Andersen Window installation. Seal bottom or assume failure at some point?
MikefromtheMountainsofUtah
| Posted in General Questions on
I have a crew about to put in 32k worth of new windows. I spoke with the Andersen window rep for my area about the installation plan, and considering I’m using prosoco WRB products (liquid flashing) for the entire house, he was ok with sealing the entire perimeter including the bottom of the window.
I understand the logic of providing an escape path in the event of a failure, but considering the windows are warrantied for a decade I’m leaning towards sealing them up so that I see the water damaging the drywall returns and know I have a window that’s compromised.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
MftMoU,
I don't think you will find advice anywhere suggesting sealing the sill. Here it would be a code violation.
The sill should be sloped to the exterior with a sill-pan, so you would never see or experience damage to the drywall returns.
Malcolm, here is the Andersen reference the Andersen rep referenced. I get it that if there is a problem you'll see it, but the part I don't get is that if the unit fails I actually want to know... Is that crazy?
MftMoU,
All of the rotten sills and framing below windows I've come across was from small amounts of persistent wetting over an extended period of time, such that it never became visible on the finished interior casing. The best way to protect the window and wall is to install a sill-pan with a path to drain or at least diffuse moisture.
What kind of failure are you envisioning? If the opening is properly flashed it shouldn't depend upon the window to keep water out.
MftMoU,
Malcom is correct, one should never seal the exterior bottom side of the window flange. The information the Andersen sheet references is likely outdated as I do recall seeing similar install suggestions 15+ years ago. You do not want to seal the bottom flange, your rep is giving you bad advice.
You do however want to seal the top and sides of the exterior, leave the bottom open and better yet use some horseshoe shims under the flange to give about an 1/8 for water to escape. Then seal all four sides of the window from the interior to make it air tight. Sloping the sill like Malcom mentioned is best practice.
I wouldn't wait for my framing and drywall to fail just to find out that my window failed...
This is just speculation on my part but it may be worth looking into: I would read the full language of their product warranty. Many building product warranties that I have read are exclusive to the product itself.
So if you have 30 windows that fail (because you are able to easily see the failure), and the manufacturer agrees to replace them under warranty, I surmise that all other work and costs associated with removal and re-installation would be the owner's responsibility.
As an example: Huber touts a 30 year warranty for ZIP sheathing. Sounds great. In essence, if there is a legitimate product failure they'll provide replacement sheets. This is basically useless in terms of cost recovery to repair a structure.
Best of luck with your project.
As an example for their flanged windows, the Anderson 200/400-Series installation instructions specifically states to apply sealant to the top and sides only.
https://aw930cdnprdcd.azureedge.net/-/media/aw/files/technical-docs/installation-guide/installationguide-0005094.pdf
Building practices are slow to change, and some manufacturers still recommend or at least include details for "full barrier" installation, sealing the bottom flange. Having worked on hundreds of renovations I disagree with the standard building science advice that all windows will eventually leak, but enough of them will leak and the damage they cause is typically subtle and slow to appear, so I always recommend letting the sill pan drain. I usually do this by sloping the rough sill, but I'm also fine with a level sill and back dam. What I'm not ok with and think is a waste of time is the typical approach of using a membrane sill pan with no slope or back dam; in that case it's not doing anything.
Right, treat the sill (and the whole opening) with the assumption that the window will eventually fail. Which is why I don't understand the original question.
I hadn't fully processed the OP's second paragraph. I agree--a 10-year warranty is decent, but almost certainly prorated, and windows should last at least 30 years. Also, many water-related issues don't even show up for 10+ years. I would not use the warranty in my decision-making process.
Thanks everyone. I will follow the wisdom here and plan on failure.