Because of the unique design of this type of roof assembly it is necessary to suggest more than one type of installation method in an effort to prevent possible condensation problems.

Below are three methods that AFS suggests and feels comfortable with. However, this type of purlin, not sub-purlin, assembly is difficult, at best, to make cosmetically appealing.

Installation Method (figure 1)
  1. Secure one side of the material to the face of the sub-purlin, beginning at the end of the hanger, after allowing for a 5-6" overlap of material on the other end (for pulling through the purlins). Staples to be a minimum of 6" apart . See figure 1b for proper measurement of material.
  2. Staple the opposite side, by pulling the short end, at the end of the sub-purlin, directly across to the next sub-purlin, and staple it tight to the end. Continue stapling, as you pull it tight, to the end of the sub-purlin.
  3. Pull the loose end through the webbing of the purlin(truss) and secure it to the ends of the sub-purlins by stapling it to the bottom facing, just past the joist hanger. Cut around any vertical webbing , or penetrations, as neatly as possible and tape only if necessary.
Alternate Method 1 (figure 2)-Facings (not Capsheets) with or without fiberglass above.
  1. Determine required length by measuring the sub-purlin , up each end and allow an extra 1.5" for stapling the ends of the material to the bottom face of the top chord of the purlin (typically a 2 x 4).
  2. Center each piece on the sub-purlins, allowing an equal amount of material on each end to staple to the bottom face of the top chord of the purlin. Staple the length of each purlin as indicated in installation method 1 above.
Alternate Method 2 (figure 3)-Capsheet (Foil/Liner/Foil) Only.
  1. Order AFS-2 (capsheet) 97" for 2x4 assemblies and 98 or 99" for 2x6 assemblies.
  2. Install material as you would in Fig.2 except, crease the ends, between the ends of the sub-purlins and the webbing of the purlin and fold them upwards, against the ends of the 2x’s.
    1. Note: This method only works with the heavy duty capsheet (AFS-2). The scrim products are too flimsy and won’t stay in place.
    2. Do Not paint the capsheet in this type of installation. The weight of the paint and the moisture can cause the ends to droop.






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