How an Architect Built a House to Withstand Mudslides

Dan Nelson has inadvertently become an expert in resilient design because of where he lives and builds houses: Washington state. His architecture firm, Designs Northwest Architects, specializes in complex residential projects in and around the Puget Sound where earthquake risk runs high. With strict seismic codes and geological restrictions for building near FEMA flood zones, Nelson and his firm have become quite skilled in designing homes to withstand the extreme conditions specific to the Pacific Northwest.

Nelson gained international renown for the Tsunami House, a family home built in a high velocity flood zone that would potentially need to withstand 300-mile-per-hour lateral waves. The Pacific Northwest isn’t threatened by hurricanes, Nelson told me. “Here, we have tsunamis which come from earthquakes and we have to design for that potential.”

His solution was to build the house on 9-foot piers with ground-level industrial garage doors that open to let the water flow through the bottom floor and out the other side. That level of the house was also furnished with waterproof furniture just in case.

When I called Nelson, we talked about his creative solutions for a lesser known, but equally interesting home: Saratoga Hill House, which has been in the same family since the 1940s and is unfortunately sited in a severe flood and mudslide zone. Our conversation has been edited for length and clarity.

I saw Tsunami House in the book Designing for Disaster and was fascinated by your approach — especially the garage doors opening to let the tsunami winds and water flow through the house. I would love to hear about how you came to focus on resilient design.

Tsunami House has been covered a lot recently, especially in light of all the environmental catastrophes — hurricanes, flooding, and everything else — going on. It resonates with a lot of folks wondering how architecture can mitigate their exposure to extreme weather.

My office is about 60 miles north of Seattle, in the Puget Sound region. The Cascade Mountains divide the state in half. On the eastern side, the ecology is drier, more desert-like, and prone to wildfire. There, we are doing quite a few houses using Firewise Design concepts, which offer criteria for building more safely in a firezone. Puget Sound is west of the Cascade Range and prone to sea-level rise and earthquake-induced landslides.

Tell me about your architectural approach.

My approach to resilient architecture emanates from the challenges of the site and how the clients want to live on the property. It was born out of solving the problem of building on a certain piece of property. And every property has its own challenges.

Designing on flood plains is only one of those challenges. Building on Camano Island requires an archaeology study because many of the beaches have tribal artifacts and archeological deposits of cultural significance.

Let’s talk about Saratoga Hill House. First, where is it? 

Saratoga Hill House is a beach house on the northwest side of Camano Island. There is no road to the property. There is a common parking area but whoever lives on that beach has to walk to their house. You can’t drive a truck or car to bring materials and equipment to the site. They have to be barged in or taken on a half-track with a tread system down the beach.

But then there are only a limited number of days or months we could get materials to the house because it is a smelt-spawning beach. At certain times of year, smelts spawn, so when that happens, you can’t do any work on the beach.

So, we needed an archaeologist and a biologist to do reports.

Saratoga Hill HouseSwift Studios

Your Habitable score shows severe flood risk. Were you aware of that? 

We knew that. And saturated soil conditions create a potential for mudslides. They are two different issues we had to address.

As for the parameters of the site, Saratoga Hill had an unstable slope. And because it’s built on a shoreline, we had to address setbacks that dictated how close to the high-water marker we could build. Also there was no septic. All these issues set the parameter of what we had and dictated the direction of the design. And it’s why we built the house on that steel frame.

Saratoga Hill HouseSwift Studios

Tell me about those decisions.

I imagine people will think, is it even worth doing?

In this case, the client had grown up in this house. He was a third generation family member and had been going to this property since the 1940s. He was committed to building here no matter what. He spent his entire life going there and had a strong sentimental attachment to the beach. And on that beach are extended families — his sister lives next to him, his cousins live down the beach. All have been there for generations and their friends have more relatives. It’s a very tight-knit community.

How did you solve this massive puzzle? 

Our first inclination was to build a retaining wall behind the house to hold the hillside back. The town planners wouldn’t let us do that because you can’t direct earth from your property to someone else’s and we were told it wouldn’t work. They said it was doubtful we could build a house there.

But the idea came to us after we did Tsunami House. If we have high velocity waves going through that house, what if we did the same with earth? We talked to the planners and proposed we find a way for a mudslide to go under the house. Instead of water, we did mud!

We worked with a geotechnical engineer who looks at soil conditions and the stability of the earth. The soil type would determine what pile systems to set our foundations on. We had to determine how much mud would come down the hill under worst-case conditions and how high would we have to set the steel frame.

Turns out, we had to go 10 feet for that lower level on the condition there was no habitable space below the house, other than the mechanical system. When we design in a flood plain, we can’t put any electrical or plumbing or mechanical systems below the flood plain. All light switches and outlets are 5 feet off the ground and anything that could get damaged by water has to be above the flood plain.

Saratoga Hill HouseSwift Studios

It’s been 10 years. Has the house been tested?

There have been mudslides in the neighborhood, but not yet on this property, And there has been flooding, but that’s not an issue for this property. We had done everything to address the flood plain — since every year now we get 100 year floods.

What are your three top takeaways for people living in a flood zone or mudzone?

If you are building a new structure, it has to be designed to meet FEMA requirements.

If you are living in a flood plain? A lot of older communities living in a flood plain actually lift the house. A house mover goes in, lifts the house, and puts a new foundation above the flood plain. You want to be a foot above the flood plain.

Retaining walls are not realistic or as effective as raising a house above the flood plain.

Are you working on any risky problems? 

I feel very fortunate that I live where I live and for what I’ve learned. At the Saratoga Hill house we used a steel frame, metal siding. And it’s a cool modern house. But without having those issues we had to address, we wouldn’t have set the house on a steel frame — we did it to solve a problem and used those problems to come up with the architecture of the house.

I always say, the expression of architecture comes out of solving the problem of that site. It may seem like there are a lot of limitations that we have to work around. But by the time we’ve solved the problem of designing a structure on that site, it dictates the architecture.

This is almost hopeful for the future of climate change. What it tells us is that we have to — and can — do some pretty cool things to solve the problem.