Securing Rainscreen Siding

Test results show how to install clapboards and strapping over exterior foam.

The test assembly was a sturdy shop-built frame securely attached to the concrete floor with metal holddowns and concrete anchors. A hydraulic ram secured to a cross-member provided the measured force.

The wall-assembly samples were clamped in place to resist movement as the piston bore down on top of the strapping; a dial indicator on the floor measured the strapping's displacement as a video camera recorded the movement of the dial.

The testers then used the realtime data to calculate the yield point of the tested fasteners. The average per fastener is half the sample average because each assembly had two fasteners.

This sample is in position to be tested, with the head of the screw just proud of the strapping surface.

As the force is applied, well beyond the yield point, the strapping begins to pull through as the screw rotates slightly.

At maximum load, the head has pulled halfway through the strapping.

The strapping in this sample has crushed the foam, which offers little resistance. Note that the tops of the two layers of foam were flush at the start.

In another test, the wood has split and the fastener rotated at maximum load.

FastenMaster uses a high-strength steel for its fasteners, evidenced by the near perfect condition of many of the screws in the test.

On a few occasions when the strapping did not split or pull through, the screw showed only a slight bend.

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