Sealing no-flange windows in a REMOTE wall retrofit
I’m planning to insulate my 60 year old house from the exterior using the REMOTE approach.
We can’t afford to replace all the windows so I hope to re-use the existing windows which are all wood framed but show no signs of rot. Some are single pane and some are double pane and I believe they’re all no-flange windows. We’ll use a combination of interior and exterior storm windows to boost the thermal performance of these old windows.
I’m thinking about how to air seal and manage bulk water at the the window-to-framing interface. Most REMOTE examples I’ve seen use a flanged window which seems to make it easier to tie flashing into the wall membrane/WRB. However I’ll be working with our existing windows so these examples aren’t as helpful. After removing all the siding and trim, I’m proposing to remove each window unit and flash all around the RO, then re-install the windows. This should leave a small gap between the wooden window frame and the flashed opening. To seal this gap I’m thinking about installing foam backer rod, and then caulking from the interior with something super flexible. Then I’m thinking of applying low expansion spray foam around the window frame on the outside for added protection. Should any of this ever leak, I figure the flashing on the RO would drain the water away.
Is this a reasonable approach when trying to re-use no-flange windows or is there an easier or cheaper method?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Mark,
Q. Is this a reasonable approach when trying to re-use no-flange windows?"
A. Yes.
Q. "Is there an easier or cheaper method?"
A. Leaving the windows in place rather than removing them would obviously be easier and cheaper. But your way is better.
Thanks Martin, I always find it helpful to confirm my ideas.
Can you suggest how best to flash the windows if we did leave them in place? Would you just run the wall membrane over the edge of the window frame and hope for the best, or is there an established way of doing this?
Mark,
Q. "Can you suggest how best to flash the windows if we did leave them in place?"
A. Older homes did not include sill pan flashing, and it is common for windows in older homes to leak. If the window receives wind-blown rain, it's possible for water to dribble down the rough jambs, and enter the wall cavity at the two lower corners of the window.
In most older homes, the small amount of water that enters a wall cavity under most window sills is able to dry out before it does any damage. In new homes, water entry under windows can lead to sheathing rot.
If you are installing rigid foam insulation on the exterior of your walls, and you include a ventilated rainscreen gap between the siding and the rigid foam, the rainscreen gap should address most of the water that gets past your siding.
But there is still a risk. Ultimately, this is a judgment call. How tall are the walls? How generous are the roof overhangs? Does the building face the ocean? There are many variables.
If you choose to leave the windows in place, without flashing the rough openings, you are increasing your risk. With the right water management details on the exterior -- for example, good head flashing above each window, and a good attempt to collect water that reaches to window sill and direct it to the exterior -- you may be fine. But if the building gets a lot of wind-driven rain, the lack of sill pan flashing may lead to problems.