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Using galvanized metal for siding

Desert Sage's picture

I am attracted to the idea of using inexpensive corrugated galvanized metal roofing material to side my new house. I think it would go well with the modern architecture and the wooded setting. I am a longtime, faithful reader of Fine Homebuilding but am (forgive me) still confused about the insulation/venting/moisture barrier issue. Here in the humid Pacific Northwest it is normal to install a moisture barrier on the inside (facing the heated area) of the building with a permeable moisture retardant layer, like a house wrap or felt paper under the siding on the exterior. If I were to use galvanized metal for siding material, would It be required that I provide a venting space behind the metal? I am imagining something like "Rain Screen". A contractor friend of mine suggests that I only need to install felt behind the metal. Any Ideas out there?

Edited 9/25/2009 12:41 am ET by Desert Sage

(post #87898, reply #1 of 22)

First, welcome to BT!  It can be a bumpy ride but if you hang around you can get some pretty good info in a fairly timely manner.  The good info and the bad come at the same price :-)  We do have several regulars here from the Pac NW too, so maybe they will respond.

Don't know much of anything about metal siding but I'm gonna throw out a coupla ideas...

Seems like the corrugation of the metal would almost create an 'automatic' rain screen effect, especially if the 'lines' were vertical and vented at the bottom.  Might need some kind of screening or something to keep the critters out though.   Maybe serve as drainage too for condensation that might occur.  For that matter, the ventilation would help reduce condensation by helping to keep the inside surface and outside surface of the cladding at the same temperature.

I think you are right to be concerned about moisture barriers and ventilation as my guess is that galvanized metal would have a perm rating of zero - ie no drying ability at all through the exterior cladding material.   Here, in NC we have a quite humid climate and we have gone to often using no vapor barriers in wall assemblies except what the sheathing, sheetrock, etc, might provide.

What is your plan for detailing the connections between the siding and the doors and windows?  Would there be some way to do this without relying heavily on caulk.  Perhaps you will have wide overhangs so this is less of an issue?

What about long term rust resistance of the material you are looking at?  Lots of cheap galvanized materials rust up in 5 or 10 years....  Or maybe you would be all right with that look???

Someplace I've seen pics of modern styled houses that had this type of siding...  maybe in FHB? 


(post #87898, reply #7 of 22)

Thanks you all for the ideas. I will look for the Galvaum. Is not that a ASC brand? My first thought was that the cheep galvanized metal would be "no maintenance" but rust within ten years is not very appealing.

Also to add: Yes I would like to install the metal horizontally because I want to accentuate the horizontal lines of the building. Good point about the straps, though. I will have to pre-drill through those, I guess. I would like to use wide corner boards and trim (1-1/2" x 6" milled from old growth Western Red Cedar, an ancient tree that blew over on my property). I am imagining using "z" type metal flashing over the window and door trim, and using the wooden "wiggle strips" under the metal and over the stud locations to fasted the gasketed screws through.

It sounds like, from what you are all suggesting, that I should provide a space to vent behind the metal but screen the openings to keep out the critters. I presume then that I should still install the vapor retarder on the inside surface/heated side of the wall. six mil poly sheeting or the like?

Any other thoughts on this would be so appreciated. Thank you!

Oh, and I did complete my profile info. I live in Bellingham, Washington. Thanks for the reminder.

Edited 9/25/2009 6:51 pm ET by Desert Sage

(post #87898, reply #12 of 22)

Greetings from close by. We do a lot with metal siding and roofing and as far as I'm concerned you could easily do a great job on a house using corrugated as siding. I would sheathe with 1/2" CDX and paper with 30# felt as usual. I would take it as a given that water will get between the siding and the felt, either as driven rain or condensation, or both. I would consider using El Dorado battens or similar to create a break between the metal and the structure. You'll need to design trim details for your doors, windows, etc., that work with the metal both mechanically and aesthetically. There's an outfit up there called Com-Steel that has supplied us with materials on occasions, they might be a good source for you as well. Ideally you can find one shop to provide the corrugated and also bend the flashings and trim pieces you need out of the same material.

There's a brand of metal that's uncoated and develops a nice rusty patina. A guy up the road from me did an outbuilding roof with it, and it looks pretty cool. Someone will be along in a minute to supply the brand name.

(post #87898, reply #13 of 22)

Hey Dave,

You have any pics of that building, the rusty patina one?



(post #87898, reply #15 of 22)

I don't. It started as a shed with a shiny corrugated roof and now I notice the roof is uniformly rusty, within a year or so.

(post #87898, reply #8 of 22)

Thanks Matt! to address your question about the details:

In my feeble mind I am thinking to butt the metal up to the vertical corner boards and screw them through the "wiggle strip" into solid corner framing. Would you suggest another approach? Maybe this does rely too much on caulking. I do have substantial overhangs (two feet and three feet) that would protect the building from rain except during periods of high winds. Let me know what you think about that if you get a chance. I am still in conceptual stages about this metal siding idea, so am welcoming any thoughts.

(post #87898, reply #14 of 22)

I'm not gonna answer your Q as I think you have some more qualified people involved at this point...


(post #87898, reply #16 of 22)

Cor-Ten I believe is the name of the steel David was mentioning.

Also for your consideration.. double sided butyl sticky tape used for glazing and penetration sealing is great stuff to use on metal sidings/roofing.
I have done several buildings with the metal horizontal , but none were well insulated/detailed as they were temp. quarters for 9 month usage.
Detailing the ends at the corners /window/ doors may be problematic. Working out from the window (for example) itself I would consider sealing with vycor to the weather paper, then wood trims, then standard metal trims made out of matching material to the siding. I have often gotten flat sheets of metal and had my favorite sheet metal shop bend them custom for me. Basically because communication was always spot on...

Sealing the bottom against critters and insects is important.

Life is Good

Life is Good

(post #87898, reply #17 of 22)

Thanks to all for the great information. I can see how the glazing tape idea could help with the flashing details. Thanks too for the profile link on the corner trim. I can see how that works.

The house is sheeted with 1/2" CDX and I could upgrade from 15# felt to 30#. My largest concern is the possibility of moisture being trapped in the wall, yet it looks like that hurdle is surmountable.

(post #87898, reply #18 of 22)

Hard to see a problem with trapping water. The corrugated in itself forms a rainscreen, and if you can batten it off the wall, so much the better. Protecting the felt from UV and preventing critters from crawling up inside will be the main issues.

One thing that hasn't been mentioned is whether or not you'll hear popping noises when the sun comes out and heats the metal. I've got a job going right now where my saw and storage setups are under a ~25 x 25 carport with a 5v crimp metal roof. You can hear within minutes when the sun hits it. Not unpleasant at all, as far as I'm concerned, but YMMV.

(post #87898, reply #20 of 22)

Thanks, I think I will do that. Batten the metal off the wall with the plastic rain screen strips covered with screen, top and bottom.

I know what you mean about the popping noises. My 28 foot square carport that I roofed with polycarbonate (SunTuf) sounds like popcorn each time the sun comes and leaves. I hope that all that popping doesn't mean there will eventually be fatigue cracks.

(post #87898, reply #22 of 22)

With metal the expansion and contraction wears on the fasteners.

(post #87898, reply #2 of 22)

DS......Welcome to BT.

If you would, fill out your profile to help us know a little bit about you and where you live.

As far as flashings and metal siding accessories to make your installation work and look better, your local supplier of corrugated will be able to supply those items. They will be listed with the company that produces agricultural/pole barn metals.

You might want to use "rat guard" as a starter at the bottom of the corrugated. Allow the housewrap to lap over the flashing portion that returns up the wall. J-channels and window/door cap flashings are also available in galvanized.

Also ask about costs and availability of different qualities of corrugated metal and coating thickness/weights per sq.ft. rather than settling for some the "lighter gauge" (cheap) metal products.

Use neopreme gasketed screws for attaching to the sheathing. Rely on a good drainage plane rather than caulking, which will ultimately fail.

The devil is in the details................Iron Helix

.......Iron Helix

(post #87898, reply #3 of 22)

I have had the same idea for siding.  Maybe even add a round "Harveststore" silo for an office tower.  I'm in the PNW and long overhangs are very important, IMO.  Keep the water off the building. 

I would like to fill in my profile but can not figure out how.  Any help on that one?

(post #87898, reply #4 of 22)

Left click on your name in THIS posts TO box, that should open up the page you want.

welcome to BT

Spheramid Enterprises Architectural Woodworks

Repairs, Remodeling, Restorations  

(post #87898, reply #5 of 22)

I'm not sure where you are in the PNW. The BC building code allows corrugated metal siding as a rainscreen without strapping if installed vertically - which incidentally is much easier. If you do decide to install horizontally you will have to be very careful with the strapping, as it has to match the location of the gasketted fasteners, which form an important part of the look of the siding.

I use corrugated siding quite a bit. It goes very well with stained cedar and perhaps surprisingly with Hardiplank, helping to keep things from getting too woodsy or suburban.

You do want to make the distinction between galvanized and galvalum siding. I'm not even sure they make corrugated galvanized anymore. Galvalum is the way you want to go.

Edited 9/25/2009 11:36 am ET by fingersandtoes

(post #87898, reply #9 of 22)

I meant to ask you in my last post about your method of dealing with corners and trim. As Matt and others have pointed out, it is best not to rely on caulking. The horizontal application of the metal sounds like it may be problematic with respect to the trim details.

(post #87898, reply #10 of 22)

Galvalum is an Aluminum - Zinc alloy coating applied to steel which is much more corrosion resistant than galvanizing. It is the industry standard for un-painted steel roofing and siding.

I use three types of trim for all common applications, and these are standard pieces supplied by the metal manufacturer: Corner pieces, J trim for the sides and top of the siding, and a drip for the bottom.

All the trim is installed before the siding. It is because the sheets have to slip into the J trim but just lap over the corner and drip trim that it is easier to do the siding vertically. The sheets have some give along their corrugated profile, but not the other way, so getting them between two opposing J trims that might commonly be used on window or door jambs is difficult.

In terms of what you use behind them, it really depends on how you plan your wall to work. Commonly, rainscreen walls here are designed to vent moisture that might get into them to the exterior. That means the interior has a vapour retarder such as 6 mil poly, and the exterior has gaps or holes left in the sheathing to allow the water to escape. The sheathing is covered in building paper or housewrap and vertical  strapping applied to provide a drainage plane.

I like this approach because it makes for a wall system that is quite forgiving, anticipating that some moisture may get into the wall and having a way of dealing with it.


Edited 9/25/2009 8:08 pm ET by fingersandtoes

(post #87898, reply #11 of 22)

I haven't been able to find a drawing of the corner trim I use. This one is similar but has a 1/2" return that mine doesn't.

(post #87898, reply #6 of 22)

If you can find past issues of "Dwell" magazine, (I no longer get it--used to subscribe) they seemed to have a house sided with corrugated galvanized metal in almost every issue. I think one of the past FHB issues on houses had one--was built in Texas, if I recall correctly, and also used local limestone. What others told you is good--something to keep mice and insects out is needed at the bottom.

(post #87898, reply #19 of 22)

The rusty corrugated metal is called RCM, no surprise. It's being pushed by "green" advocates since it uses no rare or controversial heavy metals. It's simply corrugated steel in a heavy gauge. Supposed to last 40-60 years on a roof (average).

(post #87898, reply #21 of 22)

Thanks for the link. I love the look of CorTen steel but the price of that stuff.... wow. Maybe I should look into the RCM alternative.