The Brew Cabin

Dear Tony

Since I was last in touch with your excellent site I have completed my extension and am now wishing to do the driveway in Block Paving.

I can't make my mind up as to whether I should renew the old clay sewerage pipes that run under the front garden before embarking on this project. Some of the pipework that was underneath the new garage has been renewed using your design you kindly sent me.

The clay pipe is about 3ft down, and there are tall trees within 15ft. Do you think I should assume they will probably be shot by now and just go ahead and replace. The house was built in the 1930's so they will be some 70 plus years old. Should I dig a test trench alongside and have a look. I did wonder if I was to expose them and pour concrete on them to seal them but then thought it would probably be cheaper to replace in PVC.

As a general rule would you replace anyway?

Hi Mike,

as a general rule, "If it ain't broke, don't fix it".

Do you have any reason to suspect that the existing drainage is faulty or compromised in some way, or is this a 'pre-emptive strike'? 70 years is not ancient, in terms of drainage - I've seen hordes of sewers and drains that are well over 100 years old, and are functioning perfectly.

If you do decided to replace with uPVC, then you need to consider the relatively shallow depth of cover you have. It could work out more expensive to use uPVC with a concrete casing than to use new clayware, which is capable of withstanding vehicular traffic with less cover.

A trial hole to have a look at the existing drainage can't do any real harm, but, as you can't see inside the pipe, you're not going to learn very much. However, examining a collar or two should give a reasonable indication of general condition of the drain. Look for cracked collars, and whether the joints are puddled with clay or pointed with a mortar.