Reading the  article  on Insulated Skylight Shafts in the current edition of Fine Home Building prompts me to finally get around to writing to FH about  a problem I think exists and one which I have not been able to find any guidelines in any of the technical standards for framing houses: ventilating the rafter bays under skylights.

We recently sold our wonderful home, expertly built, and are now living in our new home, a double wall super insulated air tight  (blower door test .5) .  Along the way we I have spent many years preparing for this adventure.  We will be off the grid in another 2 years.  Our old home sufferrend from ice dams.  I decided to redo the roof for the next owners wanting to make the hand off as   good as I could.  We hired a nationally recognized roofer to redo the roof.  We added ice and water shield on the  west side over the cathedral ceiling where the ice dams were most prevalent.  I had been monitoring the ice dams for several years and consulted many “experts” as to what was causing them.

Based on what I learned from the other ice problems ( this house has 4 skylights) I eventually determined that the skylights that were about 12 feet up from the soffits were holding trapped air and the heat built up in the rafter bays (2 x 12) below the skylights melting the water below the slylights which formed terrible ice dams.  So when we re roofed the roof I had the plywood sheathing (25 year old house) pulled up below the skylights to see how uch mold there might be, and most importantly we drilled 3 inch diameter holes in the center of the rafters so air could escape to the adjacent bays on either side of the skylight.  The ice dams were elimiminated, the water and ice layer was a waste of money, and we replaced one sheet of ply that was badly molded (but not suuctureally defective yet).  It was my idea to ventile the bays and it alone solved the ice dam problem below the skyliughts.  Yoiu could always see the smow melt first directly below the skylights even thought were was 10 inches of frp insulation everywhere and proper venting all the way to the ridege vents.

I have since been called to advise on ventilating rafters on new construction by people who know of my findings and research.  I have not been able to find a reference for the need to do this in the national standards, nor do any builders I have met know about this problem.  I live in New Hampshire.

Are there standards or references out there that speak to this problem? It was not discussed in the mentioned article.  It think it is very important and an oversight.

Jim