Screen Porch
Figures A through H
These illustrations show the
plans for the screen porch,
deck framing, gable framing,
ledger, truss block, side walls
and the end wall.
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A screen porch is a big improvement to an existing porch or deck, but building a screen porch is
also a big project when starting from scratch.  How to Screen a Porch will walk you through this  
simple design. You can build this screen porch 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 screen porch
design, there's no need to precisely align the overhangs.  The exposed rafters and open soffit
look great on most house styles.

Even though a screen porch is a large project, most of the construction is straightforward. If
you've built any structures before, you'll be able to tackle this job with confidence. In this article,
we'll show you the key steps for building a screen porch. How to Screen a Porch has included a
drawing that you can view for more details.

Basic carpentry tools such as, a circular saw and a drill to build this porch are required.  Also
you may want to purchase, rent or borrow; a reciprocating saw, a table saw and a power miter
box which 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 for the duration of the project.
Planning is Key!

You can add a screen porch to almost any house, but attachment details may vary from what
we have describe 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 screen 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
screen porch ties in will vary as well.

If you're not sure how to neatly join the screen porch and house roofs, we recommend hiring a structural engineer  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 screen porch according to the shown plans (Figures A – H). Then support the mocked-up truss at this height to see how the screen 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 your screen porch. This will allow enough time to work through potential problems.

Build a square and level deck

Start by marking the ledger board location on the house wall. We located the top of the ledger board 90 inches below the bottom of the soffit. This left a 6-
inch step down from the back house door to the new deck surface. Remove the siding and attach the ledger with 1/2 x 4-in. galvanized lag screws.  Make
sure the ledger is perfectly level. If the ledger is attached to concrete, pre-drill 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 and mark the footing locations. A few days before you plan to dig the
footings, call your local government to have your underground utilities marked in the vicinity of the screen 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.

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. Sight along the outside rim joist occasionally and adjust the length
of the joists as needed to keep the front rim joist straight.

Make way for the Screen Porch by cutting away the overhang and siding

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 screen porch deck. It's easier to remove extra soffit and fascia boards and patch them back after the
screen 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 screen 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 inches above the line. Chalk a new line and remove nails along the line. Then saw along the line and pry off the roof boards.
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 screen porch walls meet the siding. If your siding is stucco, brick or stone, you may want to butt the
screen porch walls to the siding. 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 screen porch roof trusses first, using the screen porch deck platform as a
work surface. Screw two sheets of plywood to the screen porch decking and use the dimensions in Figure
2 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 screen porch trusses.

Cut a rafter using the dimensions in Figure 2 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 screen porch rafters. Keep the crosstie screws clear of the bolt hole locations. Complete each
screen porch truss by screwing another pair of rafters on top.
Build the rafters with 2x8s using spacers
and crossties.

Figure 2: Truss Details
This illustration shows how to construct
the trusses.
Check the ends and tops of the screen porch rafters as you assemble the screen porch trusses to make sure they're perfectly aligned. The screen porch
trusses must be identical so that your screen porch roof boards and soffit trim will line up. Finally, elevate the screen porch 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 2). Run the 1/2 x 5-1/2-in. carriage bolts through the rafters and
crosstie ends and tighten the nuts.

Frame the walls accurately for smooth assembly

Since the wall framing for this screen 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. We recommend 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. 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 screen porch 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. Start by positioning the screen porch 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 screen porch walls are even with each other. Use a long level to plumb the
walls while you attach diagonal braces to hold them in position. Leave the braces in place until after the roofing is complete.

Round up a couple of strong helpers to assist in setting the screen porch trusses. Start by marking the position of the screen porch trusses on the top
plate and onto a 16-ft. 1x4 (you'll use the 1x4 to brace and position the tops of the screen porch trusses as you stand them up). The first screen porch
truss simply butts to the house wall. The outermost screen porch truss aligns with the edge of the top plate, and the three interior screen porch trusses are
centered on the studs below. Set the first screen porch 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 screen porch truss to the top plates. Then use a straightedge and level to stand the screen porch truss perfectly plumb and brace it to the
screen porch roof. Make sure this brace is securely screwed to the screen porch roof and the screen porch truss because the remaining screen porch
trusses will be supported by this screen porch truss until the screen porch roof tie-in framing is complete.

Lift the remaining screen porch trusses onto the top of the walls and rest them on the first screen porch truss. Slowly and carefully slide the outermost
screen porch truss to the outside end of the screen 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 screen porch 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 screen porch 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 screen porch construction is joining the two roofs. The key is to extend lines from the new screen 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 screen porch framing to compensate for the difference in thickness of the 3/4-in. plywood and 1-1/2-in. roof boards.

Start the tie-in framing by locating the point where the peak intersects the existing roof. 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.

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 screen porch
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.

Prevent water leakage

Building the tie-in framing on top of the existing shingles is a good way to keep the house waterproof as you construct the screen 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.

In general, cover the eaves and valley with strips of waterproof membrane 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 screen 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 screen porch 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.

Install the porch screens and porch screen door

Carefully unroll the screen on a large work surface and cut lengths about 3 in. longer than you need. Re-roll each piece and carry it to its location. Staple
the screening to the porch 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. We recommend
screwing these on to allow for easy removal for future screen repairs.

If you use a wood door, 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 screen porch door opening. Then hang the screen porch 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.
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