Here we cite expert advice on construction practices and home maintenance details that will reduce the risk of a future attack and damage by "Poria" the house-eating fungus.

Page top photo: extensive Poria incrassata damage to a wood-framed building. - (Verrall 1968)

This article series describes Meruliporia incrassata or "Poria" Meruliporia incrassata, previously named Poria incrassata which is better known among reporters and repairmen who see the public pale at reports of how the "house eating fungus destroys a home.

Prevention: of Poria Fungus Damage in Buildings

The water-conducting fungus, Poria incrassata (Berk. and Curt.) Burt, causes the most spectacular decay of wood in buildings in the United States.

It produces large, tough, water-conducting strands (rhizomorphs) which, when rooted at a constant and abundant supply of moisture, can wet wood of a variety of species many feet away.

Thus the fungus can destroy wood normally too dry to decay. Attacks are not frequent, but the rapidity of attack and the extent of damage make this pathogen an important enemy of wood in service. - (Verrall 1968)

Photo: leaving un-treated wood forms in a concrete slab such a the one being prepared here at a home in Tucson increases the risk of a future termite or fungal attack on the building.

The steps listed below are adapted from (Verrall 1968) cited below.

1. Use uninfected dry lumber for initial construction (6-12% moisture)
   
   and never use lumber wet to over 14% moisture. If you see white mycelium or fans on construction lumber while in storage or before use in construction, don't use that wood.
2. Control soil moisture under & near the building
   
   Roof drainage, gutters and downspouts must be working not just at time of construction but throughout the life of the structure, and surface runoff must be directed away from the building.
   
   See CRAWL SPACE DRYOUT - home

and

See WET BASEMENT PREVENTION for details.
3. Remove wood and trash around the foundation, don't allow contractors to dump wood forms, stakes, lumber scraps, or other organic trash into the excavation near the building foundation slab or walls - this measure reduces risks for both termites and Poria infestation.
4. Remove stumps and wood debris from the building footprint before building the foundation, slab, etc.
5. Avoid dirt-filled porches & terraces;
   
   Where slab on grade is used the slab must not abut the building where it will contact wood framing or siding.
   
   Detail:
   Self - supporting slabs with a ventilated space below are preferable.
   
   Dirt fills are safe, however, if the porch slab is below all wood framing or if the soil is enclosed in a separate foundation wall with sufficient space between the wall and the sill to permit inspection and ventilation.
   
   Because dirt fills encourage termite attack, they should be well treated with an insecticide ( 40 ).

6. Elevate & waterproof slab-on-grade construction.
   
   Detail: Self - supporting slabs with a ventilated space below are preferable.
   
   Dirt fills are safe, however, if the porch slab is below all wood framing or if the soil is enclosed in a separate foundation wall with sufficient space between the wall and the sill to permit inspection and ventilation.
   
   Because dirt fills encourage termite attack, they should be well treated with an insecticide ( 40 ).

7. Keep crawl spaces & basements dry throughout the life of the building.
   
   See CRAWL SPACE DRYOUT - home

and

See WET BASEMENT PREVENTION
Detail:

If the basement is damp, only pressure - treated wood should be used in contact with the walls and floor - even with 3 - inch concrete footings.

8. Use treated lumber for any wood that must be close to or in contact with the ground
   
   Details:
   
   The need for treated wood varies with climate, soil moisture conditions, and building design. Climate has its greatest effect on decay associated with rain seepage, and least on decay by Poria incrassata .
   
   In all parts of the United States pressure - treated wood or all heartwood of the most decay - resistant woods ( redwood, cedars ) should be used for the following items :
   
   Sleepers in or on concrete laid on ground.
   
   Sills or plates on concrete on ground.
   
   Framing and sheathing in walls and floors of shower stalls.
   
   Framing and sheathing in cold - storage rooms.
   
   Wood used below first - floor joists in damp basements.
   
   Similar wood should be used for critical items in regions with 25 inches or more of rain ( not total precipitation ) annually, or where swamps or seepage keeps the soil wet :
   
   Frames for access doors in foundation walls.
   
   Frames for outside doors into basements.
   
   Furring strips below grade.
   
   Sills or plates on concrete or masonry foundations less than 8 inches above grade.
   
   Wood piers in crawl spaces with concrete footings less than 8 inches above grade.
   
   Joists set into brick or concrete walls less than 8 inches above grade.
   
   For wood in contact with the soil or continuously wet concrete or masonry, pressure treatment is a necessity. Naturally decay - resistant woods cannot be relied on.
   
   Buildings of accepted design, such as houses conforming to the Federal Housing Administration's Minimum Property Requirements, are safe from the attacks of water - conducting fungi so long as the tenants do not nullify the design.
   
   See details
   at PRESERVATIVE TREATED FRAMING LUMBER

Photo: this extensive rot and insect damage to a building wall was found where someone poured a patio slab right against the wood-framed building wall.

9. Avoid dangerous practices that invite termite or fungal attack on buildings
   
   Examples of dangerous practices include the following:
   
   Allowing downspouts to become clogged or rusted through.
   
   Allowing roof drainge to spill around the building (clogged or missing gutters), especially where water splashes-up against or drains toward the building walls and foundation.
   
   Building up flowerbeds so that soil touches siding.
   
   Wetting wooden walls when sprinkling lawns. This practice has been sufficient, in new slab - on - ground houses whose owners were trying to establish lawns and shrubbery, to permit development of rhizomorphs connecting the sheathing and the soil.
   
   Letting plumbing leak for protracted periods. Promptly repaired leaks are not serious.
   
   Piling wood or other cellulosic material in crawl spaces or against sides of a house .

...

Above: two basic examples of building conditions inviting termite or mold damage:

When we see plants growing in roof gutters we know perfectly well that these gutters have been overflowing and spilling close to the building foundation and walls.

Roof spillage splash-up against the wall can bring both termites and fungal infection right through a brick veneer wall and into the wood structure. Details are

at GUTTER DEFECTS LIST

References on Poria, Identification, Properties, Damage, Prevention

• Verrall, Arthur Frederic. PORIA INCRASSATA ROT: PREVENTION AND CONTROL IN BUILDINGS. No. 1385. [PDF] US Department of Agriculture, Forest Service, 1968. Available as a free eBook courtesy of Google, at https://play.google.com/ books/ reader? id=YaMoAAAAYAAJ&hl=en&pg=GBS.PA1
  
  This bulletin reviews the literature on Poria incrassata and summarizes 30 years of experience with its control in the South. ...
  
  The water - conducting or building Poria was first described as Merulius incrassatus by Berkley and Curtis in 1849 from a sporophore on a pine stump in South Carolina.
• Miller, Dini, SIGNS of SUBTERRANEAN TERMITE INFESTATION [PDF] Virginia Cooperative Extension, Virginia Tech / Virginia State University, retrieved 2020/11/23 original source: https://www.pubs.ext.vt.edu/444/444-501/444-501.html
• Money, Nicholas, P. PLAGUES UPON HOUSES AND CARS: THE UNNATURAL HISTORY OF MERULIPORIA [ODF] GEOFF GADD is Professor of Microbiology and Head of the Division of Environmental and Applied Biology at the University of Dundee.: 289. Department of Botany, Miami University, Oxford, Ohio
  
• Royes, Joy, and A. R. Loveless. "Poria carbonacea (Berk. & Curt.) Cooke as a cause of timber rot in Jamaica." Transactions of the British Mycological Society 43, no. 3 (1960): 571-577.
  

...

Continue reading at MERULIPORIA HOUSE EATING FUNGUS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• HIDDEN MOLD, HOW TO FIND
• MERULIPORIA HOUSE EATING FUNGUS
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• PORIA DAMAGE PREVENTION
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• MILDEW ERRORS, IT's MOLD
• MOLD APPEARANCE - WHAT MOLD LOOKS LIKE - home
• MOLD ON DIRT FLOORS - where we have also identified this fungus.
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