Got any ideas about this issue?

Found this issue in an unfinished basement, brick exterior, new construction (buyers final wlkthru the next week). Down in basement, after moving insulation away in several areas of left, right and rear basement walls, found the OSB sheathing was soaking wet.
No obvious defects with cladding or grading were noticed on exterior.
Thinking well the house isnt wrapped, but buyer had pics on her phone clearly showing Tyvek on exterior of sheathing.







Could be several things:

  • Direct contact due to excessive mortar use between the mortar and the housewrap/sheathing or…
  • Insufficient airgap between the brick and the house wrap causing direct contact between mortar and sheathing or…
  • Direct contact due to excessive mortar use between the mortar and the housewrap/sheathing or… (see pic from yesterday’s inspection below)
  • Lack of a vapor barrier on the insulation is allowing moisture in the basement air to condensate on the cold sheathing at the exterior wall.

Tyvek and similar products are moisture resistant, but they are by no means vapor or moisture proof. Water will seep right through house wrap given the right conditions and especially when in contact with mortar.

This is a good article about it.

Thanks Cameron, I was having those same thoughts but without any way to visually see between the OSB and the brick…cant say for certain. Ill look into the link you posted. Thanks again.

As mentioned before the lack of a vapor barrier on the interior wall allows the moisture to pass through the insulation an condense on the first surface that has a temperature below the dew point, i.e. the OSB plywood.

shouldnt the basement wall be concrete? I have to assume this is the daylight side of a walk out basement- The only thing it really could be is condensation. A demudifier should always be installed in a basement imo

I find this slightly hard to understand. If this is in a basement, what is OSB doing on inbetween the framing material and the what shoudl be the concrete foundation? You said you checked it on three different walls, is this basement a full walk out with three sides exposed to the exterior?

If that is the case, it shows there is no vapour barrier on the inside wall. If they are running a furnace then that would explaine the condensation on the cold side of the insulation.


The pictures show OSB not PWF. Micheal needs to come back and do some explaining. If this is not a walk out there should not be any OSB. A frost wall would never be sheeted.

Sorry guys this post is not making sense.
It is Brick but has Tyvek ?

Why is there plywood behind the studs ?

Do you want wood sheet in direct contact with a concrete wall?

Maybe SIP PWF?

NVM! A SIP wouldn’t have insulation or studs…

Sorry Juan but have no idea what your abbreviation lingo says.
Can you explain in words for us simple minded ?

Well PWF is permanent wood foundation. Greg pointed out though that its osb. The AWC ( American wood council) calls for plywood. I’m not sure if OSB is permitted but its pretty obvious why it’s not in the AWC manual for PWF. Well then I thought about SIP (structurally insulated panels) that DO use OSB. It didn’t me long to realize what a dumb suggestion that was because sips wouldn’t have insulation or joists.

Maybe it is a PWF with osb instead of plywood? IDK I enjoy speculation.

Apologies for the late reply…it was a walk out basement, poured concrete foundation with the stud walls on the foundation step downs (transitions). The home is sitting on a moderately sloped yard with the top of foundation step downs well above the grade line. I have tried to contact the buyers to see if the builder had given a cause or explanation but have not heard back from them…business has been booming so I have not pushed the issue.
Also, the HVAC system was heat pump…and there was not a humidifier in the basement at time of inspection…I believe it was several factors mentioned above…construction of brick cladding, mortar in contact with house sheathing, creating a moisture bridge and Tyvek wrap which does not prevent the moisture intrusion.

reverse lap on the moisture barrier will get you every time?

vertical mulch (aka OSB )= rot in progress

lack of flashings in any given areas?

Its condensation. You can’t just insulate that wall…you need to also apply a vapor barrier over it on the inside.