Putting a deck on the side of a new garage and was told i need a barrier between the osb and wolmanized wood because of a chemical reaction between the two can cause rot? Any thoughts or material suggestions?

It’s not exactly a chemical reaction. What happens is the water gets trapped between the OSB and the pressure-treated lumber and rots the OSB. Also, I get the feeling this deck will be attached to studs rather than to the garage¹s floor framing system‹which will really put some bad loading on the studs.

My recommendation is to not put the deck on the side of the garage. Instead, build the garage and side it all the way down…whatever kind of siding you’re using is fine. Then build a freestanding deck about half an inch away from the garage. This way the rain water can freely run between the two structures, and you¹re not using the garage to support the deck.

My recommendation is to not put the deck on the side of the garage. Instead, build the garage and side it all the way down…whatever kind of siding you¹re using is fine. Then build a freestanding deck about half an inch away from the garage. This way the rain water can freely run between the two structures, and you¹re not using the garage to support the deck.

Another thought supporting this idea – if you’re in an area which has frost heave, having the deck attached to the building can eventually lead to it being twisted, or pulled, away from the building. A “free standing” deck will be able to move around with the frost heave. I know I’m not explaining it well, so let me give an example.

When I moved into my house in WNY, my back steps were attached to the house. For additional “security,” and convenience, the previous owners had run the piping for the outdoor spigot through the top bracing of the steps. Over the next two winters, the frost heave twisted the steps away from the house *and* broke the water pipe to the spigot…every year. When I replaced the steps, the engineer friend who designed the replacement, designed them to be free-standing, as in not attached to the house at all. I also had the water pipe and spigot re-routed. The replacement steps have a small deck at the top. I can see that they’ve moved away from the house some over the past couple of years. No damage to the house, or the steps.