If you are redecorating your dining room, consider replacing the chairs on one side of the dining table with a sofa. This has many advantages: it is more comfortable, which encourages leisurely dining and better conversation; it makes seating three people on a side possible even if three dining chairs won't fit the space; and it gives the banquette "look" without you having to build a banquette. However, average dining room chair seats are 16 to 18 inches high and many sofa seats are much lower. The solution is simple: raise the sofa.
Change the Legs
Most sofa legs can be removed, so remove them and replace them with legs long enough to bring the sofa to the desired height. Standard sofa legs either screw onto a bolt protruding from the sofa frame or screw into a hole in the frame. It's usually a simple matter to change them yourself. One advantage of this method is that the sofa can still be moved easily, so that people who are seated at the table may scoot the sofa back to get out. Legs are available at your local hardware store (or online) in a variety of different materials, finishes and colours, so you can either match the old legs or go for something different that will coordinate well with your dining room decor.
There are many products commercially available for raising sofas, beds, tables, desks and chairs. They are all basically small platforms that fit beneath each leg of the sofa and raise it higher up off the ground. Some of the platforms are connected in pairs to give the furniture piece greater stability; these are called sofa raisers or sofa troughs. Sofa risers are simple individual stands for each leg. Sofa raisers are available at many medical supply stores, and you can sometimes find risers at your local discount department store. Both also are available online.
Do It Yourself
If you don't want to spring for the commercial versions of longer furniture legs or sofa raisers, there are some crafty design tricks that will give the same result. For do-it-yourself leg extenders, remove one of the sofa legs, take it to the hardware store and find some metal pipe into which the leg will fit completely. Have four pieces of pipe cut to give the height you want, take them home and slip the pipe over the sofa legs. It's a good idea to put rubber protective caps over the ends of the pipes so they won't mark your floor. Alternatively, you can remove the legs entirely and set the couch on top of concrete blocks. Put a long slipcover on the couch or attach a ruffle to hide the blocks.