Nobody looks at the drains when you buy a house. That is the point of a drain survey.

Here is something most buyers do not find out until it is too late. When you pay for a survey on a house, nobody looks at the drains. A mortgage valuation does not consider them at all. A level 2 homebuyer survey will typically do no more than lift a cover, note that a chamber exists and recommend further investigation. The pipes themselves, which are the expensive part, go uninspected.

When it is worth doing, and when it is not

We would not tell you to survey the drains on a five year old house with a plastic system and plans in the file. On these, we would:

• Anything built before about 1990. Clay before roughly 1970, pitch fibre through the 1960s and 70s, concrete in places. All three fail in their own way and all three are common across this patch.
• Anything with a pitch fibre run. It blisters and deforms rather than cracking cleanly, and once it has lost its shape it cannot be lined, only replaced. It is very common in 1960s and 70s estates in Basingstoke, Fleet and Camberley.
• Anything with an extension, conservatory or driveway over the drain run. Both because the pipe may have been damaged when it was built, and because getting to it later means taking the surface up.
• Anything with mature trees close to the run. Roots find clay joints. It is the single most common defect our camera finds locally.
• Anything on private drainage. A septic tank or treatment plant is a system you are buying outright, with its own compliance obligations, and it needs assessing as such.
• Anything where the neighbours share the run. You want to know what you are joining before you exchange.

What you should get for your money

This is where surveys differ enormously, and where price comparison is misleading. Some firms will run a camera down, tell you verbally what they saw, and call that a survey. That is an opinion. It is not evidence and it is no use to a solicitor.

What a survey worth paying for delivers:

• The full length of the runs walked with the camera, not just the first accessible section
• A written report with each defect described, located by distance from a known point, and coded against the standard sewer condition classifications
• Still images of every defect, so a third party can see what you are describing
• The video file handed over to you, to keep and to show anyone
• Both foul and surface water systems where they are accessible
• A note of any connection that is not yours, or any sign that a neighbour is connected into your run
• A fixed price for remedial work, so the report has a number attached rather than a worry

Coded defects matter more than they sound. A report saying “some cracking noted” is worth very little in a negotiation. A report locating a fracture at 8.4 metres from the rear chamber, with a still image and a severity grade, is a document your solicitor can raise an enquiry on and your seller has to respond to.

Using the report in the purchase

Once you have evidence you have three routes, and you should decide which one you want before you commission the survey.

1. Reduce the price. The strongest position, because you hold a dated report with a contractor's fixed price for the repair attached. It is difficult to argue with a number.
2. Ask the seller to fix it before completion. Cleaner, but slower, and you are relying on their choice of contractor and their appetite for doing it properly rather than cheaply. Ask for the post-repair footage.
3. Walk away. Rare, and normally only where the drainage problem is a symptom of something bigger, such as subsidence, or where the run is under a structure that would have to come down to reach it.

Two things the report might tell you that are good news

Not every defect is your problem, and this is where the 2011 sewer transfer becomes relevant to a house purchase. If the damaged length turns out to be a lateral drain, beyond your boundary, it is the water company's to maintain rather than the buyer's. A survey that establishes that has just saved you from paying for somebody else's pipe. Our guide on who is responsible for a blocked drain explains how the line is drawn.

The second is insurance. Many buildings policies cover damage to underground drainage, and some cover the cost of tracing it. Insurers want dated footage, still images and a report identifying and locating the defect. If you have that from before you exchanged, you are in a much better position later.

What it costs, and what happens next

Ring us with the address and we will price it for that property, because the figure depends on how many chambers there are and whether there is a separate surface water system. You get the price before we start rather than after, and there is no charge for the conversation.

A normal three or four bedroom house takes one to two hours on site, and the report follows the same day or the next working day, written to be read by a solicitor or a lender. If there is remedial work you get a fixed price for it on the day, and if you book that work with us the survey fee comes off it in full.

And if you would rather take the report to another contractor for the repair, that is entirely fine. It is your report, and it is written to be useful to whoever ends up doing the work.

Questions people ask

Where this comes from

The rules, fees and figures on this page are taken from the sources below. Fees change, so check the current figure before you send anyone money.

• Citizens Advice: who is responsible for repairing drains and sewers
• Planning Portal: Approved Document H, drainage and waste disposal

This is general information about how the rules work, not advice on your particular property. If something here matters to a purchase or a dispute, get it checked on your own facts.