Perimeter Drains: The System You Cannot See and Should Ask About

Perimeter drains sit buried around the base of a foundation and announce their condition through problems somewhere else. On a Fraser Valley home with any age on it, this is one of the systems worth asking about before you remove subjects.

What the system does

A perimeter drain is a pipe laid around the outside of the foundation at its base. It collects groundwater and carries it away before that water reaches the foundation wall. People also call it drain tile or a French drain.

The BC Building Code, Section 9.14 sets out the requirements. Sentence 9.14.2.1(1) requires that the bottom of every exterior foundation wall be drained by drainage tile or pipe laid around the exterior of the foundation, or by a granular layer, unless drainage can be shown to be unnecessary.

So it is a required system on most homes, which is useful to know when a seller suggests a particular house does not have one.

What the code specifies

Subsection 9.14.3 covers the pipe itself.

The drain tile or pipe shall be not less than 100 mm in diameter. It is laid on undisturbed or compacted soil, with the top of the pipe below the bottom of the floor slab or below the ground cover of the crawl space. Where butt joints are used, the code provides for 6 mm to 10 mm open joints with protective sheeting over the tops. Coverage is not less than 150 mm of crushed stone or other coarse clean granular material.

Acceptable materials in the code include clay drain tile, concrete pipe, vitrified clay, asbestos-cement, plastic, corrugated steel, and polyethylene pipe meeting the specified standards. That list matters to a buyer looking at an older home, because what is in the ground depends on when the home was built.

Article 9.14.5.1 covers the outlet: foundation drains shall discharge to a sewer, a drainage ditch, or a dry well. BC Housing publishes a Builder Guide to Site and Foundation Drainage that covers the installation side in more depth.

How these systems fail

Nothing about a buried pipe is permanent.

Sediment accumulates and reduces the flow. Roots find the perforations and grow into the line, which is the reason mature landscaping near a foundation is worth noticing. Sections settle or collapse, so the line no longer runs downhill the way it was laid. Older materials degrade.

The common thread is that water stops being carried away from the foundation and starts sitting against it. The drains rarely announce this. The basement does.

What a home inspection can and cannot tell you

A general home inspection is a visual assessment, and the drains are underground.

An inspector can note the things that suggest a problem: moisture in a crawl space, staining or efflorescence on foundation walls, grading that slopes toward the house, downspouts discharging at the foundation. Those are reasons to look further. An inspector cannot tell you the condition of the pipe, and a good one will say so and recommend a specialist.

That is the correct limit of the service rather than a shortcoming. Our home inspection guide covers the general scope, and this is one of several systems where a specialist adds what the general inspection cannot.

The scope is the answer

A drain scope runs a camera through the line so the pipe can be seen from inside.

It shows blockages, root intrusion, collapsed sections, and sediment. It is the only way to assess a buried line without digging, and relative to what replacement costs, it is inexpensive information.

On an older Fraser Valley home with any sign of moisture, arrange one during your subject period. Book it early, because specialist services take longer to schedule than a general inspection and our subject removal guide covers protecting enough time for exactly this.

The questions that cost nothing

Two things to ask on any older home, before you spend anything.

Where do the drains discharge? The code allows a sewer, a drainage ditch, or a dry well. The outlet is part of the system, and a blocked or failed outlet defeats a sound pipe upstream of it. Ask, and ask whether anyone has looked at it.

Where do the downspouts go? Roof water discharged at the foundation becomes a problem the perimeter drains then have to solve. This one is visible from the driveway and tells you something about how the home has been looked after.

Ask the seller whether the drains have ever been cleaned, scoped, or replaced, and whether there is paperwork. Our older home red flags guide covers the wider set of questions on an aging home, and our property disclosure statement guide covers where a seller's answers get recorded.

Crawl spaces tell you things

In the Fraser Valley, a crawl space is often where drainage problems first become visible.

Moisture, standing water, a musty smell, or staining on the foundation wall all point back toward water management outside the house. Our crawlspace moisture guide covers what to look for and what it means, and the perimeter drains are one of the systems on the list of possible causes.

Look in the crawl space. Buyers skip it because it is unpleasant, and it is one of the more informative parts of a showing.

Stratas: common property, shared bill

In a townhouse or condo complex, foundation drainage is typically common property.

That means the strata corporation is responsible for it, and the cost reaches owners through the operating budget, the contingency reserve fund, or a special levy. A drainage project across a complex is a substantial piece of work, which is why it belongs on your reading list rather than being treated as somebody else's problem.

Look for it in the depreciation report, which sets out the expected lifespan and replacement timing of common property components, and in the council minutes, where drainage complaints and quotes tend to appear well before any levy does. Our special levies guide covers what happens when the work gets approved.

The short version

Perimeter drains are required on most homes under BC Building Code Section 9.14, they are at least 100 mm in diameter under Subsection 9.14.3, and they discharge to a sewer, ditch, or dry well under Article 9.14.5.1.

They fail through sediment, roots, settlement, and age. A general home inspection cannot assess them because they are buried. A camera scope can, and it is worth booking on an older home with any sign of moisture.

Ask where the drains discharge, look at the downspouts, and look in the crawl space. In a strata, read the depreciation report and the minutes.

We are agents rather than drainage contractors or building inspectors, and none of this is a technical assessment. A qualified drainage contractor and a licensed home inspector are the right sources for a specific property.

Key takeaways

• BC Building Code Sentence 9.14.2.1(1) requires foundation drainage unless it can be shown to be unnecessary.
• Subsection 9.14.3 sets a minimum pipe diameter of 100 mm and requires the top of the pipe below the floor slab or crawl space ground cover.
• Article 9.14.5.1 provides that drains discharge to a sewer, drainage ditch, or dry well.
• A general home inspection cannot assess a buried line, so a camera scope is the way to get real information.
• In a strata, drainage is common property and the cost arrives through the budget, the reserve fund, or a levy.

Frequently Asked Questions

What is a perimeter drain?

A perimeter drain is a pipe laid around the outside of a foundation at its base, which collects groundwater and carries it away before it reaches the foundation wall. People also call it drain tile or a French drain. BC Building Code Section 9.14 covers foundation drainage requirements, and it is a required system on most homes, which is useful to know if a seller suggests a particular house does not have one.

Does the BC Building Code require perimeter drains?

Yes. BC Building Code Sentence 9.14.2.1(1) requires that the bottom of every exterior foundation wall be drained by drainage tile or pipe laid around the exterior of the foundation, or by a granular layer, unless it can be shown to be unnecessary. That makes perimeter drainage a required system on most homes rather than an optional upgrade, so a home without any drainage system at all is worth asking about specifically during your subject period.

What size is a perimeter drain pipe?

Subsection 9.14.3 of the BC Building Code specifies that drain tile or pipe shall be not less than 100 mm in diameter, laid on undisturbed or compacted soil with the top of the pipe below the bottom of the floor slab or the crawl space ground cover.

Where does a perimeter drain discharge to?

BC Building Code Article 9.14.5.1 provides that foundation drains shall discharge to a sewer, a drainage ditch, or a dry well. Where a specific home's drains actually go is worth asking about directly, because the outlet is part of the system, and a blocked or failed outlet defeats a sound pipe upstream of it. Ask the seller whether anyone has looked at the discharge point, since this costs nothing to ask and is easy to overlook.

Does a home inspection check the perimeter drains?

A general home inspection is visual, and perimeter drains are buried underground, so an inspector cannot directly assess the condition of the pipe. What an inspector can do is note the things that suggest a problem, moisture in a crawl space, staining on foundation walls, or downspouts discharging at the foundation, and recommend a specialist from there. Actually assessing the pipe itself requires a camera scope, which is a separate service worth booking on an older home with any sign of moisture.

What is a drain scope?

A drain scope is a camera run through the perimeter drain line so the pipe can be seen from the inside rather than guessed at from the surface. It shows blockages, collapsed sections, root intrusion, and sediment buildup, and it is the only way to assess a buried line without digging it up. Relative to what replacement costs, a scope is inexpensive information, which is why it is worth booking during your subject period on an older home showing any sign of moisture.

How do perimeter drains fail?

Perimeter drains fail in several ways over time. Sediment accumulates and reduces flow, roots find the perforations and grow into the line, sections settle or collapse so the pipe no longer runs downhill the way it was laid, and older materials simply degrade with age. The common thread across all of these is that water stops being carried away from the foundation and starts sitting against it instead, and the drains themselves rarely announce this. The basement or crawl space usually does.

What are the signs of a drainage problem?

Signs of a perimeter drain problem include water in a basement or crawl space, efflorescence or staining on foundation walls, pooling against the house, grading that slopes toward the building, and downspouts discharging right at the foundation. Each one is a reason to look further rather than a diagnosis on its own, since a general home inspection can note these visible clues but cannot assess the buried pipe itself. A camera scope during your subject period is what actually answers the question.

Do townhouses and condos have perimeter drains?

Yes, buildings of every type have foundation drainage, including townhouses and condos. In a strata, the drains are typically common property, which means the strata corporation is responsible for maintaining them rather than any individual owner. The cost reaches owners through the operating budget, the contingency reserve fund, or a special levy, so a drainage project across a complex is worth looking for in the depreciation report and council minutes before you buy.

Should I scope the drains before buying?

On an older home with any sign of moisture, arranging a drain scope during your subject period is worth the cost relative to what it can reveal. It is one of the few ways to get real information about a buried system you otherwise cannot see, since a general home inspection cannot assess the pipe's actual condition. Book it early, because specialist services like a drain scope take longer to schedule than a general inspection and your subject period may be short.

Sources

• BC Building Code, Section 9.14 Drainage, BC Publications
• Builder Guide to Site and Foundation Drainage, BC Housing

Verified September 12, 2026. General information only, not a drainage or building assessment. Code requirements vary by edition and by when a home was built. Consult a qualified drainage contractor and a licensed home inspector.

Related FRIVE guides

• Crawlspace moisture, where drainage problems show up first
• Home inspection guide, and where a general inspection stops
• Older home red flags, the wider condition list
• Strata depreciation reports, where common property drainage appears
• Subject removal in BC, leaving time to book a scope

Next Steps: Work with FRIVE

A scope costs a few hundred dollars and answers a question that otherwise costs tens of thousands to discover. On an older Fraser Valley home, it is one of the easier calls we make.

If you are looking at something with age on it, start a conversation with the FRIVE team and we will tell you which specialists are worth booking. Or browse current Fraser Valley listings to see what is out there.