Moisture in Fat Walls

After a house in Devens, Mass., had its moisture and temperature monitored for three seasons, workers pulled sections of Zip sheathing panels from the test wall section.

The wall system has good drying potential to both the inside (through the painted drywall) and the outside (through the permeable Zip sheathing), but the cold OSB on the exterior does suffer increased moisture and condensation during the coldest months of the winter.

Moisture sensors in the building walls allowed the Building Science Corp. research team to remotely measure and record the moisture content of the framing and sheathing throughout three winters of house operation.

Nails had rusted slightly after three seasons of moisture accumulation—clear physical evidence of moisture attack, but not as grave as the data had suggested.

A close-up of OSB sheathing removed from contact with the low-density spray foam of the insulated wall cavity shows no sign of fungal attack at all, much less any deterioration that might compromise the sheathing’s function.

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