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Home > Products > Porches - START HERE! > ONLINE PORCH GUIDE > Understanding the Porch > Structural Porch Components > Roof & Ceiling

Roof & Ceiling

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Type of roofing material, snow load,
rafter and ceiling joists sizes, etc. should
be determined by an experienced person.

Therefore, we recommend seeking professional assistance in determining a proper roof structure for your porch. However, the design of the eave is important to our discussion of porches.

Rafters are structural members that are set perpendicular to and on top of the Beam. They extend at a slope up to the face of the building. Rafters are typically spaced 16" or 24" apart along the length of the porch. The Pitch (slope) of a roof is defined as "the number of feet the roof rises vertically for each 12 feet of horizontal measure." Hence, a 4/12 Pitch roof will rise 4" for every 12" it travels. If a porch is 8 feet deep from the face of the building to the Beam, and the Rafters are installed with a 4/12 Pitch, then the Rafters will intersect the face of the building 32'' above the porch Beam.

Ceiling Joists
Ceiling Joists are structural members placed on top of the Beam next to each Rafter. Ceiling Joists can be omitted if the ceiling is to be installed to the bottom of the rafters. Also, some rustic building styles omit the ceiling altogether and leave the rafters exposed. This can be very presentable when the roofing is metal or wood shingles. However, most modern residential roofs are sheathed with plywood and covered with composition shingles, so leaving the rafters exposed also exposes the plywood to view.
Ceiling Joist - Details
Connecting the porch to an existing wall.

Ledgers (Ribbon Boards)
Ledgers are boards fastened horizontally to the building so as to receive the ends of either the rafters or ceiling joists. We recommend the use of steel Joist Hangers as the method of fastening Joists and Rafters to the Ledgers, both for their ease of installation, and for their strength. See drawing directly above.

Fascia boards are applied across the ends of the Rafter Tails (the section of the Rafter that extends beyond the Beam creating the roof overhang). See drawing just below.

The Soffit is the material applied to the bottom of the Rafter ends to "box in" the overhang. If the Soffit is installed perpendicular to the face to the Beam, it will be much easier to add decorative trim in this area.

Lower Eave - Details
Cross section of lower eave of a typical porch.

Your porch roof should have adequate fascia and visible beam height, together with adequate soffit depth, to not only be visually pleasing, but also to permit the inclusion of "The Third Dimension" now or at a later time. The Third Dimension is undoubtedly the most overlooked aspect of modern porches and is much more important in creating a great porch than most people realize. See Porch Eave Decoration.

Standard ceiling height inside a house is 8 feet. To feel spacious, your porch should also have at least 8 feet of ceiling height, but porches with even taller ceilings are quite traditional.

However, the deeper the porch, the lower the front eave will be for a given roof slope. And, of course, roof slope must be sufficient for the type of roofing to be used.

Therefore, a properly designed porch becomes a matter of maintaining as much porch depth AND ceiling height as possible, while also working within the confines of the wall space available on the house, type of roofing planned, etc. (For 1-story homes, it is often better to start the porch roof on top of the main house roof to gain extra vertical height.)

Other factors that should be taken into account when determining ceiling height include elevation of the porch floor above grade and whether to have a flat ceiling, a vaulted ceiling (ceiling attached to bottoms of rafters), or no ceiling (exposed rafters).

It often helps to draw a 'stick figure' end view of your proposed porch, starting with a vertical line representing the front of your house, with marks indicating the top and bottom of the door, and (if a 2-story house) the top of the first floor windows, and the bottom of the 2nd floor windows.

If your drawing is done to scale (We suggest 1/4" grid graph paper with each square equal to 1 foot), you can then pencil in 8' tall Porch Posts (as a starting place) with a 6" tall beam above them that is 10' from the front of the house. You should begin to get a good idea of how the porch roof will work as you change slope, ceiling height, etc.

Ceiling material is applied to the bottom edges of the ceiling joists. There are many different materials available for ceilings; from plain plywood to highly authentic and decorative Beaded Ceiling Boards, as shown below.

Ceiling - Details
Beaded Ceiling Board - both authentic & very decorative.

Although we don't have any definite answers, here are two theories we've heard as to why porch ceilings are blue:

1. Blue reminds people of the sky above.
2. Blue helps keep mosquitoes away (or was it flies?)

However, customer D. Greer of Colorado shared this with us:
"Exterior ceilings for porches and dormers were painted a light sky blue to keep spiders from building nesting webs under porch roofs. Spiders will not build their nests under the open sky.

"I built a patio porch for my uncle. When I told my uncle about painting the underside of the roof a light blue... he did. But he didn't paint the original small covering above the back door. It remained dark brown.

"Four months later I noticed he had painted the original small covering above the back door light blue like the rest of the patio. When I asked him about it, he pointed out there was not a single spider web under the blue, but the dark brown section kept getting full of webs. He painted that blue as well. No more spider webs.

"After I built a new carport for my uncle, he painted it the same blue. Four years later, and still no spider webs. Seem that makes my reason for painting light blue a little more than just a theory. Hope that helps."

Thanks D. for sharing! Very interesting, and light blue IS the traditional color for porch ceilings.

Roof Decking
Roof Decking is applied to the top edges of the Rafters to provide rigidity to the roof structure and a nailing base for the roofing material. The two common types of decking are sheets of plywood or lath (1x4's or 1x6's applied perpendicular to the Rafters, spaced 12" - 20" apart). Lath is most often used under metal roofing, to allow space to dissipate any condensate that may form on the underside of the metal. Otherwise, the metal roofing may in time rust through from below.
Roof Decking - Details
Cut-away view of the porch roof
(with lath boards and metal roofing material).

There are numerous roofing systems available. Among them are metal skin, composition shingle, wood shakes or shingles, tile, and slate. Typically, the porch roof will match the roofing material of the building to which it is attached, although a metal porch roof is sometimes used with a composition shingle house roof to good effect.

We are available by phone or email for free personalized consultation.

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