Rigid insulation over brick and window flashing help
I’ve tried to do my homework by reading through numerous posts & articles, watched videos, etc. I think I’ve got my insulation plan all figured out but I wanted to double check with the GBA community. I also have a few questions.
We bought an old schoolhouse (climate zone 5a) that is constructed of concrete block with brick veneer. Here’s the retrofit plan:
-cover the brick with Tyvek
-fasten 2×4’s to the brick vertically, on the flat, on 16″ centers (and around windows/doors)
– lay 1.5″ glass mat polyiso between the 2×4’s
-lay full 4×8 sheets of 1.5″ glass mat polyiso on top and tape seams
-attach 1×4 furring strips through the polyiso and fasten to 2×4;s every 16″
(This is essentially the method I found in “Deep Dish Retrofits” on buildingscience.com…except they applied a fluid applied barrier instead of Tyvek. See pic.)
We’ll be keeping many of our existing windows because they are newer decent quality (vinyl, double pane, argon gas)…and because the budget is getting tight. They’re already “innies” that are inset from the brick veneer and each window has a sloped concrete sill.
I’m not sure how to handle some of the flashing details. I’ve looked through many of the pages on this site dealing with flashing windows, and “innies” and “outies”…but I’m still confused.
Here are my questions:
1. Am I correct in putting Tyvek directly on the brick as a first step? If so, do I use adhesive flashing tape to seal the Tyvek to the brick openings around the existing windows…before framing the windows with 2x4s and applying the insulation?
2. Do I need to cover the glass mat facing of the outermost layer of polyiso with Tyvek or something? Or is the glass mat facing an acceptable rainscreen?
3. After the insulation is installed, would I seal all edges of the exposed polyiso and the 2x4s around the windows with flashing tape…affixing it to the flashing tape applied in question 1 above? (I’m concerned that if water ever got behind the insulation it wouldn’t have anywhere to go.)
4. Should I be installing a drip flashing along the bottom of the wall, 3″ wide, to accomodate the 2 layers of polyiso? And wrap the bottom edge of the insulation with bug screen?
Am I on the right track? If not, can you perhaps show me a sketch of the best way to flash an existing innie window in a brick wall?
Thanks in advance for any help you can offer!!
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