Building science 101: Decks & porches
PHOTO: CA SMITH PHOTOGRAPHY. COURTESY OF BRIGHTBUILT HOME
By Parlin Meyer
THERE’S NOTHING MORE RELAXING than sitting on the deck on a sunny morning, sipping your coffee and absorbing the sights and sounds of the world around you. The last thing on your mind is whether the floor beneath you is structurally sound, and that’s the way it should be. Get peace of mind about your deck or porch by understanding the basic building science concepts behind it.
Decks and porches extend the living space of your home to include the outdoors. Screened porches are a particularly popular feature in Maine because they have the potential to add a three-season space, especially if you include a wood stove or fireplace. Whether you use this extension of your home as a dining area, hot tub platform, mini garden or reading lounge, you want to be confident that the space is safe, durable and designed to maximize use.
SAFETY FIRST
Although they seem like simple structures, decks and porches are of more concern to building codes and inspectors than any other element of the house because of the potential safety issues that can arise from a poorly designed or built structure. If a suspended deck fails because too many people join the party, the results can be devastating. The statistics vary, but some estimates say that hundreds of thousands of people are injured every year in the U.S. due to deck failures.
Because safety is such a critical factor, construction of decks and porches is more careful and thoughtful than you might think for what appears to be a basic structure. The building code is a starting point to ensure that you have the bare minimum requirements for safety. Follow the local code and consult with a structural engineer, especially if you plan to build it yourself.
PHOTO: CA SMITH PHOTOGRAPHY. COURTESY OF BRIGHTBUILT HOME
DESIGN CONSIDERATIONS
If you’re designing a deck or porch for a new home, you have some freedom to decide where it’s located. Think about the seasons and when and where you like to spend time. For example, a deck that gets full sun in the early hours and shade later in the day allows you to warm up in the morning and avoid the hot afternoon sun. For ultimate flexibility, wrap the deck around a corner so you have the option to choose the sunny or shady side any time of day. If you’re adding a deck to an existing home, you might have less flexibility based on property lines, trees, drainage patterns, location of windows and doors, and other factors.
If you’re debating between a deck and a porch, remember that a porch can impede views and make the interior darker, so think about this during the design process. Because they require more materials, porches also have a bigger impact on the budget. However, because it’s protected by a roof, a porch typically requires less maintenance and fewer repairs. In either case, remember that water is the enemy of porches and decks. The most important consideration is where the structure is connected to the building. Bolts or industrial screws—never nails—attach the frame to the house to prevent it from falling down or shifting sideways. These structural holes can also create opportunities for water to enter and cause the house to rot and weaken.
Because of this, waterproofing is critical (and, unfortunately, often done poorly), so be very attentive to this in the design process. Areas where the structural elements pass through the building structure need to be both waterproof and designed to allow water to drain down and dry elsewhere. Most builders now use peel-and-stick waterproof membranes that adhere to the building and specialized products like the rust-proof Maine Deck Bracket (invented and manufactured by a contractor in Minot) to allow water to flow between the deck and the house without pooling or going through joints.
MATERIALS MATTER
Successfully fighting the watery enemy also depends on the materials used to build a deck or porch. Decks must be built to withstand harsh conditions including full sun, rain and snow, and it can be difficult to find sustainably sourced materials that hold up.
Thermally modified wood is an exciting product that is relatively new on the scene. This durable, natural product is kiln-baked to remove the sugars from the wood so it can’t rot. Available in a range of sustainably harvested species like ash and poplar, thermally modified wood is a good alternative to engineered composite materials that are made from plastic and wood chips. It also has the added bonus of a subtle, sweet, toasty aroma! If cost is a consideration, FSC pressure-treated wood is another good natural option.
Because porches are covered, you have more options when choosing the interior materials. They’re also a great place to highlight the use of Maine woods such as eastern white pine and eastern white cedar. Tamarack, also known as eastern larch, is a classic porch ceiling material that is readily available, local and sustainably harvested. If working with tamarack, note that boards milled from heartwood are recommended. The Northeast Lumber Manufacturers Association and Local Wood WORKS are good resources for learning more about sustainably harvested wood options in Maine.
To minimize maintenance, look for a wood product that you don’t have to seal and treat. Once you go down that path, you must do annual maintenance to keep out water. If you choose to seal an interior porch floor for aesthetic reasons, use a no- or low-VOC water-based product.
TIPS FOR BUILDING DECKS AND PORCHES
Always work with qualified professionals, even if you plan to do some or all of the building work yourself. To ensure safety, follow the local building codes and have your porch or deck inspected before use. This is a legal requirement but not always followed. Inspect any exterior weight-bearing structures for damage once a year. Look for rotting boards, eroding foundations and loose hardware, especially at the joints. This includes decks, porches, balconies and stairs, including any railings that people use for casual leaning or support.
If you want to take this 101 course to the 201 level, find the section about decks in your local building code to learn about requirements for beam size and location, fasteners, vertical and lateral loads, deck ledger connections, the flame spread index and more. And if these technicalities make you think twice, consider ditching your DIY aspirations and work with a qualified builder.
The Angel Creek project in Scarborough includes four decks and a covered entry porch. Learn more about this project featured on the cover of the spring 2023 edition of Green & Healthy Maine HOMES.
PHOTOS: JEFF ROBERTS IMAGING
This article appeared in the Spring 2023 edition of Green & Healthy Maine HOMES. Subscribe today!
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