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Ask the Architect

The pluses and minuses of cedar siding


Q. We live near the water and have vertical plank siding. I’m told it’s cedar. It’s been there many years, and we noticed that it’s rotted from the back side and ready to crumble. We like the look and even have it on our family room ceiling, which still looks new, but we’re concerned about how long it will last if we have new outside planks installed. Is there a better material to get the same look or a way to prevent the rotting?


A. I was looking at my ceiling just the other day, since you mentioned it. It’s not the best ceiling in the world, but it’s definitely up there.


In the early 1980s I must have designed dozens of homes near the ocean that were covered in vertical tongue-and-groove interlocking siding. All cedar, it was coated with opaque stain that did a pretty good job of covering it and penetrating the wood. There were two problems I noticed. As often as possible, I tried to prevent potential rotting from the back side when I was either able to see the job or at least advise the owner to look for the method I specified for installation. The planks were to be installed over staggered horizontal wood strips that created a half-inch air space to allow inevitable moisture to drain downward, preventing mold and rot. The other item was to make sure the siding, and especially the joints, were fully stained to protect them.


Over the years, when an installer defied our notes on the plans by placing the planks right against house-wrap paper, I would stop by and walk up to the walls, which must have looked pretty suspicious to neighbors who wondered who was peering at the house. What I observed wasn’t surprising. The boards with the airspace lasted much longer, even though they still required expensive re-staining, than the boards with no airspace, which all deteriorated from the back side outward.


And you need not worry about the possibility of flame spread due to the chimney effect in the air space. Studies were done by several public and private agencies over the years, and they showed that flame consumes the oxygen in such a small airspace before it can replenish. It turns out that it takes at least an inch of airspace to support continuous combustion.


The alternative that will still give you the nautical look is vertical cement board, which also comes prefinished in numerous colors, can’t rot or support mildew, can’t burn and won’t chip, peel or crack. Following the manufacturer’s instructions, you still need to provide a moisture barrier that has enough spacing to drain from behind the panels. The best choice for this is a drainage fabric that resembles the intertwined look of an air conditioning filter. The best part of this choice is that the cement board siding is wind-rated for hurricanes. Enjoy your home!

© 2020 Monte Leeper. Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question”  in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper,  architect.