Biodeterioration Diagnostics Database

  I.  Title: Brown rot decay of cedar wood on exterior decking

 II.  Deterioration Agent: A brown rot fungi

III. Location: Minneapolis, MN, USA

 IV. Description of Problem: Brown Rot

This house was constructed in 1856 and resides near the University of Minnesota. It served as the home for the University of Minnesota’s first president and is one of the oldest homes in Minneapolis. It is now home to the Minnesota Alpha chapter of Sigma Phi Epsilon Fraternity. The house joined the Minneapolis Heritage Preservation Commission in 1976. It suffered a devastating fire in 1992 and portions of the house were rebuilt shortly after. There are multiple areas around the exterior (mainly the front and back porch) that suffer from brown rot decay. The re-construction of the front and back porch could have led to and or aided in the problems described below. The carpenters may have not used properly treated wood, they may have not dip-treated the ends of the boards if they had been cut to size, they used iron nails which could have been a point of entry for the fungus, and may have not taken ground moisture or rain drainage into consideration. The main area of rot occurs at the junction between the porch and a custom made pillar. Due to the custom woodwork, it is possible that the carpenters did not properly treat/close all seams and edges. There are no sporophores present but the brown rot can be identified by the presence of cubical checking, the deep brown color from the remaining lignin, and the ability to crush the wood in between fingers which forms a powder. There is also galvanic corrosion present on all of the nails. The Fenton reaction between the fungi and wood causes an early and rapid strength loss by hydrolyzing cellulose and hemicelluloses.  The rapid strength loss of the porch proves to be dangerous for anyone walking on its surface. Due to this fact, the structural boards, the decking boards, and the custom pillar need to be replaced. The Heritage Preservation Commission requires that the façade stay identical to the original design. This makes replacing these exterior structures more difficult due to the cost and expertise required to meet the Commission’s standards.

Addition completed in 2000, photo taken in 2009. Fungal decay (organism not id'ed) is extensive.

Untreated wood, most likely southern yellow pine, was used for steps leading up to the deck shown in the attached images. The steps were built in 1999 along with the house, and the decay problem was very advanced by 2004. The steps look like they were painted gray, but the paint has chipped and worn, exposing untreated wood. The deck itself was 0.25 pcf treated wood and, at the time of these photos, did not show signs of the fungus (sporophores, cubical checking, etc.). Clearly, the agent of decay is a fungus. The sporophore belongs to Gloeophyllum sepiarium, also known as the 'mazegill' fungus. You can see its sporophore as a rust-colored protrusion (a small shelf fungus) at the front end of the step. It is a brown rot, so the problem the landlord faces here is three-fold: 1) the steps need replacing, immediately, 2) the renters are at risk for falling through the deck because brown rot fungi reduce strength in wood quickly and 3) the mycelial mass of the fungus in this wood can act as a source for problems elsewhere, including the deck. Assuming CCA was the treatment for the deck boards (pre-2004), there should have been little leaching since being built and there is lower potential, but at 0.25 pcf, you could still have decay. Some brown rot fungi are more tolerant/resistant of heavy metals. Also, one of the images shows that the nail fasteners have failed, and they do not look galvanized, etc. There was likely galvanic corrosion and possibly iron leaching into the wood which, for iron-dependent brown rot fungi, may be a problem.