Craft & DIY
Deck Substructure Planner
Plan the joist count and spacing for your deck substructure for a stable, safe terrace.
A stable deck depends on the right joist spacing. Enter length, width and joist spacing to determine the number of joists needed.
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Joists needed
Pro tips
- Choose tighter joist spacing for wood decks for better stability.
- Plan a slight slope so rainwater can drain away.
All calculations are non-binding estimates provided without guarantee. For safety-relevant decisions (e.g. pool chemistry), please consult a professional.
Frequently Asked Questions
What joist spacing is typical for a deck?
Usually 30-50 cm, depending on board thickness and type – thinner or more flexible boards need tighter spacing.
How deep should deck footings be?
Below the frost line, which usually means at least 80 cm deep depending on your region, so the substructure doesn't heave in freezing weather.
What wood is suitable for a deck substructure?
Pressure-treated wood or weather-resistant species like larch, Douglas fir, or WPC joists are common, since the substructure is permanently exposed to moisture.
Do I need a slope in the deck substructure?
Yes, a slight 1-2% slope away from the house lets rainwater drain off instead of pooling.