Multi-level decks are an exciting addition to almost any outdoor area. It gives the possibility to split the deck in multiple areas with different purposes. For example, the first level would be for hanging out with friends and family, the second level for cooking out like grilling and dining, and if there is a third level it could be used for sunset/sunrise time where you can enjoy your morning coffee or your late-night tea.
When it’s time for a new complex deck like this, you as a homeowner always want it to be done right the first time. These 10 mistakes are what you can watch out for, they are also useful for a beginner deck builder who is trying to get into the decking industry and wants to know more about what the most frequent mistakes are made by professionals in this business so that he can avoid them. Let’s get right into it.
1. Ignoring Proper Structural Support
The structure mistakes that most deck builders make is that they miscalculate the weight loads or by using undersized beams. A multi-level deck is a complex structure, and it has to be done right so that it can support beams, posts and joists. One thing that leads to these issues is that builders sometimes don’t even check the manufacturer load charts the local building codes.
Tip: Use concrete footings that extend below the frost line and properly size your beams for each deck level.
2. Skipping Flashing and Waterproofing
Water intrusion can quickly damage the structure beneath a composite deck. Many builders neglect flashing at ledger boards or fail to waterproof connections, leading to rot in supporting wood components.
Tip: Install proper metal flashing at all ledger connections and consider a waterproof membrane under elevated areas.
3. Incorrect Joist Spacing
Like we mentioned in the mistake # 1, amateur contractors don’t even check the manufacturer recommendations. An expert deck builder will always start with that because composite boards are a lot less flexible than wood boards, but they still need joist space to prevent bowing or cracking. All these brands like Decorators, TimberTech, or Trex, have different recommendations for their products.
Tip: Always follow the manufacturer’s recommended span tables, and never assume standard wood spacing works for composite boards.
4. Improper Fastening Methods
Composite decks come with hidden fasteners, or special screws. If your contractor will use the wrong screws, these can cause cracks, board splitting, or they can pop over time.
Tip: Use screws and fasteners recommended by the composite manufacturer and pre-drill when necessary.
5. Expansion Gaps
Another big mistake is that deck builders install the composite boards too close to each other. These boards like wood, expand and contract depending on the temperatures. Make sure they are places at the right distance so that don’t warp or buckle.
Tip: Leave proper spacing between boards and at all edges, following manufacturer specifications.
6. Failing to Plan for Drainage
Water pooling can damage fasteners and cause mold or mildew buildup. Multilevel decks are particularly susceptible if the upper deck drains onto the lower deck without proper planning.
Tip: Design a slight slope for water runoff and ensure water does not drain directly onto lower-level decking or structural posts.
7. Overlooking Stair and Railing Requirements
The stairs are part of the safety that builders underestimate. Multi-level outdoor constructions have lots of stairs and they have to be safe. Make sure they are installed at the right height. Check the baluster spacing because all these can cause a code violation.
Tip: Check local building codes and use composite-compatible railing systems designed for multilevel use.
8. Ignoring Deck Footprint and Layout Challenges
A multilevel deck is more than just stacking platforms. Poor planning can lead to awkward transitions, unusable spaces, or insufficient headroom between levels.
Tip: Sketch the full layout and account for clearances, stair locations, and furniture placement before building.
9. Not Accounting for Weight of Furniture and Accessories
Composite decking is sturdy, but a multilevel deck supporting heavy furniture, hot tubs, or planters can exceed weight limits if not engineered correctly.
Tip: Factor in live load capacities for each deck level and overbuild supports if planning to place heavy items.
10. Neglecting Maintenance Access
Your composite deck needs less maintenance than a wood deck, but you still have to maintain it by cleaning, by checking the fasteners and by inspecting the under-deck area. Some builders don’t keep these things in mind for different reasons, and they might end up in creating spaces that are hard to access when you need to do maintenance.
Final Ideas
A multi-level deck is a big investment when you hire a decking company, make sure they know their job. These 10 mistakes are all written based on multiple complaints from homeowners online and were also inspired by other builders like the Wolf Spirit Deck outdoor living contractors.
Keep an eye on the project and if you see something is going wrong ask your current contractor about it. Keep in touch with them in a friendly way.
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