Making sure the deck’s ready for underlayment - what’s your process?

Curious if anyone’s tried using pinless meters versus pin-type for this? I’ve found pinless gives me a better sense of the overall area, but sometimes misses deep pockets.

- I’ve bounced back and forth between pin and pinless. Pinless is nice for a fast scan, but like you said, it’ll miss those deeper pockets, especially if you’re dealing with old patchwork or double layers. Pin-type is slower, but if I’m suspicious about a spot (especially near seams or patched areas), I’ll go in with the pins just to be sure. Sometimes the difference is night and day.

- FLIR’s a mixed bag for me too. Sun exposure makes it almost useless on hot days - false positives everywhere. I’ve had it show “hot spots” that were just sun-baked plywood, not moisture. Good tool for finding general anomalies, but not gospel.

- Pulling random fasteners: 100%. I started doing this after getting burned by what looked like a solid deck - walked fine, meter was clean, but pulled a few nails and found black mush around the shank. Now I always pull at least a few in suspect areas (valleys, eaves, old patched spots). It’s saved me more than once from missing rot.

- Old adhesives or stains: That’s a real headache. Sometimes my meter lights up on tar paper residue from decades ago. If I can’t tell by smell or texture, I’ll cut out a small section to check the wood directly. Not ideal, but better than guessing.

- My process now:
- Quick walkover for soft spots.
- Pinless scan for broad issues.
- Targeted pin readings where things look/feel off.
- Pull fasteners in at least three random spots per slope.
- If anything looks weird (color change, odor), open it up.

- One thing I’d add - if you’re in a humid climate or dealing with low-slope roofs, everything gets trickier. Sometimes you’re chasing old damage that’s been dry for years but still sets off every tool you’ve got.

Not sure there’s ever a perfect system... but combining tools and getting your hands dirty seems to catch most of it. The meters are helpful, but nothing replaces actually seeing and touching what’s under there.

I get where you’re coming from with the “pulling random fasteners” thing, but honestly, I’ve had mixed results with that. Sometimes I feel like it’s just poking holes for the sake of it, especially if the deck’s in decent shape and there aren’t any obvious signs of trouble. Maybe I’ve just been lucky, but on my last roof (old 1x6 skip sheathing under two layers of shingles), I did the walkover and used a pinless meter, and everything checked out. Pulled a couple nails in spots that looked iffy - nothing but clean wood. If I’d started yanking more fasteners everywhere, I probably would’ve ended up making more work for myself patching holes than actually finding anything wrong.

That said, I do agree with this part:

If anything looks weird (color change, odor), open it up.

I guess what I’m saying is, I lean more toward trusting my eyes and nose first, then using the meters as backup. If the deck feels solid underfoot and there’s no visible sagging or weirdness around seams or valleys, I don’t go hunting for problems that might not be there. Maybe that’s risky in some climates (I’m in a pretty dry area), but so far it’s worked out.

One thing I will say - if you’re dealing with OSB instead of plywood, all bets are off. That stuff hides rot way better and falls apart faster once moisture gets in. In that case, yeah, maybe pulling a few extra fasteners isn’t such a bad idea.

Just my two cents - sometimes less is more unless you’ve got a real reason to dig deeper.

I’m with you on the OSB - learned that lesson the hard way after a leaky skylight. Looked fine from the top, but once I pried up a couple nails, it crumbled like a saltine. Plywood’s definitely more forgiving. Honestly, I trust my feet and nose more than any fancy meter. If it feels solid and there’s no weird smell, I’m not poking random holes either. Around here (Pacific NW), moisture’s always lurking, but over-checking can just make more work. Sometimes you gotta go with your gut.

I’ve seen a lot of OSB failures, especially after a few wet seasons up here. Plywood holds up better when there’s been a slow leak or condensation issue - OSB just doesn’t give you much warning before it goes soft. I do use a moisture meter sometimes, but honestly, I agree that your senses are usually more reliable. If the deck feels spongy underfoot or there’s that musty odor, it’s time to dig deeper. Still, I’ll probe around suspect areas - edges, valleys, penetrations - just to be sure. Sometimes you find rot where you least expect it.

I get where you’re coming from about OSB, but I’ve actually had decent luck with it - at least when it’s properly sealed and ventilated. Up here, the humidity swings a lot, and I’ve noticed that even plywood can delaminate if there’s a persistent leak. I do agree with this:

“If the deck feels spongy underfoot or there’s that musty odor, it’s time to dig deeper.”

Can’t argue with the moisture meter - it’s bailed me out a couple times, too. Sometimes those old layers really do hide trouble you’d never spot otherwise. I still tap around with a hammer out of habit, but tech helps catch what my boots miss.

I hear you on the moisture meter - worth every penny, even if I grumble about buying more gadgets. I still trust the old hammer tap too, but last year, I found a soft spot that sounded fine but was soaked underneath. Saved me a chunk of change catching it early. For me, I also run a pry bar along the seams just to check for hidden rot. It’s not fancy, but it’s caught stuff my tools missed. Sometimes low-tech plus a little tech is the way to go, especially when you’re watching the budget.

I’m with you on the pry bar trick - sometimes you just gotta get in there and see for yourself. I’ve had spots that looked fine, meter said dry, but the bar found mush. Honestly, I still end up crawling around tapping and poking everything... feels like a weird roof dance.

Honestly, I still end up crawling around tapping and poking everything... feels like a weird roof dance.

That “roof dance” is way more important than most folks realize. I’ve seen guys trust the moisture meter or just eyeball it, but like you said, sometimes the only thing that finds the rot is a good old-fashioned poke. I’m a big fan of the pry bar too, but I’ll admit, I probably go overboard with my inspection. I’ll tap every seam and edge, especially around valleys and chimneys - those spots always seem to hide the worst surprises.

One thing I’ve noticed is that even if the top layer looks solid, the underside can be a mess, especially on older decks with multiple layers of shingles over the years. I’ve started checking from the attic side when possible, just to see if there’s any daylight or staining. Not always practical, but it’s saved me from missing soft spots a couple times.

I do think there’s a limit to how much you can rely on tools. Meters are great for a quick check, but they don’t tell you about delamination or hidden mold. I’ve had plywood that looked and felt fine, but when I pried up a corner, it just crumbled. That’s why I’m a little skeptical when someone says “the deck’s good” without actually getting hands-on.

One thing I’m still figuring out is how aggressive to get with replacing questionable boards. Sometimes I feel like I’m pulling up more than I need to, but I’d rather do that than have a callback for a soft spot under new shingles. Maybe I’m too cautious, but I’d rather be safe than sorry, especially with how expensive materials are now.

Curious if anyone’s found a good balance between being thorough and not overdoing it? I always end up second-guessing myself when I see how much decking I’ve replaced compared to some of the old-timers.

Sometimes I feel like I’m pulling up more than I need to, but I’d rather do that than have a callback for a soft spot under new shingles.

Honestly, I think you’re on the right track. I’ve had my share of “should’ve replaced that board” moments, and it’s never fun dealing with callbacks or leaks after the fact. It’s easy to second-guess when you see others being less picky, but in the long run, your caution probably saves headaches (and money). Materials are pricey, but so is redoing work. Trust your gut - better safe than sorry.

I get where you're coming from about pulling up more than you maybe need to. I’ve run into the same thing - especially when I started budgeting out my last re-roof. Plywood prices alone made me hesitate, but then I remembered the mess I had a few years ago after not replacing a questionable patch. Ended up with a leak right over my kid’s bedroom and a lot more drywall work than I ever wanted.

My process now is pretty methodical. I walk every square foot of the deck after stripping, checking for bounce or any hint of give. If there’s any doubt, I’ll use a screwdriver or awl to poke around - soft spots get marked and replaced, no debate. Sometimes it feels like overkill, but honestly, the peace of mind is worth it. I also double-check around eaves and valleys since those seem to rot out first in my area (Midwest, lots of snow melt and ice dams).

One thing I do try to balance is not tearing out boards just because they’re old. If the wood’s solid and there’s no sign of delamination or rot, I’ll leave it. I’ve seen some folks online say to just replace everything, but that can add up fast, and if it’s still structurally sound, it feels wasteful.

I’ve also started using a moisture meter after a rain (if timing lines up) before putting down underlayment. Found a couple spots last time that looked fine but were actually holding water - caught those before they became a bigger problem.

It’s definitely tempting to cut corners to save on materials, but every time I’ve done that, I’ve regretted it. Still, I don’t think there’s anything wrong with being a little picky as long as you’re not just ripping out good wood for no reason. It’s all about finding that line between being thorough and being practical - especially when you’re watching every dollar.

I get the urge to be super thorough, but honestly, sometimes I think folks go overboard with the poking and prodding. I manage a bunch of older duplexes, and if I replaced every board that flexed a little or looked “iffy,” I’d blow through my budget before even getting shingles on. In my experience, a little give isn’t always a death sentence - especially on older homes where nothing’s truly perfect anymore. I’ll swap anything soft or rotten, sure, but if it’s just a bit weathered and still holding nails, I usually leave it. Haven’t had a callback yet... but I do keep a close eye on those spots during inspections.

if I replaced every board that flexed a little or looked “iffy,” I’d blow through my budget before even getting shingles on.

I get the budget thing, believe me, but I’ve seen “just a bit weathered” turn into a trampoline after one good rainstorm. Last summer, we left a couple boards with some give (looked fine, held nails), and by fall, the new shingles had a weird dip. Boss was not amused. I’m not saying replace every plank with a personality, but sometimes it’s cheaper to swap one now than patch a saggy spot later... especially if your inspector has hawk eyes.

I get where you’re coming from on the budget, but I’ve seen too many “good enough” boards turn into soft spots after a season or two. It’s tricky, though - some flex is normal, especially with older sheathing, and not every little give means it’s toast. I usually walk the deck with a heavy boot, checking for bounce or that hollow sound. If it feels spongy or you can poke a screwdriver through, that’s a no-go for me.

One thing I’ve noticed: even if a board looks okay and holds nails, moisture can get in under the underlayment if there’s any rot starting. That’s when you get those weird dips or even leaks down the line. Had a job last year where only two planks were replaced to save money - by spring, both had swollen up and pushed the shingles out of alignment. Ended up costing more in repairs than just swapping them at the start.

I’m not saying rip out every board with a knot or some age on it. But if there’s flex that doesn’t feel right, or you see dark stains or mold underneath, it’s probably worth pulling it. Sometimes I’ll mark questionable spots and come back after lunch - if they still bug me, out they go.

It’s always a balance between cost and future headaches. If you’re in a wet climate or have low slope, I’d lean toward being pickier. Drier areas, maybe you can get away with leaving more in place. Just keep in mind inspectors (like me) are looking for anything that could compromise the roof down the road... and sometimes we’re pickier than homeowners expect.

Curious how others decide when “iffy” crosses into “replace it now.” For me, it’s mostly about how much give there is and what the wood looks like underneath - if it’s punky or soft at all, I don’t risk it.

You nailed it with the “future headaches” point. I get wanting to save a few bucks, but every time I’ve tried to patch around questionable spots, it’s bitten me later - especially in our rainy PNW climate. Even if the board seems solid up top, if there’s any hint of black staining or that musty smell underneath, I don’t mess around. I’ll admit, sometimes I overthink it and end up swapping more than maybe I need to... but it’s never come back to haunt me.

One thing I started doing is using a moisture meter on suspect boards, especially if the weather’s been rough or there’s any sign of past leaks. If the reading’s high, out it goes. And for anyone trying to be eco-friendly like me, salvaging borderline boards just isn’t worth the landfill savings if you end up tossing more material down the road.

I do agree some flex is fine - old-growth stuff can fool you with how much it moves but still holds up. But yeah, punky wood or anything even close to crumbling gets marked and pulled. Learned that lesson after a “good enough” patch job led to a full tear-off two years later... not fun.

Learned that lesson after a “good enough” patch job led to a full tear-off two years later... not fun.

Been there, too. Sometimes I think I’m being overly cautious, but every time I’ve left a questionable board, it’s come back to haunt me - especially after a heavy storm rolls through. I’m with you on the moisture meter; I used to trust my nose and a screwdriver poke, but those meters catch stuff you’d miss otherwise. Still, I’ll admit I’ve kept some old-growth planks with a little flex if they’re dry and solid underneath. Not everything has to be new, but anything even hinting at rot is just a future leak waiting to happen.

Not everything has to be new, but anything even hinting at rot is just a future leak waiting to happen.

That’s the truth - rot’s like that one guest who shows up uninvited and never leaves. I’ve had my share of “it’ll probably hold” moments, especially with those old cedar planks you just don’t see anymore. Sometimes I’ll keep ‘em if they’re still solid, but yeah, anything soft or crumbly gets the boot.

I do get a little obsessive with the moisture meter, though. Maybe it’s overkill, but after one too many green roof installs where hidden damp spots turned into mini-mushroom farms... let’s just say I trust the numbers more than my nose now. Still, I’ll admit there’s some charm in those old boards - if they’re dry and not splitting, they can outlast a lot of new lumber. But if there’s any doubt? Out they go.

Funny how much time you can spend poking around for that one bad spot while the rest of the crew is ready to roll out underlayment. Always feels like a game of “find the ticking time bomb.”

I’ve run into that same dilemma with old boards - sometimes they look rough but are still solid, and other times they hide just enough rot to cause headaches later. I’ve started using a screwdriver to poke around, especially near fasteners and seams. Ever had a spot that looked fine on top but was mush underneath? That’s burned me before. I’m curious, do you ever seal up older boards if they pass the moisture test, or is it always replace if there’s any doubt?

I’ve definitely had those spots where the top looks fine, but you poke through and it’s like wet cardboard underneath. The screwdriver trick is a must, especially around valleys and eaves - those seem to hide the worst surprises. If a board passes the moisture test and feels solid, I’ll sometimes seal it up with a good primer or wood hardener, but only if it’s minor surface stuff. Anything soft or punky gets replaced, no question. I’ve seen too many callbacks from “good enough” decking that turned out not to be.

Curious if you check for delamination too? I’ve run into a couple of older plywood decks where the layers started peeling apart even though the surface felt okay. That’s a whole different headache...

Delamination’s a sneaky one for sure. I’ve seen plywood that looked fine until you started walking it, then you’d feel that weird give underfoot - never a good sign. I’ll tap around with the handle of my hammer and listen for hollow spots, especially near old leaks or where water might’ve pooled. If the layers are starting to separate, I don’t mess around trying to patch it. Like you said, callbacks aren’t worth it. Better to bite the bullet and swap out the bad sheets before moving on.