Timber Retaining Wall Calculator
This calculator assists in estimating the materials required for building a timber retaining wall. By inputting the desired length, height, size of the retaining boards, and post spacing, you can quickly determine the number of posts, retaining boards, the total linear meters of boards,
Please Note: Walls with a height exceeding 1.5 meters require a building consent as per the New Zealand building code. Additionally, walls lower than 1.5 meters but subjected to extra loading, such as from a driveway, a building, or a steeply sloping bank, also necessitate a building consent. If unsure, it's advisable to consult your local council. It's essential to be aware that certain insurance policies may become void if retaining walls are not constructed and signed off correctly. In locations requiring a building consent, an engineer’s design certificate might also be necessary.
Retaining Wall Construction Guide:
Introduction:
A retaining wall can offer both functionality and aesthetic appeal for gardens or landscapes. It helps level sloping sections and shields earth banks.
Key Guidelines:
1 Height & consents
Walls over 1.5 m, supporting driveways, or under load from steep slopes require an engineer and building consent. All walls must comply with the NZ Building Code regardless.
2 Soil types
Best suited to firm gravel, stiff clay, sand, or rock. Soft clay, peat, or made-up ground requires an engineer's assessment before proceeding.
3 Timber spec
Posts and rails must be H5 treated. If copper-based treatment is used, fix with stainless steel nails — galvanised will corrode.
4 Post installation
Set posts in concrete with a slight lean toward the bank. Minimum 300 mm gap behind the wall face for drainage. For walls over 1.5 m, post depth must be engineer-specified.
5 Rail installation
Nail rails level, starting from the bottom and working up. Ensure boards are tight and properly fixed to each post.
6 Drainage
Critical — lay drainage metal, place drain coil at the base, wrap in geotextile fabric to prevent silting. Fill with scoria and compact. A 300 mm drainage gap against the wall face is the minimum.
Disclaimer:
Please Note: While this brochure's advice and recommendations have been crafted with care, it's intended to assist those interested in estimating projects. Aries Builders does not accept responsibility for the advice and recommendations contained herein.
Wall dimensions
Materials Needed Treated timber posts and rails, galvanized nails, concrete, drain coil, drainage metal, geotextile fabric, and timber preservative.
