PLANNING PLANT ROOMS

Energy-efficiency expert David Hilton shares his top five tips for designing a plant room into your self-build or renovation project

Energy-efficiency expert David Hilton explores what to consider when designing this all-important space in a self-build

If you’re new to the self-build or renovation game, you’d be forgiven for thinking a ‘plant room’ is some fancy title for an indoor green house or garden room (we’ve all thought it!). In fact, it’s a room dedicated to the technical paraphernalia that comes with including heat pumps or mechanical ventilation with heat recovery (MVHR) systems into your home’s heating and electrical set up, as well as other necessary clusters of pipes, cables and electronics. It’s a place for cylinders, boilers, pumps, control boards and ventilation systems, all in one centralised location that’s easy to access for periodic inspection, maintenance and repair. To help you design the perfect plant room, I’ve pulled together my top five tips to get it right from the off.

1. Do I need a plant room at all?

It’s common to ask how much equipment justifies a dedicated plant room. I tend to think that if you have anything more than a hot water cylinder and a boiler then it is worth it. That said, your plant room could be as modest as a cupboard, or it may be split into two smaller areas.those options are perfectly fine as long as they are purpose-built to allow easy ongoing maintenance and periodic inspections without the need for disruptive works.

2. What equipment might it include?

The following technologies are among the equipment often found in plant rooms:

MVHR system

Boiler

Hot water cylinder

Buffer tank

Low loss header

Central heating manifolds

Smart home wiring centres

Main electric board

Battery storage

Water softener

Photovoltaic inverter (the unit that turns DC from solar panels into usable AC electricity)

Hydrobox (the indoor unit of a heat pump driven heating system)

Services in a plant room should, as far as possible, be organised into groups, with wet appliances in one area, ventilation in another, electrics in another and so on. Naturally some appliances will belong to more than one category, but try to separate them as much as you can, use your common sense and mitigate risks as much as possible in your design.

3. Where should it be located?

Plant rooms should ideally be positioned centrally, but with access to an outside wall for services to enter the property. A centralised location will allow you to minimise the length of pipe runs through your home, resulting in less heat loss and quicker delivery of hot water. Similarly, duct runs for ventilation will be shorter, meaning lower resistance and potentially allowing the choice of smaller ductwork and fan units.

The loft isn’t the ideal place for a plant room and you will need to consider factors such as accessibility, insulation and whether the space can support the additional weight.

It’s best to avoid locating a plant room at the end of a property, especially in a single storey add-on, where access to the main building will be limited and it will be difficult to make service routes discrete.

COMBINING PLANT ROOMS WITH UTILITY ROOMS OR GARAGE SPACES

A common line of thinking that crops up when planning the location of a plant room is that they can be placed in a garage or alongside utility room equipment. It makes intuitive sense to have all the necessary but unlovely elements of your home in one place, but it needs careful consideration.

If you plan to have your utility room pull double duty and act as a plant room, then ventilation is a key consideration, particularly if it’s to contain appliances such as a tumble drier. A build up of water vapour will manifest itself as condensation, which could deteriorate the fabric of your building and damage electronics that aren’t designed for a wet environment. Depending on the appliances housed in the room it may also need to be designated as a fire control area, meaning it will need fire doors and appropriate fire mitigation products.

Garages generally suffer from being cold spaces on the edge of the home, and in the worse cases are even detached from it. These factors create a need for high levels of insulation on equipment and distribution systems to mitigate the risk of condensation and corrosion, as well as reducing the inevitably elevated levels of heat loss from pipework and ducting. This sort of set up can lead to a long lag time before hot water reaches taps. Pipework can be designed to circulate to counteract this problem, but this comes at the price of heat loss and reduced efficiency.

4. When should I design in a plant room?

A plant room should be planned for right from the beginning of the design stage. Not only should the space be big enough to house all the technologies but there also needs to be enough space allowed in the fabric of the building to get all the services and ductwork to the appliances without being aesthetically intrusive or clashing with any structural elements or other critical services.the time to get all the services designed in is after you have planning drawings but before you have the completed building control drawings and certainly before the construction drawings are frozen.

When designing a plant room it is best to get the brief defined so that you know what technologies will be included in the project and then speak with the installers to understand how much space is required for the technology and also the clearance required around the products for maintenance.

5. What’s the ideal size for a plant room?

Plant rooms vary in size depending on the amount of technology they contain. In a typical property that has a combination plant room and utility room it is usually best to design a galley layout with the plant on one side and your utilities on the other. Allow around 2.5m length by 800mm depth for the plant side and 700mm depth on the utility side. If we assume a metre-wide path down the middle, that leaves us needing a room of around 2.5m by 2.5m. That’s a good rule of thumb, but the specifics will vary case by case. If you are installing a ground source heat pump, for instance, that will add significantly to the space required. If the room you use has more than two doors, or doors on adjacent walls, you will need to use a less efficient layout and hence need more space overall. Look into pocket doors as a way of maximising the usable internal space, but be aware that services can’t pass through a wall that houses a pocket door.

BLENDING IN This home’s plant room is located in a single storey, weatherboarded section just off the utility and boot room. This allowed the air source heat pump’s internal parts to be located directly next to the external unit and in a convenient position for the plumbing to the underfloor heating and hot water systems, all without compromising the design of the main rooms. There is an external access for maintenance. The internal parts are within a bespoke unit that hides them from view.

STOWED AWAY This three-storey, four-bed, new-build cavity wall Passivhaus built by Green Building Store has a plant room at the top of the house in the loft, accessed via a bedroom. Although lofts aren’t generally advocated by Green Building Store both this project and the timber frame in Dorset on the next page have warm-roof upper floors, meaning that their loft spaces are within the thermal envelope. The storeroom-sized cupboard houses a PAUL Novus 300 MVHR system with rigid steel ducting. The central heating boiler and the MVHR system are both located in the plant room but both work independently. Most of the ducting has been concealed bar a small proportion that remains visible in a hallway.

Built to Passivhaus standards, this timber frame detached new-build in Dorset features a PAUL Novus 300 MVHR heat recovery ventilation system designed and supplied by Green Building Store. The plant room in this house is located in the loft (as in the case study opposite).