The most dangerous kinds are the so-called "dry-rot" fungi which work in many kinds of lumber after it is placed in the buildings.

They are particularly to be dreaded because unseen, working as they do within the walls or inside of casings.

Several serious wrecks of large buildings have been attributed to this cause.

It is stated[40] that in the three years (1911-1913) more than $100,000 was required to repair damage due to dry rot.
[Footnote 40: Dry rot in factory timbers, by Inspection Dept.
Associated Factory Mutual Fire Insurance Cos., 31 Milk Street, Boston, 1913.] Dry rot develops best at 75 deg.F.and is said to be killed by a temperature of 110 deg.F.[41] Fully 70 per cent humidity is necessary in the air in which a timber is surrounded for the growth of this fungus, and probably the wood must be quite near its fibre saturation condition.

Nevertheless _Merulius lacrymans_ (one of the most important species) has been found to live four years and eight months in a dry condition.[42] Thorough kiln-drying will kill this fungus, but will not prevent its redevelopment.