Building a new house in Palo Alto

Building a new house in Palo Alto

Tuesday, August 28, 2018

Stego Wrap Vapor Barrier instead of a Rat Slab

It's basically a playground, yes?
In lieu of preschool this Fall, our not-yet-2-year old gets to hang out at the construction site with us instead. So far he's mastered six very important words...dig, dig, dig, dump, dump, dump! Not bad, but in the last few weeks we've tried to introduce a few more foundational vocabulary words. The first is Stego Wrap.

Stego Wrap! Anything at the site with a dinosaur on it is worthy of investigation.


James started using Stego Wrap a couple years ago when a house in College Terrace, (a Palo Alto neighborhood with a lot of subterranean water) was having problems with moisture in the crawl space. The water was going around the seams where the rat slab connected to the foundation's stem wall.

Click on these links for more details on How to Build a Foundation and Building a Rat Slab.

Now, instead of a rat slab he covers the area with yellow vinyl 15-Mil Stego Wrap. This treatment is more waterproof since the rat slab's concrete shrinks and pulls away from the edges and occasionally cracks too. In water heavy areas it may make sense to do both Stego Wrap plus a rat slab but for neighborhoods without water issues like Barron Park, the Stego Wrap is sufficient. In addition to preventing moisture problems, the vapor barrier is also better for controlling humidity and indoor air quality. More on that here: 10 Critical Reasons Why You Need a Below-Slab Vapor Barrier.

Stego Wrap seals better at the edges of the foundation making the house more waterproof.

Palo Alto city code only requires a 6-mil polyethylene vapor retarder but James upgrades to the 15 Mil Stego Wrap. La Donna has about 1488 square feet of living space on the first floor and we used about two 14'x140' rolls. At $460/roll that's not bad except we got killed on the tape. We spent about $1500 for Stego Tape which is essential in sealing edges and any openings like the piers. This is still less expensive than a rat slab so definitely worth the upgrade if you're building a new house.

By the way, Stego Wrap can also be added after the fact, so check it out if you have moisture problems under your home. They have a product specifically designed for crawlspaces called StegoCrawl Wrap. It comes in smaller roll sizes (14'x100' and '5x200') and provides the same level of moisture protection but it's white with white tape which brightens up the space (though I still like the rubber ducky yellow look!)

Stego Tape to seal any openings is the real cash dino. We spent more on the tape than the Stego Wrap.

Might need to send him back to school to learn how to not waste tape.
Note: This home, 3727 La Donna will be available for sale* in early 2019. Email us to get on the insider's list.

*Kids not included.

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