Thread by @holz_bau

it's interesting to me that in the US, we're adding new apartments at the ground level of existing buildings - because in such poor foresight, this area was space for cars.

whereas in DE/AT - they're adding new apartments above the existing roof level, even in newer buildings.

there are some really intriguing projects by @OpenScopeStudio/@markasaurus that have been infilling multifamily ADUs in former garage/storage spaces. openscopestudio.com/multifamily-ad…

but in built up cities that aren't dominated by detached houses - there's a lot of potential for new housing.

TU darmstadt study found that an additional 1,5 million new homes could be added to existing buildings by vertical additions (aufstockungen)

holz-kann.de/wachstums-pote…

part of this is political - the building ordinances in europe are a lot less restrictive than in the US.

so adding a 2 story building on an existing 4 story building doesn't necessitate an additional stair being added. you just extend the stairwell up

treehugger.com/single-stair-b…

existing buildings in europe also tend to be solid construction - so they can mostly withstand a lightweight addition, or only need a little structural work. this isn't the case for most of the US outside of a few dense places.

holzbauaustria.at/architektur/20…

btw this is a killer app for mass timber due to its lightweight characteristics. prefabrication allowing for quick on site assembly means your building isn't exposed to elements for long, either.

archdaily.com/923537/roof-ex…

vienna has space for some 50,000 additional units through these vertical extensions.

and there are some really striking additions to existing buildings, like this 3 story addition to a 4 story gruenderzeit building

archdaily.com/217122/renovat…

and as cities continue to see growing demand, aufstockungen are a way to add new housing without increasing sealed area or changing the character of the neighborhood.

these units also tend to be lower cost than building new - as the infrastructure already exists. in some instances in vienna, these are social housing or baugruppen added to the existing building...

nextroom.at/building.php?i…

or market rate units at rooftop covers cost of adding elevator(s) or the energetic retrofit. this is part of the 'soft urban renewal' vienna does, in order to bring up buildings in gentrifying areas. also can reduce energy consumption by over 80%
schoeberlpoell.at/de/projekte/fo…

this one is a baugruppe that was a block from where we stayed in vienna when we were at the passivhaus conference. had no idea it was there. amazing light, views... www10.aeccafe.com/blogs/arch-sho…

it's nearly impossible to add new units to roof of existing wood-framed buildings in seattle, which are majority of buildings outside the historic core.

seismic, energy code and sprinkler upgrades req'd are budget busters. and then there's the issue of 2 means of egress

they're such an incredible strategy for re-compacting cities.

but they're not really feasible without good 'urbanism' bones.

more on aufstockungen in this piece i wrote for the @UrbanistOrg 7 years ago:

theurbanist.org/2014/07/24/auf…

oh and you can absolutely add stuff like this onto existing non-residential buildings as well...

BIG's transitlager in basel is housing built over an existing warehouse that was rehab'd to retail and office space. no double loaded corridor, either!

archdaily.com/799437/big-tra…