What are sleepers?
Sleepers are used in framing and placed between the deck surface and the ground or slab below it. A set of sleepers supports the decking and allows moisture and air to flow below it. Decking laid directly over concrete or packed soil will rot quickly. This happens when moisture is trapped between the two materials.
Where do we use sleepers over regular framing?
Regular framing is used when raising the deck up off the ground to a desired height. This system involves a beam with joists resting on top a fixed post. This is the easiest way to get the wanted height during construction. With the deck lifted off the ground, there is not much concern around the airflow underneath the deck. Sometimes this is not always possible and the deck has to stay as low as it can. For example on the rooftop of an apartment building, or if there are obstacles restricting how high a deck can be.
Sleepers have to maintain the structural elements found in regular framing. Spacing should still be no more than 16″ on centre between joists to ensure framing is still strong enough for the decking material being installed. Once the frame has been laid out, the sleepers are installed laying flat rather than upright like regular joists. This eliminates the possibility of using joists hangers to hold them in place. In this instance we used a pocket-hole jig to secure the sleepers to the rest of the framing. This is a strong bond that will hold the framing together for years to come.
Waterproofing the frame
Once the frame is built and put together, there are a lot of areas exposed to the elements and can mean bad news for a deck if not properly prepared. Using pressure treated wood protects the boards from moisture and rot much better than non-treated wood. But once pressure treated wood has been cut, it opens up and exposes the inside of the board. This is because the treatment only penetrates the top surface of each board an 1/8th of an inch or so. Once each board used in the framing is cut, it is brushed with a treatment solution to re-protect the surface. Boracol is a great example of this treatment solution.
Treating the cut ends of each board is not enough to fully protect the frame though. Depending on the area the deck is being installed, there may be other hazards present. For example the rooftop of an apartment building. Rooftops are sealed to protect the interior of the building and can sometimes pool water if not properly drained. In this case, spacers will be installed underneath the sleepers to create a barrier between the board and the pooling water. The last area needing attention are the pocket-holes. The design of these holes essentially creates a small hole in the wood which can fill and hold onto water that will slowly seep its way into the joints. This will cause problems down the line for your deck. Simply place some self adhesive waterproof membrane over the joints and this will protect those pocket-holes.