Proper Deck Installation

[Matt Oliverius]

The inspector that inspected my house wrote the following in my inspection report:

"The decking is installed with no voids between the planks for drainage and most of the planks are upside-down (with the grain crown down). The builder stated that the planks will shrink to provide the gaps, and that the "good" side of the planks is facing up."

I know that a few cycles of thermal and moisture expansion and contraction may leave a gap between the planks over time, but will it be sufficient for drainage? Also, the builder does not want to reinstall planks with the grain crown up. However, I believe this should be done on a new house. I have read that incorrect installation of these planks increases the chances of splintering since one side of the wood is more susceptible to this. However, I need some firm ground to stand on. Does anyone know of any ASTM standard or equivalent that might address this, or any web sites?

[Jeff Cochran]

No standards, and no general consensus anymore as to which is best. If this is PT lumber, it may not shrink enough to provide gaps, but cypress and redwood usually do fine. The theory is that boards will warp away from the crown, and if the crown is down the edges will warp up and the board can retain water. In reality, boards will warp toward the crown on occasion, and if the boards are fastened well they don't warp appreciably enough anyway.

If you're concerned, switch to a non-wood decking. I'm assuming this is a home inspector, not a building inspector, and he's covering his butt in case the boards warp and you blame him for not telling you. My inspector was very good, but I got notations about a fence latch that was slightly crooked, roofing that "looked" old but didn't show any physical aging signs and touch-up paint that didn't exactly match the wall color.

Jeff

[mark Ransley]

What type of wood, what size, how far away are your joists, and how are they fastened, nail or screw. PT shrinks if its 2x4, crown down will cup and hold water, 2x4 not much though, are all boards reversed, or did he just not check them. Screws are best

[Matt Oliverius]

Thanks for the info everyone. I had heard about the cupping of wood planks if they are installed with the grain crown down, and the potential for water absorption.

I found a website last night that explained it very well. "Flat grain lumber tends to exhibit grain raising. When the grain separates on the face of flat grain lumber, it occurs on the pith side or "heart" face of the board. To prevent grain raising problems, the most important consideration is to orient boards so that the bark side will be exposed to the weather. Deck boards should always be installed "bark-side-up" and siding should be installed "bark-side-out" whenever possible."