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Discussion Starter · #1 ·
I have a client who's insisting we somehow insulate the bottom of this window because it's exposed to the exterior elements.
http://web.pella.com/products/windows/bowbay/Pages/detailpage.aspx
(Pella bow window with 5 casements. Unfinished wood interior with enduraclad white aluminum exterior and plywood bottom. Width is approx. 110")

He believes it's silly to buy a new window to increase energy efficiency, and not insulate the bottom of it
There's nothing in the installation instructions about insulating the bottom. All the other instructions have been followed to the letter.
http://web.pella.com/products/installdocs/Documents/InstallationInstructions2009/80AT.pdf

He suggested covering the plywood bottom with 1/2 insulation sheating. (the pink stuff) then covering the bottom with aluminum. I think that could interfere with the frame expander and cause water to collect inside.

We built wooden knee braces to help support the window along with the cables. We were going to wrap those with aluminum, then insultate and wrap the rest as stated in the installation instructions.

Would you instulate the bottom of this window, and if so, how?
 

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I wouldn't do anything unless pella says to do it, call them and see what they say, if something goes wrong you will be liable for it, I would just tell harry homeowner that you can only perform a proper installation by following the guidelines set forth by the manufacturer of the said window.:thumbsup:

that should shut him up, if not buy a ball gag:thumbsup:...:whistling
 

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so if you do nothing theres just exposed ply wood?

i insulate and cover the bottoms of those kinds of windows all the time,never had a moisture problem
 

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We install about 20 or more bow and bay windows a year and we always insulate under the window. We use a 1 1/2" Blueboard with a 2" X 4" set in about 1" from the edge of the window so to have something to nail our trim on and a 2" X 4" up against the house to nail on.
Note; We rip the 2" X 4" in half
 

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Al Smith
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Cables dont shrink due to moisture content

Don't know about Pella's but the Andersen's have a void between the finished grade seat board and the rough cdx bottom that you are supposed to insulate. However. Providing what is essentially an insulated shelf with knee brackets for your window to sit on should not void any warranty. As far as the cable system goes. They come with the window. and are adjustable If you throw the kit out expect call backs for stuck casement flankers. I have seen scores of effed up bays improperly installed by "contractors" who thought they were engineers and knew better.
 

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Discussion Starter · #7 ·
I can see the value in insulating the bottom, and we won't leave him with exposed plywood.

However, the factory supplied frame expander doesn't extend low enough to cover 1/2 sheathing, or any additional framing.

Looks like we'll have to build a frame underneath to accomodate the insulation as some have suggested.

In order to do that, we'll have to wrap that framing with aluminum, and caulk the edges where it meets the factory supplied frame expander.

Thanks for the input.
 
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