Venting Wood Siding for Longer Life of Wooden Shingles and Board Siding

By Harry Watt

Recently I completed a large home in Western North Carolina where I used bald cypress lumber from Eastern North Carolina for siding.  I used shingles for the upper portions of my home and lumber in a board and batten pattern for the lower portions.

Contrary to what some people might think, wood is a very sustainable material that can last for centuries when properly prepared, installed and maintained.  Most homeowners and contractors do not know what it takes to keep wood siding flat and ensure that finishes last a long time.  The two most important factors are ventilation and balance.  Ventilation on the backside of wood siding is critical because it provides a way for moisture to escape so the wood stays dry. Balance means having an equal amount of finish on both the inside and outside of each piece of siding.

Ventilation and Balance
The walls of my home were constructed with SIPS (Structural Insulated Panels) with OSB (orientated strand board) panels. I used house wrap to enclose the exterior of the home to allow water vapor to escape from the house while preventing liquid water from entering the house walls.  I then installed 1×4’s of pine horizontally which I painted with primer paint to seal the wood.

A 3/4 inch wide dado (trench) allows for air and moisture venting

Prior to installing the panels, however, I cut vertical channels (see drawing) in each board to allow for air flow.  Specifically, I cut a 3/4 inch wide dado (trench) into the pine strip at twelve inch intervals.  These channels ensure constant air flow behind the siding (thus reducing heat gain to the house).  They also provide a pathway for moisture to escape.

 

Metal flashing at horizontal junction between the board and batten siding and shingles

At the horizontal junction between the board and batten siding and shingles I installed a metal flashing that created an opening in the junction between the boards and the flashing.  This gap acts as a chimney to allow air to escape behind the siding.  The gap was also made at the top of the walls under the roof overhangs.  Thus there is a continuous channel for air to flow from top to bottom of the exterior walls.

 

venting at bottom of battens

Venting at bottom of wood battens

I “balanced” the finishing of the siding with two coats of stain and clear sealer on both the inside and outside of the boards and shingles. I used a log cabin oil based stain because I liked its uniform cedar color and it worked well whether dipping, brushing or rolling.  I used a water based clear coat finish that dried clear and provided a thick protective coating over the stain.  It’s been my experience that stain alone does not have enough protection to last beyond one year without being covered by a clear protective coat.

 

It is important to understand that the level of maintenance on wooden siding depends on whether you use transparent stains, pigmented stains, clear cover coatings or paints.  Transparent stains are thin so you can see the wood grain and they often have to be applied every year to look good.  Pigmented stains have materials that lie on top of the wood but don’t completely hide the wood grain.  They may last a couple of years before recoating is needed.  Clear coatings can be applied directly to the wood for a clear finish or on top of a stain for several years of protection.  Paints completely cover the wood grain and may last many years depending on many factors, like a sunny versus a shady location, ventilation, moisture, etc.

Keeping It Local
As an NC State forestry geek, I like buying local wood products, so I purchased four truckloads of cypress timbers and lumber from a sawmill in Eastern North Carolina that specializes in cypress and local hardwoods.  Later, I bought two additional truckloads of lumber of cypress and yellow pine.  The yellow pine was used for roof and floor decking.  All this wood came from North Carolina growers and all the kiln drying and wood planning was done thirty miles of my home.

As an “FYI”, there were no third party certifications (as in FSC – Forestry Stewardship Council) available on these particular wood products.  However, as a professional that works in the forestry industry, it has been my experience that the current loggers and sawmill operations in North Carolina are responsible in their forestry practices.  I’m well aware that the North Carolina Forest Service has an active program of monitoring forest harvesting operations and that the level of responsibility has greatly improved.

Timber Loving Care
Overall, I am pleased that I built a timber frame home that has all wood siding, that the wood came from North Carolina forests, and that my crew and I constructed the whole house, including the timber frame, cabinets, stairs and the doors.  I’m proud of the craftsmanship that went into this home.  I’m also glad that by sourcing local wood we did our part to support North Carolina wood business.  It’s nice to know that in our own small way we did our part to keep this important local industry going.

Harry Watt is the Business Improvement Specialist with the NC State University Wood Products Extension. Mr. Watt was a valuable resource for wood selection for the Greenspiration Home, and inspired us to source as much locally grown wood for our home as possible. This is Harry’s second contribution on his beautifully constructed wood home.

2 Responses »

  1. Cutting a 3/4″ wide dado in the 1 x 6 pine horizontal furring strips is a lot of work but you are doing it the right way and I would suspect the system will outlast us both other than paint the exterior every 10 years or so. Great article on doing it right the first time. I am not too keen on OSB or SIPS and prefer 2×4 staggared studs with minimum of 8-1/2″ from FOS to FOS overall dimensions.
    We are locaated in Grass Valley, Calif. seventy miles north west of Sacramento and ninety-five miles south east of Reno, Nevada in the Sierra foothills, the Mother Lode at an elevation ranging from 2,000 to 4,000 feet. We have so many trees we can’t see the forest. Cedar, Fir, Oak, Pine to name a few. There is an old lumber mill up here, Kubich Forest Products that mills the most beautiful 1×4, 1×6 and 1×8 STK cedar tougue and groove or shiplap that I have ever seen along with cedar sawn siding that is full size 1×12, to 1×6 and looks like resawn. The price is 30-40% less than lumber yards. The mill is in a canyon and you would think you are back in the 1880′s. The full size 1×12 is my choice for vertical siding and horizontal siding and as you do cut a dado on the back side of the board on the width and at 4′ o/c 1/4″ deep the length of the board. I make the dado at 2′ on the first board and 4′ on the second board with furring strips not required.

    Thanks for the opportunity to comment.

    • Nice house. Cypress is beautiful. I have no evidence of where and how the cypress was harvested, but I think we are going a little too far on a “green” website to say

      “… there were no third party certifications (as in FSC – Forestry Stewardship Council) available on these particular wood products. However, as a professional that works in the forestry industry, it has been my experience that the current loggers and sawmill operations in North Carolina are responsible in their forestry practices. I’m well aware that the North Carolina Forest Service has an active program of monitoring forest harvesting operations and that the level of responsibility has greatly improved. ”

      Improved compared to what. I have worked with loggers to know that they cannot be trusted–money is money to them.. The FSC rating exists for a purpose. If there is no rating on a given type of wood, its use in a “green” house must raise one’s suspicions.

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