..
Fill
part of a housing solution
Fill -Backfill, Infill, Refill, Upfill
Brian T O Brien architect, consultant, lecturer, tech entrepreneur- Ireland.
[this piece was originally written for publication in a 2025 book to celebrate the 50th anniversary of The centre for Maximum Potential Building in Austin, Texas of which Brian is an alumnus]
An idea that I have never got out of my mind but unfortunately cannot cite a reference for now is the concept that the original sin of architecture is that we must occupy land at all - virgin, green, ecological land (my emphasis) land. Or to be less prosaic about it, Land- they ain't making any more of it !
So this essay is an exercise in stating the blindingly obvious: we need to use our already developed land much more efficiently and we need to systemize it.
Across the planet from towns and cities of the US[1] to market towns in Ireland and UK, to villages in France and Italy[2], we see the same crises manifesting; depopulation, main streets and whole villages dying, social alienation, and crucially, housing unaffordability.
These do form something of a Gordian knot and unravelling it must begin with following one or two threads. As a built environment professional for me the twins threads to follow are housing and building reuse. There are many explanations for the sudden rise in housing unaffordability: the recent financialization of housing and homes[3], demographic changes such as reductions in family size and migration (of all kinds).
One solution, the conventional one, is large new market enabled housing development on green field lands. But in may places this approach is hitting limits of a different kind, namely the inability of government to deliver the new infrastructure that would provide land, access, water, public transit and utilities to these land holdings. Though as we will see this inability may be catalyst for much more integrated and multifaceted solutions than the large new build projects on greenfield locations they might have facilitated.
So let me set out four related initiatives to use our land more wisely while regenerating our towns and leaving the abovementioned ecological land for other species and future generations.
Fill
The theme of the next 4 ideas is fill, the action of filling up a container that’s already been created. They all rest on the premise that in our already developed townscapes: streets, communities, zones and sites, we already have an infrastructure of wastewater, sewers, water supply mains, fire hydrants, public transit routes-all already in place adjacent to the site's boundary. For the last two solutions, we additionally already have built structures with foundations, walls, roofs, windows, and usually utility connections and telecommunications wired in. All already built, already there and already paid for.
Another premise for filling is that in most cases any target site is already embedded in an established community: near schools, churches, post offices, pubs and social and cultural facilities. They are already located in the right places to benefit new resident and existing community, to enrich social life (and to minimize further damage to the environment)[4].
Acknowledging again then that I'm stating the obvious, the filling I propose is that of squeezing more usage into the same built out areas: fitting more homes into residentially zoned areas, more dwellings into apartments structures, more dwelling into an already built row or terrace.
Infill.
The first Fill I would like to explore is infill. Infill is the concept that we take the gaps in our streetscapes, our malls, our terraced houses and we fill them in. The journals and online posts are replete with initiatives and projects to do just this. Taking the 5 meter gap between two shops, the overhead space of an alley opening or the strange side garden at the corner of a single family housing estate[5] and designing a new building for it is infill at it’s best[6]. Usually we fill the gap with a building of a similar type as its neighbours, adding retail in a retail gap, a house in a residential row, a new coworking space or café in a commercial street and so on.
But also I've seen many good projects published where an optimization is achieved between carrying out this infill respecting the existing usages while also exploring new approaches and typologies. After all there's no point in creating a three story five bedroom townhouse infill if modern demographics requires studio apartments instead. We are seeing new topologies of studio over shop and live-work spaces, two plex or three plex in place of a large single home and many more[7]. And while these often challenge planning paradigms, they meet future demographics better than continuing with what we have always done. Cities and planning authorities shouldn’t be portrayed as always resisting these changes either. Some local authority become active agents in the transformation providing design resources[8], easing access to approvals and even assisting with lot consolidation[9].
Even when sticking with the established typology, it can often be the manner in which we do it that make the difference: a modular insertion that minimizes disturbance time, a colourful façade that puts that street on the map and increases footfall for neighbouring businesses, can all transform the experience and perception of filling in, not to mention providing new homes.
For this and all the fill approaches below the benefits of having the new project arise in an established community are significant. Compared to building new homes on the city edge or in a new town where providing new roads, sewers, mains and transit (public transport for those of us in Europe) is expensive and likely to be subject to public resistance, filling many smaller home into a community that already has these assets is easier and thus faster.
So there are cost and environmental impact upsides but there are also social ones|; Adding smaller houses, for starters or for downsizers, to a neighbourhood brings in different types of people: new couples to a community of empty nesters, digital nomads drawing a salary from far away but spending it here, key worker (fire fighters, mail carriers or teachers) that can now live in the community they serve.
And there are obvious environmental benefits too in that buildings that are attached (duplex, fourplex) and parts of terraces have less heat loss and by definition co location generate less traffic and thus less emissions[10].
The challenge for many of these interventions, indeed for almost all of the Fills I'll talk about, is that under conventional approaches, a bespoke design and a site specific construction solution is required, ones that are different for each gap. And at the numbers we are talking about, solutions become difficult to imagine being deployed at scale. We'll come back to this.
Backfill
The second Fill I'd like to look at is backfill. This is the idea that we take our backlands whether they be the large gardens of US homes in single family zoned area, the identical rear gardens of repeated pattern type developments in countries where more centrally planned housing was built, or just left over bits at the rears of our streets[11] and we redevelop them.
One example of this where we are seeing a solution being deployed at scale across the US is the ADU movement. Once prohibited out of fear of reducing the value of the parent house within a homeowners rules restricted development or single family zoning, city after city is now exempting or easing their path through the consent processes and in some cases actively promoting them such as with financing or pre approved house plans[12].
Indeed this trend is not confined to the US. Other countries that are said to be closer to Boston than Berlin in economic outlook (and land development patterns inevitable follow) such as Ireland, are considering making ADUs (back garden houses in Irish nomenclature) exempt from the need for planning permission also[13]. By some estimates hundreds of thousands of new homes could result.
Gaining new starter sized homes in established communities, on public transit routes and near schools are benefits enough to argue for removing any obstacles to secondary homes /ADUs as soon as possible. Add to those, the fact that combining a small affordable home with a larger family home on the same site unlocks opportunities for intergenerational migration, up and down sizing, additional income and live in care, and we see social and even emotional benefits also, ones that can never appear on any balance sheet but make a great difference to a family.
The final no brainer for me on ADUs is that that while providing another home where it's needed and so addressing housing availability and unaffordability, they are also most likely to be financed and developed privately. So there’s no need for the city to raise new bonds or for governments to add to their borrowing deficits. All of which avoids controversy and reduces or neutralizes resistance so facilitating a rapid deployment of this important contribution to the solution.
Refill
My third Fill is the idea that we take existing empty or underused ground level buildings on the streets of towns all over the world and we start to use them for the things that society really needs.
Why do buildings that could be in use sit empty, especially on streets with customer footfall ? It’s a good question. I referred before to the financialization of home building being one of the root causes of housing unaffordability and in many ways it's cousin, property price appreciation[14], is the culprit for storefront vacancy.
Simply put if the exchange value or price of property is rising faster than the income one could get from renting or developing that property, minus the costs of maintenance and any taxes incurred, it benefits building owners to leave them sit empty. It doesn’t however benefit the community who host those buildings, it harms them[15].
We need intervention, fiscal and reputational to unlock this, carrots and sticks to break the deadlock of which more later.
And yes these buildings need creativity to bring them back into use - both in terms of envisaging a viable use[16] for them and in terms of adapting them to modern standards. Adding comfort sustainability and safety aspects to them is a challenge but it can be done. And we shouldn't always assume that a former storefront should continue as a retail use. We know that a store or shop can easily be changed to being a work hub or café among many adjacent uses.
In Ireland we’re finding other reversion options are viable also. We have a scheme here where any empty former pub can be converted into a residence without having to go through the planning system. It's a small example and one that may be very country specific in a land where every town was awash with pubs and now can only support one or two, but it illustrates nonetheless that some fresh thinking can be brought to bear in any context in any country.
And we’ve already alluded to the benefits: these buildings (main street stores above and upper floor below) have already built and paid for the inputs that are so expensive, foundations, walls, roofs, floors and services connection, all already in place. Building the new equivalent of these elements rather than adapting them is both expensive in material terms, costly in environmental impacts and labour intensive at a time when labour is in short supply. But also bringing them back into use not only benefits the new occupants but has outsize upside for community life: more footfall, more customers, more fun.
Upfill
The fourth Fill I’d like to look at is what I call upfill. It’s related to infill but extends the idea to address the vacant floors above our urban street businesses and attempts to unlock their potential for reuse, often as housing. Going back 100 years in most towns, the owners of the business on a street lived above their store or shop. Prosperity and upward mobility dictated they move to the suburbs when they had reached a level of affluence and that has continued, leaving us with many an empty upper floor.
In Ireland we've had 30 years of attempting to solve what's come to be known as the ‘living over the shop’ problem, so we're quite familiar with the barriers to it.
One inapparent cause of the emptiness and vacancy seem to be that it's often the situation that the business on the ground floor has long since paid off its building costs and is turning over a comfortable profit leading the perhaps aging business owners to view taking on a new capital project like upgrading the upper floors as a headache they don't need. Add to that the fact that on paper the building is worth more tomorrow than it is today despite even empty upper levels and that in many regimes taxes don't have enough ‘stick’ to neutralize the gain, and we have the situation where empty upper floors can persist with very little downside to the owners.
But also there are specific challenges to the adaptation: In many jurisdictions a new apartment, albeit a retrofit in an old building, must reach the same standard of safety and energy performance as a brand new build one. This can be a major stumbling block. For decades the assumption was that the additional profit from being in a city centre location would justify the additional investment required to bring an old building up to code over new build. As expectations, demographics and even politics have changed, the market has passed judgment on this approach and activity in redeveloping upper floors had slowed. A more recent solution to this attempted in some jurisdictions was to give planners and building control officers more flexibility, allowing them to exercise their own discretion in considering individual permit applications and leaving it to their judgment to propose or accept bespoke solutions. Anecdotally in Ireland and UK we are finding this is even less effective as most such officers had already locked in a mindset of being the adjudicator on proposals not the generator of solutions and seem to default perhaps understandably to refusing a solution they haven't seen before rather then run the risk of being the person who approved something that later went wrong and became a public mistake or worse.
Other barriers to this approach are that lot divisions in this situation tend to run vertically through the floor levels and are narrow, while the optimum apartment layout wants to be horizontal and wider than the typical footprint of a street front shop below. Finding some mechanism to easily facilitate the transfer of ownership, say two adjacent owners agreeing to swap a level above, across the two plots so generating a new more viable floorplate for each of them to develop as a new apartment, would be a solution to this.
Other practicalities such as fire compartmentation, emergency egress and fire suppression which are very difficult to introduce to an existing structure, all need new solutions to be applied or at last considered. Could doubling up on heat detection and suppression (modern micro sprinklers and misters) justify a relaxation on fire compartmentation? Could regular resident fire drills (common in non residential buildings but not in apartments) and fire fighter rehearsals allow a second escape stairs be omitted ? While this all needs further study to be sure, we shouldn’t pretend that the only techniques available to us today are the same as the ones that existed fifty years ago either.
Enablement
And when owners are motivated, and I believe that some combination of incentive and penalty, combining grants, tax write downs, reputational pressure and process systemization could make them all so, there are still specific challenges that make adaptive reuse across all these fill approaches difficult.
Ownership
Ownership, or ownership at scale is often a barrier: We saw in Upfill above how the floors of a narrow lot make a horizontal apartment unviable while in the case of backfill or infill two opportunity sites whose owners want to combine may be separated by a narrow strip, in the ownership of another who wont sell.
Access ownership is also a part of this. The way into an ADU site at street level may be constrained. Previously public laneways that could now provide access to backland sites may have been reclaimed and built on. The street doorway and stairwell up to an upper floor may have been absorbed into the shop below.
Clearly owners cooperating and negotiating sales and swaps can solve many of these conundrums but governments and foundations can also help. Local agencies providing grant aid to cover the cost of quick design explorations that might unearth solutions could help as might making pro forma legal agreements to facilitate land or floor area swapping available (to reduce legal expenses) also.
Or city departments could scale up their efforts at site consolidation. There are public interest arguments for confiscating persistently derelict or vacant properties in strategic areas. Dereliction of one building on a street has been shown to be contagious[17], demotivating adjacent owners from maintaining their buildings and beginning a spiral of decline. Eminent domain and compulsory purchase powers are the solution to this but a city needs the will to apply them and their overseeing politicians need to have the courage to face down the property owners, who may be doners, who will resist.
Another aspect of this are the properties that no one seems to own. This is not as uncommon a problem[18] as it sounds[19]. Here I’d propose an unconventional solution also.
In Ireland during the economically challenging 80s our government came up with a way to borrow money from the private sector. It was called the dormant accounts fund[20] and had enormous success legislating the banks would credit to the government money sitting in bank account if the account holder has not been in contact for decades. Such money was and is still used for government expenditure on ‘measures that address economic, social and educational disadvantage, or support those with a disability’ and if an account holder turns up looking for their funds, these are immediately returned with the lost interest, by the government. Never once have I heard a complaint about the operation of this scheme. We need a similar approach to acquiring and utilizing vacant property whose owners have disappeared, especially property that falls into dereliction.
In other cases the land is already in public ownership and its more a case of the department that has title transferring it to a program or unit that is enabled to make it available, perhaps in a partnership or simply as a public interest sale, for immediate use.[21]
Design
For all my fill approaches, there are fundamental problems with trying to generate an individual design for each site, building and even floor level. Quite simply there aren't enough designers to tackle each and every one of these gaps individually. We need some other solution. It may be that other professions than designers and architects can be given just enough skills and knowledge to provide the design schematics that could be applied at the for individual scale. I'm sure many of us would have had hopes that AI would help also but I'm now becoming sceptical that this is so. The solution probably lies in some kind of standardized toolkit approach[i] combined with libraries of pre approved plans on a per city, per building type, and per typology basis perhaps with some kind of algorithmic optimization[22].
I have no easy answer to this but I look forward to the other ideas to see what new approaches might be emerging.
Labour
And once the design is done we have a similar problem with having to find the workers to go into each and every backland site or building and to build out the bespoke solution that has been prescribed by the designers. This requires tailored construction solutions on tight and inaccessible locations at a time when in many countries with housing affordability problems there’s a parallel shortage of labour.
But to my mind there are pools of labour that could be persuaded into service. Retirees that don’t wish to sit out their last active and still skilled years and would work part time as trainers, the 58% of GenZ-er that can't find work[23] or the 4.3 million people not in employment education or training (NEETs)[24] in the US. Could we start a new movement, a kind of cross between the (US) highway building or rural electrification programs of the inter war years, military (but civil and voluntary) service, and a massive internship scheme deployed to bring together those with skill and those with time and reframing it all as a societal moon shot mission.
In countries where the debate about migration hasn’t become so polarized, one could consider allowing migrants of all kinds (yes there are many kinds), and indeed homeless people, become involved, recognizing that the very buildings we are upgrading can provide the basic shelter such humans need to remain off the streets and safe while integrating and getting new skills.
Conclusion
Clearly there is an inertia to be overcome to enable the wholesale revitalization of these vacant and underused plots, buildings and storeys. And while there may be many reasons for not going ahead; land value appreciation or shortage of labor, lack of skill or knowledge are not among them. We know what to do, it’s just a question of finding a way to align the forces: opportunity, motivation, timing and reward to get started.
Once begun, most projects tends to be completed.
References
[3] https://blogs.lse.ac.uk/lselondon/financialization-of-housing-a-tale-of-13-cities/
[8] https://lewishamsmallsites.co.uk/25-infill-development/
[9] http://www.dublincityarchitects.ie/fishamble-street/
[10] https://sandiegoeco.org/urban-infill/
[11] https://allisonramseyarchitect.com/urban-infill-how-small-developers-are-reshaping-our-cities/
[14] https://www.irishexaminer.com/news/spotlight/arid-40354274.html
[17] https://communityprogress.org/blog/how-vacant-abandoned-buildings-affect-community/
[22] www.opoplan.com