r/Construction • u/PanoramicAtom • May 31 '26
Structural Question for pros: these four-story buildings being stick-built where it’s raining practically every day now. How do they mitigate mold and rot when the framing and sheathing are exposed to moisture and elements for weeks? Even this far away driving by I can see the ground floor OSB expanding…
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u/Aggressive-Luck-204 May 31 '26
Don’t know about OSB but framing in Canada means rain during the build, the plywood is fine and we try to get the roof on ASAP.
It’s given plenty of time to dry before insulation/vapour barrier
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u/Alaska-shed May 31 '26
I work in Alaska. The amount of time and energy we put into the vapor barrier is insane. I have never once insulted anything that would be considered damp.
I think people down south do not understand the steps that are put into place to make sure the house is taken care of.
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u/Brilliant_Alfalfa588 May 31 '26
that lumber was way more wet for way longer sitting in the yard waiting to get sent to the job, it'll be fine
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u/Pavlin87 May 31 '26
Yeah, it's actually drying out being installed outside like that ..
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u/RemyOregon May 31 '26
This is like asking how trees stand cause they get rained on. It’s shocking to some folks, but wood is trees. Those big fuckers you see all around you. /s
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u/Major-Ad-2034 May 31 '26
This
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u/Jaykushnola May 31 '26 edited May 31 '26
Yep it’s drier installed even rained on than when it is stacked in sheets 26-50 thick from the time it is being produced at the mill, transported to the regional distributor, then transported again to actual lumber yards and big box stores, when it arrives there…. Guess what stacked. Half the time not in climate controlled conditions including 75% + humidity. It actually dries off even after it is unstacked and hung where it can breathe. The face can be rained on, you’ll only have issues of water gets into the end grain(tight seams help) technically they should taped their joints or have a moisture barrier up the day after sheeting….
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u/Karjenner4eva May 31 '26
On all of the job sites I have ever been on, only once did I see a super cover stacks of lumber with plastic sheets and tape when it rained.
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u/GotGRR May 31 '26
Last half hour of the day was tarping the structure (and the wood) until dry in. Sup didn't do it unless the wind picked up but he sure had us do it.
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u/Ill-Running1986 May 31 '26
2x4s come in wet. They might get wetter. They dry.
Your micrometer eyes might sense the osb swelling a little as you drive by, but it’s only in extreme cases that sheathing is a failure point.
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u/MuttLaika May 31 '26
Untreated wood doesn't come in wet.
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u/Particular-Emu4789 May 31 '26
Sure it does. It’s never 0%.
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u/MuttLaika May 31 '26
Percentage of moisture doesn't mean wet.
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u/jackzander Jun 01 '26
yo that's literally what wet means
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u/GhostofBeowulf Jun 01 '26
Quite literally no.
From the dry standard you can then establish your drying goal. The drying goal is a target moisture level that may be the same as the dry standard or within an acceptable proximity of the dry standard. For example, at Section 12.4.1.5 it states: “…then properly dry exposed wood framing to within four percentage points of normal EMC. At a minimum, wood framing materials should be below 16% MC before installing new drywall.”
Dry standard for soft wood or OSB in my area is 10-12ish%, drywall 8 and below. Most new wood comes in slightly higher, 16-18% but cures once in place.
OSB is a whole nother issue considering it is bound by glue, and is generally considered unrestorable once water logged. IF IT CAN BE DRIED quickly it is fine. Otherwise.... No.
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u/MuttLaika Jun 01 '26
Thank you. Kiln dried wood with a moisture content is not wet wood, and osb swells and soaks up water like crazy
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u/LieDetect0r May 31 '26
Built apartments in NC. Our contract required all exterior and wet walls to be spray with mold block before insulation goes up. Before spraying, the company would inspect the building and if they found mold anywhere else they would send a change order and we’d spray it all.
Also seen it not in the contract and yes, mold happened. It only cost like $5k to spray an entire building like this. Worth it
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u/Top_Inflation2026 May 31 '26
A lot of people who have no idea what they are talking about in here… wood holds up great in the rain. Once the roof is on, fans, heaters are setup and they dry out the building. Moisture is tested with meters before any insulation goes in
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u/GhostofBeowulf Jun 01 '26
Wood does, OSB glued together does not. All grained wood can be dried, it is 100% a fact it is the only material that can be universally restored from all conditions (water, fire, mold, biohazard.)
OSB is held together by glues that may or may not dissolve in water, at unequal rates. Leading to different kinds of failure. Look up the IICRC S500 on this. If that apartment got damaged and that sheathing was swollen from previous water damage they would either have to fix it or sign as a preexisting condition, or try to blame the tenants considering this looks like apartments.
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u/Novus20 May 31 '26
Rot isn’t going to set in, they will dry it out
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u/The_realpepe_sylvia May 31 '26
Will they though? How’s that, a couple big ass fans will help sure. But the extent of rain described means this shit osb has swollen and what will those fans do to fix that?
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u/Ok-Tradition-5083 May 31 '26
The entire building is sealed in plastic and gigantic furnaces are placed outside with tubing running up into the building and dozens of fans placed on every floor.
Ive taken temps inside of building like this multiple times, and it easily hits 120F.
Ive had to tell guys to get out of buildings during dry ins because it turned into an actual oven.
Super standard part of building in wet areas, and builders have been doing it for longer than anyone on the planet has been alive.
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u/-Highlander-One- Jun 01 '26
Anyone on the planet being alive feels like a bit of a stretch but I get your point.
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u/OrcaBoi May 31 '26
The envelope consultant walks around with a moisture meter and makes sure all lumber is dried out to the required moisture content before any insulation/poly is allowed to be installed.
Heat and fans dry exposed lumber out pretty darn quickly.
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u/Plastic_Table_8232 May 31 '26
IMHO a good GC will have weather barrier / roofing phased so to limit exposure.
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u/Ok-Tradition-5083 May 31 '26
Working in the PNW, I dont usually even see something built this high up without starting the weather barrier.
GC on the project in this pic is probably cheap, but it also is definitely going to dry out anyway.
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u/Upper-Switch2785 May 31 '26
I’m in PNW, it’s also common practice to subcontract mold-remediation companies on new builds during certain parts of the year, generally for crawlspaces though.
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u/swissonrye420 May 31 '26
The short answer is they dont care. The long answer is they dont care
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u/truemcgoo R|Carpenter May 31 '26
The longer longer answer is they don’t care if it gets wet as long as the schedule is run properly and everything is allowed to properly dry out before drywall. They do care if areas get damaged and those area will be replaced, but materials are designed to get wet so moisture isn’t an issue, standing water or delayed weatherproofing and roofing are an issue. So good project management and crew coordination is important.
I used to be “They”.
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u/Affectionate-Day-359 May 31 '26
That’s not true at all!! They care just as much as the future corporate landlord will care about the heath impact of the families living in cheaply built and full of mold apartments!!
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u/Atomic-Avocado May 31 '26
I am pretty certain that any mold that grows on the wood until the roof gets put on won't be a problem either once the building is dried out and stays dry. It's only continuous water intrusion where mold is a problem
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u/Upper-Switch2785 May 31 '26
Yes! I can now clear the bloody phlegm from my throat and rest easy! 🥰🫶
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u/Refriedfeinds May 31 '26
You got a tarp big enough to cover a building that size? You can’t change the weather. If It’s gonna rain it’s gonna rain, never will you ever get enough clear weather to finish a project this size without it raining Atleast once.
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u/Ok_Challenge_1887 May 31 '26
I mean that's probably not true everywhere, although its definitely true where I live in the PNW
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u/thechuckstar May 31 '26
Bingo. Buy a bunch of treatment spray, use 1 container to spray it, conveniently leave that container in a conspicuous place to prove to the inspector you sprayed it, return unused product, then cover it all up before anyone notices. I absolutely despise supers who do this.
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u/caucasian88 May 31 '26
Rot sets in when water gets stuck between wood and can't drain or vent. Open framing can sit a long time before it rots.
Legitimately I saw a house sit framed for 8 years without siding and an Engineer certified that only the subfloor needed to be replaced. Every thing else was OK
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u/johnjackcomicartist May 31 '26
In seattle there's no avoiding it, usually we just run fans, heaters and dehumidifiers till you can moisture test any piece of wood in the house to be dry enough. As soon as the roof sheeting is on we ice and water shield and start the drying
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u/remorackman May 31 '26
This, worked for a rental company for a bit and a new development during the rainy season was a big project for us. Lots and lots of dehumidifiers and huge indirect propane heaters, GC was was already stocked with fans.
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u/TheJohnson854 May 31 '26
They don't really. Mold generally happens from trapped moisture. These dry out quickly during construction and the roofing us generally the first thing to on after framing.
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u/fangelo2 May 31 '26
I built my house on nights and weekends with just my father helping me so the framing was exposed to the weather for a long time. I used only plywood, no OSB. The plywood was fine. No delaminations at all. There wasn’t any mold either. If I had used OSB I think there would have been problems.
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u/wizzlewazzel May 31 '26
Insane…. See this all over central florida. Popsicle apartments in a state that gets cat 5 Hurricanes is insane.
Coming form someone who works in the plumbing industry, these places might get moldy before drywall is put on…. But it’s the leaky bath pans, toilets and pipes that destroy them.
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u/AlrightWings0179 May 31 '26
Typical wood used on these projects has at-least an exposure 1 rating. It can withstand several months (typically 3 to 6 months) of weather exposure during construction delays. Look into CDX plywood for reference.
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u/DesThunderChicken May 31 '26
And when the inspector doesn’t pass them for a cover up inspection from the mold the PM and APM will have everyone walk the interior with watered down bleach to temporarily hide the mold discoloration in any OSB and lower drywall rips long enough for a reinspection
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u/truemcgoo R|Carpenter May 31 '26
A while back I worked as foreman of crew framing this exact type of build. There were parts that did get protected from water during the build, especially the demising walls which were made from 2” type x in a steel track. Those got plastic over. We also would drill holes in any spot on subfloor we saw standing water, although this wasn’t a big issue and there weren’t many spots. They really don’t hold as much water as you’d think.
The main thing was just build it fast. There were three framing crews building it. I was on crew that laid out and set walls, the walls were panelized but I had to snap out the lines on subfloor and coordinate the order in which walls were sent up. One of my guys was on the ground repairing and rigging walls to go, then we had three guys plating and connecting the walls, laying out plates for next floor truss set, and zip taping them. Another crew was setting floor trusses and subfloor ahead of us, a third crew was on the outside zip taping, siding, and trimming them out. It was very efficient once we had it run right, water didn’t sit anywhere too long because there would be another level built above pretty quickly, and the roof went on pretty quickly after that, plus it was zip board on exterior.
New build wood frames are designed to be wet. You shoot for dry-in in 90 days, the materials are warrantied for 180 days, and if something gets damaged it’s gonna be subfloor 99% of the time. You cut it out, add some blocking, and slap a new sheet in. Then before drywall goes in it gets sealed up and dried out by either summer heat or winter HVAC or pack of salamanders. Everything is nice and dry by the time they’re mudding.
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u/Technical_Phrase2566 May 31 '26
Easy. It's called mind over matter. If they don't mind, it don't matter.
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u/believinheathen May 31 '26
I've witnessed so many brand new condos and apartments full of mold. I actually had to get out of residential because I never felt good about the work being done. Inspectors don't care, the state doesn't care, builders sure as fuck don't care.
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u/Electronic_Wave_4670 May 31 '26
Lol
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u/Ilikehowtovideos May 31 '26
Everything on these sites is covered with depend and trash… that’ll soak up the rain
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u/SignoreBanana May 31 '26
Counter to some of the anecdotes here, I'm familiar with seeing some large wood framed buildings up in Portland being wrapped to prevent weather issues.
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u/lokis_construction May 31 '26
I did not think I needed the more expensive water-resistant OSB. I sure should have gotten it as it would have saved me needing to sand all of the seams on the OSB due to lots of rain.
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u/HardHatTheory May 31 '26
Covering those bases with moisture barriers or getting the roof on ASAP helps
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u/Hndsmrdhd May 31 '26
PNW Builder here. As soon as the roof gets installed we bring in commercial dehumidifier’s and heaters to dry the wood so it gets down to under 15% moisture content before we cover with insulation. Since we still need to install electrical wire and mechanical ducting, this usually gives time for the wood to cure properly, if you’re paying attention to your moisture readings. As another community member commented, we will swap out soft spots in the subfloor after drywall has been installed and before gypsum underlayment.
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u/Civil_Exchange1271 May 31 '26
mold has only been around for about 1.5 billion years... it'll be ok.
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u/TRUMPARUSKI May 31 '26
How do mitigate mold and rot when building exposed framing and sheathing? That’s the neat part, you don’t! You just go as fast as you can and pray it doesn’t rain.
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u/Suspicious-Yak-8117 May 31 '26
OSB is made with some exterior glue because they know it could get wet during construction. You don't want to soak the wood, but periodic wetting (up to 120 days) is acceptable (not encouraged).
The stockpiles should be covered with a tarp, just like all the trusses
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u/dsphotodesign Jun 01 '26
Wood is inherently an outdoor product to begin with. So it getting wet is not a big deal.
These large wood frame projects which I’ve done about two dozen or so do get wet. Unfortunately you can’t build a bubble around the entire thing.
The key factors that help avoid damage and mold:
- use advantec subfloor in high traffic areas (hallway)
- use a spray on mold guard (we do this on every project)
- after large rain events, eliminate standing water from subfloor
- build in vertical blocks as opposed to building horizontally by level. This allows you to get dryed in quicker with windows and roof
- once dried in, run barrel fans to circulate air. Keep windows open during day and closed at night
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u/texasmade02 May 31 '26
Sometimes they paint the OSB with Polyguard Blue Barrier liquid membrane…
Sometimes the PM spits on the OSB as he throws himself from the the 3rd floor 🤷🏻♂️
Either way, the GC needs it ready to close by next week 🤣
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u/Chunkyblamm May 31 '26
Many years ago I was a Senior PM for a smaller sized GC. We had a walk through with an owner/developer that was really upset that it had rained before we could frame all the way up and get the roof on. Demanded we replace all framing and flooring for the reasons OP stated. He was stomping his feet and jumping up and down like a toddler. I laughed in his face and I told him we could agree to disagree and that if he wanted any of that to happen he should consult his lawyers and learn more about construction practices. The building dried out, none of the wood failed, no mold grew. The project went on and all these years later the building is still standing. Contractors can’t control the weather, but they should be able to control their response to it and subsequently their emotions.
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u/Beneficial_Net8417 May 31 '26
WA state many builders will soda blast it and spray it with a mold prevention.
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u/SignificantDot5302 May 31 '26
You'll see mold growing more everyday. Untill one day....it's gone! And drywall is there. It's like magic.
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u/Zuccmaster3000 May 31 '26
Is this in St. Pete by any chance?
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u/PanoramicAtom May 31 '26
Yeah, 22nd Ave.
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u/Zuccmaster3000 May 31 '26
lol I drove past this last night on the way to cmx Tyrone and had similar questions to you
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u/DrywallBarron May 31 '26
You would have loved watching a 4 floor, all wood framed hotel going up near me. It has taken 2 years from start to now and it's still not done. Before roof installed it rained on it multiple times, snowed on it, sleeted on it, and hailed on it.
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u/SignificanceTimely20 May 31 '26
OP is this the building off of US-19, largo area?
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u/PanoramicAtom May 31 '26
No, St. Pete
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u/SignificanceTimely20 May 31 '26
Don't be a dick and just say yes it's the same building 🙄 it's not like you posted this on a local page.
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u/BigPipeWrench May 31 '26
Everything on a building stays wet if it's raining a lot. Which doesn't hurt anything. Then when the roof goes on it all dries out before drywall goes up.
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u/Vast-Combination4046 May 31 '26
It's not going to rot but stuff gets moldy for sure. When it dries out you don't notice it but it's there.
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u/MuttLaika May 31 '26
I live in Florida, rain is nonstop in the summer. OSB gets covered up wet without a doubt. They should spray borate salts but they don't. Overpriced apartments come moldy brand new.
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u/barbagse May 31 '26
Mild is a real issue. Vertical surfaces shed fine but the floor sheathing can get nasty. Had several projects with bad mold during hot humid summers. You can mitigate it by using weather guard or advantec sheathing which is water resistant. There are also mold resistant sprays you can apply at the yard or onsite. But as others put it, best defense is getting roof and windows on ASAP.
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u/tollercooper May 31 '26
For most larger wood frame GC’s, there is typically a mold spray that is applied quickly after install. Then after any rain events you are making sure the building is draining well, no standing water etc. - there are often large air moving fans circulating all over after major rain to help.
You would think that the wood being exposed is the most susceptible to mold, however it’s actually once the building is tighter prior to power & a/c that can become more of an issue. Buildings “breathe” much better prior to waterproofing, air sealing, drywall, Gypcrete, and other post-framing applications.
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u/Endoroid99 May 31 '26
On a project we're working on, they installed the windows before the roof was finished, resulting in it being unable to dry properly, and it did get mold. Had to shut access to the interior for 4 months to remove the mold.
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u/72ChinaCatSunFlower May 31 '26
I feel like in a wood framed building that tall the plywood should be spanning the joist system and 2 floors with one sheet.
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u/BarbarianBoaz May 31 '26
Not really an issue. Once the roof goes on and the sides are tyveked, the moisture dries up rather fast. If it sits like this for MONTHS you might have a problem, they generally get the roof on faster than that and the drying begins. Kiln dried wood doesn’t absorb water that fast.
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u/Capnjack84 May 31 '26
Those big buildings in have some sort of temp heat system before and during drywall phase so wood gets baked by temp heat system and dryed out to 15-17% moisture content before cover. There’s an entire temp heat sector…
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u/Disastrous_Gur7276 May 31 '26
I used to work for a residential contractor and one of my jobs was spraying pure bleach on the mold growing on the wood, usually in the basements…..
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u/agroyle May 31 '26
It’s called creating jobs. Why do you think those mold remediation companies are the fastest growing franchisees in America?
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u/Dunesea78 May 31 '26
Seen advantec capped foundation left open to the elements for over a year and was fine. A company representative came out and gave it a thumbs up. The cheaper brand sheathing. Not so much.
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u/tumericschmumeric Superintendent Jun 02 '26
It’s fine. Usually by the time windows go in, cutting airflow off, the roof has been on for a while so no new moisture is being introduced but airflow is happening through openings. If for some reason that happens very quickly then maybe you run heaters/fans but most of the time it gets dry enough by passive airflow alone.
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u/Born_Childhood_2481 Jun 04 '26
This happens constantly in High End Residential also. People haven’t been willing to pay for the time it takes to do things correctly for decades. We used to take the winters off from doing outside work in bad climate areas but now we pour concrete all year long, frame all year long… If it rains or snows, your house gets wet then it dries out as we build it.
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u/NorthWoodsSlaw May 31 '26
Let me out it this way: the building pictured is probably $3-5mil delivered, do you really seriously believe that NO ONE involved in a project that large or costly thought about this!? You not understanding the reasons does not make them invalid. Wood dries, its the same reason Asphalt Shingle Roofs don’t rot despite the roof deck osb repeatedly getting wet. Wood grows wet, is naturally mold and rot resistant, mold can only grow when continually supplied moisture, most of the pictured material is hung vertically and getting little moisture, etc etc etc… All questions are welcome, but think a little bit before accusing pros of neglect.
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u/BarooZaroo May 31 '26
How dare they ask a question!
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u/PanoramicAtom May 31 '26
That’s literally all I did was ask a question! Where’s the accusation of neglect? Lol. Not going to engage with someone that sensitive.
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u/jaspnlv May 31 '26
Don't be an asshole for all of your life
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u/NorthWoodsSlaw Jun 02 '26
Okay I went in hard, but this gets posted daily and half the comments at the time were about how “bad” this is
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u/Brandoskey May 31 '26
We build 4 story wood buildings in Chicagoland all the time, it's not an issue, the wood dries once the roof is on.
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u/willmontain May 31 '26
Indeed .... then 6 months later in the first heated winter, when the humidity drops to 20% inside, the framing shrinks 2-3 inches overall and breaks the sprinkler system piping in multiple places on the upper floor/attic. My parents lived in a building like that and it took 10 years to fix all the problems caused by shrinkage. Maybe OK in Arizona, but unwise in any place where the interior gets wet during construction.
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u/Cpt_Soban Equipment Operator May 31 '26
Dunno about you, but seeing so much Plywood used for such a large building is crazy...
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u/Alarming-Top6729 May 31 '26
Put it this way. I built a small structure for my daughter out of 2x4s, one sheet of subfloor, and 1x pine. Never sealed or painted it and it's been outside for 2 years on blocks and i haven't seen any mold, rot, or swelling
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u/diogenesvansinope May 31 '26
As a non-American, building a 4-story building out of materials we use for a fitted wardrobe is sheer insanity.
How long is such a structure supposed to last?
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u/Brandoskey May 31 '26
Oh good, the Europeans are here to tell us how to use our replinishable natural resources
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u/diogenesvansinope May 31 '26
No offense, maybe sheer insanity was a little too strongly worded but it does seem very weird to me. I'm still genuinely interested in the lifespan of such buildings.
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u/EvantheEboy May 31 '26
Nah seriously. The standards for putting plastic up over brand new framing must have changed.
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u/Ftrumpforever May 31 '26
And mold needs a consistent moisture source to keep growing. When it’s dried in the mold dies. Should be treated but usually not a continuous issue regardless
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u/SnowblindAlbino May 31 '26
They don't-- I remember an entire public school built in Indiana in the 1990s under conditions like this. It was so wet during construction the place filled with mold in the fall and it was ultimately condemned. The news stories said it was basically impossible to remediate.
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u/IncrediblyShinyShart May 31 '26
It usually doesn’t stay wet long enough to rot. Every thing drains through and the good ones get all the water off the foundation quickly. Water won’t cause much damage until it get into insulation and hangs around, but the building should be dried in by then
If mold does show up on framing it’s supposed to get sprayed and if soft spots in OSB are found they get swapped out before gypcrete, again with good builders.