Corrugated metal siding in humid climate zone 3
user-7591817
| Posted in Energy Efficiency and Durability on
Greetings,
I am currently building a small, economical, and efficient home in costal NC. Corrugated metal roofing seems like a simple and durable siding choice. I am seeking recommendations on installation details. The walls in question are 2X8 with fiberglass batts and 5/8 CDX plywood. Would simply screwing the panels down over 30lb felt be adequate or am I asking for condensation problems? I assume that the corrugations will function as ventilation, but are rain screens even recommended in the humid south?
Thank you,
Ben
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Replies
Are you going to apply the corrugated horizontally or vertically?
if horizontally, you can attach vertical 1/2" furring strips where you want to install the fasteners and would not need to use any rainscreen material.
And you did not ask, but in case it is not already in your plan, DEFINITELY seal at the perimeter of each piece of plywood - seal REALLY well. Are you using felt paper in lieu of housewrap? If so, why? Consider using high quality housewrap and also sealing that well. Air sealing results in a HUGE improvement in comfort.
Thank you for the response.
Vertical lines probably will look the best on this structure. I am planning on taping the plywood seams with 3m flashing tape and running 30# felt on top of that. I am strongly considering an adhered and air barrier wrap (Henry Blueskin).
I am really trying to wrap my mind around what the moisture situation will be like behind the metal. Since metal is the ultimate impervious surface, it seems like moisture problems could easily get out of hand. Will the outside of the house wrap be the coldest surface or the back of the metal sheets? Do I want ample ventilation between there or should I go with flat metal panels that are tight to the house wrap (or 30# felt) and keep air out? Would foam sheets and no air gap be the best? I know rain screens are becoming quite popular, but what climates should they not be used in? What climate and metal panel siding design would guarantee moisture problems? My hunch is that a rain screen under metal without any type of house wrap or coating in the tropics with heavy air conditioning would be the worst possible design.
You have a few issues going on here.
1. Keeping the air out - ie air sealing your house. Go with the Henry Blueskin or similar if your CDX plywood is already installed. There is a recent podcast on the Unbuild It show - maybe #69 - in which they discussed ease of application of a few of these products. I think maybe the Benjamin Obdyke products were easiest to install but I could have that wrong.
2. Allow condensation on the back metal to weep out. It is a separate issue from everything else. If you have a good air barrier that also acts as a vapor barrier, all you need to worry about is that the water drains. Install the metal on some vertical furring strips and call it a day. Figure out how you are going to keep critters from nesting in the grooves of the corrugated. This is another reason you want to add 1/2" furring strips. You can then add a 1/2" thick drain channel along the bottom, and put one of those premanufactured foam closure strips they sell at the orange box in front of the drain. Use the same at the top to let air in at the top and keep critters out.
3. Continuous foam on the exterior will DEFINITELY help eliminate thermal bridging and can help other issues as well. Others can give you better info on how important that is in your climate zone.
ETA: Your siding is not what keeps your house airtight or keeps water out. Sure, it repels bulk water, but your air, vapor and waterproofing layer need to be BEHIND your siding. The siding is then just the aesthetic piece, and other than aesthetics, its main purpose is to protect the air, vapor & waterproofing layer. EVERYTHING should be air sealed, insulated, water sealed and vapor addressed BEFORE the siding is applied. That includes the windows & doors. It took me a long time to wrap my head around this idea, because that is so totally different from how houses were built 100 or even 50 years ago. Maybe looking at it like that will help.
What is you flashing plans for around doors and windows? Do you have detailed drawing?
I have seen several very poorly install windows and doors in metal building I am sure the plan was to figure it out in the moment and leaks and rot set in when the caulking failed.
I know you have no plans to sell any time soon but the truth is every property will get sold someday and maybe you like the look of corrugated steel I can a sure most buyer will not so you are spending extra to build a white elephant.
We almost never see roofing felt in walls anymore Seems like house wrap has replaced it.
Why spend extra for plywood sheeting and then cover it with steel seems like over kill to my ears.
Reconsider vinyl siding if low cost is the driving factor in this choice.
Walta
Ben,
You may find this useful: https://www.rockwool.com/syssiteassets/o2-rockwool/documentation/brochures/commercial/exterior-wall-solutions-for-hot--humid-climates.pdf