0 Helpful?

Fentrim tape worth the expense?

Can anyone weigh in on this super tape? My client is balking at $2k in tape, vs $400 for grace vycor. We have euro windows with no built in flashing.

Asked by Lukas Schwartz
Posted Jun 12, 2018 5:57 PM ET



You didn't really tell us how you are using the tape, expect to say that it has something to do with flashing your windows.

Fentrim is basically an air-sealing tape. It isn't really use for flashing.

Ideally, you will install flashing on the exterior side of the window -- designed to integrate with the water-resistive barrier (WRB), and to direct water away from the building. This is often a combination of metal flashing and peel-and-stick flashing.

The air sealing work usually happens on the interior side of the window.

Answered by Martin Holladay
Posted Jun 13, 2018 5:17 AM ET


The plan is to use the tape behind wood trim to integrate with the wrb for exterior moisture control. We will use metal flashing under the bottom of the window to shed water to the outside.

Answered by Lukas Schwartz
Posted Jun 13, 2018 5:48 AM ET


Before buying the Fentrim, I would call the specialists at 475 High Performance Building Supply and ask them which of their tapes is best for flashing. My guess is that it wouldn't be Fentrim, but I might be wrong.

When it comes to flashing windows, plenty of builders have had good results with American-made peel-and-stick products like Vycor. The Passivhaus crowd always reminds us that these products aren't vapor-permeable, but that fact almost never results in failure (in my experience), as long as your WRB is vapor-permeable.

Answered by Martin Holladay
Posted Jun 13, 2018 6:35 AM ET


475 certainly won't recommend Fentrim, because they sell Pro Clima products, and Fentrim is a Siga product.

I like and spec both brands, and Fentrim specifically for challenging locations, because it sticks to everything. On a recent project I consulted on, the owner/builder used Fentrim (purchased here: ) to seal his flange-less, inset, tilt/turn windows to the Siga WRB.

If you have flanges on your windows, I would consider Fentrim to be overkill--use Vycor, or 3M 8067, or Zip tape instead, if you want to save money. Or use a less-expensive Euro-tape like Pro Clima Tescon Vana, or Siga Wigluv. If you have flangeless window, and/or you are using exterior sheathing as your airtight layer and need to integrate the window into your airtight layer, or you have inset windows are the tape is part of the water management system, I would not skimp. There are a lot of ways to install windows, and a lot of products that can work, depending on the situation.

Answered by Michael Maines
Posted Jun 13, 2018 8:41 AM ET
Edited Jun 13, 2018 8:41 AM ET.


Thanks for reminding me again (I think this is the second time I made this mistake) that 475 does not sell Siga tapes.

And thanks for your suggestions for Lukas.

Answered by Martin Holladay
Posted Jun 13, 2018 8:56 AM ET


thanks for your great advice!

Answered by Lukas Schwartz
Posted Jun 14, 2018 5:43 AM ET

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