Masonry Against Wood
Keep them apart, and live happily ever after
I know that stone and concrete shouldn't be in contact with the siding, but there are places where that seems impossible to avoid. A front stoop, for example, is often built against the siding, and I haven't noticed a problem with rot where this is done. Why not?
— Steve, East Setauket, NY
Tom Silva replies: Probably because you can't see behind the stoop, which is where the problem will fester. Masonry front stoops should never be placed directly against wood—that's just asking for problems.The rot won't affect just the siding, either. Eventually, the sheathing will go, as will the framing. Even then, you'd probably think everything is just fine until the damage shows from inside. By then, you probably have attracted termites, which love to dine on moist wood. Even without them, repair costs will be serious.
So here's what I do. Before the stoop is installed, I protect the sheathing with a layer of 30-lb. builder's felt or bituminous waterproofing membrane. I run it down from the underside of the door sill so it overlaps the junction of wall sheathing and foundation. After the stoop is in place, I cover the area between the door sill and the top step of the stoop with a kick plate—a horizontal piece of 5/4-inch or thicker trim stock nailed to the sheathing. I leave a ¼-inch space between the bottom edge of the kick plate and the step, and I seal the trim stock on sides, faces, and ends.
I then bring the ends of the clapboard up to the sides of the stoop, but stop just short of touching the concrete. This prevents water from being trapped and doing any damage to the siding.