Figure 1-23: Fiber cement siding, blind nailing method (C) Wiley and Sons, S BlissFiber Cement Siding Defects
How to troubleshoot fiber cement siding problems: peeling, breaks, loose, buckled, gaps, butt joint openings, caulking issues, paint failures

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Fiber cement siding defects, failures, problem troubleshooting:

This article describes the types of problems that occur in fiber cement siding installations in North America, including siding shrinkage gaps at butt joints, cracks, breaks, and loose or buckling siding boards or shakes.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Fiber Cement Lap Siding Board Installation SNAFUs

Gaps at butt joints of HardiePlank siding on an 8-year-old home  (C) Daniel FriedmanArticle Series Contents

Fiber Cement Siding Butt Joint Gaps Mean Extra Leaks in the Exterior Wall

Open fiber cement siding butt joint shows no back flashing was installed (C) Daniel Friedman E Galow

Gaps at butt joints in fiber cement siding as well as questions about where caulk should and should not be applied are discussed separately at SIDING, FIBER CEMENT GAPS.

As you can see in our fiber cement lap siding butt joint gap photo at left, the gap is unattractive; in this installation we see the housewrap in the siding gap opening - telling us that there was no back-flashing and that wind-blown rain will certainly pass behind the siding at rates above usual - possibly leading to leaks into the building walls.

Other fiber cement installation & maintenance problems are described in the remainder of this article. .

But whose fiber cement siding is this?

Installed in 2003 the siding has been "repaired" (caulked butt joints) at least once, with gaps continuing to open, leading to a very unhappy homeowner.

Our second siding gap photo (below left) tells more about the history of this fiber cement siding installation.

Counterfeit "brand name" Fiber Cement Siding?

Gaps at butt joints of HardiePlank siding on an 8-year-old home  (C) Daniel Friedman

The combination of an open lap siding butt joint and torn caulk in the same opening tells us that someone tried caulking the butt joint gaps, probably shortly after the fiber cement siding was installed.

Continued fibre cement siding shrinkage tore the caulk and increased the butt joint gap significantly.

Some manufacturer's instructions make clear that caulking of the butt joint in pre-finished textured lap siding is not recommended - most likely because the result is a still more ugly cosmetic defect.

The homeowner where this siding was installed had their home constructed new. The owners thought they were contracting for HardiPlank® siding. On investigation James Hardie's rep informed the homeowner, their attorney, and their special invetigator (not us) that the product was not from James Hardie. There was a suggestion that the product was from CertainTeed.

With assistance from the repair contractor, Galow Homes, [19] we visited the site both at initial siding assessment (2012) and during siding removal and exploration (2013), to collect fiber cement siding samples for further investigation. No one seemed to know whose fiber cement siding was installed. We confirmed that the siding was not made by James Hardie nor by Certainteed.

Fiber Cement Siding Installed When "Too Wet" - Shrinkage Gaps

Hardieplank fiber cement siding as delivered (C) Daniel Friedman Eric Galow

A chief cause of excessive fiber cement lap siding shrinkage in new installations is the installation of siding while it is too wet. Manufacturer's instructions generally say that the contractor should not install wet siding.

Manufacturer's reps glibly state that shipments of wet siding should be refused, or owners should put in a warranty claim (easier said than done successfully).

Our photo shows water inside the plastic wrap on a bundle of new fiber cement siding. But just how wet is "too wet" and how the siding contractor is supposed to decide that the material is too wet to install is left a mystery.

Missing Caulk of Fiber Cement Siding at Vertical Trim Joints

Gaps at vertical trim joints of HardiePlank siding (C) Daniel Friedman

In any event, the installation troubles documented here are largely attributable to failure to follow fiber cement board lap siding installation specifications from either of the major U.S. manufacturers.

At left we illustrate another failure to follow the manufacturer's installation instructions. The siding is not caulked at its abutment to vertical trim.

JamesHardie's installation guide recommends caulking at the abutment of HardiePlank siding boards to vertical trim boards.

CertainTeed's installation guide has the same recommendation and is an extensive document with plenty of advice for the installing contractor and homeowner.

Generally the manufacturers do not recommend caulking at factory-painted fiber cement siding butt joints, presumably because it creates a cosmetic defect; some instructions permit caulking at primed (and smooth) siding, presumably because the caulk "cosmetic defect" will be hidden by the finish paint job.

At left we illustrate another failure to follow the manufacturer's installation instructions. JamesHardie's installation guide recommends installation of weather flashing behind the horizontal lap siding board butt joints and requires it in some products - it was omitted completely in this installation.

Similar advice is found in the CertainTeed lap siding installation guide.

Inadequate Nailing of Fiber Cement Siding - Loose Siding

And of course the fact that I can lift the board away from the wall suggests inadequate nailing as well.

Gaps at vertical trim joints of HardiePlank siding (C) Daniel Friedman

And of course the fact that I can lift the board away from the wall suggests inadequate nailing as well..

Loose HardiePlannk siding at gable end cuts (C) Daniel Friedman

Unfortunately more nailing defects were apparent at the gable ends of the home where the lap siding abutted (or was supposed to abut) the gable end trim.

Left un-nailed the corners of most of these siding boards were curling away from the building. .

Gaps at vertical trim joints of HardiePlank siding (C) Daniel Friedman

Consistent with our earlier warning that one bad installation feature suggests more SNAFUs are in store, even in a casual inspection we noticed other disappointing details on this home that was less than ten years old:

Buckled or Warped Fiber Cement Siding

In our OPINION fiber cement siding is not likely to actually "warp", as it's a cementious product; but indeed if the product is not properly installed, including end gaps at vertical trim abutments and proper nailing using the specified fasteners, at the specified intervals, and nailed into sound sheathing of adequate thickness or into wall studs, then expansion due to moisture uptake and/or thermal changes may result in buckling of the material, particularly on sun-exposed walls.

Buckled fiber cement siding (C) Daniel Friedman Eric Galow

My finger is pointing to an area of buckled fiber cement siding above a garage door; we think that the buckling occurred because of failure to provide the required clearance gap at the abutment of siding ends to vertical trim, but feeble nailing may also have been a factor.

Missing Head Flashing at Windows & Doors Leads to Window & Trim Rot

Why windo trim rots - no head flashing, no caulk (C) Daniel Friedman

The omission of head flashing over windows & doors invites leaks behind the siding, rotted window & door trim, and a need for early exterior window & trim repairs or replacement. The home in our photo was about ten years old. We found rotted trim on all sides of the structure.

Improperly-Installed HouseWrap Means Wall Leaks Behind Fiber Cement or Most Other Siding Products

Why windo trim rots - no head flashing, no caulk (C) Daniel Friedman

When the siding was removed from the building in our photos we saw that the installers had installed the building house wrap improperly.

The top edge of lower sections of housewrap were lapped over rather than under upper housewrap sections.

This means that any water leaking behind the siding will find its way behind the housewrap, increasing chances of water entering the building wall cavity itself.

Water inside a building wall cavity means wet insulation, higher heating and cooling bills, mold contamination risks, and risk of wood structure attack by carpenter ants, termites, and wood-rotting fungi.

J-Channel Installation Defects with Fiber Cement Siding

Home Inspector Comment: Builders using vinyl-siding J-Channels with Fiber Cement Siding?

Builders are using J-channel windows, and other fittings and accessories originally designed for use with vinyl siding, but now with fiber-cement siding. In other words, they are using details that intentionally let water getting behind the siding, but not in a planned rain screen assembly.

Jame Hardie actually has a tech bulletin for this (attached, see p. 123), but I've literally never seen a builder use it (and when we contact Hardie about it they always side with the builders and claim that their recommendations are best practice but not required). Builders claim that the WRB and tape window flashing suffice, but it makes no sense to me to dump water behind the siding. The practice apparently does not violate any code provisions, window manufacturers have nothing to say about it, some fiber-cement manufacturers (other than Hardie) ignore it, others seem to address it in installation instructions but not to the extent that Hardie does.

Do you have any opinions or ideas about this, and/or do you know a building envelope consultant who might be interested? I am thinking of proposing an article on this to JLC, but know it would need expertise of a building envelope specialist to carry any weight. - Anonymous pending agreement, the writer is a professional home inspector working in the South Eastern U.S. by email 2016/06/12


The detail you mention and the manufacturers' bulletin combined with actual practices combined with manufacturer's defending builders (who they correctly see as their actual customer) is an important detail and might be a contributor to some of the buckled or other fibre cement sided home complaints that keep cropping up.

OPINION: Few builders were English majors and fewer are inclined to read the manufacturer's installation details, less to follow them. There are quite a few products & systems (e.g. EIFS) for which the manufacturer writes an installation specification that enables them to defend against product complaints by finding that the product is almost never in total compliance with the specs. A good design is for what people will do in construction, not what they should do. The fiber cement complaints, while probably doing less total building harm than the EIFS issue, have some similar features.

A builder might think that by using housewrap and flashing tape around openings, the abutment to trim or windows and doors is not a critical joint.

But a read of the requirement to keep the FC siding dry until installed offers a clue. After all, this is an exterior cladding. Why can't it get wet? Perhaps because the back-coating is not so water-resistant as the exposed face of the siding. In turn that means that water running down the sheathing against the siding back is likely to contribute to water absorption. If the siding went on really dry (as it ought but often does not) I might expect some buckling problems to ensue.

I wouldn't go so far as to say the builder is "intentionally" letting water behind the siding but rather that they're ignoring both the practices guide and the problems that may ensue.

The Hardie practices you sent, on discussing use of J-channels, focuses on directing water out from behind siding at the bottom of the vertical J's but omits a top J-channel detail that can send enormous amounts of water running down the exterior wall above a window or door into the space behind the vertical J-channel.

Specifically, the installer has to cut the top long, then trim its J-channel face, leaving 1" or more tabs of the J-channel bottom that are bent down over the *outside* of the vertical J-channel's interior "U". This detail keeps water collected by that top horizontal "gutter" from being sent into the wall behind the siding regardless of whether the siding is vinyl, aluminum or FC.

  1. Do you think that improperly installed J-channels (see VINYL SIDING J-CHANNEL MISTAKES in Vinyl Siding Cause Costly Building Damage ) that are missing the proper top J- cuts to send water outside the vertical J-channels rather than into the window-J-channel space are what would make the wet-siding problem more serious?
  2. Or do you think that the builder should omit J-channels entirely and caulk against horizontal and vertical trim?
  3. Do you think that water behind the FC siding is a concern for reasons other than buckling? E.g. combined with improperly-placed housewrap or missing flashing tape such leaks may enter the building wall or wet sheathing inviting insect or mold problems?

I'm neutral on Hardie's Optional rain screen suggestion for residential properties. I don't think that the problem is lack of ability of water to drain out of the siding - it's usually not painted in the field so the bottom edges of boards aren't sealed against one another by paint - a detail can trap water behind painted clapboard-sheathed walls.

I think that if housewrap and flashing tape are properly done we may still keep water out of the wall cavity itself. In that case it's the issue of wetting the siding back that's probably going to contribute to cosmetic complaints of buckling and bending. (There's a whole separate set of gripes about shrinkage of wet siding).

I note, however that Hardie says that while a rain screen is optional, they state up front in bold:

Note: James Hardie has a capillary break requirement when installing HardiePanel on a Multi-Family/ Commercial project. Please visit for further information. - Hardie FC Siding Best Practices cited above.

I've not personally seen a home with FC siding that used a furring applied siding mounting system over a rain screen.

Now you've gone and added another water intrusion point that I will have to add. Thanks; by this posting we'll welcome comments, information, field reports from other interested parties. Readers please use the page bottom COMMENTS BOX or find our email at page top or bottom CONTACT - Ed.

Paint Failures on Fiber Cement Siding

Damaged fiber cement siding - Rhinebeck NY (C) Daniel Friedman

The peeling top coat on the siding shown above (Rhinebeck, NY) shows a white primer remaining in place on the fiber cement siding. The siding paint damage was largely due to excessive wetting from rain-splash.

Mechanical Damage to Fiber Cement Siding

The mechanical damage to fiber cement siding shown below is obviously from impact and is not a product defect. Just about any building siding material can be damaged by external events, though some products such as fiber cement siding, and asbestos cement shingle siding are more vulnerable to breakage compared with vinyl siding (which can still be punctured or broken under some conditions) or aluminum siding (which dents and which can still be punctured under certain conditions).

Damaged fiber cement siding - Rhinebeck NY (C) Daniel Friedman Why windo trim rots - no head flashing, no caulk (C) Daniel Friedman

The repair for the damage shown above on a building in Rhinebeck, NY, requires that the damaged boards be removed and replaced. Failure to repair punctures such as those we show means increased risk of wind-blown rain leakage into the wall structure.

Defects Discovered During Removal of Fiber Cement Siding

Discovery of More Original Siding Job Installation Errors

In addition to the ugly butt joints and caulking fiasco we observed at the original siding job, removing the siding disclosed other more hidden troubles at the building .

In fact, the progoma; siding had so many installation errors, missing flashing, crooked, trim rot around windows and doors, building leaks, that a patch job was in our opinion and that of the owner and contractor, likely to lead to a lifetime of aggravation for the building owners.

Our photos below illustrate what we found when taking a closer look at this installation: leaks at window tops and rotted trim everywhere on the building. This was a ten-year-old home.

Leaks in the fiber cement lap sided wall (C) Daniel Friedman Leaks in the fiber cement lap sided wall (C) Daniel Friedman

My definition of non-destructive rot-inspection is if I can push my finger into the wood trim, it was already severely rotted - I didn't cause damage to the building. (Photo above right).

At below left we can see why conventional brick mold window trim will be rotted on a fairly new house: the omission of head flashing over windows and doors combines with the soft common pine finger-jointed brick mold to rot and leak. And as you can see from my finger-poked rot hole above and at left, water would also have been entering the wall behind the siding.

Why windo trim rots - no head flashing, no caulk (C) Daniel Friedman Why windo trim rots - no head flashing, no caulk (C) Daniel Friedman

In our photograph at above right you can see that the original siding installers (that was not by Galow Homes), the fellows were not quite sure about the truism that "water runs down hill" - the building house wrap was installed "upside down" with lower segments lapped outside or on top of upper segments, guaranteeing that any leaks past the siding itself would find a ready path behind the protective housewrap barrier and into the building walls.

The miracle of modern housewrap materials is not so wonderful if the product is not properly installed. In the photo below the contractor is demonstrating "backwards" installed housewrap that would readily admit water behind the wrap itself.

Housewrap improperly installed, lower course upper edge laps outside of upper course (C) Daniel Friedman Eric Galow


Continue reading at SIDING, FIBER CEMENT DEFECT DIAGNOSIS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SIDING, FIBER CEMENT SHINGLE-BOARD DEFECTS - a field report of fiber cement siding product complaints in California,

Or see SIDING, FIBER CEMENT GAPS where we discuss fiber cement siding gaps, clearances, butt joint specifications and sealing and caulking specifications.

Or see these

Fiber cement siding articles


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