Proper way to flash exisiting windows when installing new fiber cement siding, plus..

deminimis · 09-21-2010, 02:13 PM

Hey all. Great site. I've been lurking a while now. Before I get to the obvious question, a bit of background with this current house project:

1915 kit home bungalow with wood siding. No sheathing. Interior previously remodeled, fiberglass insulation/dry wall. Behind siding is 1915 thin tar paper manufactured with holes in it (yea, I've never seen it before). Since the ext walls are straight and the siding is flat (beveled edges, however), the plan is to leave the siding in place (well, I have to as it provides shear strength), remove all trim boards, NOT sheath it with OSB or anything, wrap with 30# felt, fiber cement siding and LP trim boards. Since the 1915 paper certainly breathes with the holes in it, I'm not concerned about trapping moisture between the outer felt and the inside felt (but that's for a different discussion if needed). My concern is flashing the windows. The windows were previously installed vinyl windows. I'm going to assume they were caulked under the nailing flanges and installed correctly (at least I'm hoping that's what I'm going to find). So the question becomes how do I treat these existing windows? I'm not going to be pulling them, so I'm thinking flash the windows with self-adhesive flashing to start, (over the drip cap), and felt over that (top to bottom of course), caulking as required, trim over the works. But, now I'm starting to question that plan. I think the above would work well to keep water from getting into the walls from around the windows, but the LP trim might be at risk even if caulked. Perhaps a dip cap over the top trim piece? So, any thoughts on this would be greatly appreciated. Grumpy, I bet you have a workable solution. Thanks!!

**kwikfishron** · 09-22-2010, 05:48 PM

You’ll find Grumpy next door in the roofing room.

deminimis · 09-22-2010, 05:57 PM

...or others.

creamaster · 09-23-2010, 08:15 AM

I used this drip cap on the top of my top trim piece

http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

**kwikfishron** · 09-23-2010, 08:27 AM

I’m assuming that once you remove your trim you’re looking at the nail flanges. If so then pull the nails on the lower flange and slip a 12” piece of felt under the flange and re-nail. Then install your sticky tape, bottom first then the sides and top. Install the felt then your window trim. Install the drip cap over the trim and tape the top of the flashing. Make sure the felt above comes over the top of the flashing.
I’m not a fan of LP anything for siding but whatever you use make it thick enough so the trim stands proud of the window so you have a good offset to caulk. Make sure your lower felt gets tucked up under the felt you put under the lower flange.

cumak · 09-23-2010, 09:27 AM

Quote:

Originally Posted by kwikfishron

Then install your sticky tape, bottom first then the sides and top.

If you're using flashing tape like Grace Vycor, you're not supposed to tape over the bottom flange as that can trap moisture that might find its way in elsewhere. Generally you tape the sill, install the window, and then tape the sides and head. If the window is already installed, you might try to slip the flashing under the bottom flange but definitely not over.

deminimis · 09-23-2010, 11:43 AM

Thanks folks!

**kwikfishron** · 09-23-2010, 11:45 AM

Quote:

Originally Posted by cumak

If you're using flashing tape like Grace Vycor, you're not supposed to tape over the bottom flange as that can trap moisture that might find its way in elsewhere. Generally you tape the sill, install the window, and then tape the sides and head. If the window is already installed, you might try to slip the flashing under the bottom flange but definitely not over.

Ya got me there, don’t know what the heck I was thinking.

Tom Struble · 09-23-2010, 10:55 PM

actually there are some situations where the bottom flange does get taped,but for most normal installations its not