Garden office water supply

[rlovers]

I've built a posh garden office. It will be used for office-ing and occasional sofa-bed guest room. Its under permitted development and so far no building regs or planning permission involved. (<2.5m high, <15 sqm, <1 m from boundary wall).

It will feature a small sink and toilet (saniflo compact) which will pump the waste ~15 m back to the house via 40 mm waste pipe (1/40 fall, AAV at highest point).

My problem is getting the fresh water from house to new building. I can tap off a washing machine supply in the garage, but the pipe needs to get past an area of decking over concrete, a raised concrete patio, and a recently installed gravel area. Frost protection is my main concern. The pipe will be in regular use most days for a small amount of water, but we could go away from home for a couple of weeks in which case it will be unprotected and water will be static.

View attachment 340644

View attachment 340645
Here is my plan.
The pipe exits the garage wall and is laid on top of the concrete slab/under the decking, insulated and mechanically protected (SHalloduct or similar).
The decking will be extended to meet the concrete patio slab so the pipe will be covered up to the patio.
Then the pipe is buried 300 mm deep under the concrete raised patio and gravel area - still in SHalloduct.

The pipe then travels along the back of the new building (as it enters the building at the far back corner). It will be buried around 100 mm deep and right up against the insulated concrete slab foundation. I'm not worried about frost protection here. The concrete slab will be acting as a thermal battery/storage heater for the building. The insulation is only 25 mm thick around the sides, so this will keep the adjacent ground temperature stable even over a prolonged period.
The pipe will then pop up out of the ground where it enters the building, this short section will be Insuduct or my own sketchy DIY imitation made from EPS insulation and treated exterior ply.

Considerations:
Will the SHalloduct solution be adequate protection laid over the concrete slab under decking? Will it be enough buried shallow in the concrete raised patio?
Do I need to add trace heating at least for the under-decking section?

Am I overthinking it?

 

[flameport]

. Its under permitted development and so far no building regs or planning permission involved.

Wrong in both cases, as installing a toilet is notifiable to building control regardless of the building size, and any new building containing sleeping accommodation requires planning permission.

 

[rlovers]

Wrong in both cases, as installing a toilet is notifiable to building control regardless of the building size, and any new building containing sleeping accommodation requires planning permission.

Thanks for the response flameport - I'll look into the building control. I understand it is notifiable work (maybe was getting mixed up with building control/water regs). I will be getting a qualified plumber to complete connections at both ends and take care of relevant notifications.

I do not believe planning permission is required though. It is not 'habitable' ie it has a toilet, but no kitchen - you could not live in it. Although the building could occasionally be used for accommodation, its primary use will be as an office. You could put a sofa bed in a summerhouse and sleep in it without requiring planning. I understand planning refers to the primary use of the building, which in this case is not accommodation.

That is my understanding - interested to hear if you maintain a different view.

 

[rlovers]

Update.
I spoke to my local building control, who told me on no uncertain terms that building regs are not necessary for the construction with respect to occasional use for overnight sleeping. They also advised the same for planning permission, but I’ll note that is not their department. Actually what they said was “if it’s not for living in, just don’t open that can of worms. Good idea to put a smoke detector in there though.”
The plumbing works do of course need building regs, and I will employ a plumber registered with the competent person scheme who will handle that.

So my question remains about the frost protection. What is likely to be a suitable approach? Any thoughts?
Obviously I will discuss this with a plumber when I manage to find one who can visit!

 

[Agile]

Buried water mains are meant to be at least 750mm deep so that they will not normally freeze.

Your proposals make it sound to me as likely to get frozen pipes whenever we have a cold spell.

With all those water items in your office you will need background heating there.

 

[rlovers]

Thanks Agile, this is exactly what I’m concerned about.
The building itself is better insulated than our house, (sips/triple glazing) will be in constant use, and has a massive insulated concrete slab with UFH acting as a thermal battery. The control system for that also has frost protection but I expect it to take several weeks to cool below 10c. So not worried about plumbing inside.

750 deep is simply not possible so I’m looking for alternative approaches to provide frost protection. I’m designing for -10 c over 2 days, not in use, which would be exceptional for Surrey.

My current plan protects the pipe in 2 different ways:
1. Within Shalloduct and possibly with trace heating for 5 m, laid under decking.
2. Within shalloduct and buried 300-500 mm deep for another 5 m

Based on the shalloduct website, it would be protected for 24 hours laid on the surface at -10 degrees. Hence the thought of trace heating. Then again, under the decking adjacent to the house and in a sheltered position, it would never really see -10 even if that’s the outside temperature. So perhaps I’m over engineering it. I’d rather not use trace heating if avoidable.

Does any of this change your view? Is there anything else I’d need to do or is 750 mm deep the only possible solution?
Obviously pipes routinely surface outside houses where the entry is external, so it cannot be 750 mm or nothing. The question is - what is good enough?

 

[Agile]

The Water Regulations stipulate the 750mm depth.

Where it comes up to the surface it needs to be insulated.

 

[Harry Bloomfield]

I've built a posh garden office. It will be used for office-ing and occasional sofa-bed guest room. Its under permitted development and so far no building regs or planning permission involved. (<2.5m high, <15 sqm, <1 m from boundary wall).

It will feature a small sink and toilet (saniflo compact) which will pump the waste ~15 m back to the house via 40 mm waste pipe (1/40 fall, AAV at highest point).

If it is just for very occasional use, as you suggest, the quick, cheap, simple, easy option, is to consider the use a caravan toilet, water system, maybe even a shower.

 

[rlovers]

The Water Regulations stipulate the 750mm depth.

Where it comes up to the surface it needs to be insulated.

Agile,
I cant actually find anywhere the regulations require this depth specifically.

2.3.7 says:
(4) Any water fitting laid below ground level shall have a depth of cover sufficient to prevent water freezing in the fitting.

So this gives freedom to find any suitable way of protection from freezing (not limited to 750 deep).


Part II regulation 5 also states:
5.—(1) Subject to paragraph (2), any person who proposes to instal a water fitting in connection with any of the operations listed in the Table below–

(i)any water system laid outside a building and either less than 750mm or more than 1350mm below ground level.
...
(a)shall give notice to the water undertaker that he proposes to begin work;
(b)shall not begin that work without the consent of that undertaker which shall not be withheld unreasonably; and
(c)shall comply with any conditions to which the undertaker’s consent is subject.


So if less than 750 deep, I have to give notice, and comply with any conditions.

This guidance by Southern Water also describes flexibility around the 750 'rule',

https://www.southernwater.co.uk/media/uidd51te/watersupplyregs.pdf

Specifically that water pipes located above ground must be insulated (thickness to BS EN 1057)

Elsewhere the regulations describe the requirement to protect from freezing, but the only mention of 750 mm in the entire document is the one pasted above.
My take here is that I can work out a reasonable and compliant way to protect it from freezing, and must ask permission of the water company.

Does anyone have any thoughts on my proposal with SHaloduct and trace heating?

Thanks

 

[rlovers]

If it is just for very occasional use, as you suggest, the quick, cheap, simple, easy option, is to consider the use a caravan toilet, water system, maybe even a shower.

Thanks Harry,
The toilet wont be for occasional use - the office will be in use all day mon-fri as my wife works from home - this is the primary purpose of the toilet and sink.
Sleeping in the room overnight will be occasional, with the toilet an added benefit. There will not be a shower.

So this idea isn't really practical.
I did also consider rainwater harvesting with a large water butt, since it doens't need to be drinkable water. This is also excessively expensive and complex though, probably cheaper to just dig a deeper ditch!

Thanks