1. Decide How You Will Use the Deck Before Choosing Its Size

Do not begin with:

“We want a 16-by-20 deck.”

Begin with:

“What needs to happen on this deck?”

Possible uses include:

• outdoor dining;
• grilling;
• family seating;
• entertaining;
• container gardening;
• morning coffee;
• children playing;
• access to the yard;
• covered outdoor living;
• a future outdoor kitchen.

The deck dimensions should come from those activities.

Measure the Furniture, Not Just the Yard

A dining table does not only need space for the table.
It needs:

• chairs;
• space behind occupied chairs;
• walking space;
• access to the house;
• access to stairs or other deck zones.

The same applies to lounge furniture.
A deck can look large on a plan and feel cramped once a sofa, dining table, grill and circulation route are added.

Better Planning Method

Place the major furniture on a scaled plan first.
Then establish the deck perimeter.
Furniture → circulation → deck dimensions
is more reliable than:
deck dimensions → hope everything fits

2. Plan the Deck Around the House

A deck is not an isolated structure.
It becomes part of the circulation of the home.
Consider:

• which interior room opens to it;
• door location;
• door swing;
• kitchen proximity;
• grilling route;
• dining route;
• views from inside;
• stairs to the yard;
• privacy from neighboring properties.

Kitchen Access Matters

If the deck is primarily for dining or grilling, direct access from the kitchen or main living area can reduce unnecessary traffic through the house.
Ask:

• Where will food travel?
• Where will hot dishes travel?
• Where will trash return?
• Does the door create a bottleneck?

Plan the deck as an extension of the indoor circulation.

3. Study the Site Before Drawing the Final Layout

A deck should respond to the actual property.
Review:

• ground slope;
• drainage patterns;
• trees;
• neighboring windows;
• existing retaining walls;
• property lines;
• views;
• sun;
• shade;
• existing utilities;
• areas that stay damp.

Seattle’s permit process can become more involved when environmentally critical areas or significant site conditions are present. Deck projects in or near an ECA require a pre-application site visit before the permit application proceeds. (Seattle.gov)

Important Planning Question

What does this site want the deck to do?

A steep site may support an elevated or stepped solution.
A flat backyard may work better with a low platform.
A property with an important view may require careful railing and seating orientation.

4. Check Seattle Deck Permit Requirements Before Finalizing the Design

This needs to happen early.
Seattle currently requires a deck permit when the deck is:

• more than 18 inches above the ground;
• a roof deck;
• located in an environmentally critical area. (Seattle.gov)

Most qualifying decks can use a Subject-to-Field-Inspection construction permit, but not every project qualifies. (Seattle.gov)

When Can a Deck Need a More Extensive Permit Review?

Seattle currently identifies several conditions that can move a deck into the addition/alteration permit process, including a deck that:

• exceeds 8 feet above the ground;
• includes beams 14 feet or longer;
• is a roof deck;
• is in an environmentally critical area;
• uses solid-surface deck flooring without gaps;
• exceeds 750 square feet. (Seattle.gov)

That last point matters for drainage planning.
A conventional deck with water-draining gaps between boards and a solid-surface elevated deck are not automatically treated the same.

5. Deck Height Can Affect More Than the Permit

Height influences:

• structure;
• stairs;
• railings;
• views;
• privacy;
• usable space underneath;
• permit requirements;
• lot coverage;
• setbacks.

Seattle currently requires guards when a deck is more than 30 inches above adjacent surfaces. For applicable residential decks, Seattle lists a minimum guard height of 36 inches and limits guard openings to 4 inches. (Seattle.gov)
Do not finalize the deck elevation without also looking at railing and stair implications.

6. Plan the Structural Loads Before Adding Special Features

Do not design the frame first and decide later that you want a heavy feature.
Possible high-load features include:

• hot tubs;
• large masonry or stone elements;
• certain outdoor-kitchen components;
• unusually heavy planters;
• specialty structures.

Seattle currently specifies a 60-pound-per-square-foot minimum live-load design for decks. That does not mean every standard deck is automatically suitable for every concentrated or specialty load. (Seattle.gov)

Planning Rule

If a hot tub or another major load is even a realistic future possibility, say so during structural planning.
Do not wait until after the deck is built.

7. Decide How the Deck Will Connect to the House

An attached deck may use a ledger connection to the house.
This is a structural and water-management detail.
Seattle specifically requires deck ledger connections to be designed so the deck will not pull away from the house during an earthquake, with prescriptive provisions available in the Seattle Residential Code or an engineered alternative. (Seattle.gov)
Planning should also address how water is managed where the deck meets the building.

Important Question

How are structure and moisture protection being coordinated at the house connection?

Do not treat those as two unrelated details.

Where deck attachment affects exterior cladding, coordinate the detail with any planned Seattle siding replacement before construction begins.

8. Choose Decking Material Based on Maintenance, Not Appearance Alone

There is no universal “best decking material for Seattle.”
The better choice depends on:

• appearance;
• maintenance tolerance;
• sun exposure;
• tree cover;
• moisture;
• budget;
• desired board texture;
• product-specific installation requirements.

The main material families commonly considered include:

• pressure-treated wood;
• Western Red Cedar;
• composite decking;
• PVC decking.

Pressure-Treated Wood: When Does It Make Sense?

Pressure-treated lumber can be useful where initial material cost is an important consideration and natural wood maintenance is acceptable.
Evaluate:

• appearance;
• drying and weathering;
• finishing expectations;
• board quality;
• fasteners;
• ongoing maintenance.

Do not choose it only because of the initial material price.
Ask how you want the deck to look and how much maintenance you are willing to perform several years from now.

Western Red Cedar: When Does It Make Sense?

Western Red Cedar can be a good fit when the homeowner wants:

• natural wood appearance;
• visible grain;
• a traditional Pacific Northwest material;
• the ability to stain or finish the deck.

But natural wood still needs maintenance.
The Western Red Cedar Lumber Association states:

“A deck that dries after wetting will last longer than one that stays damp.”

Its maintenance guidance also emphasizes drainage, ventilation and keeping leaves, dirt and other debris from trapping moisture against the deck. (Real Cedar)

Cedar Planning Question

Do you like natural wood enough to accept its cleaning and finish-maintenance requirements?
If not, compare manufactured decking before committing.

Composite Decking: When Does It Make Sense?

Composite can make sense when reducing refinishing work is a high priority.
But low maintenance does not mean no maintenance.
Trex, for example, states that all exterior building materials require cleaning. Its current care guidance recommends product-appropriate cleaning and notes that dirt and organic debris can support mold growth if allowed to remain on the surface. (Trex)
Evaluate composite based on:

• board appearance;
• texture;
• color;
• product line;
• heat exposure;
• cleaning requirements;
• scratching characteristics;
• installation instructions;
• warranty terms.

Do not evaluate “composite” as if every manufacturer’s product were identical.

PVC Decking: When Does It Make Sense?

PVC decking is another manufactured option worth evaluating when moisture resistance and reduced refinishing are priorities.
But the framing, spacing and installation still need to comply with:

• local structural requirements;
• the exact manufacturer’s instructions;
• product-specific expansion and spacing requirements.

A low-maintenance surface does not eliminate the need to properly design the structure underneath it.

9. Design Drainage Before You Pick the Final Details

This is one of the most important parts of Seattle deck planning.
Water management is not one detail.
It is a system.
Think about at least six areas:

1. deck-board drainage;
2. framing moisture;
3. house connection;
4. ground drainage;
5. space below the deck;
6. solid-surface or covered conditions.

Seattle’s new 2026 Stormwater Code and Manual became effective July 1, 2026 for applicable new applications, so project-specific stormwater requirements should be checked against the current code rather than an old deck article. (Seattle DCI)

10. Deck Boards Need a Water-Drainage Strategy

For conventional open deck surfaces, properly designed gaps between boards allow water to pass through.
Do not copy one universal gap dimension from an article.
Spacing depends on:

• decking product;
• installation temperature;
• material expansion and contraction;
• fastener system;
• manufacturer requirements.

For example, TimberTech’s current installation guidance calls for product-appropriate spacing and describes typical side-to-side spacing in the 1/8- to 1/4-inch range for relevant products. (TimberTech)

Better Rule

Follow the exact manufacturer’s current installation instructions for the product being installed.
Do not apply one composite manufacturer’s spacing to another product.

11. Do Not Use a Universal “Slope Every Deck X Inches Per Foot” Rule

This is an important correction to generic deck advice.
Open-board decks and solid-surface decks manage water differently.
A conventional deck may rely substantially on:

• board gaps;
• drainage beneath;
• flashing;
• framing protection;
• site drainage.

A waterproof or solid walking surface has a different drainage strategy.
Seattle even treats solid-surface deck flooring as one of the conditions that can require the more extensive addition/alteration permit process. (Seattle.gov)

Planning Question

What type of deck surface are we building, and exactly how is that system designed to remove water?

Answer that before assigning a generic slope.

12. Protect the Framing From Repeated Moisture

The surface boards are only the visible part of the deck.
Below them are:

• joists;
• beams;
• rim members;
• hardware;
• connections.

Water passing through board gaps can repeatedly wet this structure.
Depending on the selected construction system, moisture-management measures can include properly detailed flashing and products designed to protect vulnerable framing locations.
For example, Trex describes butyl joist/beam tape as a method for reducing water penetration around wood framing and fastener penetrations. (Trex)
That is a product-specific option, not a substitute for correct structural design or code compliance.

13. Decide What Should Happen Under an Elevated Deck

This decision changes the drainage design.
Ask:

Is the Space Below Only Landscape?

Then water may be allowed to pass through the deck, provided the ground and overall site drainage are properly addressed.

Will the Space Below Be Storage?

You may want better water control.

Will It Become a Patio or Outdoor Room?

An under-deck drainage system may become part of the design.
Systems such as Trex RainEscape are specifically designed to collect water below deck boards and direct it away so the area beneath an elevated deck can remain drier and more usable. (Trex)

Important

Make this decision before framing and drainage details are finalized.
Adding a dry-under-deck strategy after construction can be less straightforward than designing for it from the beginning.

14. Manage Water at Ground Level Too

Do not focus entirely on the deck boards.
Look underneath.
Ask:

• Does water collect near footings?
• Does the soil slope toward the house?
• Does runoff concentrate beneath stairs?
• Will downspouts affect the deck area?
• Will landscaping trap moisture?
• Will leaves accumulate under a low deck?

Seattle’s current permit/pre-application process can specifically identify drainage patterns and site conditions during required site review for applicable projects. (Seattle.gov)
Water management should therefore include both the structure and the site.

If surrounding grade and hardscape direct water toward the house, include retaining walls and pavers in the broader site-drainage discussion.

15. Ventilation Matters for Low Decks

A low deck may have limited airflow underneath.
That matters particularly for wood framing and natural wood decking.
Western Red Cedar maintenance guidance specifically recommends allowing adequate drainage and ensuring under-deck ventilation is not obstructed. (Real Cedar)
Avoid creating conditions where:

• wet leaves accumulate;
• soil sits against wood;
• dense vegetation blocks airflow;
• stored items prevent drying.

16. Plan Stairs Around Where People Actually Need to Go

Stairs should not be placed simply where they are easiest to draw.
Ask where people are going after they leave the deck.
Possibilities include:

• lawn;
• garden;
• driveway;
• lower patio;
• side yard;
• detached garage.

Then evaluate:

• traffic path;
• landing space;
• safety;
• railing;
• lighting;
• grade.

Seattle currently lists residential stair criteria for applicable decks, including minimum tread and maximum riser requirements and handrails for stairs with four or more risers. (Seattle.gov)
Final dimensions should follow the code applicable to the actual project.

17. Choose Railings After Studying the View

Railings affect much more than safety.
They affect:

• sightlines;
• privacy;
• architectural style;
• maintenance;
• budget.

Possible approaches can include:

• wood;
• metal;
• mixed-material railings;
• cable systems;
• glass.

Do not choose a railing from a sample board before standing where the finished deck will be.

Sightline Test

Stand or sit at the likely seating position.
Ask:

• Where will the top rail cross the view?
• Will vertical elements block an important sightline?
• Is privacy more important than openness?
• Will the railing be difficult to maintain in this location?

Seattle also has specific guard requirements and additional requirements for glass guards, which can require project-specific engineering. (Seattle.gov)

18. Plan Privacy From the Seating Position

A privacy screen can look correct on a plan and fail when people sit down.
Study:

• neighboring windows;
• upper floors;
• adjacent decks;
• nearby streets;
• side-yard views.

Possible solutions include:

• screen panels;
• planting;
• trellis elements;
• railing design;
• deck orientation;
• partial enclosure.

Do not automatically surround the entire deck with privacy screening.
Block only the sightlines that need it.

19. Plan Sun and Shade Before Adding a Cover

Before choosing a pergola or roof, observe the site.
Look at:

• morning sun;
• afternoon sun;
• summer exposure;
• tree shade;
• prevailing rain exposure.

A roof or cover can affect:

• natural light inside the house;
• deck drainage;
• structural design;
• permits;
• attachment to the house.

Treat a covered deck as a design decision, not an accessory added after the deck footprint is finalized.

When a permanent roof or covered structure connects to broader interior work, coordinate it with any home-addition planning at the design stage.

20. Plan Lighting Before Construction

Deck lighting can serve three different purposes.

Safety Lighting

Useful at:

• stairs;
• level changes;
• entrances;
• walking paths.

Task Lighting

Useful around:

• grilling;
• outdoor kitchens;
• dining.

Ambient Lighting

Can support:

• seating;
• evening entertaining;
• architectural emphasis.

Plan wiring and fixture locations while access is easy.
Do not wait until finished decking and trim make routing more difficult.

For circuits, controls and exterior fixtures, review CHC Remodeling’s Seattle exterior electrical work.

21. Plan Grilling and Outdoor Cooking Carefully

If grilling is one of the main uses, identify the grill location during layout planning.
Consider:

• circulation;
• distance from the door;
• work surface;
• storage;
• nearby combustible materials;
• manufacturer-required clearances;
• smoke movement;
• utility needs.

For a larger outdoor kitchen, determine early whether you need:

• electricity;
• gas;
• water;
• drainage.

Those requirements can affect framing and construction sequencing.

22. Do Not Add a Hot Tub to the Plan at the End

A hot tub can introduce a concentrated load far beyond normal furniture.
If one is planned—or realistically may be added later—tell the designer or structural professional before the deck framing is finalized.
Seattle’s standard deck live-load requirement should not be interpreted as automatic approval for a filled spa or other major concentrated load. (Seattle.gov)

Rule

Design the structure for the feature.
Do not buy the feature and then ask whether the existing structure can support it.

23. Match Board Direction to Structure and Appearance

Board direction affects:

• visual proportions;
• framing orientation;
• transitions;
• waste;
• border details;
• manufacturer spacing requirements.

Diagonal or complex patterns can require different framing support than a simple perpendicular layout.
Do not choose a decorative board pattern after the framing design is already complete.
The decking design and framing design need to be coordinated.

24. Plan Maintenance Before Choosing the Material

A material is not right for your deck if you are unwilling to maintain it properly.

Natural Wood

Expect ongoing inspection, cleaning and finish maintenance appropriate to the exact material and finish system.
Western Red Cedar guidance emphasizes keeping surfaces free of dirt, leaves and debris, maintaining drainage and ventilation, and maintaining exterior finishes as required. (Real Cedar)

Composite

Composite avoids the same staining/refinishing cycle as natural wood, but it still needs cleaning.
Trex specifically states:

“All exterior building materials require cleaning.”

Its maintenance guidance recommends removing dirt and organic debris using product-appropriate methods. (Trex)

Better Material Question

Don’t ask:

“Which deck requires no maintenance?”

Ask:

“Which maintenance routine am I realistically willing to perform?”

25. Create a Seattle Deck Maintenance Routine

Regardless of surface material, visually inspect the deck regularly.
Pay attention to:

• trapped leaves;
• blocked drainage gaps;
• loose components;
• railing movement;
• damaged boards;
• visible fastener problems;
• moisture-trapping planters;
• areas that stay wet unusually long.

For natural wood, follow the selected finish manufacturer’s maintenance instructions.
For composite or PVC, follow the exact decking manufacturer’s cleaning and care guidance.
Do not use one generic pressure-washing recommendation for every deck surface. Different products have different limitations. Trex, for example, permits certain pressure-washing methods on some current product lines but specifically warns against them on some older products. (Trex)

26. Plan for Leaves, Moss and Organic Debris

A shaded deck under mature trees will behave differently from a deck in open sun.
Leaves and needles can:

• block gaps;
• hold moisture;
• collect against posts;
• accumulate under furniture and planters.

Natural-wood industry guidance emphasizes removing this debris so the deck can drain and dry properly. (Real Cedar)
If the site has substantial tree cover, maintenance access deserves consideration during design.

27. Plan Planters Without Creating Permanent Wet Spots

Large planters can trap water and organic debris beneath them.
If you plan container gardening:

• identify planter locations;
• consider drainage;
• avoid blocking critical deck drainage paths;
• allow access for periodic cleaning;
• consider the loaded weight of very large planters.

Western Red Cedar maintenance guidance specifically recommends moving planters and other accessories periodically so areas underneath can dry. (Real Cedar)

28. Make Deck Decisions in the Right Order

Do not begin with railing color or decking samples.
Use this order.

Step 1: Use

What will happen on the deck?

Step 2: Furniture

What physically needs to fit?

Step 3: Site

Study grade, doors, views, privacy and drainage.

Step 4: Permit Feasibility

Check height, location, ECA conditions and permit path.

Step 5: Structure

Determine loads, framing concept and house connection.

Step 6: Drainage

Decide how water moves through and away from the deck.

Step 7: Decking Material

Choose based on appearance, maintenance and installation requirements.

Step 8: Stairs and Railings

Coordinate safety, access, views and privacy.

Step 9: Utilities

Plan lighting and any outdoor-kitchen requirements.

Step 10: Details

Finalize board pattern, trim, color and accessories.

Expert Planning Insight

The visible material should not determine the project before the site, structure and drainage have been resolved.