If you missed my post last week on the Massive Stucco Failure, I'd highly recommend reading that post before going further here…
In general, you are always better to cap your parapet walls with metal rather than Stucco'ing over them. But, what if your client/architect doesn't want that look? I'm building a Spanish Colonial Style house on Lake Travis right now and my clients/Architect on the project really wants the traditional look even though I've got some flat roofs and stucco. Here's an elevation from the Architect. It's tough to see in this drawing, but the roof over the front door is a flat roof with a stucco parapet cap.
In light of those massive failures I showed last week, I thought I'd show you how to avoid those issues and do this Stucco Parapet Cap the Best Practice way!
First, have your carpenters frame the parapet cap with slope to the inside so any standing water will drain in the proper direction. You don't want a true flat cap. Next, I have my frame carpenters wrap the house in Tyvek Commercial D and fasten it with a Stinger Cap Stapler. This is my go-to house wrap when I'm installing stucco, or just about any facade really. This crinkly version of Tyvek Commercial wrap is both jobsite tough AND will provide a nice drainage plan behind the stucco. Here's a neat video I made a few years ago to show how well the crinkles move water out of a leaky assembly.
Next, I'll bring in the roofer to do the underlayment for the pitched roofs. My go-to roof underlayment is Carlisle's WIP 300HT for any roof I build here in Texas. I also have them install the roof membrane on flat roofs during this visit. I use Carlisle's white TPO which is perfect for our hot climate. Always remember to work from the BOTTOM TO THE TOP when doing waterproofing. You really want that Flat Roof membrane down before doing the parapet cap waterproofing.
I like to get to bare plywood before doing any peel & stick membrane as I know I'll get good adhesion to the plywood. I recommend using 3M High Strength 90 spray adhesive before adhering the Tyvek Flexwrap in the corners to ensure a good sticky bond to the plywood. Lastly, we do the real waterproofing. The Flexwrap is what I use to make sill flashing pans for my windows and it's a very versatile product that works great in this application. The sheet membrane we apply next doesn't stretch so Flexwrap in the corners makes this tough spot easy to detail.
OK, Now it's time for the bulk of the cap flashing. I like Carlisle's CCW 705 peel & stick membrane. This is a 40mil thick product and is very similar to an ice/water shield product you may have seen used on roof edges & valley's up North to prevent leaks from ice damming. It is a rubberized asphaltic product that has good self-healing properties around nail penetrations. You really want this thick membrane under the stucco cap because water WILL get through the stucco cap someday. There are a few other manufacturers of this type of 40mil product but you might need to hunt around to find it as it's not typically stocked at the lumberyards. I buy it from a Commercial Waterproofing Supply house in Austin called All-Tex supply. You might also find a similar product at a roof supply house. You could use WIP 300HT also. But, whatever product you pick you want to ensure it wraps over the entire cap in one piece and hangs down 4-6" for a good shingle effect.
One of the reasons I like CCW 705 is that I can buy it in various roll sizes. They stock it in 12", 18", 24", 36", and 48" rolls at my supply house. Sam my carpenter is running roughly six foot lengths so we can ensure a smooth wrinkle free (ish) install. We always overlap the sheets by 6-8", and if you're concerned about adhesion you can spray the overlaps with High Strength 90 adhesive primer.
Now you can see why we really want the Tyvek Commercial D house wrap on first before waterproofing the caps.
There you go, that's Best Practice for Stucco'd Parapet Caps. This took some work and some dollars in product, but I'll sleep well at night knowing these caps won't end up looking like this someday!
I'd love to hear your comments about this installation.
Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.