By Ann Robinson and Annie Vernon

We’ve run into an interesting design situation quite a lot recently. When a home has multiple stories, like a basement, main floor and second floor, they are typically stacked on top of each other with a roof on top. Sometimes you will find second stories that are smaller than the main floor, so there are roofs of varying heights. But on occasion you’ll find a deck or a patio instead of a roof over indoor living space.

We had one client who expanded their basement to build an underground storage area, and they topped their new storage area with a new, enlarged front porch. We had another client who wanted an exercise room in their walk-out basement and decided to top it with a veranda on the main level.

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With an exercise room on the bottom level, a deck in the middle and a master suite on top, this house has uniquely layered indoor and outdoor spaces. Replacing roofs with decks or patios is an interesting way to expand a home’s living space.

These can be fun and creative uses of space. The key to their success is proper design and construction so the outside space protects the inside space as well as a roof would.

The biggest concern is water. Concrete or wood may be used as the ceiling of the inside space and the floor of the outside space. But neither concrete nor wood is waterproof, so both must be covered with a waterproofing material.

You have two main options for waterproofing. The first is a rubber membrane called EPDM — ethylene propylene diene monomer. Engineering specifications describe EPDM as “ideal for outdoor applications because of its excellent resistance to ultra-violet light, ozone, oxidants and severe weather conditions.” It is also made to last 20 years or longer.

Because this is a relatively thin material, it cannot be walked on and care must be taken not to puncture or damage it. You should not use nails or screws to install flooring materials on top of it. You can use pavers that sit on top or a wood deck built in sections and simply laid on. You could also apply another thin layer of concrete over the membrane, which can then be stamped or stained or have outdoor tile laid over it.

The second option is an elastomeric coating. This liquid urethane rubber is mopped over the underlayment and dries to a hard finish. This coating can be walked on, so the waterproof membrane is also the finished floor. With elastomeric coating you have several options for colors and textures, and you can have sand added to create a less slippery finish.

It is also essential that you design your deck or patio to slope at least 1 inch per foot away from the house so the water will drain properly. Roofs over these outside areas — such as a covered porch — are helpful because they also direct water away from the house.

Finally, it is also possible to build indoor space over outdoor space. Our client with the veranda over their exercise room topped the veranda with a master suite. You will still need to manage water and slope the outdoor floor, and you will also need to properly insulate the floor of the area over the outdoor space. Cold air blowing beneath the floor will result in cold feet if there is not sufficient insulation.

Combining indoor and outdoor spaces can make for an interesting design. With careful attention to detail and construction, these areas can compatibly co-exist, staying warm and dry no matter what the weather outside. As always, we welcome your home architect design questions at

Blend inside, outside spaces