Wood siding failure prevention  (C) Daniel Friedman Wood Siding Failures - Causes & Prevention

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Wood siding failure diagnosis for siding installed over foam insulation:

This article discusses the causes and cure of wood siding failures including when siding is installed over rigid foam insulation - how to prevent siding cupping, siding nail pops, siding splitting, & siding separation or misalignment at butt joints and other wood clapboard and hardboard siding failures. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Wood Siding Failures when Siding is Installed over Rigid Foam Building Insulation

Nails A Poppin: how to keep wood siding from wriggling over foam sheathing - links to the original article in PDF form immediately below are followed by an expanded/updated online version of this article.

This article explains the causes of wood siding failures and continues with advice on how to prevent siding cupping, siding nail pops, siding splitting, & siding separation or misalignment at butt joints when wood siding is installed over rigid foam building insulation.

As early as in 1979 failures of wood siding were reported when that material was installed over foam sheathing. By 1982 the problem was under study by the National Forest Products Laboratory and the Society of the Plastics Industry (representing insulating foam building sheathing manufacturers) and a 1983 report by that group made suggestions to avoid siding failures but did not identify the underlying causes.

In addition to the wood (clapboard-type) siding failures listed just above, wood product siding failures in the hardboard siding family were reported: siding waviness, hardboard siding dimpling (caused by over-nailing), or hardboard siding buckling lengthwise when hardboard siding gets wet on its back or building-side face.

Other hardboard siding failures are discussed at SIDING HARDBOARD, and still more serious building damage including rot and mold where leaks occur between synthetic stucco are discussed at SIDING EIFS & STUCCO.

Text below excerpts from and paraphrases the original wood siding failure over foam insulation article shown in the links above.

Causes of Wood Clapboard Siding Failures

Improper nailing of wood siding: Among wood clapboard siding failures when that material is installed over insulating foam building sheathing, the articles above report that improper nailing is the most frequently cited cause.

To avoid these problems it is important that the installer use nails of sufficient length to penetrate both the foam sheathing and the wood framing beneath, and also the siding should not be nailed so hard that it is cupped (lengthwise) by having compressed the foam sheathing. Contractors who installed siding using 7d or 8d siding nails were using fasteners that were too short - the nails barely made it through the foam and siding easily came loose later.

Moisture damage to wood siding: Cupped wood clapboards (across the width of the board) are caused primarily by water or moisture penetrating the wall and becoming absorbed into the clapboard through its back surface. Flat-sawn clapboard stock will cup more than vertical-sawn.

The moisture problem in a clapboard wall may come from the building exterior (such as due to wind-driven rain, installation and flashing errors), from the building interior (indoor moisture problems, missing or defective vapor barriers), or from the wall cavity if ice dam leaks, roof leaks, or plumbing leaks wet the wall cavity.

Siding quality affects siding failures: poor wood siding stock is more prone to failures. Lower quality wood clapboard siding qualities that affect its failure rate include:

However the impact of these characteristics on siding failures varies by wood species. For example, redwood siding is reported to perform well even at thinner thicknesses and when not primed or coated.

Foam sheathing contribution to siding failures: Contributing to moisture damage in wood clapboards nailed over foam is the observation that because the foam provides no support for the nails passing through it, any movement in the wood (such as due to thermal or moisture changes) can cause the wood to loosen and drop out of alignment.

Hardboard siding installed over insulating foam sheathing may also suffer from lateral waviness or "cupping" due to over-nailing that compresses the foam sheathing behind the nail. Observing hardboard siding under proper lighting conditions can make this defect easier to see if you sight along the siding rather than observing it head-on.

Prevention & Cure of Wood Siding Failures

Nailing Advice for Wood Siding

Finishing Advice for Wood Siding

Using Strapping or Furring Strips to Install Exterior Wood Siding

Wood Siding Moisture Leaks, Traps, & Dryout

Earlier in this article we cited several possible sources of moisture penetrating wood siding materials, especially from the siding back, leading to a variety of types of siding damage. Best practice to avoid moisture damage to wood siding will include proper siding installation - that we have discussed just above. But in addition to properly selected, installed, nailed, and finished wood siding, here are some other steps to avoid moisture or water damage to wood building siding products:

Siding wedges used to prevent paint failure and siding damage

Wood siding wedges (small wooden wedges, or small plastic wedges) are designed to create a gap between the bottom edge of clapboard siding and the surface of the board below, allowing wall moisture to escape. Especially on older buildings sheathed with wood clapboards that have been painted several times, the paint can seal the bottom edge of each clapboard against the board below, making it more difficult for moisture to escape the wall. Wedges sold for this purpose can be driven up below the clapboards to create a vent opening as a building retrofit. We're uncertain about the effectiveness of this solution to paint and siding failures:

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Original article (expanded above)


Continue reading at VAPOR CONDENSATION & BUILDING SHEATHING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Readers researching wood siding problems should also see PAINT FALURE, DIAGNOSIS, CURE, PREVENTION


Or see SHEATHING, FOIL FACED - VENTS - do we need to vent building walls with siding installed over foam board insulating sheathing?



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SIDING WOOD, FAILURES OVER FOAM BOARD at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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