Wall Assembly for Marine Climate
Can anyone point me to some proven wall details for a very exposed wall in a marine environment? The plan is to use metal panels or cement siding. Probably metal panels, but flexible.
From the exterior of the studs the construction is currently:
studs, gypsum fire board, woven rain barrier, plywood, residential tyvek, 4×8 cement panels, paint.
A siding contractor added the tyvek and 4×8 cement panels on top of the plywood siding.
The wall has a significant stack effect. Rough plan is to demo exterior to the studs, air seal, re-insulate, new fire board, new plywood, potentially an inch of closed cell over the plywood, then siding.
I’m looking for a proven method for a very exposed marine environment that alternates frequently from fog to sun, creating a lot of vapor in materials storing moisture.
My main area of concern is the detailing for a potential rain screen to promote drying and if the 1″ closed cell makes sense over that. My priority is promote drying, but would like to insulate on the exterior to avoid any cavity condensation.
Any innovative product suggestions are appreciated, especially anything that combines the fire rating of the gypsum board with insulation.
Thanks, all!
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Replies
Hi Rob,
This article might be helpful: https://www.greenbuildingadvisor.com/article/efficient-walls-budget.
Peter Yost also references a couple of additional resources near the end of the article.
Hi Steve, thank you for the article. Very informative and useful for my application. I was surprised the rain screen that was vented at the top and bottom performed slightly worse than the rain screen that was only vented at the bottom. Perhaps the top/bottom vented rain screen delivered more moist air due to air currents.
I live part of the year in a marine environment and it is very difficult to build for. What is particularly hard is that the temperatures tend to be moderate, and building science tends to assume that there are long stretches of the year when there is a significant temperature gradient across the wall. We don't air condition at all in the summer and have long periods in the spring and fall when we don't heat. So you can't count on heat transfer through the wall driving moisture out. Also, it is often humid enough that small differences in humidity can lead to condensation.
Unfortunately I don't have a lot of advice on what works, although I do have a couple of observations. The first is that you have to be absolutely ruthless in preventing water intrusion, because once it gets in it won't leave. Experienced carpenters around hear use far more flashing tape than people elsewhere do around doors, windows, corners. This also includes sources of moisture inside the house. All cold water pipes need to be insulated, and thoroughly -- even an inch of exposed pipe will cause a drip. Insulated toilet tanks are popular, as are tempering valves that mix in some hot water into the toilet supply to warm it above room temperature.
The most reliable drying force is the sun. Roofs and walls that are exposed to the sun can assume there will be some moisture drive. However, walls that don't get the sun -- and this applies particularly to basements -- should use only completely impervious insulation. By which I mean closed cell foam.