View Full Version : Vinyl siding over LP panel

Brandon Whitmore
06-02-2008, 12:45 PM
My morning house had LP panel siding originally. They installed Tyvek over that material and installed the vinyl over the Tyvek.

My concern is that the original windows were installed behind the original panel LP so there is no way to properly flash the windows to the new membrane. I pulled a couple of the viny pieces off at windows and found that the installers left about a 1" gap between the Tyvek and window frames, and of course there is no flashing anywhere around the windows. Since vinyl siding leaks, my concern is that now water is going to seep onto the LP sheathing and rot out the wall.

I am sure most of you have seen this-- what do you usually recommend?

There is of course the other typical retro fit installation defects with the new Tyvek where it does not run all the way to the base of the sheathing, where the sheathing (LP siding) is visible at penetrations, etc.

Brandon Whitmore
06-02-2008, 02:55 PM
I think my recommendation is going to be to leave each window where it is (like retro fit ones), install the lower flashing, then side flashing. I think if they carefully detail some Z metal/ drip cap flashing along the top and then install a flashing membrane above it, it should be good to go. So basically a properly detailed window flashing system without using the nailing flange as part of the system.

What do you all think.... any takers?

Jerry Peck
06-02-2008, 05:52 PM
I would recommend (when talking to my clients) that the vinyl siding be removed, the windows be flashed with peel-n-stick flashing which is applied to the windows and the hardboard siding to protect the hardboard siding joint (with proper lapping), then another layer of peel-n-stick to the window and the building wrap (in the proper sequence and lapping), then reinstall the vinyl siding. Do this while explaining the reasoning behind it and what each layer is for.

In my report I would recommend the windows be properly flashed and that the vinyl siding be installed to the windows properly ('J' trim, etc.)

We all know they are not going to do the first thing, it will cost too much, but at least the client will know more about what it takes to seal windows than when they started talking to you. In the report you leave it up to the professional doing the work to do it right. Your client will have some brief and limited background knowledge of what is being done and how wrong it might be.

I hate to assume that the original windows are properly flashed. By flashing them to the original siding, you are reducing (not necessarily eliminating) the potential for leaks. The building wrap under the vinyl siding acts as the drainage plane, keeping much of the water off the original siding, the peel-n-stick flashing keeps much of the water off the original siding and out from behind the building wrap.

Brandon Whitmore
06-02-2008, 10:32 PM
Thanks for the reply Jerry,

I am having a little trouble understanding what you are saying. Are you saying you would recommend the windows be brought to the outside of the sheathing (old LP) and then the typical 2 layer flashing system be installed? Without bringing the nailing flanges to the outside of the sheathing, I can't see how you could install the 2 layers of flashing (peel and stick) you speak of.

This is to panel siding, so there is no original flashing.

I think we are pretty much on the same page, except for the fact we explain and understand things differently.

Jerry Peck
06-03-2008, 05:21 PM
I'm not recommending the windows be moved, only that the peel-n-stick flashing be applies to the windows and to the original siding to serve as a secondary seal (flashing) in addition to whatever was installed originally.

By sealing the windows to the original siding, you are reducing the potential for water to migrate through the window/original siding joint.

By installing the peel-n-stick to the original siding behind the building wrap, you are reducing the potential of moisture using the building wrap as a drainage plane from migrating behind the edges of the building wrap and getting to the original siding.

By installing the second layer of peel-n-stick over the building wrap, you are further reducing any moisture or flowing water which is on the surface of the building wrap from migrating behind the edges of the building wrap.

You end up with two layers of peel-n-stick flashing from the window to the original siding/building wrap spanning the joint around the window, reducing the potential for moisture and water migrating beyond the edges of the building wrap.

It's called 'adding layers of resistance' with the purpose of 'reducing the potential for' leaks - nothing can make that joint waterproof, you are just trying to increase its resistance to leaks around the windows and doors. Then, the main thing you have to deal with is leakage withing the window or door frame itself. Many failures occur within the window assembly itself, those are more difficult to stop. This is only trying to address the failures which occur where the window or door assembly is installed to the structure, around the perimeter of the window or door assembly.

The ASTM E-1105 water penetration test only tests the window assembly itself - for a true ASTM E-1105 test.

However, most testing in the field is done testing the perimeter joint of the installed assembly to also test the waterproofing around the window.

Knowing what a true ASTM E-1105 test tells you is one thing - that the window passes or fails the test.

Knowing that the installed assembly including its perimeter waterproofing actually tells you a lot more.

Brandon Whitmore
06-03-2008, 06:24 PM

I appreciate the explanation.

Jerry Peck
06-04-2008, 12:16 PM

I was looking through the Vinyl Siding Institute installation instructions today for something else and there on pages 19 and 20 is the answer to your question.

It is what I described, except that I described it with the siding in place, and their "Flashing Previously Installed Windows" section shows it without the previously installed siding, which you would have.

Brandon Whitmore
06-04-2008, 08:09 PM
Thanks Jerry,

I had looked at that right after posting the original question. Without the nailing flanges, it makes it more interesting. The contractor will just have to be careful with the detailing and install the Z metal to kick the water out as much as possible.