Wall chases - how deep can I go?

[mk2phil]

I've just bought my first house with the missus and the radiators are drop feed into my living room/dinin/kitchen using microbore pipework.

However, this has been done by running the pipework down the wall with capping over the top which I dont like. I plan to replace the copper microbore with Hep20 and am planning to chase the wall out, fit round conduit and then plaster over the conduit. This will allow me to then run the new pipework through the conduit.

The question is how deep can I go into the wall for the conduit? If the conduit is 15mm diameter and I'm assuming I'll have to leave an additional 5mm for the new plaster to effectively cover it, is 20mm too deep?

 

[noseall]

i would think 1/5th the depth of the masonry sounds about right.

 

[gangman]

It's 1/6th horizontal and 1/3rd vertical of the leaf thickness.

 

[mk2phil]

how can I work out the depth of the wall though - I can see the external total thickness of the wall, but I'm assuming there is an inner and outer course.

One wall is also a party wall so I have no way of determining its thinkness?

 

[noseall]

if it's a party wall then assume it is a minimum of 100mm thick.

just make sure you do the work whilst the n'bours are out.