Celotex old insulating board © Daniel Friedman at InspectApedia.comFiberboard Mold Contamination Damage
Insulating Board Sheathing Mold Resistance

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Mold contamination in or on fiberboard insulating sheathing used on or in buildings.

Fiberboard mold: occurrence & detection of mold contamination on fiberboard & wood-fiber-based insulating board sheathing.

This article discusses flood damage and mold damage on fiberboard insulating products and building sheathing products such as Homasote, Celotex, and Masonite insulating board sheathing.

We also answer these questions: Does insulating board or fiberboard support mold growth? How to recognize Celotex®, Homasote®, Masonite® and other insulating board building sheathing products. Repairing or replacing "blackboard" fiber insulating board on homes.

This article series gives the definition, ingredients, history, use, fire resistance & insulating properties of fiberboard sheathing. This article describes and provides photographs that aid in identifying various insulating board sheathing materials used on building walls and roofs, such as Homasote, Celotex, Insulite, and Masonite insulating board sheathing products.

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.

Mold Growth Susceptibility of Fiberboard Building Insulating Sheathing Products

Moldy Homasote insulating board sheathing © Daniel Friedman at InspectApedia.comWe do not usually find mold growth on fiberboard building insulating sheathing nor insect damage to this material.

Possibly the resin binder and coating is unattractive to insects and the moisture resistance of some coatings also reduce the ease of mold growth on this material.

However in sufficiently challenging conditions such as very wet conditions or prolonged exposure to water and moisture or insects, we have found both extensive mold growth on Homasote type insulating board (photo, left, in a wet basement against a masonry wall) and evidence of insect damage to an interior wall fiberboard sheathing product, probably Beaver board or Upson board (in the attic of a leaky building, below right).

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Mold on Building Insulating Board Following Hurricane-Caused Flooding

Question: how much wet Celotex™ insulating board should be removed after flooding

We are survivors (not victims) of the Tennessee flood that came on May 1st 2010. Water was in our home for 34 hours including the 1st level (basement) and 3 feet on the main level.

We have taken everything out of the building, removing interior materials down to the studs (walls) and joists (ceilings and floors). Our Insurance is ready to make their first offer.

Insulating board in Tennesse flooded home © Daniel Friedman at InspectApedia.comThey asked about the sheathing saying if it was chip board it would need to be removed. Or plywood should be OK if ventilated correctly.

Well, it's neither, occurring to your website it's Celotex™, the back is smooth while the inside is fibrous.

I cut a chunk out and it's wet. Should that come out? I say yes. The home was built. 1970s

How do you replace wet fiberboard insulation? Remove outside brick? Remove the stud walls. Surely not!

Also FEMA says the basement is the 1st level of the home, because it has a door to enter & exit to the outside. Insurance saying it's a basement - which covers nothing.

If you are unable to do this Pro-Bono, we understand, and we thank you for your web site. - T.

Answer: remove flooded, wet or moldy materials to a 12" or greater margin of clean, dry material

OPINION: Since we have certainly seen that Celotex and other fiberboard insulation products can sometimes support mold growth, the wet insulating board should be removed.

Remove insulating board that is or has been soaked by flooding, that is swollen, expanded, softened, or mold-contaminated.

Watch out: beware of arbitrary heights given for removal of flooded drywall or insulating board such as "two feet" or "four feet" since those numbers may not be adequate. Remove such flood damaged materials until you have found at least a 12-inch margin of clean, dry, un-damaged insulating board. That height above the building's floor will always be somewhere above the maximum high water level in a flooded building.

How is Wet Insulating Board Removed Where a Masonry Veneer is Installed Outside?

Weep openings provide drainage in this brick wall © Daniel Friedman at

At BRICK VENEER WALL REPAIRS in FLOOD PRONE AREAS we describe repair procedures to remove flood or water-damaged or moldy fiberboard sheathing behind a brick veneer wall and how to repair the exposed wall cavity to reduce future water damage from flooding.

Sketch courtesy of Carson Dunlop Associates.

Unfortunately to completely remove the wet insulating board from this building will be a costly and destructive task.

You probably don't have the option of "removing the studs from inside" since the brick veneer is typically tied to and thus supported by the wood framing.

Interior-Side Cut-out Removal of Flooded Insulating Wall Behind a Brick Veneer Wall

The most-common approach to removing wet insulating board is to cut it out from the stud bays from the wall's interior side.

This approach makes more sense than may first come to mind. Consider that in a flood-damaged building water has entered the building interior to some height above the lowest floor or floors. That will have soaked drywall, electrical wiring, and other mechanical systems that all need to be addressed.

Wet drywall and wet insulation need to be removed. That will leave the wall cavity exposed to permit cutting out and removing flooded insulating board IB sheathing or fiberboard on the exterior wall.

Cut out insulating board vertically along the wall stud sides and horizontally along the wall sill plate (at the wall bottom), and cut horizontally above the highest point at which the insulating board is or was wet or visibly mold-contaminated.

Remove the insulating board, then clean and dry the exposed surfaces.

Complete Stud-Wall Removal Behind a Brick Veneer - is this a good approach?

Temporary support wallSaving a Brick Veneer Wall: support the veneer, remove the stud wall, rebuild stud wall, use retrofit veneer wall ties: high cost, high labor, maybe unnecessary

The illustration above, contributed by a reader's contractor or insurance provider, illustrates the placement of a temporary support wall to allow repairs to the building's exterior wall.

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It is important that the brick ties are re-connected securely to the new or replacement framing.

If necessary, retrofit veneer wall ties can also be installed from outside of a building by drilling and inserting patented anchors through the veneer wall and into the supporting structure behind it.

The contractor and other parties involved as well as local building officials need to agree on a safe procedure for the particular structure involved. But here are some general comments about how insulating board is removed from a building where an exterior veneer of brick or stone are installed.

A temporary support wall is constructed inside the building parallel to the wall where the insulating board must be removed. The support wall involves a top header, support posts, and often a sill plate that distributes its load safely across the floor below or down to a basement slab or footings.

We have repaired a brick veneer building from the inside (for example in a non-flood case of extreme termite damage) by working carefully on the interior side of the veneer wall, in small sections so that there was not a risk of wall collapse.

We removed and replaced damaged wallboard, insulation, and studs. New studs and sill and top plates were installed and metal ties were reconnected to the studs to continue to secure the brick veneer wall. It was technically not difficult, but it was a labor intensive procedure.

The temporary support wall allows the contractor to remove sections of exterior wall studs (and the insulating board between the wall studs and the exterior masonry veneer) without risking the ceiling above collapsing. The support wall is spaced far enough in from the original exterior wall to give access to the original studs and wall, but close enough to the outside wall to safely support the floor above - often just a couple of feet.

The support wall is usually constructed using a heavy beam or header rather than a simple flat 2x4 top plate. The beam allows the temporary wall's supporting posts to be placed 4 feet or more apart, giving plenty of working space.

Watch out: this is a costly, risky, labor-intensive procedure. See the alternative discussed at BRICK VENEER WALL REPAIRS in FLOOD PRONE AREAS where we describe repair procedures to remove flood or water-damaged or moldy fiberboard sheathing behind a brick veneer wall and how to repair the exposed wall cavity to reduce future water damage from flooding.

Mold growth on gypsum board building sheathing?

About mold growth: the simple absence of light is not sufficient to cause problematic mold growth in building cavities.

See details about mold growth on fiberboard sheathing at FIBERBOARD SHEATHING MOLD CONTAMINATION

See MOLD EXPERT, WHEN TO HIRE for help in deciding if in your particular case hiring a competent professional to inspect and test the building is justified.

Requirements to Remove Old Siding & Sheathing When Re-Siding a Building?

Finally, I've not found any national building code that requires a homeowner to replace one existing siding or wall sheathing material with another. The decision on siding-over existing surfaces vs. doing a (more expensive) tear-off depends on at least these considerations:

Watch out: be careful not to add multiple vapor barriers to a building wall. Installing an air and moisture resistant vapor-permeable housewrap should be fine however, and is required by some building codes and some product manufacturers.

What about leaving the veneer and installing plastic or some other barrier against the inside of moldy insulating board?

Insulating board in Tennesse flooded home © Daniel Friedman at InspectApedia.comWatch Out: In this case someone recognizing the great cost of redoing the brick veneer may want to try installing a very very secure barrier between the celotex and building interior - it might work but this questionable approach risks leaving a mold problem in place - something that could later be a problem for building occupants, especially people at extra risk such as asthmatics, elderly, infants, immune people.

As we describe at BRICK VENEER WALL REPAIRS in FLOOD PRONE AREAS, a preferred approach that may be quite reasonable is to remove wet or moldy fiberboard sheathing from the building's interior side, followed by cleaning and then a careful choice of insulating materials and weep opening installation to reduce future water damage from the next flood.

Because flood-damaged, wet, or moldy drywall and insulation need to be removed the building interior that is going to leave the interior face of the exterior sheathing board accessible and removable.

Watch Out: Leaving wet insulating board in place and then re-building over it creates a very high risk of later hidden mold in building walls and ceilings. It is tricky to decide that the insulating board is really dry throughout as its dryout can take weeks, even months where the insulation is covered by a brick exterior wall, by contacting wood framing, or by other materials.

Watch Out: The photo above above tells us that interior drywall or plaster were removed only for the first four feet of the flooded wall.

This is about 12" above the high water level in the building.

There is a chance that water wicked higher into building materials including the drywall, insulation, and fiberboard insulation in these walls. Leaving wet, possibly moldy insulation in place also leaves a future property resale difficulty as the home may be "stigmatized" as not having been thoroughly cleaned and repaired following a major flood.

Watch out: Be sure to inspect the wall-cavity side of remaining drywall for mold contamination or evidence of having been wet - remove such materials to give at least a 12-inch margin of clean, dry gypsum board or plasterboard before beginning further wall repairs.

A photograph of moldy insulating board in a flooded home is shown in our photo at left and as discussed also at MOLD GROWTH & WOOD BORING INSECT Susceptibility of Fiberboard Building Insulating Sheathing.

Also see INSULATION MOLD CONTAMINATION TEST where we describe non-visible but significant mold contamination found in fiberglass insulation that has been wet or exposed to high moisture or high mold levels.)

How Much Insulating Board to Remove?

red mold in a wall cavity that was thought to be "dry" and clean. © Daniel Friedman at InspectApedia.comYou might know better just how much of the insulating board needed to be replaced above whatever has been soaked if you have a very thorough inspection and testing for mold, including test cuts to check the hidden side of the insulating board (such as Celotex™ material) in the most-suspect locations where moisture may have been present.

Remove all insulating board that was wet or is wet or is visibly moldy. Remove the material until you have left a clean 12" or greater margin of clean, dry, un-damaged material. Typically this will require removing drywall, insulation, and exterior wall sheathing insulating board or IB from the floor height to at least a foot above the high water line.

For a building that has been flooded and wet for days, it is likely that you will have to remove more material for two or more feet higher-still.

Watch out: when leaving drywall on upper walls of a flooded building, inspect the cavity side of the drywall to be sure it is free from water stains and mold.

Inspect that area again before restoring insulation and new drywall, and be sure that all of the wall (or ceiling or floor) cavity surfaces are completely cleaned and dry (below 18% moisture) before beginning further restoration work there.

My photo of red yeasts and mold shown here was taken of the wall cavity interior of a drywall-covered wall after a "water extraction" company reported that the building was clean, dry, and free of mold. They were mistaken.

Where Does Mold Occur on Insulating Board?

Where we have found insulating board products such as Homasote or Celotex to be moldy, it has been in areas of flooding that wet the board.

If none of the dry, un-damaged insulating board is found to be moldy, where it is left in place, the seal up approach or use of a fungicidal sealant on dry surfaces might be fine. If you can you send us photos of the home inside and out we may be able to comment further on where to look for hidden problems.

But the best approach is to bring in an experienced inspector who knows where to look and how to test building materials for wetness, dampness, or mold.

What Are the Structural Differences Between Chipboard, OSB, and Insulating Board?

You won't find "chipboard" used as building sheathing. "Chipboard" is compressed sawdust-like material, often used for shelving. But you might find oriented strand-board or OSB sheathing in place, depending on when your home was built.

That is probably what your insurance company meant by "chipboard" sheathing. Ask your Insurance company if their issue with OSB sheathing that has been soaked is a structural concern or a mold concern.

Insulating board products such as Celotex™ or Homasote™ are not structural. Where those products were used as wall sheathing you'll typically find either diagonal wood or metal bracing at the building corners, or structural plywood used in those locations. We illustrate diagonal bracing in a photograph later in this article.

Bottom Line: Don't Leave Wet or Moldy Materials In Place After Building Flooding

Watch out: in any case don't leave a mold reservoir in place in a building following flooding. Doing so simply risks having to do the whole job over again later.

Bottom line, we expect that in your case, since you described soaking wet insulating board materials, the Celotex™ needs to come out because of the mold concern. Any attempt to reconstruct the building while leaving soaking wet material in place will very likely produce a new wall or ceiling cavity mold problem and the whole job would end up needing to be done again.

Finally, your insurance company may define the lowest floor of your home as "basement" in order to reduce their loss coverage expense. But if the lowest floor opens to grade on at least one side, and was finished as living space, especially supported by FEMA's own description, you may be able to satisfy your insurance company that this was code-approved living space not "basement" (a non-living space area).

There are no fees to consult with us regarding natural disasters such as area flooding.

Insect Damage Found in Fiberboard Wall Sheathing Products

This discussion has been moved to a new article found at FIBERBOARD SHEATHING INSECT DAMAGE


Continue reading at BRICK VENEER WALL REPAIRS in FLOOD PRONE AREAS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see DRYWALL, FIBERBOARD, PLASTER INTERIORS - home, where we discuss the types of non-structural interior sheathing boards (plaster, gypsum board, drywall, fiberboard) that were used on building interior walls and ceilings.


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