EXTERIOR
How to Estimate Retaining Wall Drainage
Contractor method to estimate drainage behind a retaining wall by wall length, drain pipe, gravel, fabric and labor with clear materials and labor lines.
Water is what kills a retaining wall, so the drainage is where a good bid earns its keep. Pipe, gravel, filter fabric and the labor to set them make up most of the price. This guide covers how to measure the wall, run the drain and quote the backfill so the wall stays dry behind the face.
THE SHORT ANSWER
How to Estimate Retaining Wall Drainage
A 40 ft wall with 20 ft of perforated drain, 1 ft of gravel, fabric and 10 labor hours at $70 totals about $3,420.
Measure the wall and the drain run
Drainage is priced by wall length. Measure the wall, then decide how far the perforated pipe has to run to a daylight outlet or catch point.
- Wall length
- Perforated pipe run
- Gravel volume
- Filter fabric
Gravel is the real backfill
Free-draining gravel behind the wall is what moves water to the pipe. Volume comes from the wall height and thickness, so it can surprise a low bid.
Filter fabric keeps the gravel clean
Fabric stops fine soil from clogging the stone. Skipping it saves a little now and shortens the wall's life, so keep it in the quote.
Compare drainage bids by scope
Get quotes that separate pipe, gravel, fabric and labor. Confirm the outlet and the slope of the pipe, then compare like for like.