It seems that no matter what size house you have, you always want more storage space. Basements and attics are often ideal places for storing a variety of things, but there are other places you may not have thought of for storage, and ways of making the most out of existing storage space.
Built-in closets are a relatively modern phenomenon - pieces of furniture (armoires and the like) were used in the past and can still be used today. For example, a sideboard or pantry-like cupboard in a hallway can be a handy place to store linens, phone books, etc. Pine and cedar chests and blanket boxes can serve dual duty as bedside tables and for much needed storage. If your den also serves as your home office, rather than leave your computer and other office equipment sitting in an open desk, "store" them out of view in a computer armoire.
Do you have a bay window or a window alcove? If so, add a window seat with a flip-toplid that opens to a roomy storage locker and you'll have a cozy seating area while increasing your storage space.
In large rooms, you can create an entire wall of closets by putting up a wall parallel to an existing wall. (Save valuable room space by installing bi-fold or sliding doors - this way you won't have to worry about arranging furniture to leave space to open the closet doors.) Create storage centres in existing closets by adding shelves, cubicles (for shoes, etc.) and rods placed at different heights. Vinyl-covered wire shelving (available at most home building centres) provides good ventilation and allows maximum visibility of the items stored. Such shelving comes in a wide variety of shapes and measurements and is inexpensive and easy to install.
In two-storey homes, areas under the stairs can also be tapped for storage space. If the area under the stairs is large, a full closet (with a door) can be added; if it is a small space, a closed cupboard can be built. Alternatively, open shelves can be added under stairs to become a design element in the room. And don't limit yourself to adding horizontal shelves - since the space under the stairs already features a sloped side, why not add diamond or triangle-shaped partitions and create a wine-rack!
Some people rule out their basement as a place for storing things because they are concerned about moisture. Not all basement moisture is costly or difficult to remedy, however. Condensation (caused when the interior air, which may be warmed by hot water heaters, washers, dryer, etc., meets a cooler masonry wall) can be easily minimized by improving ventilation and decreasing the humidity. To determine whether the moisture in your basement is just condensation, dry an area of the wall and tape a hand size piece of aluminum foil to it using duct tape. Moisture on the foil the next day indicates condensation; if the tape has kept the moist air out, the wall surface under the patch should be dry. If you are satisfied your basement is dry enough, create functional storage centres by adding shelves, racks, rods, clothes hook and pegs. And if you only want to use some of the basement for storage, section it off, i.e., basically build a separate storage closet.
Attics are sometimes overlooked as storage space, especially if they are difficult to access. Often simply putting in a better staircase to the attic or moving the staircase to a more convenient location (e.g., from the center of the attic to a corner or wall) encourages use of the attic. If the attic floor is weak, additional floor joists can be added to insure sufficient floor support. Then, like basements, elaborate storage centers can easily be created.