Wood is the predominate building material in the US and what’s the #1 enemy of a wood structure? Water! The details of your Waterproofing are SO important because one small slip in the waterproofing layer and you’ve got a problem.
So, with that in mind I’ve been reluctant to rely on solely tape products to waterproof my houses. In fact, I’ve poo-poo’d Zip Wall from Huber for a while. However, this past year I had the opportunity to build a SIPS & Timberframe house designed by Architects Aamodt & Plumb and built in conjunction with famous Timberframe company Bensonwood Homes in New Hampshire. (Side note, I first heard of Bensonwood while watching This Old House in High School. It’s a dream come true to build a house with their Timber/SIPS package)
Bensonwood has been using Zip in their SIPs (Structural Insulated Panels) process for a few years now and has really liked them for several reasons.
WHY ZIP SYSTEM:
#1 Easy install. Huber Zip is pretty darn easy to install for your carpentry crew. Their tape they sell for the seams is really Top Notch too. I’m very impressed with this tape after my first project. It’s an easy system to learn because they aren’t as concerned about the Shingle effect & where to layer things. Simply butt panels and Tape them.
#2 Air Tightness. I believe that air tightness is really the missing link in terms of efficiency for many builders across the country. This house we did with Zip Wall blew a very good Blower Door test. (stay tuned to find the results)
#3 Cost. The Zip materials themselves are a premium cost compared to some other “housewraps” but the big savings on Zip happens with Labor. The Zip Wall house requires one trip around the house compared to two with more traditional systems.
#4. Early Waterproofing. This is a big one for me. Especially with the roof panels. Usually after my framers lay the roof plywood or OSB I’m waiting a few days for the roofer to “paper” the roof for a temporary waterproofing till they come back to install the roof. With Zip you have them deck the roof and tape it same day! Drying the house early in framing is really nice and frankly pretty important if you’re building a house in under 6-9 months.
Using Zip: After using Zip on this first house I’ve become very comfortable with their system overall. But, I think there are some small modifications that need to be made to ensure maximum durability of your house for the next few hundred years. Let’s look at this Bensonwood project to see how we modified Zip to suit my desire for ultimate durability.
Advice/Tip #1 ROOF UNDERLAYMENT IS KEY:
Early dry-in with Zip Tape is great, but I’m a big believer in putting a full Ice/Water shield product on your roof as underlayment especially if you have an un-vented roof assembly. This SIPs framed roof has 12″ I joists filled with cellulose insulation and I need to ensure they stay dry for the life of this house. I typically use Carlisle’s WIP 300HT for my roof underlayment. This 40 mil product is rated for high temps and has some self-gasketing abilities.
Advice/Tip #2 BASE WALL FLASHING:
In almost every house I remodel I find rot at the base of the outside wall sheathing. I believe you MUST use a base wall flashing to protect the raw edge of whatever sheathing product you use. I’ve used Carlisle’s CCW 705 for a few years now. Here’s a blog post for more info about how to use CCW 705. You’ll see in the later photos that we used Zip tape on top of the Carlisle 705 to ensure it would stick properly to the Zip Wall. That gave us about 16″ of extra protection at the bottom of this slab-on-grade house.
Advice/Tip #3 RAINSCREEN ALL YOUR CLADDINGS:
Rainscreen is basically adding an air gap behind your cladding (siding/stucco/brick/etc). In my opinion this air gap makes a HUGE impact to the durability of your house. Any water that gets behind your cladding has air gap layer to drain & dry. Simple, yet it’s done so little in this country. If you build with Zip and add an Air Gap (rainscreen) I expect your house to be in great shape 100+ years from now. This house has a mixture of stucco and wood siding so here’s how we got a Rainscreen air gap.
For a more in depth look at the Delta Stucco rainscreen system see this blog post from earlier this year.
Follow this advice and I think Zip is a great system. By the way, this house blew a .92 ACH50 in our Blower Door test! Just shy of Passive House standards and 5x tighter than code for Austin TX. I like an exterior taped system if I can add my extra tips for Durability!
Stay tuned for more on this project. I’ll be blogging more about this BUILD in the near future. It’s almost done, but here’s a few pictures of the almost complete house.
PS> I didn’t make specific mention of this in the list, but always… ALWAYS set your windows with a sill pan underneith. Zip has directions on their site for making window sill pans with their products, or you go with my standard method using DuPont Flexwrap. No matter your choice of materials, never rely on face sealing alone for windows. Make a pan so a future window leak will drain to the outside and not get into your structure.
Matt Risinger – Risinger Homes in Austin, TX