Scope of works carried out by the plumber
Traditional plumbing skills used to involve all things metal and any component which was being used to carry liquids; hence a plumber may well be employed to install lead flashings around a chimney, to install gutters and downpipes or to get involved with underground drainage installations. However, this is not so common today and you’re likely to have groundworkers complete your drains, roofers complete your leadwork abutments and possibly carpenters to fix your gutters.
Today, the plumber is really only focused on the internal plumbing which includes above ground drainage (waste pipes), hot and cold-water supply systems and space heating. Some plumbers will focus more heavily on heating products and, in these situations, they are likely to label themselves as heating engineers whereas others may have packaged themselves as expert bathroom installers and offer complementary skills in ceramic tiling and wet room floor design. But it’s unlikely you’ll find a boiler and heating specialist who will also be interested in quoting for your bathroom floors so you need to pick the right skill set for your project.
Two elements are regulated here; the first being heating where boilers and pressurised hot water cylinders may only be installed by trained and qualified heating engineers, and the second being the water supply and waste pipe design and install. Heating installs are more seriously regulated through Building Control as the consequences can be extreme, but it’s really only on new build where Building Control are beginning to make a difference with compliance to The Water Supply (Fittings) Regulations 1999 (and subsequent later/related versions). So, if you want to get an understanding of the regulations the best place to start is the Building Regulations, approved document Part G which covers sanitation, hot water safety and water efficiency. Other important references are contained in Part F (ventilation), Part H (drainage) and Part J (combustion appliances and fuel storage).
Design responsibility
Very few self-builders will opt for a mechanical design and, in truth, unless your project is a large one, not many M&E Engineers will offer design services at a domestic level. This means that the design of most self-built systems will inadvertently be placed in the hands of the successful heating engineer. And this is highly significant as the design of the installation may be capped at a winning price level and without an adequate discussion with the client/self-builder/end user about performance, capacity, warranty, control and/or efficiency.
So, if you’re relying on their design services, your appointment of the successful contractor must include reference to this as part of the scope which is likely to include, the above ground drainage, the hot and cold-water supplies, the installation of your sanitary ware (and fittings) and the space heating and domestic hot water. Your initial brief must give performance criteria which is important to you, including controls, and you should also discuss the installation layout in terms of future maintenance before the work actually begins; for example, access to waste pipes, location and access to pumps and motorised valves, and general stop cock and isolation valve positions etc.
Space heating
The two key questions here are what will be your heat source (boiler, pump and fuel) and how will the heat be distributed (emitters). For wet central heating the heat source will usually be a boiler although there is an increasing interest now in heat pumps (air and ground source) which can be a complete substitute for lower temperature emitters like underfloor heating. But, for the majority, a gas or oil boiler will still be the norm.
Most boilers have exceptional efficiency ratings at well over 90% which means that nearly all of their heat output is being channelled correctly into generating hot water in the primary coil as opposed to disappearing through the flue. The primary coil is a sealed loop of pipework which is pumped on rotation through the boiler and then, by controllers, redirected to the heating emitters (for space heating) or the hot water cylinder (for domestic hot water) as required. Condensing boilers, which effectively recirculate flue gasses for a second pass/extraction, have made a huge impression on the efficiency gains and the technology continues to improve year on year. Gas boilers are less expensive than oil and gas is considered a cleaner fuel to burn so, if it’s available, almost everyone will opt for mains gas. Boiler sizes are more discrete and, with balanced flues, can be positioned within small cupboard spaces as long as there is some ventilation to prevent overheating.
Underfloor heating is a popular choice especially for ground floor distribution and, with such good building fabric insulation and air tightness in new homes, serious consideration should be given to no heating at all on the first floor with the exception of bathroom heating towel rails and local underfloor/tile heating for comfort. One of the heating engineer’s design responsibilities is to carefully calculate heat loss projections for the property (based upon your chosen fabric) and with full underfloor heating to the ground storey, limited additional heat upstairs should be necessary. Many folks just opt for small designer style radiators with individual thermostatic valves to provide a boost from time to time.
Cold and hot water
With an adequate minimum water pressure deliverable from your main supply, almost all new installations include a mains pressure cold water system. This means no cold-water storage tank is required in the attic and mains pressure capacity will be delivered at each tap outlet all of which is at a drinking water standard. It’s also a cheaper install but with two potential draw backs; the first is that you have no stored cold-water capacity in the house in the event of a supply interruption and the second is potential noise in the system due to higher pressure supplies.
However, this additional pressure is a benefit for the hot water whereby the hot water cylinder will be fed with a guaranteed mains pressure usually capped down to 3-bar as a preferred operating standard. These cylinders are known as pressurised vessels and, as such, are unvented and instead have their own expansion facility either integrated internally or fitted to one side. It’s a regulated install and requires an accredited engineer just like the boiler.
The heat source inside these pressurised unvented hot water cylinders will be one of three options or a potential combination of all three; First, and most likely will be a copper coil which allows the primary circuit from the boiler to flow through the inside of the cylinder, the second would be an electric immersion heater (usually as a backup) and the third might be a secondary coil to take another heat source, e.g. a solar panel or heat pump.
Some smaller properties may not have space for a stored hot water capacity and here the usual option is a combination boiler (combi) which can deliver the space heating in the same way as described above but heat the domestic hot water on demand. Pressure and capacity can sometimes be an issue here.
Above ground drainage
The wide diameter pipe which connects the waste pipes to your underground drainage system is known as a soil and vent pipe (SVP) stack. These are mostly installed internally to improve external imagery but not enough consideration is then given to providing practical access for maintenance purposes. Smaller bore plastic waste pipes from basins, showers, sinks, etc., all feed into these stacks and should be designed with appropriate gradients and minimum lengths. Given the number of bathrooms we now want, it is not uncommon for a single house to have three of four SVP’s. These need to be properly vented where usually at least one should be open to atmosphere to prevent pipe siphonage. The others can have air admittance valves fitted to allow air in but to keep smells out. These pipes are assembled with permanent joints having a solvent weld and traps and rodding locations having screw fittings for ease of maintenance. Hair, shampoo, toothpaste and kitchen waste will eventually block any waste pipe/trap assembly so make sure you specify easy access units so that once every three months they can all have a good clean.
Using greywater and rainwater
With water being a precious commodity, many folks are seriously considering and installing grey water and rain water recycling/harvesting technologies in their properties. Sometimes it’s difficult to justify the capital cost and to some extent we will probably be led by prevailing weather patterns to generate enthusiasm and stimulate demand. But the regulations now limit the notional use of water in our homes to 125 litres per occupant per day which, for those us who love long showers, will be a challenge. The recycling of grey water (bath and shower waste) makes great sense to be filtered and then reused for flushing WC’s. The loos probably consume 20-25% of our daily usage and baths and showers perhaps over a third. So, to use one to service the other is a win/win situation. In new build this need not be so difficult but does involve some extra expense and some early thought about what components need to go where.
Different types of pipework & managing noise
Traditional post war cold and hot water supplies use copper pipe with soldered joints and neatly clipped runs. The most common diameter sizes are 15, 22 and 28mm with the plumber selecting their sizes based upon the flow capacity and distances required. However, many folks are now firmly committed to the plastic pipe alternatives, some with push fittings rather than compression joints. The main benefit seems to be ease and speed of installation but it can also lead to poor installation practices with loose and unclipped pipes unsupported throughput voids. Hot water distribution should also be insulated to prevent heat loss on route to an emitter which might give uncontrolled heat to the wrong zone. It can also inadvertently heat the cold-water supply if hot and cold pipes are running parallel. Waste pipes are always in plastic and of a much greater diameter. Underfloor heating pipes are usually in plastic with many suppliers using their pipe specification as a differentiator; i.e. ease of bending, ease of installation, bore capacity, pipe diameter and oxygen diffusion prevention etc. Beware noise in your plumbing which is usually to do with higher water pressures, longer pipe runs, undersized pipe diameters, under capacity pumps, location in voids, lack of insulation, nature of fixing and restraint, amongst other more sophisticated design issues.
Written and published in September 2017
