I had such a simple plan in mind. Some dimensional lumber trusses laid straight across the top plates, covered with simple panels of plywood, followed by simple panels of rigid insulation, and covering that in turn with a single sheet of EPDM. I thought I was prepared with the proper adhesive, plenty of fanfolded insulation, the proper nails and screws, all that. I was wrong.
This would be a good place to make a sandwich to eat while reading. It’s a longish post.
First, of course, there is the extra layers I’ve already added, that make up the insulation sandwich. They are really important to break thermal bridging, but add expense, labor and height. Next, it turns out the fanfolded insulation I have “might” not be the correct kind for my brand of EPDM (it’s hard to know for sure because my manufacturer has been absorbed by Firestone, and their requirements “might” be different ~ it’s common with EPDM manufacturers to each have very narrow and specific needs for each brand). The safest route is to use 6 inches of polyisocyanurate insulation on top of the roof deck, and fully adhere the rubber layer on top of that. Uh, oh, I don’t have 6 inches extra height to spare. Plus, that’s OMG expensive. I’m feeling a little panicky now.
After much investigation, it seems most brands of EPDM can be applied directly to wood, but only smooth-as-silk wood like Fiberboard, which is a very bad product to use in this wet environment. So add more hours of investigation. It looks like silicone is compatible, and can (probably even should) be used to fill all holes, gaps and cracks larger than 1/4 inch in the plywood decking I have to create a smooth surface. So, off I go to buy silicone. Not the mixed stuff, only pure silicone, since I couldn’t find evidence confirming the compatibility of the mixed stuff with EPDM. So I buy several contractor tubes of silicone and a spatula thing to smoosh the stuff into crevices. FINALLY, ready!
Oops, no. Any and all splinters or rough bits need to be sanded off or there’s a risk of the rubber tearing. Fine. I do some research and buy a powered sander. Hand sanding will take forever, and sunny days are rare and precious here. I’ll need to sand the barn wood interior anyway, so this extra purchase doesn’t dismay me, not too much.
At this point things get fuzzy. I literally can’t remember why exactly I deemed it necessary to purchase a gallon of liquid EPDM, I really can’t…somewhere in here my doctors changed my meds and I sleep-walked through a couple weeks. But I bought the stuff and am going to brush it onto all the plywood edges for waterproofing and over the clips to soften their sharp edges.
Somehow I’ve gone far astray from my “simple” roof solution! Tomorrow is supposed to start a week of dry sunshine, all my newly purchased stuff has arrived, and my knee is down to a dull ache. My plan is to sand, sweep and silicone. I have no idea how long it will take, but hopefully not more than a day or two. Fingers crossed!