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How durable is unfinished cedar lap siding installed over a rainscreen?

Rachel Wagner | Posted in Energy Efficiency and Durability on

I typically specify cedar lap siding to be sealed on all 6 sides prior to installation, whether installed over furring or not. In a current project the client and I want the cedar to “gray out” and we are also on a tight budget, but are not sacrificing high performance construction. Is it a bad idea to install the cedar lap siding over 1 x 4 furring with no finish and let it just age naturally? The roof has deep overhangs, good flashing details, etc. The assembly will have good drying potential. Or should we use some kind of transparent stain or sealer, at least once?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Rachel.
    I believe that the siding will be very durable, although the color will not be uniform. The homeowners should be prepared to accept color variations; the lower courses of siding will not look like the siding under the eaves, and different orientations will also take on different colors.

    Make sure than any exposed nails are stainless steel, of course.

  2. Rachel Wagner | | #2

    Martin you are quick to respond! Thank you. Yes, stainless steel ring shank siding nails. Will the color variations lessen over time, with the siding becoming a more uniform color? The contractor also suggested possibly using a bleaching oil to provide uniformity.

  3. J Chesnut | | #3

    I've seen an example of unfinished board and batten (poplar) that has proved durable for over 16 years. The homes were well designed with an eye towards water management and were in the woods which reduced the impact of the UV rays.
    I think part of the durability of this application was the consistent 1" actual thickness of the board and battens however.

    Because of weathering and erosion caused by sun and moisture not coating the cedar in an appropriate manner with proper maintenance when needed will reduce its lifespan. By how much I can't say.

  4. John Brooks | | #4

    I will echo J's warning about UV
    depends on climate and sun exposure
    I have seen Cedar really "cook" in North Texas
    Especially on a western exposure.

  5. Matthew Amann | | #5

    Rachel, without back priming, or fastening (visibly) the bottom of the lap siding, cupping, and warping between rainscreen strips is a likely possibility. I assume this siding is 1/2" or so at the bottom to 1/8" at the top? This stuff even when made from clear cedar likes to move a lot, and with spanning over assumed 12-16" spans, I'm not sure about it holding up that well..... it's the sun that kills.

  6. Chris Koehn | | #6

    Wood siding was used traditionally without finish and it can be very durable in the circumstances you suggest. I've found that the grade of cedar (western red cedar, correct?) has more to do with durability than the finish.
    Using clear grade material will maximize durability and finish becomes less important, though clear grade siding is more expensive to be sure. Clear grades tend to be more dense and thus offer better rot resistance as well.
    There is huge variance in quality, dryness, and sawing technique on the market and it's important to understand what you're buying. I generally specify select knotty K-D when budget rules.
    Finishes protect siding by limiting the effects of UV. Grey wood is the result of UV degradation; this layer serves to protect the undamaged wood below. How long the grey layer protects depends on conditions of service and quality of wood.
    See
    http://www.wrcla.org/cedar_products/cedar_siding/lap/grades.htm
    for more info on grades.

  7. Rachel Wagner | | #7

    The site is on a lake in Northern MN. Very cold climate with open southern exposure and more protection on north, east, and west sides. Also a full-length covered walkway on the west side so there will be very little prolonged direct western exposure. One story building with gable end exposure on south and north sides. Furring is 16" o.c. and 6" exposure for the lap siding, face nailed, so I'm not concerned about cupping or warping, not with the rain screen detail. At this point, though, since it is western red cedar, not white cedar (and as I've now learned will not "go to gray" necessarily), so we still may treat it with a clear sealer prior to installing, just once, and then wait and see as time goes by.

  8. GBA Editor
    Martin Holladay | | #8

    Rachel,
    Many of the homes I built have unpainted white cedar shingles, so I am more familiar with white cedar than red cedar.

    I don't believe that the color changes will even out over time. It's best to be honest: different levels of sun and rain exposure will result in different colors. If that's not what you want, get out your paint brush every 6 years.

    In Your Engineered House, Rex Roberts wrote, "With no hesitation I cross off all finishes applied either to wood or metal for the purpose of increasing durability. ... I have never been able to see anything wrong with the original color of maple, mahogany, walnut, pine, spruce, or oak. ... When left alone, any kind of wood goes toward a darker shade of brown, of some hue or another, depending on the kind of wood. Sunlight accelerates the process. Rain turns the color toward gray. ... Sun and rain, gray. All sun, brown. A vertical board ... would turn out like this -- with brown at the top shading down to gray at the bottom."

  9. J Chesnut | | #9

    A clear sealer serves more to keep moisture out of the wood than protect it from UV light. Its the pigments in solid color stains and paints that take the hit from the UV light instead of the wood. (Unless there are UV protection clear coats that I am not aware of.)

  10. Allan Edwards | | #10

    Rachel:

    I have a bit of cedar lap siding on my house and I coat it with stain and sealer every few years. My neighbor built her house with all cedar siding, wanted that gray look as you describe, has not put any stain or sealer on the siding. It looks horrible, In some areas it has actually turned black, it is not weathering evenly at all, and she has had it this way for 5 years. Not to mention the possible wood rot I think she now how on the areas close to the ground where there has been a lot of back splash.

    Allan

  11. Matthew Amann | | #11

    Rex may also like the color of mildew on most of those species he listed, which is also likely to become present on the surface. @ J.Chestnut, there are clear UV inhibitive sealers and finishes, but nothing last that long, again keeping the truth in mind. @Rachel, hopefully that face nailing is under the lap point of the piece below, or else cupping will only be increased. If you REALLY want consistency of weathering, you should use the BLEACHING OIL!!! One coat of sealer or finish is NOT going to help, only put it off a couple of years, and working with it a lot, I will say that Western Red Cedar definitely goes gray. Starting off gray is your best bet IMO.

  12. GBA Editor
    Martin Holladay | | #12

    Allan,
    You mentioned that your neighbor's siding faces "possible wood rot ... on the areas close to the ground where there has been a lot of back splash."

    As I'm sure you know, the solution to rotting siding due to splash-back is not paint -- it's lowering the grade or changing the surface where the water lands.

  13. Rachel Wagner | | #13

    So, I'm definitely considering bleaching oil. Have found only one; it is from a name-brand - hard to get the MSDS on it. Any worries about linseed oil based bleaching oil as a product? I've seen some low-VOC clear finishes that are supposedly UV resistant, but if we don't necessarily want to keep refinishing, it still seems to me the bleaching oil makes the most sense if I want to get a more uniform finish.

  14. Matthew Amann | | #14

    When it comes to giving the wood what it needs, which is penetration, oil is king. You could conceivably make a bleaching oil, but would have to experiment with it. For the grey look you can use a Potassium
    Dichromate solution, and I have also used ferrous sulfate, which turns new wood into old barn wood grey in moments time. The ferrous sulfate actually reacts with the wood chemically to do this, so it is not a coating. You can buy it as "grass fertilzer" at a lot of garden centers. It is a natural by-product, and mixed in a rich solution with water greys the wood or also stains concrete to rich brown-red-orange variable tones. This is the poor man's concrete stain. As far as I know, the Cabot bleaching oil has linseed and tung oils in it, with petroleum solvents, and heavy metal driers in it, so if you don't like the sound of that stick with the ferrous sulfate, still wearing gloves of course.

  15. Peter Powell | | #15

    Rachel, If you want a natural weathered look, you should consider atlantic white cedar instead of red cedar. Unfinished red cedar will turn dark gray to black and be blotchy. The white cedar starts as a light color and weathers to a medium gray color- but will not be completely uniform especially under overhangs etc. No finish is required and if reasonably thick, will not curl. Red cedar bevel siding unfinished will curl unless face nailed- this stuff is just too thin. You could also consider t&g or b&b or shiplap to minimize curling. If you still prefer red cedar and a lapped siding look, consider 1x8 boards rather than beveled. Start the first course with a spacer and the rest installs normally and will look like beveled but will not curl and does not require face nailing.

  16. user-7022518 | | #16

    Has anyone heard of using potassium silicate to gray wood? It seems to be a key ingredient in some European wood treatments and has the benefit of also being a fire retardant. If so, do you know the concentration level that is effective?

    Lisa

  17. Hugh Weisman | | #17

    Almost every dwelling on Martha's Vineyard is sided with white cedar shingle with no finish. They grey out like you want, but there is often variation under overhangs, porches, etc. Typically lifespan is 40 plus years. I've also seen some horizontal cedar siding, but typically it would be a full 1 x dimension (i.e. 3/4" thick) in a T&G or shiplap configuration. However, The salt air certainly contributes to the greying.

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