Planning a New Deck in Upper Merion Township

A deck looks simple from the yard: posts, joists and boards. Most of what makes it safe and long-lasting is hidden. The footings, the connection to the house and the flashing behind the ledger decide whether a deck stays solid for decades or starts to sag, rot or pull away from the wall.

This guide covers what homeowners in King of Prussia and the rest of Upper Merion Township should think through before a new deck is built: the permit process, footings and frost depth, how the deck attaches to the house, what sloped lots change, and how to choose materials.

Permits in Upper Merion Township

Pennsylvania adopted the Uniform Construction Code (UCC) statewide, and Upper Merion Township administers building permits and inspections for projects within the township. Decks attached to a house, and decks raised above a certain height, generally need a building permit under the UCC. Some low, freestanding platforms may be exempt, but the exemption has specific conditions, so it is worth checking rather than assuming.

A deck permit application typically includes a site plan showing where the deck sits on the lot and how far it is from property lines, and construction drawings showing footing size and depth, post, beam and joist sizes, spans, ledger attachment, guards and stairs. The township reviews the plans and schedules inspections during construction.

Zoning also applies. Setbacks from property lines and limits on lot coverage can affect how large the deck can be and where it can go. If your home is in a townhome community or a neighborhood with an HOA, the association may also require its own approval for size, materials and color, separate from the township permit.

Contact the township's building and code office early in the planning process. Rules change, and the township is the final word on what your specific design requires.

Footings and frost depth

Southeastern Pennsylvania gets repeated freeze-thaw cycles each winter. When soil freezes, it expands and can lift anything resting on it. A deck footing has to bear on soil below the frost line so the deck does not heave up and settle back unevenly year after year.

The required depth is set by the local building code. It is commonly 36 inches in this part of Pennsylvania, but confirm the number for your permit. Footings are usually poured concrete, either in round forms or as a pad under a post base. Their size depends on the load they carry and the soil. Most jurisdictions inspect footing holes before concrete is poured.

Call before you dig

Pennsylvania law requires notifying PA One Call (dial 811) before digging, so gas, electric, water, cable and other underground lines can be marked. Lines are often shallower than people expect, and a footing hole is exactly the kind of digging that hits them. Private lines, such as a buried line to a shed or a sprinkler system, are not marked by the utilities and should be located separately.

Attaching the deck to the house

The ledger is the board bolted to the house that carries one side of the deck. Ledger failures are one of the most serious deck problems, so this connection gets close attention from inspectors.

A proper ledger is fastened to the house's band joist, the solid framing at the floor level, with through-bolts or structural screws in a specified pattern. It is not nailed on, and it is not attached to siding, brick veneer or an overhanging cantilever. Flashing goes above and behind the ledger so water running down the wall is directed out over the deck framing, not into the house.

Brick and stone veneer walls

Many split-levels and colonials in King of Prussia have brick or stone veneer on part of the rear wall. Code does not allow a ledger to hang on veneer, because veneer is a facing, not a structure. The options are to remove a strip of veneer and attach the ledger to the framing behind it with proper flashing, or to build the deck freestanding with its own row of posts next to the house. Freestanding decks avoid penetrating the wall but need more footings and lateral bracing.

Sloped lots and walkout lower levels

Parts of Upper Merion are hilly, especially the neighborhoods rising toward Valley Forge National Historical Park and around Gulph Mills and the ridges above the Schuylkill. A yard that drops away from the house changes several things:

• Taller posts need to be sized and braced for their height.
• Stairs get longer and may need a landing partway down.
• Guards are required along any open side more than 30 inches above the grade below.
• The space under a high deck becomes usable, which raises questions about drainage, lighting and whether to add an under-deck ceiling.
• Footings on a slope need to be deep enough on the downhill side, not just measured from the high point.

Choosing materials

Material choice affects cost, upkeep and how the deck looks in ten years.

Framing

Almost all residential deck framing uses pressure-treated lumber rated for ground contact where required. Joist hangers, post bases and other connectors should be rated for use with treated lumber, typically hot-dip galvanized or stainless. Some builders add joist tape over the tops of joists to shed water from fastener holes. Whether the decking is wood or composite, the frame underneath is still wood and needs to be built well.

Decking

Pressure-treated decking costs less up front and can be stained any color. It needs cleaning and resealing every few years, and boards can check, cup or splinter over time. Composite and PVC decking cost more but do not need staining and resist rot. They can still get surface mildew, especially in shaded yards, and most require closer joist spacing and a minimum ventilation gap underneath, which matters for low decks. For a deeper comparison, see composite vs. pressure-treated decks in Pennsylvania.

Railings

Railings can be wood, composite, aluminum or cable systems. Guards have to meet code height and opening requirements, and posts have to be attached strongly enough to resist a lateral load. Manufactured railing systems come with tested post-mounting details, which simplify inspection.

What drives the cost of a deck

The biggest factors are size, height and complexity. A deck close to the ground on a flat lot needs fewer, shorter posts and no guards. A second-story deck on a sloping yard needs taller posts, more bracing, longer stairs and guards all around. Decking and railing choices make a large difference, as does any work at the house wall, such as cutting back veneer or replacing damaged rim framing.

F2 Home Improvement recently added deck building to its services in the King of Prussia area. We plan each deck around your lot and the township's requirements and quote after a site visit. Learn more about deck building in King of Prussia, or contact us to set up a free estimate.

Frequently asked questions