Every great outdoor living space starts with a good plan and a solid foundation—which is what our decking series is all about. In this series, we sit down with our good friend Kevin Kunka of Trex Company to cover some of the ins and outs of executing a successful decking project. Trex is the world’s largest manufacturer of wood-alternative decking products and a veteran in the outdoor living industry. Over the years, the Trex name has become synonymous with quality manufactured decking. 

This week, Kevin and I discuss ventilation best practices when building traditional or rooftop decks. Watch our conversation above or read the highlights below.

Proper deck ventilation

In the Pacific Northwest, ventilation is an important consideration no matter what material you’re using—even manufactured decking. When building with manufactured deck materials, Kevin recommends leaving at least 3 ½" inches between the ground (or any other surface) and the bottom of the decking board. This gap not only provides airflow, but contributes to reduced maintenance overall.

With attached decks, it’s also important to consider how the deck might impact ventilation for other parts of the house. For example, crawlspace ventilation can easily be obstructed by deck framing without proper planning.

Ventilation for rooftop decks

Rooftop decks are becoming more and more common in the Seattle area, especially among new construction apartment buildings and townhomes. Because of a roof’s waterproof membrane, installing a rooftop deck isn’t as simple as laying out joists or fastening deck boards directly to the roof. In this application, Kevin recommends a couple best practices.

First, use an adjustable pedestal system—this will allow you to solve for the roof’s slope and create adequate space between the waterproof membrane and deck surface. Second, install decking boards in a 4' x 4' grid system. Using a grid design allows you to easily lift individual squares to access the rooftop underneath for regular maintenance or in the event of a leak. 

For more manufactured decking best practices, check out our recent posts on installation basics and stair stringer requirements for manufactured decking.