6 Concrete Foundation A concrete foundation is the most durable option and if properly sealed, will protect you from the elements for years. And as you can guess, the heavier the greenhouse, the more important it is to build a strong base to support it. Concrete is often necessary by your city planning office if job specific engineered drawings are required. Bricks or Cinder Blocks Bricks or masonry blocks are also an option, but you must have a flat surface to fasten the greenhouse to. This means that the gaps and holes are closed off. Settling and cracking is common with bricks or cinder blocks so care must be taken to prevent holes or cracks as pests will find any way to get into the greenhouse. Often a treated timber top plate covered with a metal flashing is an easy way to provide a smooth, stable surface to anchor the green- house and you can buy regular sealant to fix any cracks or gaps. Above, cinderblock and below, brick foundations.