Preventing freezing of over-ground outdoor pipe

andre_xs

Hi Everyone!
During Covid, we created a little home office in the shed. There's a toilet in there, so we put a water (15mm plastic pushfit) and waste pipe (40 mm with macerator pump). Because we needed it quick, we did it as a quick and dirty job, and the pipes are overground. I want to dig this a little bit in now, but there are some bits where I can't get the pipe underground (e.g. patio slabs, tree roots).

Last winter, the pipes actually froze 2-3 times for a few days. Luckily without any damage (are these speedfit pipes frost save?), but I don't want to take the risk...

So, I thought about the following for the (fast approaching!) winter

1. create a duct for everything which runs to the shed (warm water, cold water, waste pipe, electricity (armoured outdoor cable), ethernet)
2. Whenever possible, dig in this duct (not too deep, just 10-20cm or so). Probably just deep enough to simply cover it on top with a decking board or so.
3. Try to insulate the duct with left over styrofoam and proper pipe insulation.
4. However, I think the above won't be enough to prevent freezing in colder spells (luckily I'm in the south of England, so it rarely gets really cold), so I thought adding a heating element which lays with the other stuff in the duct. If frost is forecast, I would turn it on, otherwise it stays off (=fully manual control)

The duct needs to be very roughly 18m long.

The heating shouldn't cost too much, so I thought about the following options:
1. Plant warming cable (e.g. for greenhouses). 20m (6W/m), IP68, £45
2. Underfloor heating cable kit (just a loose cable, not fixed into any shape). 12m/150W (so 12.5W/m). £70 (but I would need two of those)
3. Probably very expensive: There seem to be snow-melting and self-regulating cables, e.g. for roofs and gutters (e.g. 'warmup').

I would think (1) is the optimal solution. It's not getting very cold here for long times, so that this cable should be warm enough. I also would think that the wattage is low enough that even if someone puts it on during the summer / forgets to put it off to pose a fire risk? The warmth/heat should always be able to dissipate well enough in the duct.

However, I don't know anything about this at all, so maybe I'm missing something and this solution is not good / dangerous, or there are better solutions available?

Any help greatly appreciated!

Ebe_Scrooge

It might be a pain, but if you're able to get the whole length running underground then it's job done.  The recommended depth for water pipes always used to be 2' - no idea what the regs are these days.  But in practice, if you're able to bury them about a foot deep then there's almost no chance of them freezing - especially in the south of England.  Tree roots can be cut out of the way if needed.  For the patio, would it be feasible to lift just a few slabs for the area you need?

I'm just thinking that if you can do this, you won't be worrying about the running cost or safety of having a heating element running underground.  Depends on the layout of your garden, of course - it might be totally impractical.

Section62

andre_xs said:

However, I don't know anything about this at all, so maybe I'm missing something and this solution is not good / dangerous, or there are better solutions available?

The work you are doing requires building regs approval, and you won't get that unless the job is done properly.  Without BR sign off you might have difficulty selling your property when the time comes (the hot water supply and macerator arrangement would be particular red flags to a surveyor) - so the amount of money you spend on anything other than doing the job properly should be commensurate with having to rip it all out before you sell.

The heating element idea is not a good one. Your duct will contain services made from various plastics, and you can't really control which of the pipes/cables the heater could come into contact with.  Repeated application of heat can cause plastics to go brittle and fail, so this would be ill-advised.

It might be safer, though more expensive in running costs, to leave the hot water pipe uninsulated and use that as your 'heater' when required.

When choosing insulation materials you need to be aware of the need to dissipate heat away from electricity cables, and if the insulation prevents cable cooling then your electrician would probably need to install a cable with a larger CSA (i.e. more expensive) to prevent overheating.  Also be aware that some insulating materials (e.g. expanded polystyrene) can cause deplasticisation of other plastics (e.g. PVC) that it comes into contact with. This again leads to brittleness and failure.
 
Plastic water pipes designed for interior use aren't frost proof. Although the plastic is usually more flexible than copper, it doesn't have the same strength, particularly around the joint area. Failure is likely to be sudden and total, so it would be sensible to have easy to access shut-off valves, and to isolate the supply when there is nobody at home for any length of time when frost is likely.

andre_xs

Hi,
thanks to both.
(1) properly digging it in the whole way isn't really an option. There are a couple of tall trees with major roots and the pipes run directly next to two of those trees.

(2) Thanks for the advise regarding of materials interacting, etc. That's exactly the information I was looking out for. The 'shed conversion' is done so half-heartedly (and cheap), and we don't have any plans to sell, so I won't worry about resale value (or simply rip it out again). However, naturally I want it save. Yes, shutting off water and having a drainage valve at the lowest point would maybe be the easiest/cheapest and safest option.

FreeBear

Pipes and cables should be buried a minimum of 750mm below the surface to protect from frost and damage from digging. You also need to maintain a minimum distance of 50mm (maybe more) between any mains cables and data - This is to prevent the data cables picking up hum and interference.

In situations where pipes are at risk of frost damage, there are special heating cables designed for the job - Look for "Heat Trace Cables". It is worth connecting any heating cable to a smart control system that will only power them up when there is a risk of frost. Leaving them on 24/7 all year is a waste of energy.

Eldi_Dos

You can dig down either side of tree roots to suitable depth  then poke services through underneath tree roots,not the easiest job in the world but that is one way utility workers sometimes deal with the problem.

Harrywayon

I did this properly with building regulation, electrical and gas certificate .My  garden is very big  it allowed us to make a big one it's cost including planning permission around 80k. Done properly can increase house price but done cheaply when you come to sell the buyers might not be able to get a mortgage as it dangerous.

The pipes can be covered using pipe foam insulation. The macerator pump toilet we had got blocked every time it was used. We had to install a manual flash which was costly but 100 times better.

I dont think your will be covered under home insurance we had to pay extra to cover.

andre_xs

Thanks to all.
- Insurance is a good point, will look into that.
- £80k: That is very clearly a completely different project than ours. Think of old tool shed. Covid started, "Oh, let's put a desk in there". "Ok, cold, a little bit insulation and an electric heater". "Toilet would be nice, let's put it in this corner." And so forth...
- Our macerator pump works perfectly well for a year now (although it was a cheap one from eBay). But we take good care to not throw anything else in there...
- Digging either side of tree roots: Yes, I thought about this as well. But before I spend that much effort, I would just shut off the water and drain the pipes...
- "Heat Trace Cables": Very helpful tip, it's exactly those keywords one needs to learn about. Without the right search term, it's hard to find. I'll look into those. Of course it was never meant to be left on all the time, only during times of frost.

Norman_Castle

For the few weeks a year freezing is a possibility not using and draining it seems the easiest and most practical. How much of a hardship is it to use the toilet in the house for those few weeks?

coffeehound

10-year freezing events like the beast from the east caused frozen water mains three feet underground, so maybe the trace heating would be a nice-to-have.  IIRC there are some self-regulating types to give peace of mind that it won’t get too hot.  You could then have it controlled overall by a frost-stat in case you are away from home, etc. 

Another_Level

If the water pipe is on the water companies mains pressure water supply burying it to the required depth would remove many risks including freezing.

Mains water pipe can be run in other ways closer to the surface although Advanced notification is required 

If the water pipe is not mains water, the water company is not interested   

Happy digging!