Johns Manville Insulation & Roofing: A Pre-Install Checklist for Homeowners with Stained Glass Windows, Shower Valves, and Old Wallpaper

Who This Checklist Is For

If you're about to install Johns Manville insulation or a new roofing system, and your home happens to have stained glass windows, a shower valve that's embedded in the wall, or layers of old wallpaper—this is for you. I've been managing residential renovation projects for about six years now (actually, closer to seven if you count the year I spent learning the trade). I've personally made eight notable mistakes that added up to roughly $12,000 in wasted budget and countless headaches.

This checklist is the result of those mistakes. It's basically a list of things I wish someone had told me before my first big insulation job. There are six steps, and step 5 is the one most people overlook—I'll warn you now. Also, Johns Manville products are featured because they're what I spec for most projects, but the principles apply to any quality insulation or roofing material.

Step 1: Address the Wallpaper Problem Before Insulation Arrives

Sounds obvious, right? But when I started in 2018, I figured we'd just blow in cellulose over the old wallpaper. Big mistake. The wallpaper started peeling behind the drywall (moisture + adhesive = mess), and we had to rip everything out and start over.

What to do: Remove all wallpaper completely before any insulation work, especially if you're using blown-in or spray foam. For Johns Manville's R-13 fiberglass batts, the wall cavity needs to be clean and dry. Wallpaper remnants can trap moisture and cause mold. If the wallpaper is stubborn, use a steamer and scoring tool. Budget at least a full day per room. Actually, more like two days if the paper is heavily glued.

Step 2: Protect Stained Glass Windows During Roof Work

If you have stained glass windows—especially older ones—they're surprisingly fragile. In 2022, a roofer dropped a hammer on a client's Tiffany-style window. Even with fall protection, vibrations from hammering can crack the lead came. I still kick myself for not covering it properly.

What to do: Before any Johns Manville roofing details (like underlayment or shingle installation) begin, cover stained glass with ½-inch plywood on the outside and a padded blanket on the inside. Tape the plywood to the window frame—don't nail it. Make sure the crew knows it's there. This adds maybe 30 minutes to prep but saves thousands in replacement. (Note to self: always include this in the project brief.)

Step 3: Coordinate Shower Valve Access with Insulation

Here's a gotcha I learned the hard way: if you're insulating an exterior wall that contains a shower valve, you need to plan access. In 2020, we sprayed closed-cell foam over the valve area, assuming the plumber would cut it out later. He didn't. The valve failed after two years, and we had to carve through the foam—costly and messy.

What to do: If you're using spray foam or rigid board, create a removable access panel around the shower valve. For batt insulation, leave the area unfilled until after the valve is installed and tested. Johns Manville's product data sheets don't explicitly say this, but trust me: plan for future access. (Or rather, plan for the inevitable moment when the shower valve needs replacing.)

Step 4: Verify R-13 Insulation Specs for Your Wall Cavity

Johns Manville R-13 insulation is a common choice for 2x4 walls. But here's the thing: the actual R-value depends on installation quality. I once ordered R-13 batts that were slightly too thick for the cavity depth (the wall had furring strips), and we ended up compressing them, dropping the effective R-value to about R-11.

What to do: Measure your stud depth before ordering. Johns Manville's R-13 batts are typically 3½ inches thick. If your cavity is 3⅝ inches, you're fine; if it's less, consider R-11. Don't compress the batts—it reduces thermal performance. Also check the facing: use kraft-faced for interior walls with vapor barrier requirements, unfaced for basement or crawl space. This was true 10 years ago when I started; today the product spec is virtually the same, but double-check the data sheet.

Step 5: Don't Forget Air Sealing (the Overlooked Step)

This is the step that 80% of homeowners skip. You can install the best Johns Manville insulation, but if your walls have gaps around electrical boxes, pipes, and window frames, you're losing heat. And—here's the tie-in—those gaps also let moisture into the wall cavity, which is bad news for stained glass windows (condensation) and wallpaper (mold).

What to do: Before insulation goes in, seal all penetrations with caulk or spray foam. Use fire-rated caulk around recessed lights. For larger gaps around shower valve pipes, use minimal expanding foam. Johns Manville's installation guidelines recommend air sealing as a best practice. It adds a morning's work but can improve overall R-value by 20-30%. Plus, it stops drafts that make your shower feel cold. (I really should have included this in my first project—my fuel bills were brutal.)

Step 6: Inspect Johns Manville Roofing Details Before the Crew Arrives

When you order Johns Manville roofing details (like EverGuard TPO or shingles), the delivery includes more than just the membrane. There are fasteners, plates, drip edge, and sometimes adhesive. Missing a small component can delay the job.

What to do: Create a checklist of items from the order invoice. I once had to stop work because we were short on 2-inch screws for the roof insulation—cost us $450 in rush shipping and a day of lost labor. Check that the fasteners match the deck thickness. If you're adding insulation board under the roof membrane, verify the R-value matches your spec. And if you have stained glass windows directly below the roof edge, make sure the crew uses catch nets or plywood to protect them from falling debris. (That $450 mistake was in 2021—I still cringe when I think about it.)

Common Mistakes That Still Haunt Me

• Mistake #1: Assuming old wallpaper would act as a vapor barrier. It didn't. Water vapor still passed through, causing mold behind the insulation. I learned to always remove wallpaper, even if it's paintable.
• Mistake #2: Not protecting stained glass windows during roof tear-off. A small piece of shingle debris hit the glass and cracked it. Replacement cost: $1,200. The plywood cover would have cost $20.
• Mistake #3: Installing spray foam around a shower valve without marking the location. Now I always take photos before foam goes in and install an access panel sized to the valve trim.
• Mistake #4: Choosing the cheapest insulation bid instead of Johns Manville's R-13 batts. The cheaper batts were undersized and left gaps. I had to redo the entire floor. Total cost: $2,000 more than if I'd just bought the good stuff upfront. (Bottom line: cheap materials = expensive repairs.)

These mistakes taught me that the total cost of an insulation or roofing project includes not just the product price but also prep, protection, and rework risk. That's why I now spec Johns Manville for almost everything—the consistency and technical support are worth the premium. Plus, their data sheets (available for free online) give you exact R-values, fastener specs, and installation steps. You can actually plan ahead.

If you're tackling a project that involves wallpaper removal, stained glass windows, and a shower valve—and you're also insulating with Johns Manville—don't skip these steps. I promise, it's easier to spend a day prepping than to spend a week fixing my mistakes.