Roof Sheathing Buckle

[Robert Manley]

Hey Guys,
I already did this inspection and informed the buyers to consult with a licensed contractor to further evaluate and estimate repairs. The roof was covered with snow. But this is the absolute worst buckling I have seen. Evidentally the roof had been replaced within the last 8 years, but it appeared by the newer sheathing likely sooner. Very cold here and yes some definite expansion, but just some ideas on why so severe, normally this is a slight rise due to ventilation issues and or insulation (moisture issues). I figure they did not leave the space between the sheats for expansion, but it was as much as 3-4 inches in some spots.

[Kenton H. Shepard, CMI]

The only buckling I've see that approached that was during the rainy season in CA when the roof sheathing was exposed for a number of weeks and the was daily heavy rain. Panels expand a lot more with moisture than with temperature, and with cold temperatures, they shrink, not expand.

My guess:
Sheathing was installed right after it was delivered and had very low moisture content (4-6%). Before it was covered with underlayment or roofing, it got wet and stayed that way for a while. Where is the home located?

[Robert Manley]

The home is in Minnesota.. This has probably been this way for a while, but according to the buyer the roof was replaced years ago, however, I find it hard to believe that with this huge bulge in the roofing someone did not see this before or a problem.. Anything is possible. Just know that this will need to be repaired! If the boards got wet recently with our cold temps, then the water freezes which would expand the board but not that much.. This was likely this way from shortly after installation. Cold here has much different effects on homes than in California, Cold Sucks!!!