Drainage for a granny annexe

[pasty_girl]

Hello,

We just got planning permission for an annexe in our garden after a year battle with planning, hurray!

So now we are thinking of the practicalities.

The annexe will be over 30m away from the main house. The house connects to the mains sewer via a manhole located in a shared drive at the front of our property. I have two questions:

1. What kind of professional would we need to do a site visit to advise re options for routing the waste water from the annexe to the mains sewer? (e.g. do we have enough drop in height over 30m for the pipework etc)

2. Will we need to pay a sewer connection charge to the water company or would it come under the house connection?

Forgive my ignorance. We do have a builder who will carry out the project but none of us have even done an annexe before!

Many thanks.

 

[wessex101]

1. Had a job recently where we couldn't connect to the existing foul drain as it was too high so I put in a small domestic sewage pump. It is a self contained unit about the size of a standard manhole buried in the garden. Cost about £1500. Different sizes available depending on height and distance you need to pump.

2. As its an annexe you should be able to connect to existing house drain.

 

[oldbutnotdead]

Last one first- presumably your annexe is on one of those 'can't be sold separately from the main house' type permissions? If so then there shouldn't be a charge from the drainage lot if all the pipework and the manhole are within your boundaries. Likewise with water. Though do be prepared to get smacked with a separate council tax bill for the place (even though you can't sell it without selling the main house).

Measuring up for fall- you can do that yourself with a cheap laser level, a dark night and some sticks (to determine the difference in ground level between the end of the garden and your manhole- the sticks are for intermediate levels, you won't get pinpoint accuracy but it'll be plus or minus 50mm). Then lift the manhole lid and measure how deep the bottom of it is below ground level. Minimum fall for 4" plastic is 1 in 80 so for 30 metres you only need about 400mm. Run the pipe in a straight a line as possible.

Your practicalities are going to go beyond drains though- how about electricity and gas? Annexes are normally attached to the main house so can share services (especially heating)- you need some expertise there straight away. If the intent is only to have 1 gas meter (in the main house) then the supply pipe to the main house may need upgrading- this is all specialist work by your gas supplier/distributor, definitely not DIY or builder. If you put all the heavy energy demands from the annexe (heating, cooking, hot water) on gas then you may be able to power the rest from the main house electrical supply without that being upgraded. Or you may not- depends how big the annexe is going to be and what final circuits you are providing.

If you're going for separately metered supplies to the place then you should already have had conversations with the utilities and will already have prices for the connections (in the thousands almost certainly, though if you can get them to share the drainage trench (assuming it goes deep enough) you should be able to reduce that cost).

 

[Footsoldier888]

Hi and congrats on the pp, must be exiting.

In some ways the answer to your question depends on your relationship with your builder as regards the whole project. Like you may have a very good relationship with your builder, in which case the drainage is something he can easily advise you on when he visits.

However some people prefer to work with an architectural technician say who would be able to draw up a good set of plans for you with the works detailed so that you could invite three builders to give you a price for the build.

Generally speaking it's a very good idea to get your building control drawings done at this stage so that all the services and building work is planned for.

A good starting point is to find the sewer and water connection map that you paid for when you bought the house, they can be quite useful.

I am no expert on this but I think the idea of an annexe is all the services are charged at the main house, I think you need to be really careful over this regarding the council tax. It is after all an annexe not a separate dwelling.

 

[pasty_girl]

Thanks very much everyone. Really appreciate these replies. We will be getting buildings regs drawings done now we have the planning permission so hopefully that will make things clearer. We have found it is a good idea to have a basic understanding ourselves of the issues involved though.

Yes we will have to pay council tax - love the fact council planning dept goes to great lengths to ensure it is not a separate dwelling whilst the council tax dept don't have any issues with charging It will be 50% rate though as the annexe is for a family member.

*oldbutnotdead* thanks for your thoughts on the services. We are not planning on running gas down to the annexe. We have been chatting to someone who works with pre insulated piped systems and we are considering running hot water direct from the house down there (in an underground pipe). We are still in the process of thinking this through and other ideas would be welcome!

 

[pasty_girl]

PS - house and garden are also having a complete overhaul (it's a big project) so electrics / boiler etc are all going to be upgraded anyway and digging up the garden won't be a big issue...

 

[Footsoldier888]

Good stuff

It's a very good move getting involved like this.

I have this book 'How to manage your builder' by Ashton Paul. Really good book as it tells you how to avoid all the common mistakes people make in the building process. There are a number of real life examples and a good case study.

Having a proper contract with your builder and spending money for good detailed plans can save a lot of hassle and money in the long run, making changes to the build during it can bump up the cost a lot.