Jons

Electrical - Western Power or Scottish Power depending on where you are in Ceredigion (roughly north for SP and south for WP). Water and Sewer - Dwr Cymru/Welsh Water Phone line - Open Reach Good luck with all of them on both costs and dealing with large organisations based in a universe far far away!!

As far as the roof cover is concerned I shouldn't worry about rabbits/rats etc. We have an old water tank with an earth cover and there has never been sign of them being interested despite rabbits in the field and rats near the adjacent stream. I don't think the earth is deep enough to be hospitable - also when you are living in the building there will be too much disturbance/noise for them to want to hang around!

No particular reason for the size - it's more for natural light as we are planning to spend most of our time in the extension, moving into the 'snug' in winter evenings. We will not be using the roof as we have plenty of garden/field space around the building.

I am finding the discussion really helpful in considering the options. Just to clarify - the photos I took may have been misleading as we only have two columns. I've attached the plan we have which shows the existing rectangular tank with the extension on the east and south sides. The roof is about 150m thick concrete with a similar depth of soil over. We are planning to put roof lights over the bedrooms and snug with the kitchen, dining and sitting area in the extension. We are not looking at a Grand Designs approach with much of the work being done by ourselves and local builders. Any clarification of details please ask.

It's the £250 legal costs that Welsh Water want to charge me after I've undertaken a survey and produced a method statement on how I plan to remove the redundant equipment on site that I thought I owned - I find difficult to get my head round!!

Thanks for the advice so far - I've taken some pictures which may be of some help. (I'm not entirely sure this will work due to my technical incompetence!) Outside of the tank Inside of the tank Section of the wall

Good morning everyone We have just obtained planning on a disused, earth covered, water storage tank and are in the process of deciding on the details of construction. We are not sure how to insulate the structure which has thick (about 900mm - 600mm) concrete walls. Do you insulate the outside and include the walls in the building envelope or insulate the inside and treat the walls as just a structural part of the building? We are planning to retain the earth cover on the roof and two sides with an extension on the east and south facing sides, so over all the building will be an "earth sheltered dwelling". We would appreciate peoples opinion on the most appropriate option as I can see pros and cons in both approaches.