Roll up your sleeves!
A screen porch is a big improvement, but it's also a big project, one that might consume most of your spare time this summer. So, we're keeping this porch design simple. You can build it with standard dimensional lumber, and it doesn't require heavy beams or complex joints. The simple 2x4 walls are light and airy looking. Two horizontal bands of 2x4s, set 10 in. from the top and bottom of the wall, add a design element and stiffen the 2x4 framing enough to support the hand-built trusses. With this design, there's no need to precisely align the overhangs. And the exposed rafters and open soffit look great on many house styles.
The total cost of this porch was $6,500, but you could save hundreds of dollars without sacrificing quality by substituting treated decking for the cedar or using tongue-and-groove pine rather than cedar on the ceiling. Even though it's a large project, most of the construction is straightforward. If you've built decks or sheds, you'll be able to tackle this job with confidence. In this article, we'll show you the key steps for building this porch. Study the drawings and photos for more details.
You'll need a full set of basic carpentry tools, a circular saw and a drill to build this porch. In addition, a reciprocating saw, a table saw and a power miter box will make the job go quicker and give you better results. To reach high places safely and easily, we recommend renting a rolling scaffold system (Photo 8) for a month.
Plan ahead to avoid construction headaches
You can add this porch to almost any house, but attachment details may vary from what we show here. On most two-story houses, you won't have to worry about tying in to the roof, but you may have to situate the porch carefully to avoid covering a window. The house roof sloped 5 in. per foot (this is called a 5/12 slope) and extended 18 in. at the overhang. Your roof may vary from this, and the details of how the porch ties in will vary as well.
If you're not sure how to neatly join the porch and house roofs, we recommend hiring an architect to help work out the details. Another option is to build a full-size mockup of a roof truss out of inexpensive and lightweight 1x4s. Figure out where the top of the wall plate would be if you built the porch according to our plans (Figures A – H). Then support the mocked-up truss at this height to see how the porch overhang meets the roof. If you don't like the way the overhangs intersect, adjust the level of the deck slightly, alter the wall height or change the width of the overhang.
Contact your local building inspections department to find out what's required to obtain a building permit. Start this process at least a month before you plan to build. This will allow enough time to work through potential problems.
Plans for building the porch.
Figures A through H
These illustrations show the plans for the porch, deck framing, gable framing, ledger, truss block, side walls and the end wall.
To print these plans, see Additional Information at the end of this story.
Build the deck square and level
Start by marking the ledger board location on the house wall. We located the top of the ledger board 90 in. below the bottom of the soffit. On our house, this left a 6-in. step down from the patio door to the deck surface. Remove the siding and attach the ledger with 1/2 x 4-in. galvanized lag screws (Figure D).Make sure it's perfectly level. If the ledger attaches to concrete, predrill holes and insert lead shield lag screw anchors before installing the lags.
After you mount the ledger, use stakes and string lines to outline the deck frame according to the dimensions in Figure B and mark the footing locations. A few days before you plan to dig the footings, call 411 to have underground utilities marked in the vicinity of the porch. Your local building department will specify how large and deep the footings should be for your climate and soil conditions. Pour a concrete pad in the bottom of each footing hole after they've been inspected. Let the concrete set overnight.
Next choose the six straightest 2x10s for the perimeter beams. Cut the 2x10s for the two side beams to length and nail the pairs together. Use 16d stainless steel or double-dipped galvanized nails for all of the joist framing and to attach the joist hangers to the ledger board. Rest one end of each side beam in the double joist hangers and prop them up level with a stack of wood (Photo 1).
Nail through the joist hangers into the beams at the house to hold them in place. Then connect the opposite ends of the two beams at the front with a 2x10 cut to the same length as the ledger. Adjust the resulting frame until the diagonal measurements are equal. Then brace the frame against stakes pounded into the ground to hold it square while you install the treated posts, joists and decking (Photo 2). Sight along the outside rim joist occasionally and adjust the length of the joists as needed to keep the front rim joist straight.
Cut away the overhang and siding to make way for the porch
If your house has an overhang, you'll have to cut it back flush to allow the innermost truss to fit against the wall. Start by removing the soffit and fascia boards above and several feet to each side of the deck. It's easier to remove extra soffit and fascia boards and patch them back after the porch is done than to calculate cutoff points now. After the soffit boards are removed, use a level to plumb up from the house wall to the underside of the roof boards, in line with the outside edges of the porch.
Mark the two points. Then drive a long screw or nail up through the roof boards at the two marks. Snap a chalk line between the nails and remove the shingles below and about 6 in. above the line. Chalk a new line and remove nails along the line. Then saw along the line and pry off the roof boards (Photo 4). Be sure to wear safety glasses and hearing protection when you're sawing. Finally, cut off the rafter tails flush to the house wall.
You'll have to decide whether to cut a slot where the porch walls meet the siding (Photo 3). If your siding is stucco, brick or stone, you may want to butt the walls to the siding. Photo 3 shows how to cut a slot for the wall. Set the saw blade just deep enough to cut through the siding only. Remove the siding. Waterproof the slot with No. 15 building paper.
Construct a jig to assemble the roof trusses
Prime and paint the truss parts, wall frame and screen stops before assembly. Prime the wood with a special stain-blocking primer such as Zinsser's oil- based Cover-Stain. Then brush on a coat of acrylic exterior house paint. Make sure to prime every cut end as you work; otherwise these areas will absorb moisture and cause staining. We prefinished the roof boards with an oil finish (Cabot Clear Solution Natural).
It's easiest to assemble the roof trusses first, using the deck platform as a work surface. Screw two sheets of plywood to the decking and use the dimensions in Figure J to chalk lines indicating the top of the rafters and the bottom of the 2x6 crosstie. Cut triangular blocks and screw them to the plywood to hold the rafters in alignment as you assemble the trusses (Photo 5).
Cut a rafter using the dimensions in Figure J and use it as a pattern to mark the remaining rafters. Place a pair of rafters in the jig and screw the tops together. Next screw the 2x6 crosstie and 2x8 spacer to the pair of rafters. Keep the crosstie screws clear of the bolt hole locations. Complete each truss by screwing another pair of rafters on top.
Check the ends and tops of the rafters as you assemble the trusses to make sure they're perfectly aligned. The trusses must be identical so that your roof boards and soffit trim will line up. Finally, elevate the truss on blocks of wood while you drill a pair of 1/2-in. holes into each end of the crosstie for the carriage bolts (Figure J). Run the 1/2 x 5-1/2-in. carriage bolts through the rafters and crosstie ends and tighten the nuts.
Build the rafters with 2x8s using spacers and crossties.
Figure J: Truss Details
This illustration shows how to construct the trusses.
Frame the walls accurately for smooth assembly
Since the wall framing for this porch is the finished surface, it's worth taking a little extra time to make the framing material look good. We chose the nicest cedar 2x6s we could find and ripped them into 3-1/2-in. and 1-1/2-in. boards. We did this to create sharp, clean edges (we also ripped off all the factory rounded edges).
Cut the studs and crosspieces to length and screw the walls together (Photo 6 and Figures F – H). We used a power miter saw for clean, square cuts, but a circular saw will work too. Use a crosspiece as a spacer when you're attaching the studs to the top and bottom plates (Photo 6). Then cut a 10-in. spacer block to position the crosspieces for assembly.
Plumb and brace the walls, then set the trusses
The key to standing the walls is to check and double-check along the way to make sure they're straight along their top and bottom plates, perfectly plumb and square, and securely braced (Photo 7). Start by positioning the walls with their outside edge flush to the deck and screwing them down. Next screw the corners together, making sure the top plates of adjacent walls are even with each other. Use a long level to plumb the walls while you attach diagonal braces to hold them in position (Photo 7). Leave the braces in place until after the roofing is complete.
Round up a couple of strong helpers to assist in setting the trusses. Start by marking the position of the trusses on the top plate and onto a 16-ft. 1x4 (you'll use the 1x4 to brace and position the tops of the trusses as you stand them up). The first truss simply butts to the house wall. The outermost truss aligns with the edge of the top plate, and the three interior trusses are centered on the studs below. Set the first truss against the house and carefully center it so that 1-1/2 in. of the bottom 2x6 overhangs the top wall plates on each side.
Screw the truss to the top plates. Then use a straightedge and level to stand the truss perfectly plumb and brace it to the roof (Photo 8). Make sure this brace is securely screwed to the roof and the truss because the remaining trusses will be supported by this truss until the roof tie-in framing is complete.
Lift the remaining trusses onto the top of the walls and rest them on the first truss. Slowly and carefully slide the outermost truss to the outside end of the porch. Align the marks on the 1x4 with the truss at the house and the outermost truss and screw it to the trusses.
Center the outermost truss on the walls and toe-screw it to the top plate of the walls. Stretch a string line between nails at the peak of the two trusses. Align the remaining trusses with the string line and the marks on the 1x4 and top plates and screw them in.
Line up the tie-in framing with the porch for a seamless blend
One of the trickiest parts of the porch construction is joining the two roofs. The key is to extend lines from the new porch and mark where they intersect the existing roof. Do this by using a taut string line or a long, straight board. Remember to raise the tie-in framing on the existing house roof ¾ in. above the porch framing to compensate for the difference in thickness of the 3/4-in. plywood and 1-1/2-in. roof boards (Photo 12).
Start the tie-in framing by locating the point where the peak intersects the existing roof (Photo 9). Then cut the 2x8 roof plates. If you're not good at calculating roof angles, start by estimating the angles and cutting the plates an extra 6 in. long. Then set them in place, remark the angles and recut them until they fit. Screw the roof plates through the roof boards into the rafters below. Next measure for the ridge, estimate the angle and cut it a little long. Trim the angle to fit and screw the ridge rafter to the first truss and roof plates. Complete the tie-in by installing a pair of rafters (Photo 10).
Photo 11 shows installation of the roof boards. Set your table saw or circular saw to 23 degrees and rip a bevel on the groove edge of the first board. Align the board with the ends of the trusses and nail it with 16d galvanized nails. Install the remaining boards, making sure to snug the joints tight before nailing them. Let the boards hang out past the last truss to form the gable end overhang.
When you're done installing the roof boards, snap a chalk line at the gable (outer) end and saw them off to leave an 18-in. overhang. Finish the gable end overhang by installing a pair of rafters and the 1x3 trim. Hold the gable end rafters tight to the underside of the cutoff roof boards and screw through the roof boards to hold the rafters in place. Then cut 1x3 trim to cover the end grain of the roof boards. Extend the trim around the corners and return it along the roof edge to the house.
Pay attention to flashing and roofing details for a watertight job
Building the tie-in framing on top of the existing shingles is a good way to keep the house waterproof as you construct the porch, but when it comes time to install the roofing you'll have to cut the shingles along each of the valleys with a hook-blade utility knife. Then pry loose the cut shingles to make a wide path for the valley flashing (Photos 12 and 13).
We won't go into roofing details here. In general, cover the eaves and valley with strips of waterproof membrane (Photo 13) and install the sheet metal valley. Place roofing nails about 12 in. apart along the edge of the metal valley. Cut a short piece of valley metal to complete the top on each side, overlapping it about 6 in. onto the long piece.
Staple No. 15 building paper to the remainder of the porch roof, starting at the bottom and working up. Overlap each row 3 in. onto the one below. Install shingles to match the house. Follow the manufacturer's instructions for starting, overlaps and nail placement. Use 1-in.-long galvanized roofing nails to avoid nailing through the tongue-and-groove ceiling.
Fill in the gable ends
Cover the triangular opening in the truss above the house wall by building a 2x2 frame and nailing 1x6 tongue-and-groove boards to the back. Then slide the frame into the opening and screw it into place. Fill the triangular space above the outside wall with a 2x4 frame (Figure C).
Then staple screening to it and cover the screens with stops, just as you do with the walls below. Practice on scraps to make accurate patterns for the steep angles. Then transfer the angles to the actual framing members. You may have to cut these angles with a handsaw; they're too steep for a miter saw unless you build a special jig.
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Install the screens and screen door
The charcoal aluminum screening we used is strong and long lasting, but you have to handle it carefully to avoid creases and dents. Carefully unroll the screen on a large work surface and cut lengths about 3 in. longer than you need. Reroll each piece and carry it to its location. Photo 15 shows how to staple the screening to the framing.
After you stretch and staple each section, cut off the excess screen with a sharp utility knife. Then cover the edges with 2x2 trim pieces (Photo 16). We screwed these on to allow for easy removal for future screen repairs.
If you use a wood door like ours, start by trimming it just enough to fit in the opening. Then set it in place and mark the door for final fitting. Use a sharp plane or belt sander to trim the door. You may have to repeat this process a few times to get a good fit.
Nail 1/2 x 2-in. wood stops to the framing at the door opening. Then hang the door using galvanized or brass screen door hinges. Mount a latch and door closer to complete the job.
The joists and corners are covered with trim.
Figure K: Corner Details
This illustration shows how the corners are assembled and the trim is installed.