Residing Over Existing Plywood Panels
Hi,
Apologies if this has already been addressed elsewhere in the forums, and for the length of this post, but I haven’t really found the answers I’m looking for yet. I have a 1980’s house (Climate Zone 4A, non marine) with the following typical exterior wall assembly: 1/2″ GWB at the interior, 4” nominal wood studs w/ fiberglass batt, 1/2″ rigid foil faced insulation (my guess is XPS), and finally 5/8” thick T1-11. There might be a layer of felt between the rigid foam and the T1-11. All kinds of weather damage, warped edges, and woodpecker (!) damage on the T1-11. My guess is that the window (fiberglass casement) flanges are installed on the outside face of the rigid foam. There is no exterior trim around the windows and exterior doors – the T1-11 was cut tight to the fenestration frames and caulked. The exterior nosing of the window frames extend only about 3/8” beyond the exterior face of the T1-11. My thought is to (1) repair/replace the warped/damaged T1-11 with the same thickness (5/8”) plywood sheathing, (2) install a new WRB layer on the outside of the T1-11/ plywood layer plus woven rainscreen matrix (or bumpy WRB with integrated rainscreen), then fiber cement lap siding. My question is related to installing a new WRB and properly flashing it to the windows and doors. It doesn’t seem there are that many good options for flashing, and just contemplating the flashing issues makes me think of perhaps scrapping the whole plan listed above, ripping everything off (T1-11 and foam) and starting from scratch. I’ve considered (Option A) cutting out a +/-3” rectangular “donut” out of the T1-11 around each window or door, essentially warping the new WRB over the “donut cutout,” and hopefully having enough working room to install flexible flashing tape over the WRB/ window flange joint. Then just letting the new fiber cement siding “cantilever” that last 3” to the window frame. Option (B) is to just run the WRB to the edge of the window frame, cut it, somehow tape the WRB to the (very narrow) 1/2″ width of the fiberglass window frame extrusion, say a little prayer, and precision cut the fiber cement siding (if it were flat sheets of fiber cement w/ open joints, on 1/2″ rainscreen battens) up to the inside edges of the window frame, covering up the flashing tape. Not even sure the casement windows would be operable at that point. But I’m in Tennessee, not Switzerland, so I don’t think that would be executed well. Option (C) might be to custom fabricate an aluminum extrusion “picture frame” at each window, maybe with a 3” leg against the T1-11, and a 1/2″ leg perpendicular to the T1-11, with welded & mitered joints. The aluminum picture frame would be sized with a clear opening maybe 3/8” larger on all sides than the existing window frame. In theory, the picture frame is fastened to the face of the existing T1-11 (or replacement plywood) at each window or door. Then, the WRB runs up to the outstanding leg of the picture frame, and is taped to the longer (3” leg) of the picture frame. The picture frame is then just caulked directly to the window frame, with that intentionally oversized 3/8” gap. Then the cement board just goes up normally, on top of the rainscreen layer. It’s a contemporary house style, with minimal trim, so the thin exposed aluminum edge and siding up to it would be appropriate. This is really mainly a question of just managing the bulk water, not getting into issues related to air barriers or the quality of insulation. And hopefully not having to rip the entire skin off the house and starting from scratch. I’m sure the aluminum “picture frames” would not be cheap, but probably cheaper than ripping all the siding off and having to start from scratch. Any insight or thoughts would be appreciated.
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Replies
Jamie, what condition are your windows in? Many modern windows are worn out after 40 years and likely need replacement or repair anyway.
If they are still in good condition, it's very important to maintain a continuous water control layer, and it's also important to maintain a continuous air control layer. There are some European specialty tapes that have partial adhesive on both sides that can be helpful in situations like this. You might be able to cut just 1 1/2" around the window frame and use tapes to connect the window flange to your new WRB.
Michael, the windows are probably Andersen casements. I think they’re the fiberglass 400 Series. Mostly all in good shape (except a couple that will need replacing). I had not considered the double sided tape, but that might be a really good solution. I can see trimming back the sheathing like you mentioned, applying the double sided tape to the window flange, pressing on the WRB, and maybe even applying a second layer of single sided tape on top of the WRB. If you could share 2 or 3 manufacturers’ names for the 2-sided tape, I would appreciate it. Thanks for the suggestion!
Now that I look I can only find one product that has the double adhesive:https://foursevenfive.com/contega-solido-exo-d/.
Alternatively, you could use a separate strip of double-sided tape, such as one of these:
https://sigatapes.com/product/twinet/
https://www.rothoblaas.com/products/airtightness-and-waterproofing/tapes-and-profiles/double-band
https://www.rothoblaas.com/products/airtightness-and-waterproofing/tapes-and-profiles/supra-band
https://foursevenfive.com/duplex/
Thanks Michael, I will check these out.
Jamie,
It sounds like you want to do what I did last summer. Repaired the T1-11 that was damaged, new windows, new WRB, new flashing, rain screen, new siding on top. Attached a couple progress pictures in particular order. Learned everything on how to do this from this site.
It wasn't bad, other that learning new things I've never done before, bit of a learning curve. We get driving rain frequently, so I did everything I could in terms of flashing.
Craig,
Yeah I think we're on the same page. But I'm trying not to replace the existing windows, unless they're obviously damaged. Attaching a typical exterior pic, and some schematic details for addressing the issues outlined above. Suggestions welcomed.
Jamie,
I think what you have drawn will work. Couple small details: for the sill trim, bevel the top edge so it doesn't create a pooling spot of water and directs it away from the house.
Add a metal flashing to the head and adhere it behind the WRB. It will help "kick" water away from the window instead of dropping backwards onto the window.
Good points, Craig. Thanks.