View Full Version : hot OSB?

Perry Hilbert Jr
09-14-2017, 6:07 PM
The siding on the back of our new house got all wavey within a few months. It is a 2 story modular and is wonderful in almost every way. The builder has been good and sent a person to inspect and then a crew to replace some of the sheathing. They said the OSB was still hot when installed and so it lost shape and bulged between the studs. Now indeed it was bulged between the studs when they pulled the siding and plastic off. Everything was bone dry underneath. No water marks etc. It happened again in the repaired area. Crew came out and checked. same thing, bulged between studs and bone dry. I asked for an explanation of this "hot" OSB. the last foreman here said the glue in OSB takes a while to actually set/cure. The OSB is not actually warm, but still so fresh that the glue has not fully set/cured. He says it can take a week or two to fully set. If the OSB is put up too soon, it sags due to gravity, or bulges due to heat from the sun. It had definitely bulged and it was definitely dry. I overheard him talking on the phone with the builder about the problem and the foreman said yeah hot OSB again. He told me the builder orders OSB by the railroad car and they had the same problem a few years ago and had to re-sheath several of their homes. I have been to the builders business and they do order by the train load. There is a siding next to their warehouse. I saw them unloading skids of 2x's from several flat cars.

Is there really such a thing as hot OSB or am I being spun?

John K Jordan
09-14-2017, 6:53 PM
I never heard of that but I only build for myself. Never had a warped panel. I found this about warping OSB. It seems to me that putting it up too dry and vertically as they mention could easily cause it to buckle as it absorbed moisture:


I don't see anything about the glue not cured. I'm not expert but the glue issue sounds fishy to me. I understood glue was thermally cured in a hot press during manufacture. Just wondering: if these guys are not letting it acclimate and putting it up too dry, then maybe they have come to believe their own myth about the "hot" glue.

When I built my shop I did unstack all my OSB and perhaps accidentally let the moisture equialize. I leaned each sheet up against something and spray painted one side and let dry before leaning them together in a loose stack. I used them as sheathing on the walls and roof (under roofing paper and galvanized roofing) and not one buckled.

Here's something you might try - as suggested in the article take a moisture meter and check some of the sheets they are about to put up and compare with some of the buckled ones.

Hopefully someone with a deeper understanding of this than me will answer.

I can ask my builder friend who has a bunch of experience but probably not until this weekend.


Perry Hilbert Jr
09-14-2017, 7:24 PM
Thank you John. That article answers a lot of questions. The OSB was put up vertically and put up too dry. When it acclimates, the OSB expands across it's width. If an expansion joint is not left, you get buckling. Not exactly hot or glue, but using it before it gets to ambient moisture makes sense.

Mark Bolton
09-14-2017, 7:54 PM
You likely have an interior vapor barrier problem. If the osb was hot (expanded) it would pull tight like the skin on a drum when it cooled. I've been in the construction biz for 30 years and never heard of hot OSB. Sounds extremely corny. My guess with it happening twice is you have an interior vapor barrier issue that is causing the sheathing to gain moisture and expand causing the warpage. Often times the moisture gain on a roof deck will cause the edges of the sheets to swell and mash into each other if not properly spaced (all osb should be gapped on install not butted up tight) and this will cause the sheet perimeter to telegraph through shingles showing every sheet below through the shingles.

I cant say I've ever seen osb severely bow between framing after install so my guess is something substantial is going on with the building envelope.

Perry Hilbert Jr
09-14-2017, 8:10 PM
Interior vapor was my first thought, except the OSB and insulation was dry. The osb was put in without a gap the second time and the now between 16 inch center studs was out a good 3/8 to half inch. The problem with the vapor idea is that the problem is on the exterior of the living room wall no windows, no plumbing, no heat vents or anything where the siding buckled. Don't know if it matters, but the house came in 4 pieces on four tractor trailers. Because of add ons to the sides and front, only the rear lower part of the house came with siding. And that is the only place where the siding is all wavy. The parts where the siding was installed after the house was up, are fine.

Mark Bolton
09-16-2017, 12:24 PM
One thing to remember is that just because you didnt see/feel liquid water in the insulation or sheathing doesnt mean there isnt a moisture issue. As John mentioned, I would think on a second go around someone would be poking around with a surface read, or probe type, moisture meter to rule in or out a moisture problem.

Given your issue with the parts where the siding was pre-installed being of issue I would still lean towards some type of issue with a change in moisture content. Perhaps the facility the home was made in has a higher MC than your location and even with the second go around that area had not reached equilibrium with your climate and was still moving a bit when the second batch of sheathing and siding went on.

To me personally, the only things that I could imagine being happening is #1 the sheating is taking on moisture and is expanding (in the case of 16" on centers bowing between studs by 3/8 that would be drastic MC gain). or #2 the structure in that area is at a higher MC and is shrinking which would make installing new, dry, sheathing, bow once fastened (its not moving but the structure is somehow shrinking).

All in all to get OSB to bow 3/8" on 16" in centers is extreme.

Id be starting with a moisture meter as John stated. Checking the structure and the sheathing. Once thats ruled out the puzzle gets even more fun.

Chuck Ellis
09-22-2017, 11:28 AM
I retired from an export packing firm that built boxes for ocean shipments... we never used OSB as it acts like a sponge and absorbs water readily. All of our boxes were from 1/2" plywood. We often were called by local steamship companies to come down and repair boxes that had fallen apart from being sheathed with OSB.