| Author | Message | ||
     Tim Dittmar Junior Member Username: Tim_dittmar Post Number: 12 Registered: 05-2008 |
Marilyn- there are ideas going around about indoor air pollution being heightened by houses being too tight- you may be heading that way from what you've described.. do you plan this attic to be heated-finished footage? In many regards, it may be wise to provide for introduced eave or soffet air to move on the underside of the roof deck and be vented(gable-wise or by ridgeventing) to the outside- windbeams above your headroom in that space would provide the framing for a ceiling ventspace for power exhaust or gablevents. Slate retains heat quite dramatically and passive venting might be quite wise- also, were the roof to leak sometime, the above would help to reduce damage from water that was slow to leave these insulated areas. Your query sounds like a multi-variable choice scenario- I'm listed in the consultant section- weekends or evenings are great.. | ||
| Marilyn Cusick-Jones New member Username: Marilyn Post Number: 1 Registered: 07-2008 |
QUESTION: Closed cell or open cell insulation affixed to underside of roof deck under SBS peel & stick with 3/8" slate roof on top? I need advice as to whether I should install open cell foam insulation or closed cell foam insulation applied to the underside of a roof deck upon which I have installed a slate roof. Facts: I am building on Kiawah Island, South Carolina (approximately 20 miles southeast of Charleston, SC) a two story house approximately 1200 feet from the ocean. Most of the roof is Buckingham Virginia slate with a thickness range of 3/8" to 1/2" with slate widths of 9", 10" , 11" or 12". Each slate is 18" long with a 7" reveal. The roof pitch is 12 in 12. The main portion covers flat floor area of 40 feet by 32 feet. Another portion coovers flat floor area of 28 feet by 16 feet. The roof deck consists of #1 grade southern yellow pine 2 X 8s milled to be tongue and groove. IN other words the roof deck is 1 1/2" thick by approximately 7" wide tongue and groove. Prior to installing the slate the decking was covered with an SBS single ply peel and stick roof with a 12 year warranty of its own.The slate was then installed on top of the SBS material. Thus if a hurricane flipped off shingles, the stickdown would hopefully keep the house dry. I plan to have a 2 ton air conditioner for the attic only which will dehumidify and keep the attic temperature at approximately 76 to 78 degrees. Considerations: The closed cell foam insulation is somewhat appealing because it adheres to the roof decking and rafters thus providing extra strength in a hurricane. However from reading The Slate Roof Bible and discussions with framers in the Charleston area I am concerned that encapsulating the wood between the airtight SBS stickdown on top and a fairly airtight closed cell foam underneath could lead to dryrot. With the attic being airconditioned and dehumidified I don't think moisture caused rot would be a problem. Open cell foam insulation has been recommended by independent thinking persons (as opposed to closed cell advocates) in that it would allow the wood to "breathe" and if any moisture were available, having drier air in the attic would hopefully take care of any moisture problem. What is your recommendation? |
