Celotex old insulating board (C) Daniel FriedmanFiberboard Mold Contamination & Insect Damage
Insulating Board Sheathing Mold & Insect Resistance

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Insect damage or mold contamination in or on fiberboard insulating sheathing used on or in buildings:

This article discusses the occurrence of mold contamination and also insect damage on fiberboard sheathing used on roofs, walls, ceilings in buildings and on building exteriors.

This article series gives the efinition, 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.

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Mold Growth & Wood Boring Insect Susceptibility of Fiberboard Building Insulating Sheathing Products

Moldy Homasote insulating board sheathing (C) Daniel FriedmanWe 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.

[Click to enlarge any image]

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 above, 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).

See FIBERBOARD SHEATHING MOLD our full article on mold growth on or in fiberboard sheathing.

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

Insects in fiberboard products: Reader comment: insect attack through fiber-type flooring

Moldy Homasote insulating board sheathing (C) Daniel Friedman

(Feb 27, 2013) Teresa Mietus said:

I live in a 50's home.

Termites literally built an entire empire between the top and bottom layers of a fiber type floor board.

If not for the mud tunnels, the floor would have fallen through

! What you don't see - can hurt you.

Research on Insect Damage to LDF & MDF Fiberboard Products

Question: Question about Homasote product from 1940s. Mold problems on gypsum board exterior building sheathing?

Gypsum board wall sheathing (C) Daniel Friedman

Was there a Homasote product used in the early 1940s on the exterior of houses that looks like sheet rock? How long does this last for?

If it is still on the house, could it contain mold due to lack of sunlight?

Was there "code" at some point that would have forced individuals who were to replace vinyl siding on the house over these boards to replace with proper products after a certain date? Thank you, K.B.C.

Reply: Properties of Homasote® type fiberboard compared with gypsum-based exterior wall & roof sheathing boards

Homasote® fiberboard sheathing is a wood fiber product, not a gypsum or plasterboard product. However there were indeed gypsum-based sheathing board products used on buildings both as wall sheathing (under siding and over studs) as well as roof sheathing.

Having inspected quite a few buildings that used this material, my OPINION is that it has proven surprisingly durable so long as it was kept dry. Wet the material can become soft, and also one might find mold growth on the paper backing of the gypsum board.

We describe these two different product types


at FIBERBOARD SHEATHING - Sheathing Celotex Homasote & Other (this article)

as well as an introduction in FRAMING MATERIALS, Age, Types where we describe the history of building framing and sheathing materials.

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

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.


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