Building a porch roof or screened in porch roof over an existing deck or patio can be fairly straight forward or very complex depending on the type of roof you choose.
We show you how two different roofs are constructed so you will know what is involved.
Most porch roofs are typically shed roofs or variations of hip roofs.
The biggest challenge is determining the rise and run and cutting a "bird's mouth" at the outer end of the rafters that rests on the header.
Know and comply with your local building codes regarding roof construction in your area. In addition, pull the proper permits as required. Many people, especially DIYers, do not like to get permits due to time and costs.
However, doing so ensures that your work is to code in order to protect you, your family, and your property. In addition, many insurance companies may not pay claims in situations where work was not to code. Words to the wise.
When building a porch roof you have to determine the rise and run of your porch roof. Normally, you will want to replicate the same rise and run you have on the main roof of your home.
Sometimes this is not feasible due to window placement but you want to get as close to it as possible.
Next, determine the location on your wall where you will attach the rafter plate to get the proper rise and run. Our basic rafter length calculator will give you a general idea of how long your rafters must be for a given rise and run.
Now that you know the rise and run, you know where to place the rafter plate on your wall. Make sure it is at least 3 inches below any windows allowing for the thickness of your roofing materials (at least 2 inches).
Snap a horizontal chalk line at this point a minimum of the length of the flooring below. This will be your "upper" line measurement for the rafter plate.
Measure down from this line the width of your rafter plate. Usually, it is a 2x6 board, so in this case, measure down approximately 6 inches.
Snap a horizontal line at the mark - it is your "lower" rafter plate line. These two lines represent the location of your rafter plate.
Carefully remove the siding contained within those lines to expose the wall studs or other supporting material. Disregard if placing rafter plate on brick, etc.
Fasten the rafter plate to the wall studs with lag screws. However, this may not always be the case. Sometimes you may run into an I-beam or truss situation. A different fastening system will need to be used in those cases.
Snap a chalk line on top of your porch or deck on the outside line of the beam that supports your flooring. You'll have to locate the beam underneath (usually visible from each end).
You will locate, as a minimum, one column on each end at least 3 inches in from the corners and one every 6 to 10 feet apart. Consider openings for stairs when determining the actual placement of columns.
You will typically need one on each side of the stairs. As a rule of thumb, try to use an odd number of columns; it's more aesthetically pleasing to the eye.
Check with your codes department to ensure you set the right amount based on the width and type of roof being constructed when building a porch roof.
Place a column in the anchor on one end of the decking, plumb, and secure properly. You may need to brace the column while you continue.
On this building a porch roof project, a beam is placed against the ledger board and fastened to the top of the end column. Plumb and square the column. Brace as necessary.
(This board may not be required in your situation. If you don't have a ledger board, you will need to create blocking to accept the beam. Use the same procedure for installing a rafter board above).
Repeat this on the other end as well.
I've seen and done this several different ways. One is to anchor and brace all of the columns. Another is to anchor and brace the outside columns and then anchor the header on each end. It depends on the length and height of your roof.
When building a porch roof, an important goal to have is to make sure the columns are square to the house and the floor.
On this particular project, we reused the old header and due to it's length, installed it on columns in sections as depicted below.
You will normally build a header out of 2x6 or 2x8 planks. Sandwich a piece of 1/2 inch plywood in between the boards and nail together. When building a porch roof, the header carries most of the weight of the roof.
Ensure that it is substantial. Place the header on top of the columns and secure by toe nailing. Continue this process the length of the porch.
Before you install the rafters you will have to make special cuts called "tails" and "bird mouths". These notches are designed to fit against the rafter board and over the header.
You will need a rafter square in order to lay out the cuts on the boards. Building a porch roof requires accurate measurements. Although not difficult, laying out the cuts to fit precisely requires practice and skill.
For this building a porch roof project, we needed to provide nailing support for siding and to enclose the ends. We did this by installing jack studs and plywood on each end of the roof.
A fascia board is installed on the rafter tails. Gutters will be attached to this later. Although we did not use them on this porch roof, you could install "lookouts" that attach to the end of the rafter tail and the header. These provide a flat surface on which to nail the soffits.
Sheathing (1/2 inch plywood or OSB) is nailed to the rafters. Once completed, roofing paper will be installed. Then attach drip edge over the roofing paper. When building a porch roof, asphalt shingles (or other roofing material) are then attached over the roofing paper and drip edge.
An Often Asked Question
We are often asked how to integrate a new porch roof's shingles with those on an existing home if the roof line is extended over the porch.
As you can see in the picture above, now is the time to install your electrical wiring for lights, fans, and receptacles according to your plan.
Planning to install outdoor ceiling fans now or in the future. Now's the time to add additional blocking to support the fans!
TIP: If building a porch roof (or any roof) in snow country you should consider using an ice and water barrier along the edge of the roof line. It usually comes in three-foot rolls and prevents damage from ice dams that may form on your roof.
Aluminum flashing is used to wrap the exposed wood on the beams and sides. A special machine is needed to bend the flashing to fit over the wood. It really helps to have experience prior to attempting this to ensure it looks good on your home.
See our porch ceiling section for construction, tips, and ideas!
A planar truss, like the one above, lies in a single plane and is usually used together to form the roof support structure. They are extremely strong and normally constructed off site and made to specific measurements. Therefore, it is very important to ensure your measurements are correct before ordering.
Porch roof construction using trusses is much like using basic rafter construction as outlined above with a few exceptions. Trusses definitely expedite the process.
Beams need to be installed to support the roof trusses. In the photo below, beams are supported temporarily with bracing which will be removed later in the construction process.
Squaring the beams and bracing them to ensure the maintain square is essential to the roof building process.
Once the beams are in place mark the spacing for the trusses, normally 16 inches apart. Mark both the house wall and the carry beam.
Now its time to position the trusses. If everything is square and your measurements are correct, installing the trusses is fairly easy.
When building a porch roof with trusses on this type porch, the corner and subsequent trusses are built a little differently due to the slope of the roof. As you can see, the truss angles are constructed to maintain the same slope.
Next, soffit framing is installed along the roofs edge.
Finally, the framed roof is now ready for sheathing as outlined in the roof construction steps above.
Use our porch roof design ideas to see your options. . You'll see some intriguing designs along with traditional shed roofs, flat roofs, gables, hip, and many others.
Get insider tips from Nancy Moore for choosing a good contractor of integrity, and learn how to prepare. Take your time on this.