Building a Three Season Porch
A Review of the Steps involved in Building a
Three Season Porch
By Mark J. Donovan
Building a three season porch is a
great way to expand your home’s living space and enjoy a little more of the
outdoors, without the insects.
Building a three season porch begins
with a building plan. It is important to consider several key items before
developing your plan:
How big should the three season
How will it tie into the existing
How do you plan on using the three
Where will the entrance be from the
house to the porch?
Should you future-proof the porch to
enable it to eventually become a full home addition sometime later on down the
With these key questions answered,
you should have enough information to begin the building of your three season
Usually your plans do not need to be
too complicated. Typically all that is required are some scaled drawings with
dimensions included. You will also need to have a few cross-sectional drawings
showing the key structural support areas, e.g. foundation to the walls, to the
Your three season porch drawings
should include the locations of all doors and windows, roof pitch, wall
thickness, deck construction and foundation/footing construction.
Permits for Building a Three Season Porch
Once you have completed your plans
and sketches, you should apply for a building permit for building the three
season porch. Depending on your specific
plans, you may need to pull construction, wiring, and plumbing permits.
Without a building permit you will be
subjecting yourself to problems down the road, both with your local municipality
and your homeowner’s insurance policy.
During the building of a three
season porch you should have scheduled inspections performed by the local
building inspector to ensure your building your porch to the approved plans. You
do not want to get to the stage where you have installed sheetrock on the
interior walls and then ask for a rough framing inspection.
Inspections are usually conducted
Completion of pouring
Completion of rough Framing
Completion of rough Electric
Completion of rough Plumbing
(probably not required in this case)
Completion of Insulation
With permits in place you can begin
building your three season porch.
Footings when Building a Three Season Porch
Once you have identified and marked
the location of your new three season porch, using string and stakes, you can
next locate where you want to install your porch’s footing pads. Make sure when
marking the corners of your three season porch that they are perpendicular and
parallel to each other and the existing house. Using a string, measure on the
diagonals to confirm the sides are of even length and square.
Normally three season porches are
built on Lally columns or wood posts that sit on top of footings. The footings
are concrete pads that have a base that sit well below the frost line. Footings
can be constructed using Sono-tubes or by making up a form. Footings should be
2-3 times the area of the support posts. The footing pads should be constructed
using poured concrete and should be allowed to set up for 2 or 3 days.
If the three season porch is to be constructed on
top of a full foundation, then perimeter footings and concrete pads will be
required. The perimeter footings will support the foundation walls and the
concrete pads will support Lally columns that are typically located in the
center of the room space.
Framing the Three
Season Porch Deck
Once the footings have been poured
and are cured, you can begin to frame the three season porch.
Framing of the porch begins with the
building of the porch deck. The porch deck is constructed by first installing a
ledger board onto the existing house.
Once the ledger has been attached to
the home with lag bolts, side rim joists can be attached to the ledger board.
Then the front rim joist can be attached to the side rim joists using joist
Once the perimeter of the deck has
been framed, level and square it up. The rim joists can be attached to the deck
posts that rest on the footing pads. Again, make sure the deck is square by
using string and measuring on the diagonal.
Note that depending upon how large of
a deck porch you are building, and the size and type of floor joists you are
using, a center beam may be required.
With the perimeter of the deck level
and square, attach the joists hangers to the ledger board and the front rim
joist. Then install the floor joists to the hangers. Typically you will want
floor joists installed on 16” centers.
With the deck frame in place, install
floor sheathing (e.g. 3/4th inch tongue and groove plywood) to the
Framing the Three
Season Porch Walls
Framing the walls of your three season
porch is relatively straight forward. Frame the walls on the deck and then raise
them into place.
Note that you may need to remove a
portion of the eaves from the existing home’s roof to raise the walls into
place. You will have to cut into the existing roof to do this.
Once the walls have been constructed,
raised into place, secured to one another, and are confirmed square, you can
move on to the roof.
If you did not add sheathing to the walls
while constructing them on the deck, add the plywood / OSB sheathing to the
walls after they have been secured in place.
Framing the Three
Season Porch Roof
The porch’s roof should tie into the
existing home’s roof line. You can either stick build your roof or use pre-built
roof trusses. My recommendation is to use pre-built roof trusses. For a three
season porch, the size of the roof trusses are manageable to install with 2 or 3
When installing the roof trusses start at
the outer end of the porch and work your way inwards towards the existing house.
Once the roof trusses are in place, use a string line to determine the length
and location of the ridge board. The ridge board attaches from the last truss
installed to the existing home’s roof.
Next install valley rafters and jack
rafters perpendicular to the ridge board and with the same roof pitch as the
With the roof framing nearly complete,
you can append an overhang on the outer gable end of the roof. You can than add
plywood sheathing to the roof trusses, install the soffits and fascia boards,
and shingle the roof.
Installing Doors and Windows
With the porch walls and roof in place,
it is now time to install the doors and windows. If you framed out your door and
window openings properly they should be about 2 inches wider/longer than the actual
rough window sizes.
Install the doors and windows into the
rough door and window openings ensuring that they are installed properly. Make
sure that the doors and windows are square and plumb when fastening them to the
exterior wall sheathing.
Installing Exterior Siding
There are a number of exterior siding
choices to choose from, however you should try to match the siding material that
is on the existing home. If it is clapboards that you are installing, start at
the bottom of the porch and work your way upwards, maintaining the same reveal
as the existing home siding. Use a chalk line to ensure your lines remain
You may want to add a trim skirt along
the perimeter of the porch walls to make your exterior siding effort easier and
more appealing, however, this is somewhat predicated on how the siding is
attached on the main part of the house.
Punching into the Existing Home (Creating the Doorway to the house)
With the three season
porch closed in from the elements, this is usually a good time to punch into the
existing home to create the doorway. You will want to take care not to cut any
live electric wires, and you will want to demo the area carefully to limit the
First remove all of
the home’s exterior siding around the interior of the porch area.
Next mark the area of
the future doorway, and use a circular saw to cut around the mark. Do not set
your blade deeper than you have to (the width of the home’s exterior sheathing).
Now remove the
sheetrock from the area inside the house. Again, you will want to mark the rough
area for the opening. The use of a carpenters knife may also help to minimize
the demolish-in and mess.
With the sheathing
removed, you should now have access to the wall studs. Remove the required
studs, and build a new header for the doorway opening. Note, if there are
structural concerns, you may need to brace the ceiling prior to removing the
Rough Electric (Plumbing)
With the porch
buttoned up, you can now install the rough electric wiring. The wiring should
tie back into the main circuit breaker box, however it should not be connected
into the main circuit panel until the finish electric is complete.
If plumbing is required, also rough
it in at this point and time.
If you want to future
proof your porch, you may want to consider installing insulation into the porch
walls, roof, and floor areas.
Once the rough
electric and insulation have been installed, you can now install your interior
sheathing. This could be drywall, bead board, or paneling.
drywall, it is best to prime and paint it before moving onto the interior trim
Once the interior
sheathing has been installed, you will want to install the interior trim around
the doors and windows.
Finish Electric and Plumbing
Now install the light
fixtures, outlets and switches, and any plumbing if it is required.
All that remains is
to install the finish flooring and painting the exterior walls and your three
season porch is ready for use.
For more help on building a Three Season Porch or Family Room, see HomeAdditionPlus.com's
Room Addition Bid sheet.
Room Addition Bid Sheet
will teach your how to hire the right general contractor and
subcontractors for your family room addition, and help to ensure that your
project is completed on time and budget.
Related Information on Building a Three Season Porch and Home Additions
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