An acquaintance has a 5 year old SIPS house with visible ridging happening on the (unvented) roof. The builder (not me) went back and taped the seams. The question is whether there are other measures that the homeowner should do at this point, other than eventually adding ventilation to the roof? And does anyone have ideas as to what exactly causes the ridging?
Yes. The edges of the OSB top layer is expanding due to moisture (and heat) exiting the house through the seams in the SIPS, hitting the moisture impermeable roofing, condensing on and essentially rotting the OSB. Seal the joint on the interior with a high quality acrylic peel & stick tape. You can also vent the roof, so all that moisture (and accompanying heat) is vented away and doesn’t damage the OSB. Or better, can seal the joints and cover the SIPS with enough sheet insulation to prevent condensation and keep the moisture and heat inside the house. This involves adding another layer of sheathing.
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