From beginning to end, a fairly straight forward 1100 square foot second story addition to an existing home in Seattle

Sometimes the only option to get more space for a home addition is to build up! Second story additions can dramatically change the appearance and function of a house, so it’s important to get them right. Here are some issues to consider when designing a second story addition:

Second story additions require structural upgrades

Since building up places additional mass on top of the existing building, structural upgrades are usually necessary. Typically this means assessing the existing foundation and footing sizes to see if the foundation is capable of carrying the additional loads. The ability of the existing house to resist lateral movement due to earthquakes or wind also needs to be assessed- often, retrofitting is needed to be more securely attach the house to its foundation.

The new floor assembly

To be less disruptive to the existing house, the existing ceiling and ceiling joists are often left in place while a new floor structure is added above them. This allows for electrical lines, recessed can lights, and other elements to remain in the ceiling below the new addition. However, it also results in a very thick floor assembly! This can mean additional stairs are necessary to reach the top floor, (which take up more room) and on the exterior special attention needs to be paid to the resulting proportions, so that the house doesn’t look too top-heavy.

Consider vaulted ceilings on the new upper level

Many times the second story addition can use scissor trusses, which create a vaulted ceiling within the new space. If the roof is being stick-framed (rather than trusses), consider adding vaulted ceilings in master bedrooms or other spaces.

Heating and cooling the new space

It’s not always feasible to extend existing heating and/or cooling to the new upstairs, so it’s often easier and better to add separate equipment for the new floor. Usually, the upper level of a home is hotter than the rest of the house, so having a separate system on its own zone will help provide for more comfort in the addition.

Assess where plumbing drains will go in the addition

It’s important to assess how new upstairs bathrooms will connect to existing plumbing below. If there is an existing bathroom below, it may be possible to tie into existing plumbing. Otherwise, drains may need to head down through the main level to a crawl space or basement. The route of the drains, whether it be horizontal or vertical should be planned for in the design phase. Many times, the floor structure will need to be designed to accommodate drains (or even ductwork). This is much more easily accomplished when worked out in the design stage. If left until construction this process will usually result in many on-site changes, which will hold up the project and add to the project cost.

Make the stair a focal point

The stair is the one element that connects two levels together, and it becomes an opportunity to create a dramatic space. Consider adding skylights at the top of the stairs so light floods down to lower levels, or adding dramatic lighting to make the center hall a space where art can be displayed.

Don’t necessarily make all the upstairs rooms bedrooms

A den or family hang-out space is useful to have upstairs and the space can double as a guest room if a sofa bed is used. If space is not available for an entire room, consider making a nook for kids to do homework, or parents use a computer. While a second story addition has its challenges (what project doesn’t?), it’s often the only way to add space. It will radically change the exterior appearance of a home, and can make the interior much more spacious and functional. If careful attention is paid to the design, the addition will also add character and drama to the house.