Lean-to greenhouse are as traditional as it comes in greenhouse terms. The Victorians knew the value of placing a greenhouse against a wall in their walled gardens - The wall acts as a heat sink - absorbing the heat during the day and releasing it over the cooler night to help keep the temperature even. These days you can choose a lean-to as small as 4x2 to garner those same properties. Things to think about with your lean-to: check your height carefully (including any metal base plinth) to make sure that your ridge doesn¹t clash with any obstacles such as windows or drain pipes. If you have limited height then you may prefer the lower heights of the Southwold (4ft wide model), or the Robinsons Six foot wide. If your Lean-to is going over a door on your house then it must be glazed with toughened safety glass. Also watch out for flues: if you have a flue from a boiler exiting your wall, you can not let that discharge into your greenhouse.