Installing Octagonal Window question...

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  #1  
Old 03-25-08, 06:47 PM
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Installing Octagonal Window question...

I have a two story shed/workshop and I'm finishing the second story. Last week I was at Lowes and saw they had a 29 inch octagonal window on clearance ($50 bucks marked down from $375). Apparently it was a custom order that was returned or never picked up.

Couldn't beat the price. I've decided to put it in the second story of my workshop. I've framed everything out and I'm ready to cut the rough opening tomorrow.

Here's my question.

The shed has vinyl siding. I've worked with vinyl before and J-Channel. I'm just not sure how to go about this odd shaped window.

There's no nail flange.

I bought some five inch wide flashing material (the newer rolled black adhesive stuff) and plan on doing the normal flashing weather proofing. Entire shed is wrapped in sheeting under the siding.

I'm not sure how to do the J-channels. I pre cut 8 pieces to day -- one piece to fit each side of the window.

The plan is to nail one on the bottom edge and move from bottom to top and as you would a square window.

Is this the normal approach? or is there a better way?

I was thinking after installing the window and installing the J-channels I could tape all the joints on the back/nail flange of the J-channel with foil tape.

Or is this overkill?

Thanks in advance.
 
  #2  
Old 03-25-08, 07:10 PM
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You will want a REAL nailing flange on the window. If it doesn't have one, order some. It should be available from the manufacturer if nothing else. If it's not available, (or if it doesn't have a slot for a nailing fin) you can make something out of a roll of galvanized flashing... make an L-shaped piece and cut 8 lengths that will be long enough to do each side of the window, and overlap them a bit. Start with the bottom, then the next side, etc. until you reach the top so that each one will shed water on the next. Screw each piece of the nailing fin flashing onto the window with some short #8 stainless steel screws. Seal the flashing to the window with a good sealant like OSI Quad, or use some 100% silicone. It would be best if you did this ahead of time so it could dry. On many windows, the nailing flange is located approximately 1 to 1 1/8" back from the front edge of the window.

Once the window has been prepared for installation, you'll want to remove a few rows of vinyl siding in the area where you will install the window. Remove enough so that it is not in the way of your nailing flanges.

Cut your hole, making the rough opening 1" larger than the window is. Ensure that you have building paper around the opening, and install the window. Once it's installed, you could install some window flashing membrane over the nailing fin and to the building paper. You'll want a drip cap over the top that will cover the top half of the window (3 sides in all). It's a good idea to apply an additional layer of building paper over the drip cap so that if water leaks in from above it doesn't go behind the drip cap.

Once that's done, you would install your j-channels around the octagon, starting from the bottom and working your way up and around to the top. It's kind of pointless to seal the j-channels to the window because when you use vinyl siding, water can enter between the siding and the j-channel. (hence the importance of using building paper behind the vinyl siding).

You really should not use the j-channels as your nailing fin. I don't think you would be able to make it 100% water tight if you tried.
 
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Old 03-26-08, 09:48 AM
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Originally Posted by jollybgood View Post
Entire shed is wrapped in sheeting under the siding.
If by "sheeting" you mean a water resistant barrier (such as Tyvek) also take a look at the flashing details here for examples of the correct sequencing of flashing at the WRB.

Also, if you do not have one, it helps to have a siding removal tool for popping off the siding where you will be installing the window.
 
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Old 03-26-08, 09:51 AM
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Thanks, Michael for posting that PDF. I'm sure that is going to be helpful to a lot of people. Is that information available in one of the "stickies"? I don't recall seeing it.
 
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Old 04-10-08, 07:53 PM
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Meant to reply a few weeks ago but couldn't sign in -- thanks for the advice.

I've got the window in and everything seems to have gone well. Heavy rains the last few days and everything is nice and dry on the inside.
 
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Old 04-11-08, 04:11 AM
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Thanks so much for posting back and letting us know your project went well!
 
 

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