Planning An Extension

Did you know that there's usually a sewer pipe that runs under your garden that you don't necessarily own? 

Did you know that this same sewer pipe takes your dirty dish water and also gets rid of your poo?

Did you know that in the 1950's nobody gave a crap about where these pipes ran or how deep they were?

If you answered no to these three items, then welcome to my voyage of discovery! I found all the rules, permissions and who needs to know what to be a bit confusing so I'm going to try and help anyone who reads this in the future by breaking this down to the major stakeholders...

The Neighbours

Specifically, the Party Wall Act. My starting position was definitely "WTF, how on earth do I know if it's a party wall or not?!". Well allow me to explain:

A party wall is a wall that is shared between two properties. Literally shared. So both properties would have to rely on a single wall for their structure to stay upright. This is not the same as having two extensions butting up against each other at the property boundary - these are two separate walls that each provide support to their own structures. 

Equally, we're not planning on building over/under the property boundary nor undermining any of our neighbours foundations - thus the Party Wall Act does not apply in our case. So that's a few thousand pounds that don't need to be spent!

The Water Company

Back in 2011, the water companies took ownership of shared sewer pipes. So they'll want to know if you're building over or near any of these pipes and what mitigation you're going to put in place to stop them getting wrecked. From what I've read so far, this seems to be just providing photos rather than having a physical inspection. 

But again, WTF defines a shared sewer?! Here's a handy simplified drawing to show the principle (for a more detailed guide, see here):

Orange lines are the responsibility of the water authority (i.e. shared) while pink lines are the responsibility of the property owner (i.e. private)

In the more complex situations, they may ask for a new inspection chamber to be added too. And, of course, there's a fee you have to pay for you to provide them with all this information. Yes, you read that right - you do all the legwork, they charge you a fee.

The Local (Planning) Authority

Planning Permission, Prior Notice or Permitted Development?

Whatever path you're on, it's going to involve money going to your local authority. In our case, we're going the Prior Notice path. This means that we can extend out a little further than the 3m allowed under Permitted Development rules but we don't have to apply for full planning permission. 

We'll also have to submit our plans to Building Control who just want to make sure that we're keeping to modern standards and not creating a death trap. I believe this also requires site inspections during construction but they don't come cheap. Hopefully this won't be too much of a burden.

The Role of the Architect

What I didn't realise is that there are (effectively) two sets of drawings required. A less detailed set for the Prior Notice application and a more detailed set for building control (this last set is also used to get quotes from builders).

The architect will design the structure of the extension, taking into account the latest building standards, doing calculations on airflow, light, thermal efficiency etc. Unless you pay extra, they aren't going to be drawing the locations of the plumbing or electrics or anything like that.

I read that architects like to know the budget so that they can design something to meet your requirements but also for it to be within your means. The ones we are using didn't care about the budget and so I'm now in the scary situation of having designed an extension without knowing how much it will cost to build it.