Doors on the stairs to keep the noise down, heat down, and/or pets on one side or the other.
10 Ideias para Aproveitar o Espaço Embaixo da Escada
Storage Nooks - what a cute little pantry! It looks like a little store window!
minha casa, meu mundo: decoração
Casa Estilo Foursquare Americano!por Depósito Santa Mariah

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Under stair storage.....this would be great to do since will be replacing stairs in HS house.
More great under the stair ideas
11 Clever Way to Mix the Shelving and Cabinets for More Extra Storage under the Stairs
love this use of space under the stairs...
Under stairs storage
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No dead space
7 Bold under stair storage ideas | Small Room Ideas