Garden office with a toilet

[siimon]

I'd like to get a water supply from my house to a toilet in a garden office building (not yet built) but there's a public sewer pipe between at approx 350mm depth.

Is it breaking any rules to just mole under the sewer pipe at depth 1m? The pipe would be coming from near the boiler in my garage, so assuming I don't want to break the DPM (and a lot of concrete!), there's no way to have it already at 1m depth when it leaves the building, so should I just use some heating tape/insulation for the first couple of meters? How is this normally done?

The other question I had is about the toilet waste. There's a nearby plastic inspection chamber with one unused input, and the invert level (for that input) is ~450mm below the top of the cover. The intended position of the toilet is 7m from the IC. 7000/40 gives me 175mm higher up at the toilet end (assuming that's how it's calculated, e.g. 1/40 drop). The ground level at the toilet site is about 100mm below the IC cover. In other words, not a lot to play with!

I have read somewhere that waste joining soil stacks must do so at least 450mm above invert level of the bend at the bottom, but does the same apply to a toilet flush which presumably has a bit of oomph behind it as opposed to some little trickle coming from a sink or WM? By my calculation, assuming I add the 450mm, the toilet waste needs to be 275mm above ground so does that mean I should stick my WC pan on a raised floor?

thanks for any advice,
Simon.

 

[joni os]

Fall of 100mm over 7 metres will be OK for toilet from garden office provided pipe is properly bedded and won't settle when backfilled. Floor of office should be 150mm above ground level so plenty of fall for intended purpose. Where top of pipe close to surface protect with concrete slab. Excavate trench for water main 750mm deep, going deeper to mole under public sewer if necessary. Without undermining public sewer, diameter can be checked from top and depth of mole set accordingly. Length of scaffold tube or similar knocked through with sledge hammer normally sufficient for purpose. As you will have a trench 750mm deep up to your garage it would be better to break through and bring up internally but an alternative would be to box in external with 100mm celotex. Fit isolation valve inside garage.

 

[SimonG]

Building regs required. Building control will keep you right, for a fee

 

[siimon]

Building regs required. Building control will keep you right, for a fee

Not sure about 'keep you right'. Mine normally turns up and either passes it without looking at anything, or points out something trivial that's got nothing to do with the job, e.g.: Only two hinges on a door in another part of the house. I'd definitely ask about footings depth, insulation and stuff like that, but I've learnt that there are things they care about and then 'the rest' where 'the rest' is 80% of the job, and likely to make my life a misery if I get it wrong, whilst being OK from their point of view!

Pretty sure I'd get nothing like the quality advice from Joni :smilewinkgrin:, but I will ask of course.

 

[Radioman]

Our local building control in North Herts are excellent at giving free advice, even popping in to the site if they in the area. Great bunch. Your installation will definitely need signing off so don't delay in making the application, it's a lot cheaper than doing it retro.