Where should the holes be on a French drain?

Author: Prof. Jovanny Dare V  |  Last update: Monday, June 16, 2025

The drain holes on your pipe should face down if the pipe is half perforated.

Should a French drain be perforated?

French Drain Pipe Characteristics

Regardless of what the pipe is made of, it must be slotted or perforated at regular intervals to allow water to enter and flow through the system.

What is the spacing for perforated pipe holes?

Pipe Dimensions

In addition, the perforations on the pipe should have a specific size, spacing, and pattern. The hole size should be between 1/8 inch and 1/2 inch, and the spacing should be between 4 inches and 24 inches. The hole pattern can be customized based on the application requirements.

How to position a French drain?

Make sure to place the pipe with the drainage holes facing downward — so that it's in contact with the gravel and away from the foundation — so it'll pull the water down. Test the drain flow by running water into the basin with a hose.

What are weep holes for French drain?

The weep holes are to prevent the water from building up on the outside of the wall, when that happens it'll eventually wick through higher up or develop hydro-static pressure which can put quite a bit of force on the wall and lead to other problems, the holes just allow the water through easily which doesn't hurt the ...

HOW A FRENCH DRAIN WORKS

Where do the holes go on a French drain?

Lay the connected pipe structure in the trench on top of the layer of crushed stone, and make sure the drainage holes in the perforated pipe are pointed downward.

Where should weep holes be located?

Gravity draws water to the bottom of the wall, just above the foundation, where weep holes allow it to escape. They are located above all windows, doors, and other openings. Weep holes are also located on window tracks.

Do you need to put gravel under a French drain?

A French drain needs to be surrounded by gravel in order to filter out silt and prevent clogging the drain pipe.

Should a French drain have standing water?

Crawl Space French Drains and Interior Drainage Systems

Standing water can have many adverse effects on your home's foundation and structural integrity if left unattended.

How do I know if my French drain is working?

To test the condition of your French drain, you need to find the ground-level access point, which is usually an above-ground grate or the end-point of a downspout or an above-ground pipe. Running a hose down the pipe will show how effectively the drain is working.

Should French drain holes go up or down?

Contrary to popular opinion, the most effective method is to have the holes facing down.

What is the distance for perforation?

Recommended distance between the holes is by default minimum 2 x the plate thickness. Depends on the desire for design and function. The recommended standard is min. 2 x plate thickness.

Where not to put a French drain?

Clay soil has poor permeability, meaning it doesn't allow water to pass through easily. In such cases, the effectiveness of a French drain may be limited as the water may struggle to drain away from the area efficiently. French drains may not be suitable for areas with high water tables.

Does a French drain need an inlet?

A French Drain Done Right Does Not Need Inlet Drain to Take in Surface Water. Here's a completed French Drain, with the last piece of sod yet to be put in. You can see how the channel, full of stone and pipe, is fully contained by a filter fabric.

Why do French drains fail?

Clogging and Blockages

Clogging is one of the leading causes of French drain failure, often due to root intrusion or sediment build-up.

Do you need a permit for a French drain?

If installing the drain involves diverting a stream or affecting a wetland, you likely need a permit to move forward. Generally, a small French drain on your property that doesn't change the flow of runoff entering and exiting your yard won't need a permit.

What is the average cost of putting in a French drain?

Installing a French drain costs $500 to $18,000, with a national average of $9,250. On average, you can expect to pay $10 to $100 per linear foot, or between $500 and $5,000 to have a 50-foot French drain installed.

How far off the ground should weep holes be?

As a general guide weep holes at floor level should be a minimum of 75mm above finished ground levels.

What do weep holes look like?

Weep holes in brick look more like places where the brick mortar appears to be missing in between two bricks. The vertical line of mortar will strategically not be there where two bricks meet. The mortar is not missing, it's not there on purpose and leaves an opening in the wall structure.

Can I drill my own weep holes?

It is difficult to add weep holes after the walls are constructed. If the weep holes are drilled, they will typically puncture the flashing. This is true even if a special guide is placed on the drill. If the hole does not go all the way through the mortar then it will be ineffective.

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