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

Sometimes even a solid-looking board can surprise you...

- Had a deck once that looked fine - walked across it, foot went straight through. Turns out the rot was hiding underneath, right where water pooled by the grill.
- Moisture meters are cool, but my wallet says “nah.” I usually poke around with a screwdriver and, if it sinks in like butter, time to replace.
- Shaded spots are always the sneaky ones. Learned to trust my nose - if it smells musty, there’s trouble brewing.
- Butter knife? Haven’t tried, but hey, whatever works in a pinch. Just don’t use your good cutlery...

Moisture meters are cool, but my wallet says “nah.” I usually poke around with a screwdriver and, if it sinks in like butter, time to replace.

That’s pretty much my approach too. I tried borrowing a moisture meter once, but honestly, the old screwdriver test tells me what I need to know. I’ve also learned the hard way that just because the top looks fine doesn’t mean there isn’t a swamp underneath. Had a board by the stairs that looked perfect - until I leaned on it and nearly ended up in the crawlspace. Turns out, the joist was toast from years of rain sneaking in at the edge.

I do a “tap test” sometimes - just knock along the boards and listen for that hollow sound. Not exactly scientific, but it’s saved me from a few surprises. And yeah, shaded spots are always trouble. If it smells funky or feels spongy, I’m not taking chances.

Never tried the butter knife trick, but I’ve definitely sacrificed a few old screwdrivers to the cause. Better than risking a trip to urgent care, right?

I do a “tap test” sometimes - just knock along the boards and listen for that hollow sound. Not exactly scientific, but it’s saved me from a few surprises.

I get the appeal of the “poke and tap” method - cheap, quick, and you don’t have to dig through the garage for fancy gadgets. But I’ll be honest, after patching up more than a few decks that looked fine on top but were basically compost underneath, I started leaning on moisture meters a bit more. Yeah, they’re not cheap, but neither is replacing half your decking because you missed a soft spot.

I’ve seen plywood that passed the screwdriver test but was still holding enough water to make a mushroom farm jealous. Especially after a wet spring, those hidden pockets can sneak up on you. I’m not saying toss out the screwdriver (mine’s got battle scars too), but sometimes a little tech saves you from headaches down the road.

And about the “smells funky” test - my nose isn’t what it used to be after years of solvents and shingles. I’d rather trust a meter than my sinuses these days.

I’m with you on the moisture meter - after a few “looks fine, falls through” moments, I stopped trusting just my eyes and ears. I still do the tap and poke routine out of habit, but if I’m prepping a deck for underlayment, especially in older buildings or after a wet season, I want numbers. The meter’s paid for itself just by catching those spots that felt solid but were quietly rotting from the inside out.

One thing I’ve noticed: even with a meter, you’ve got to check more than just the obvious trouble spots. Corners and edges near flashing or where water might pool are always suspect. I’ve had decks where the middle was bone dry but the perimeter was a swamp under the surface. Sometimes it’s not even visible until you pull up a board.

I do still rely on my nose sometimes, but like you said, years of paint fumes and whatever else have dulled that sense. If it smells musty, it’s usually bad news, but lack of smell doesn’t mean you’re in the clear.

Curious if anyone’s tried those infrared cameras for this? I’ve only borrowed one once and it was interesting - picked up some cold spots that lined up with wet wood - but not sure it’s worth buying unless you’re doing this all the time.

For me, it’s a mix: tap test for quick checks, moisture meter for anything serious, and if there’s any doubt, I’ll pull up a board or two. It’s a pain in the moment but way better than dealing with callbacks or repairs after the fact. Anyone else run into issues with hidden rot even after using a meter? Sometimes I wonder if there’s ever a foolproof method...

- Totally agree on not trusting just the “poke and prod” method - my knuckles have been wrong more than once.
- I use a meter too, but yeah, it’s not magic. Had a deck last fall where the joists read fine, but one end was mush under the flashing.
- Corners and anywhere water sneaks in are always on my hit list.
- I’ve borrowed an IR camera a couple times - helpful, but honestly, it’s more of a backup than a main tool for me.
- Pulled up boards “just in case” plenty of times...sometimes you find nothing, sometimes you find a science experiment.
- Foolproof method? Not yet. Just layers of paranoia and experience, I guess.

Foolproof method? Not yet. Just layers of paranoia and experience, I guess.

That pretty much sums up how I feel tackling my own deck for the first time. I’ve tried the meter and poking around, but like you said, it’s not always reliable - especially near flashing or where water might pool. Pulled up a couple boards last weekend “just in case” and found some soft spots I never would’ve guessed were there. It’s a bit nerve-wracking, but hearing that even experienced folks don’t have a perfect system is honestly reassuring. Guess it’s just about being thorough and not skipping steps, even if it feels like overkill sometimes.

Funny how you can poke and prod all you want, but sometimes the worst spots are just invisible until you actually pull up a board. I’ve had decks that looked fine - solid when you walked on them, meter readings normal - but then you open up a seam near a valley or chimney and there’s rot hiding right underneath. It’s tedious, but I’d rather be a little paranoid and spend an extra hour now than have to go back and fix something after the underlayment’s down. If it feels like overkill, it probably means you’re doing it right.

Had a deck last year that looked like it could hold up a marching band - solid as a rock, or so I thought. Pulled up a couple boards near the skylight just to be thorough, and boom... found a patch of rot the size of a dinner plate. The rest of the crew thought I was being picky, but I’ve learned the hard way that water finds its way into places you’d never expect, especially around chimneys and valleys.

I get why some folks skip the extra checks, but honestly, I’d rather deal with a little eye-rolling from my team than have to explain to an owner why their brand new underlayment is bubbling up six months later. Sometimes it feels like overkill, but in my experience, paranoia pays off - at least when it comes to roofs. Plus, there’s something oddly satisfying about catching those hidden trouble spots before they turn into real headaches.

You’re spot on about water finding its way into the weirdest places. I’ve seen decks that looked perfect from the top, but once you start poking around - especially near penetrations like skylights or chimneys - it’s a different story. I get pushback too when I slow things down for extra checks, but I’d rather be the “paranoid” one than deal with callbacks or worse, mold complaints down the line.

Here’s how I usually break it down: First, I walk the whole deck and look for any soft spots or discoloration. Even if everything feels solid, I’ll still check around all the roof penetrations - skylights, vents, valleys, you name it. If there’s even a hint of water staining or a musty smell, I’ll pull up a couple boards. Sometimes it feels like overkill, but every time I’ve skipped this step to save time, it’s come back to bite me.

I know some folks just want to slap on underlayment and move on, especially if the schedule’s tight. But like you said, explaining to an owner why their new roof is bubbling or leaking is way worse than taking an extra hour upfront. Plus, once you’ve seen what hidden rot can do - especially in wetter climates - it’s hard to unsee it.

One thing I started doing is keeping a cheap moisture meter handy. Not perfect, but it helps spot trouble before you even pull boards up. And if there’s any doubt about a section, I’d rather replace a few feet of decking now than risk the whole job later.

It might feel like nitpicking to some crews, but in my experience, those “paranoid” checks are what separate a quick fix from a job that actually lasts. You’re not alone in being thorough - even if it means catching some side-eye from the team now and then.

It might feel like nitpicking to some crews, but in my experience, those “paranoid” checks are what separate a quick fix from a job that actually lasts.

Couldn’t agree more with this. The folks who roll their eyes at “overkill” are usually the same ones who end up with callbacks or warranty headaches. I’ve lost count of how many times I’ve found rot hiding right around a vent or skylight that looked totally fine from the surface. It’s wild how water will snake its way in, especially if you’re in a spot with freeze-thaw cycles or just a ton of rain.

I’ll admit, sometimes I get pushback too - guys want to move fast, especially if weather’s closing in. But like you said, explaining to a client why their “new” roof is leaking is a nightmare. I’d rather take the hit on time than reputation.

Moisture meters are underrated, honestly. Not perfect, but they’ve saved me from missing stuff more than once. And if you’re thinking long-term, especially with green or cool roofs, that extra diligence up front is non-negotiable. Once you’ve seen what trapped moisture does under a living roof system... yeah, you don’t forget it. Keep doing what you’re doing - your future self (and your clients) will thank you.

That’s the truth. I’ve had a couple times where I thought, “eh, looks solid enough,” only to find out a year later that a little soft spot turned into a full-on headache. My place is old, and around here we get those wild spring thaws - water finds every weak spot, no matter how small. Slowing down to check for moisture or hidden rot has saved me more than once. It’s not always popular with whoever’s helping me, but I’d rather patch a small area now than rip up a whole section later. You’re spot on about the long-term payoff.

Slowing down to check for moisture or hidden rot has saved me more than once.

I hear you on that - rushing always comes back to bite. I usually go board by board with a screwdriver, poking for soft spots, especially near seams and edges. Curious if you’ve ever used a moisture meter, or do you just rely on feel and visual cues? Sometimes I wonder if I’m being too cautious, but like you said, water finds every weakness...

I’ve tried both ways - old-school poking and using a moisture meter. Honestly, the meter’s handy for peace of mind, especially after a rainy week, but I still trust my eyes and a screwdriver more. Had a spot last year that looked fine but the meter spiked, so I pulled the board and sure enough, rot underneath. I do think it’s possible to overdo it, but I’d rather be too cautious than miss something that’ll cost more down the line.

I’m with you on not relying 100% on the meter. I’ve had those false positives too, but sometimes it’s the only way to catch stuff you can’t see or feel. I usually poke around with a putty knife, especially near the ledger and any spots that stay shaded. Curious - do you ever check underneath from below, or is your deck too low for that? Sometimes I crawl under with a flashlight just to be sure I’m not missing anything. It’s not fun, but it’s saved me from surprises more than once.

Funny, mine’s just high enough that I can squeeze under if I really have to, but man, it’s a tight fit. I’ve found a couple of soft spots that way I’d never have noticed from above. Not my favorite chore, but beats having to redo the whole thing later. I do wish there was an easier way, though...

I’ve found a couple of soft spots that way I’d never have noticed from above.

Yeah, crawling under there is a pain, but it’s wild how many issues you can spot from below - especially with older joists. I ended up using one of those cheap inspection mirrors and a flashlight to check the tightest spots. Not perfect, but better than trying to wedge myself in every time. Wish there was a robot for this stuff...

Inspection mirrors are a lifesaver, but I’ve started using my phone camera for tight spots - just snap a few pics or record a quick video under the deck and zoom in later. It’s not perfect, but it’s saved my back more than once. Have you ever tried gently tapping the joists with a screwdriver handle? Sometimes it’s the only way I catch those hidden soft patches before they get worse. Curious if anyone else relies on sound as much as sight when checking for trouble...

I get the appeal of using your phone for those awkward spots, but I’ve had mixed luck - sometimes the glare or shadows make it tough to see what’s really going on. I still trust my hands and a pry bar more than anything. Tapping joists is good, but I’ve found that sometimes rot doesn’t sound off until it’s already pretty far gone. I usually poke around with an awl or screwdriver tip, just to be sure. Sound helps, but I wouldn’t rely on it alone.

I usually poke around with an awl or screwdriver tip, just to be sure.

Same here - my phone’s just a flashlight half the time. I’ve found more rot with a cheap screwdriver than any fancy tool. Once poked right through a joist that looked fine from above... learned my lesson quick.

Had a deck job after a hailstorm where the homeowner swore everything was solid - looked fine, barely any staining. I started poking around with my trusty screwdriver and, sure enough, nearly put my foot through a “good” board. Sometimes I think rot’s got a sense of humor, hiding right where you least expect it. I’ve tried moisture meters, but honestly, nothing beats a sharp tool and a suspicious attitude. If it feels spongy, it’s coming out... even if it means more work.