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Ideas For Designing And Building An Attached Greenhouse

Photo by Robyn Rosenfeldt

An attached greenhouse is a great feature in any permaculture design because it serves so many functions and is a great way to integrate zone one and zone zero. Your greenhouse can become not only a growing space but also a living space.

Zone zero

An attached greenhouse

  • is an integral factor in the passive solar design of a home, letting in sunshine and trapping and storing heat
  • provides an air lock and living space in colder months
  • is an efficient and convenient work/storage space throughout the year.

Zone one

An attached greenhouse

  • provides a protected environment for growing seedlings
  • extends the growing season into cooler months
  • provides shade through hot months and shelter from extreme weather events (e.g. frost, hail, wind)
  • controls the growing environment (e.g. irrigation, beneficial insects, nuisance animals).

Refer to Greenhouse living article page 34 for an example. To begin, work out how you will use a greenhouse – is it mostly for gardening or is it to warm or extend domestic space? Site considerations include: slope; orientation; location of services (power, water, drainage); altitude and latitude; climate and weather (e.g. prevailing winds); space available; access to garden and relevant features (e.g. location of compost); potential for shading (of and by it); and fire risk. The most efficient greenhouses in temperate Australia face north or slightly north-east.

Design considerations include:

  • budget – will limit size possible and choice of materials; using standard dimensions is economical; attached greenhouses can be cheaper than freestanding ones
  • aesthetics – influenced by the architectural character of the house or other buildings (e.g. overall shape, proportions)
  • sustainability – active and passive features required (to store heat, screen, ventilate and circulate air); choice and availability of materials (including recycling/reuse of timber, windows and doors, paving); hygiene (how will you clean it?)
  • personal and practical – a layout to fit your gardening style, tool use, physical circulation (e.g. to move a wheelbarrow) and storage needs; the sorts and size of plants you want to grow; time of day/year you will be active there – do you need supplementary lighting?; your interests – do you want somewhere to eat breakfast, read a book or entertain?; if you want benches – what style, height, structure and materials will suit?
building-greenhouse
Robyn Rosenfeldt

Construction and materials

When constructing a greenhouse there are a few essential to consider:

Thermal mass

Temperature control is critical as plants will suffer from extremes. Thermal mass stores heat from the sun during the day and radiates it out to warm the space overnight. It can be included in floors and walls with either concrete, bricks, mudbrick or similar blockwork, or movable, this might be black water-filled plastic containers or ponds.

Insulation

Most glazed surfaces will allow heat to leak out of the greenhouse in cold weather unless you insulate them with blinds, shutters or foam panels. You will also be able to use these to shade the inside space in hot weather, although it may be more efficient (e.g. for metal-framed windows) to keep the sun off as heat will leak inside by conduction. Careful adjacent planting with deciduous trees or vines can help with shading.

Ventilation

Ventilation is also critical and requires intelligent placement of openings. Air rises when it’s hot, so include openings high up to suck hot air out of the space, and low to suck cooler air from outside. Air circulation within the space also matters, to even out temperatures and manage moisture and moulds.

You will be able to pick up most things you need secondhand. Using old windows and glass doors is probably the most economical way to build. When designing your greenhouse and choosing materials be sure to consider the extent of warming or cooling required; the likelihood of strong winds or storm events; and budget.

Flooring

Foundations and flooring will vary with style, and may be integrated with a slab floor or you could choose a surface of pavers, gravel or earth or even coverings (e.g. matting).

Walls and roof

When choosing roof and wall materials you need to consider:

  • glass (types and thicknesses) or synthetics (e.g. macrolon, fibreglass, acrylic, polycarbonate, polyethylene), reflection/ transmission/diffusion
  • framing – structural, functional (e.g. light blocking?), character
  • access doors to the house (optional), and to outside)
  • airflow
  • insect screening
  • thermal mass and insulation
  • drainage within and around the structure.

Finishes. Protection of the many surfaces inside and outside the greenhouse needs to be considered. Greenhouses are hot and moist environments, with plenty of UV light, and either have to resist those things or be treated initially and over time (e.g. painted, cleaned, replaced). The use of colour is also important as dark colours absorb light, and pale colours reflect it.

Monitoring and maintenance. Greenhouses are out in the sun for a reason, and unfortunately temperature and humidity are destructive to the structure – especially wood – and its contents, and often unwanted in an adjacent house.

Further reading; – there is plenty to choose from in books and on the web.

Marshall, R (2006), How to build your own greenhouse: designs and plans to meet your growing needs, Storey Publishing.

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