Window flashing: no nail fin, 2″ foam, rainscreen, siding
I am working on some details for a project and want to bounce a question off people here.
Wall structure is 2×6 frame, 1/2″ sheathing, 2″ foam (2 layers 1″), 3/4″ strapping, siding.
Most details and all I have done place the nail fin on the outside of the foam with the strapping over the nailing fin. However for this project the Inline windows do not have a nail fin and we do not want to go with the expensive brick mould to add them.
The first thought was to set the face of the window frame flush with the face of the strapping, and then install head drip flashing up and into the foam, but that doesnt really address the other 3 sides. Without a nail flange there is still the 3/4″ air space gap to contend with. Or do they simply caulk the window to the strapping/siding since any water will flow down beside the window anyway?
What are people using to use windows with masonry clips and thick foam?
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Replies
Jesse,
We are doing a similar but deeper detail in our prefab shop right now.
On a 10" 2x stud wall, the windows are placed in the middle of a plywood buck. The buck is flashed with Siga wigluv 100 tape or, liquid applied Prosoco R guard Fast Flash. Both create a vapor permeable WRB. If the window leaks, it won't rot out, it can dry out. We've used both. On this project we are using the Fast Flash.
To seal exterior window frame to buck, we use one of three products: Tremco Exoair expanding foam tape, Tremco Illbruck duo tape, or Siga Wigluv 100 at the exterior and Siga corvum 12/48 on the interior with LEF in between. It depends on the window type. The Siga tapes are face applied while the Tremco tapes are applied to the R/o edge of the window frame. After a few hard starts, we've got the trio expanding foam tape working well. All of these methods are vapor permeable. We don't use a non permeable flashing anywhere.
If I was doing 2" foam, I'd use a plywood buck taped with Wigluv since I can bring it from the interior window line, out to the buck edge and drop down onto the foam before the battens go up on all four edges. This way when the battens are added, They remain outside of the WRB. then add a stainless sill pan on top of it all and coming forward of the siding. This only has to catch bulk water. The buck is flashed well enough that if any water gets below or behind the pan, it's caught by the Wigluv before it reaches wood.
Jesse & Albert,
I'm just curious here, but why or what criteria you have for choosing a window with no flanges? Are there any advantages? As you guys point out, they are harder to install and have more chances for leaks. There are other high end windows in the market with flanges where the corners are cut out, and the manufacturer sends a peel-n-stick foamy corner instead.
Armando
As I mentioned, Inline windows do not come with a flange currently. In order to get the flange you have to add an aluminum brick mould they provide. They are rather pricy, so we were trying to find a way to use the flangless (standard) design. Maybe I just need to spend the extra 1k-1500 on the brick mould.......I guess I could eliminate the trim around the windows and save some time and cost associated with that to help offset.
Jesse, I was asking in case you would had other reasons other than price; but looking at just price, 1k divided in 5 windows is expensive, but in 20 windows, it maybe a good QA investment.
HI Jesse.
While I do not have an answer, I have the exact same question as you and I am also using inline windows. I would be grateful if you could share what you did for your project to assist. Where in the opening did you mount the window and what type of detail did you do?
Many thanks for your help!! Chris
Flanges can and do leak. Eliminating the flange is necessary if you're installing "innie" windows like Albert is doing (gets the glass within the insulation layer rather than out beyond it; also reduces windwashing). Tape is a better solution, but don't skimp on the tape. If we're strapping the wall we install a 6" Advantech panel around the opening and tape the window to that.