Re: Building a garage above public sewer (UK)

I built a garage over a sewer and we were told dig the foundations deep enough to uncover the sewer and then cover the pipework with "jablite" polystyrene and fill the trench with concrete over the sewer. We had to dig about 7 feet deep trench and step it back up to normaldepth it used a lot of concrete. Talk to the building control dept at the local council ive found them very helpful at queries like this.Rob

From the chaotic regions of the Cryptosphere, snipped-for-privacy@my-deja.com (Nigel Jones) wrote on 13 Jul 2003 15:17:30 -0700:

It's down to the water company. IMHO, there's a chance that you may be allowed to build over the 150mm diameter sewer, but that would almost certainly not be the case with the 300mm. With the both in combination, it looks even less likely.

If it were able to be built over, the foundations would have to be excavated to a depth of 150mm below the invert of the sewer. Piling would be problematic, as they would have to be augered rather than driven, ruling out a mini-piling rig. If the sewers are very deep (I can't see the depth being 25", that's only 635mm, which wouldn't be enough cover on a 300mm pipe), a raft would be a better prospect, as the total additional load on top of the pipe would be quite low.

One of the water company's concern is gaining access in the future, so they may well object to a timber garage also (this would have other problems in terms of Building Regulations in relation to combustible material less than 1m from your boundary).

If there is an easement, you should talk to the City Engineer. You may be able to build over it. In the US, the owner is liable for the cost of the easement owner accessing the underground utilities. It could mean your garage is damaged when the sewer is repaired some day and you would be responsible for the added cost of them dealing with your garage as well as the cost of repairing the garage. However, with no manhole nearby, the City Engineer can work with to determine if you can built and what restrictions and risks you will be facing.

Sincerely,

Donald L. Phillips, Jr., P.E. Worthington Engineering, Inc.

snipped-for-privacy@worthingtonNSengineering.com (remove NS to use the address)