down to the valley rafter on 16" centers. The jack rafters have to be mitered cut on the ridge board end and compound miter cut on the valley end.

Most designs call for an overhang on the gable end to protect the end wall from the elements. Most overhangs extend a foot or two, but try to match the house's overhang.

To make the overhang, scab on rake boards -- mitered to match the peak -- onto the gable truss rafters. Nail on 2x4 lookouts spaced along the rakes every 16". Cap the lookouts with fly rafters mitered on the ends to match the peak.

NOTE: Each side of the rake assembly can be built on the ground and raised into place with additional help.

After the trusses, tie-in rafters and overhang are on, the roof is ready for sheathing and shingling.


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