For a full height housing you have two full length sides, the top and bottom are usually have less depth than the other units, say 500mm, same for the other fixed dividers. This is to allow for air flow. The back is in two bits, one from base to "shelf" that the oven sits on, the other from top down to "shelf" above oven, this creaters two cupboards with a good air space behind.
The shelf that the appliance sits on usually has extra support as well as cam & Dowel fixings in the form of WMelamine wrapped battens or metal angles.
Most flat pack housings come with a multitude of holes and the shelves can be set to suit the particular appliance, be it a single, double, singel plus built in microwave or combination oven.
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