New Construction Winter Outward Moisture Drive Getting Trapped Behind Peel & Stick

[TezraE]

I'm looking for information on rotting sheathing around windows where self adhered flashings (SAF) are used. I've heard of this on a few projects I've had some proximity to and could swear I've seen information online, but I am coming up empty handed. Can anyone point me in a good direction?

The latest project this happened on had the following wall assembly:
Interior to Exterior:
Latex paint
1/2 gypsum
5 1/2" studs filled with dense packed fiberglass
1/2" OSB
Tyvek Drainwrap wrapped into rough opening
Finned Vinyl window
~6" wide Peel and stick (unknown manufacturer)
1x SPF trim and horizontal Hardi siding

Project was sided in February of last year. New build was completed in the spring/summer. Project is in the Portland, OR area.

Rot was limited only to areas behind SAF and ate through to interior side of sheathing.

From what building science tells me, the interior relative humidity during the various stages of construction would be drying outward. SAF is vapor impermeable and thus the vapor gets trapped. Add winter environment and the sheathing doesn't get warm enough long enough for moisture to migrate around the SAF.

Thanks for any direction to studies or articles on this.

[dgbldr]

Re: New Construction Winter Outward Moisture Drive Getting Trapped Behind Peel & Stic

Can't analyze your problem without seeing it, but I sure wouldn't put the window flange on top of drain wrap and then flashing tape over that. For the obvious reasons.

[Ted S.]

Re: New Construction Winter Outward Moisture Drive Getting Trapped Behind Peel & Stic

Pictures would help especially if they detailed the flashing installation. I have heard of this in theory but never seen it happen.

[CASHCOW]

Re: New Construction Winter Outward Moisture Drive Getting Trapped Behind Peel & Stic

I don’t need to see more info, I can tell you that a room temp cure adhesive subjected to temp, pressure, moisture, vibration, etc, won’t last. It was never designed to. Go to any manufacturer and ask them to show you 30-40 year cycle test, you'd be lucky to see 10 alot of builders don't track. Better if cured at a higher temp and pressure under a controlled clean room environment that eliminates voids and delamination’s, hard to do in construction. There won’t be a lot you can do, look for peel and stick third party test results that give the highest ‘lap shear’ and lap tensile’ available. In a wall more shear. Good luck!

[NW Architect]

Re: New Construction Winter Outward Moisture Drive Getting Trapped Behind Peel & Stic

If the SAMF was applied over the WRB then vapor should condense outboard of the WRB. I have not seen the problem you describe except when the SAMF is applied directly to the sheathing - and then the moisture source is not vapor drive so much as drying of damp sheathing originating with rain during construction.

And I have only ever seen high moisture readings, never rot through the sheathing.

I would suspect a leak somewhere, or exfiltration of high humidity air via an unsealed gap between edge of window frames and rough opening.

[Bill Robinson]

Re: New Construction Winter Outward Moisture Drive Getting Trapped Behind Peel & Stic

Interestingly enough this has become an issue in the Portland area.

And I have heard other mentions of this problem in other areas with climates similar to Portland.


At the JLC show there I heard about it from a local building science guy.

It does make some sense that whatever moisture getting around the sheathing needs to eventually equalize somewhere.

I imagine we will hear more about this in the coming months as the conditions leading to this failure continue.

Certainly the dens pack cellulose is part of the equation. Due to the affinity for moisture present in cellulose.

It would be interesting to get a closer look at the details:
How the window was wrapped
the detailing of the wrb and sat
interior temp and humidity
Type of window
interior finishes and window coverings
HVAC system with ducting and all