Materials to Build a Porch

A porch makes a useful addition to any home, adding space for hosting barbecues and parties or just enjoying the outdoors. Adding a roof or screening to the porch will allow you to enjoy it in all weather conditions. All porch designs use the same basic materials. Certain design choices like railings or roofing may require more of the same materials, or different materials that can support weight or withstand weathering better.

Porches and decks are both constructed out of decking lumber, which consist of smooth planks cut in different widths. High-end or exotic woods make a long-lasting porch with the right maintenance, says the Bob Vila website, while composite materials made of PVC and other plastics offer the look of wood with less maintenance and shrinking. Cheap decking lumber may be cut unevenly, leading to a crooked porch structure, or shrink and curl excessively when exposed to rain and changing temperatures. Dense heartwood planks cut from the center of a tree will last longer, no matter what type of wood you choose. Almost all wood decking requires a coat of water repellent that will also work to keep insects from burrowing into the wood. Some coatings include a UV blocker to protect the color of the wood you've chosen. Composite decking doesn't require a coating.

Joists are the pieces of lumber that support the floor of a porch, similar to rafters in a ceiling. Sturdy porches rely on a strong attachment between the porch joists and the side of the foundation or exterior wall. Joist hangers are specially designed metal hangers that keep the joists attached to the structure and the porch from collapsing. A piece of treated lumber known as a ledger or band board is first attached to the structure with threaded bolts and washers, according to Ask the Builder. The ledger creates a strong support on which to hang the joist hangers. You can construct a joist hanger out of a 2-foot by 4-foot piece of lumber, but it will need to be treated and will require more maintenance than metal joist hangers.

Installing a moisture barrier above or below the floor joists when you are constructing a new porch may extend the life of the whole structure. Joists often expand and push apart the decking lumber when they absorb too much moisture, leading to unwanted gaps in the porch floor. Moisture barriers help prevent this from happening. Moisture barriers come in a variety of different materials, including plastic vapor barriers that you staple to the bottom of the floor joists, or tar paper that you nail on. Brush-on liquid moisture-resistant sealants also work, says the Southern Pine Council.

Nails aren't strong enough to keep decking materials attaching to the floor joists as they shrink, which all wood does to some extent. Decking screws are used for a strong and sturdy hold. Decking screws are treated with special coatings to prevent them from rusting when exposed to moisture. Coarse-threaded screws are the best choice for attaching anything to wood, according to HammerZone.