The Victorians popularised greenhouses, stocking them with plants from all over the empire. Most of those greenhouses were constructed on top of brick walls for both permanence and architectural elegance.
The majority of greenhouses today do not have these brick foundation walls for two main reasons. Firstly, aluminium frames are much cheaper to manufacture and erect; secondly, by being glazed right down to the ground, they maximise the amount of light they admit. This is important for high productivity during our short British growing seasons, especially if it is a commercial greenhouse.
These fully-glazed frames are intended to be functional and are rarely designed to look good or last for very long; however, for something you can enjoy for years to come and that will enhance the value of your home, the answer is still brick. If you live in an area prone to strong winter gales, you might also need this brick foundation for practical reasons.
Basing greenhouses on brick foundation walls is not as expensive as some people assume. Unlike modern house builds that have inner and outer walls, only a single skin of bricks is usually needed. You do not need to protect your plants from damp breathing through the walls, and moisture can evaporate easily without internal rendering obstructing it. The windows and roof above will still be a lightweight frame and, unless you are planning something extra-large, easily supported by a single brick wall.
This will generally only be a few courses high – just enough to raise up the roof sufficiently to create space for high-climbing or tall plants. This is one of the key advantages of a brick-based greenhouse, as most ordinary-frame greenhouses would be too unstable if they were made higher; however, they frequently do not provide quite enough height even for common popular grows such as sprawling tomato plants. This extra height will also allow you to locate the door on one side rather than on the gable end, and to enjoy a full view through the windows without crouching down.
A brick-based greenhouse can provide you with all the sunny luxury of a far more expensive double-skinned conservatory or sun-lounge extension at a fraction of the cost; in addition, the low wall adds a little more privacy when you are laid out on a sun-lounger! Choose bricks that match your home to maximise the value it adds to your property.
There are several more practical advantages to the brickwork; for example, the low-level shade provided is much appreciated by more delicate plants and young seedlings. The bricks warm up slowly during the day and release the heat at night, keeping the chill away and effectively extending your growing season. The low wall is just the right height for adding cold frames, or storage bunkers for garden tools. It is easier to safely add cables and sockets for heating and lighting when you have a wall to mount them on; in addition, they are protected from rot or corrosion by keeping the timber or metal frame away from the ground.
If you are planning a really large greenhouse, it is worth considering a double-skinned wall; however, for most greenhouses, this brickwork will cost little to erect and be worth its weight in gold.