Joe Mabel CC-BY-SA-3.0, via Wikimedia Commons

is a German term for a vertical addition. That is, an increase in height by the addition of one or more floors to an existing structure. Aufstockungen are quite common in Europe, and have been for generations. Unfortunately, they’ve been rather underutilized in Seattle–at least outside of single-family housing. However, as the demand for housing increases in the city, this could be an innovative strategy to address the shortage without losing the soul of the city.

One of the projects I’ve been working on is an addition to an existing low-rise apartment building. Inquiries to add additional units to existing buildings have seen an uptick, though most of these have been along the lines of converting storage spaces to dwelling units. Many of these buildings aren’t maxed out on zoning height, though may be height restricted due to building type and level of protection. This uptick has been noted in local media, including a recent Capitol Hill Seattle post on sneaking in new units where possible.

Ample benefits

There are a plethora of reasons it would be beneficial for the Council to promote such a tactic. Just a few:

  1. It would reduce pressure to tear down older buildings by increasing their income potential. This is especially critical as land values continue to rise, along with corresponding rents.
  2. It would accommodate additional density. While Seattle unfortunately lacks quality perimeter block development (partially a result of bad land use regs and historic underdevelopment of lots), a 2011 study in Graz, Austria, showed a 1-2 story increase could result in 40-80 additional units per block. Graz, like Seattle, suffers from a heinously amount of area dedicated to quasi-suburban living (detached single family housing) – however the downtown core features a number of fabulous perimeter blocks with great courtyards.
  3. It extends the usefulness of the building.
  4. It preserves the character of the street. I’m constantly shocked at the number of urbanists that find block after block of banal developments acceptable, especially as they consume Seattle’s gritty heritage–heritage that contributes to the vitality of neighborhoods like Capitol Hill. I’m a big fan of granularity, diversity, and keeping something other than a semblance of old facades.
  5. Sustainability, sustainability, sustainability.
  6. They could also allow for preservation of in-city green space–both immediate (vertical rather than horizontal additions into courtyards or adjacent yards) and regional, by reducing pressure on sprawl.
  7. It can drive (actual) innovation. In many European cities, units or floors are being installed as prefabricated elements, saving substantial time (installation of lightweight wood panels or modules in a few days or less), money – and in some instances, both. The wood industry has even undertaken the development of a systematized addition for this typology.

Design considerations are something often taken into account with aufstockungen. The largest being to set back the addition from the perimeter of the existing structure. The issue of compatible versus contrasting materials, and whether the addition should complement or clash is a constant topic of debate in Europe–generally this isn’t much of an issue, except for buildings of note. A quick image search (dachausbau or aufstockung can give a pretty good sense of the scope and scale of these projects. Skyscrapercity has a short page on some incredible aufstockungen in Graz. Vienna’s got a ton, one of my favorite’s being Josef Weichenberger Architekten’s Margaretenstrasse 9.

Photos by: Erika Mayer (Josef-Mayburger-Kai 2a; 5020 Salzburg;;

Potential for adoption?

This typology isn’t unheard of in the US–rooftop additions and penthouses are fairly common, though generally reserved for the wealthy. What intrigues me most about these is that in Europe–there is phenomenal diversity of the buildings and tenants–spanning from ultra luxe to social housing. I am guessing a lot of that has to do with smart planning rather than carved out exceptions and loopholes. The German Fire Code for low and mid-rise construction is much less restrictive than the US, and this is further aided by a history of mostly masonry/concrete buildings. Seattle’s older low-rise multifamily buildings outside of downtown are generally wood, and so this would need to be coordinated with the Fire Code. For older buildings that aren’t sprinklered, this could be an opportunity to increase heights for those that undertake sprinkler retrofits. Or better yet, allow another story or two if the owner undertakes a whole building modernization or EnerPHit (Passivhaus retrofit).

There have even been some undertaken in Seattle. The Reedo Building (Elysian Fields) is a good example, although a commercial instead of residential.

Belltown’s 81 vine lofts are another one that stand out. The Washington Shoe Building on Jackson underwent one of sorts, with a 2-storey addition – albeit in 1912.

Another big difference, at least here on the West Coast, is our lovely increased seismic risk over cities like Vienna and Berlin. This could be partially mitigated, at least with wood buildings here in Seattle, with a substantial upgrade of the facade, which is why I’m intrigued by pairing this with Passivhaus retrofits. If you’re already ripping off the facade to add new sheathing for the vertical addition, it would also be a smart time to add exterior insulation (mineral wool) and quality windows. There is a fair amount of precedent for this in Europe, including an exemplary retrofit and addition to a building in Hannover, Germany which saw a whopping 93% reduction in energy usage over the existing building.

Though Aufstockungen aren’t as nifty as new construction, they should be encouraged as an innovative tool to help address the housing shortage. City Council should find a way to creatively allow this typology to take shape, carving out an exception in the Land Use Code if needed for adding units above height limits for existing buildings.

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Mike is a dad, writer, and mass timber architect with a passion for passivhaus buildings, baugruppen, social housing, livable cities, and safe car-free streets. After living in Freiburg, Mike spent 15 years raising his family - nearly car-free, in Fremont. After a brief sojourn to study mass timber buildings in Bayern, he has returned to jumpstart a baugruppe movement and help build a more sustainable, equitable, and livable Seattle. Ohne autos.

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Matt the Engineer

Somewhat related: I’ve always wondered if 2 Union was designed to have another tower retrofitted someday. Check out the very large diameter structural pieces they have all over the podium.

Mark Hogan

It seems like the added costs on a wood building a seismic zone would be prohibitive, as many interior walls would have to be stripped down to the framing for reinforcement in addition to foundation and facade upgrades. Many existing buildings on the west coast were not particularly well-built 100 years ago- we frequently find buildings in the Bay Area sitting on brick foundations (or no foundation at all in a few memorable cases!). I can’t see this penciling out for anything other than luxury development.

Matt the Engineer

I don’t know if this was code driven or insurance driven, but around 2000 I noticed a lot of old buildings in SF retrofitted with diagonal steel structure. You can notice them in the windows of old brick buildings there.
Threaten to take away a building’s occupancy certificate*, and suddenly amazingly expensive things like steel structural retrofits begin to pencil out.
* note: again, I don’t know if this happened. but something was driving these retrofits

Mark Hogan

I believe what was driving those retrofits was the dotcom era conversion of many of those old buildings to new uses, many of those buildings were either vacant or being used for light industrial purposes and were converted to office or residential (or live-work) at that time.

mike eliason


in this instance, the cost of the seismic and sprinkler upgrades were not greater than the cost of additional housing – though there were extraneous costs that pushed it up. if the owner could have been allowed another floor for the retrofits, then the numbers may have worked well.

the problem we’re running into now (and i’m sure same goes for SFO) is the cost of housing is getting to be so skewed, that in either case luxe development wins out. it doesn’t make economic sense for owners to hold on to under-zoned, low-income housing on land that’s seen tremendous increase in value over the last few years. and we don’t seem to have any mechanism for finding ways to allow that affordable housing to remain.


I like this idea. What are the specifics about how council could promote this through policy?

mike eliason

i’ve been trying to think this one through a bit. the existing building code allows for additions as long as they don’t increase the height or area allowed by the IBC (which is based on building type – wood, concrete, heavy timber; and level of protection – sprinklered, rated assemblies, etc).
the issues we ran into – while not at max allowable height: the existing building was limited to two floors without sprinklers. and because it was an older wooden structure, seismic upgrades were also needed. in order to go up, there needed to be both sprinkler retrofit and seismic upgrades. it may be difficult to recoup these on an existing building without raising rents substantially – which I’m not a big fan of.

there are exceptions in the LU code for multifamily zones regarding additional height (stair penthouses, greenhouses, play structures set back from the edge, etc). it would be interesting to see if the LU code could be amended (if wholesale height increases aren’t implemented) to allow additional floor area to existing buildings that also undertaking seismic, energy and/or sprinkler retrofits. if the city wants to see more existing buildings maintained, and hopefully keep rents somewhat affordable, it needs to be able to pencil out for owners. it’s tough to recoup the savings of such retrofits with little to no additional capacity on low-rent structures.

Matt the Engineer

One way forward would be to exempt existing building components in a major retrofit. If you aren’t modifying the lower floors, they should be allowed to remain unsprinkled. This would require the new top floors to be sprinkled, plus the exit passages through the older part of the building. I know the energy code acts like this (you don’t have to go back and add code-level insulation to all of the walls just because you’ve added more cooling). It’s worth looking at the building code to see if something like this is allowed, though at some point you get into the “major renovation” category.
Of course, on top of this give buildings an incentive to retrofit sprinklers. I like your additional height incentive.

mike eliason

seattle’s existing code sort of allows this – however, the height/area increase can’t be more than what’s allowed in the IBC. so in a lot of cases, older buildings not protected or sprinklered would need to at least be sprinklered to get another floor.

this is one of the reasons it’s easier to pull this off in central europe, where wood isn’t a common building material.