In plain sight: A new planning rule could unlock up to 350,000 small homes

Homeowners are currently entitled to build a small office, gym, or garage on their property without applying for planning permission. They are not entitled to build a small home.

It is hard to comprehend how many homes Ireland needs to build. The Housing Commission reported that in 2022 Ireland’s deficit ranged between 212,500 to 256,000. That is over 200,000 homes to catch up with existing demand. The commission estimated that Ireland needs to build 60,000 homes per year, every year, to meet growing demand. That means we have to build a new Galway city every six months. Or build a new Dublin city every four years. 

Filling the gap is a difficult task. There are significant constraints. These constraints are made more difficult by where the homes need to go. The government has targeted 40 per cent of new housing to be within our towns and cities. To reverse environmentally damaging sprawl and to create sustainable communities, the government set out its compact growth targets. These targets aim to put 40 per cent of new development within and close to existing settlements. We know that delivering compact growth has to be part of the solution to Ireland’s housing shortage. The difficult part is how to deliver new homes at scale within existing urban and suburban areas. 

Building within existing settlements is hard for at least two reasons: it’s complex and it’s expensive. 

It’s complex because there are often multiple owners of land. This means it is hard to find available and serviced land in the highest demand areas. 

It’s expensive to build in built-up areas. That’s because of the type of housing you can build there: apartments. Dublin is the second most expensive city in Europe to build an apartment. Apartments can’t be built in urban areas for less than €379,000 to €479,000. The cost of delivering apartments rose by 9.6 per cent in 2022. 

Seomraí (or granny flats, as they are sometimes called) can solve both of these problems. A seomraí is a small unobtrusive secondary dwelling built either behind or to the side of an existing property. Such dwellings typically have a separate entrance to the primary dwelling on the plot. They may be attached or detached. Their use may be as a form of private rental accommodation or for the use of a family member or friend.

Irish cities simply do not have enough brownfield land on which to build 24,000 homes per year. What they do have is an abundance of suitable privately owned residential land in the form of gardens. There are 3305 hectares or 33,051,889 square metres of private garden space in Dublin city council’s area. That is about 300 St Stephen’s Greens. 

The second hurdle any scalable Irish housing policy must overcome is the cost of construction.  Where an apartment can cost over €400,000 to construct in Dublin, a seomraí can be delivered for around €70,000. The simplicity of seomraí design allows them to keep costs down. Seomraí are affordable by design.

Low construction costs are not just a matter for developers. Rising construction costs ultimately mean higher rents. The simplest way to ensure affordable homes is to design the property with affordability in mind. Due to their scale and simplicity, seomraí are affordable by design, without sacrificing quality. 

While it’s hard to develop land in existing urban and suburban areas, there is more than enough land to go around. 

Seomraí are an integral part of healthy housing systems in other countries. In Vancouver, 35 per cent of all single-family homes have some form of seomraí.  In California, 11.5 per cent of all permitted homes were accessory dwelling units (ADU) – a form of seaomraí – in 2020. 

Unlocking seomraí at scale is achievable. Several jurisdictions have had tremendous success by removing some of the legal and regulatory barriers to building seomraí. For instance, by removing some barriers such as owner-occupancy requirements, Seattle increased ADU permits by 253 per cent in just three years. In six years, California increased ADU permits by 15,334 per cent. As of 2022, 19 per cent of all housing units produced in California – or nearly one in five homes – was an ADU.

Seomraí are popular. Other countries are beginning to recognise the potential impact of seomraí on housing supply, sustainable development, and accommodating demographic change. Accelerating granny flat development is a national policy priority in New Zealand. In Switzerland, they are considered an investment opportunity for retirement. This year, the French Senate proposed a bill to allow more development in private gardens. In Australia, there is a growing appreciation of the potential of granny flats. The New South Wales government encourages them; in Victoria, they do not require a planning permit; and in Western Australia, they are exempted from the planning approval process altogether. 

Ireland should pursue a seomraí policy, delivering thousands of homes as a result.

Seomraí could deliver up to 350,000 homes

Progress Ireland’s modelling suggests that a seomraí policy could unlock 348,730 developable sites. What this means is, we estimate there are up to 350,000 properties with enough space, and high enough local rents, to justify building a seomra.

To estimate how many developable sites could be unlocked by a seomraí policy, we randomly sampled 200 properties using eircodes. The properties were randomised using a random number script ranging over all registered Eircodes in the country. Properties were assessed to have the physical potential for a seomraí based on two broad criteria: size and access. 

Our assessment of physical suitability is based on the assumption that the seomra is minimally 25 square metres. The garden was sufficiently large if it met the following conditions: we assumed a minimum garden size for a 25 square metre seomra of 62.5 square metres. We assumed the seomra would be at least one metre away from all property boundaries. 

Our size assumptions are conservative. We decided to err on the side of underestimating the number of homes that meet our size criteria. Separation distances are subject to the time it would take for a fire to spread; this number can be brought down by using fire-resistant materials. So, our model will understate the number of seomraí that will be within separation rules. Seomraí may be attached to homes, so our assumption of a minimum garden size no smaller than 2.5 times the minimum seomra size is also conservative, and will likely understate the number of physically suitable sites. 

We considered a property to be accessible if it met two criteria. First, the property must be accessible by a side passage no smaller than one metre. This size is greater than the minimum required for disability access. 800 millimetres, ie 0.8 metres, is sufficient to allow access for construction crews and their equipment to access the garden. Here again, we chose to be conservative in our estimates to allow for measurement errors. 

We did not consider access from the back of the property as accessible for the purposes of the model. In reality, such access would be sufficient and, in many cases, preferable to the use of a side-passage. Back access was excluded due to the difficulty in measuring access which is often not visible from an aerial view. 

Second, the property must be within 45 metres of a vehicle access point. This distance is required by law to enable fire services to access the property. 

The next test is financial: are the all-in costs of a seomra (construction costs, finance cost and a 15 per cent margin) greater than the value a seomra would be expected to add to the value of the house?

To estimate what a seomra would add to the value of the home, we used two numbers: the an estimate of rent on offer and on of the gross yield (the rate at which rents convert into house prices).

We derived our estimate of the rent from Daft.ie data. We took the average market rent for one-bed apartments in the county, then discounted it by 15 per cent to account for seomraí’s relatively small size.

To convert the rent into the capital value of the home, we used a gross yield of 13 per cent. Choosing a yield is inevitably a finger in the air exercise, since it’s our estimate of the market’s estimate for something that doesn’t exist yet. Here’s how we landed on 13 per cent. We started with the market’s average yield for one beds which is currently 7.8 per cent in Dublin City and 10 per cent on average outside of Dublin. We then discounted the market’s yield to account for the illiquidity of seomraí – they can’t be easily sold in isolation, like a normal apartment. We landed on 13 per cent.

Bear in mind that we’re advocating for seomraí to be included in the rent a room scheme, which would allow €14,000 of rent to be drawn down tax free. The market’s gross yield is a pre-tax figure. In other words, the yield we have chosen is about twice as high as it would be if it were compared like-for-like with after-tax market yields.

Adding a seomra would undoubtedly be adding complexity, for the homeowner. They would become landlords, with all the obligations that implies. An important detail is that there might be a difficulty selling or remortgaging the property if a tenancy is still ongoing. A homeowner would be better entering into a lease if they were confident they wouldn’t be selling or remortgaging during the period of the agreement.

Our estimate of how many homes are suitable for seomraí is calculated as the proportion of homes that meet space, access, and financial criteria. 20 per cent of homes in our sample met these three requirements. This scales up to 348,730 homes across Ireland.

The model we have built is interactive. To interact with the model’s inputs, visit the model then make a copy of it under the File menu in Google Sheets.

The case for Seomraí in Ireland

The first benefit of Seomraí is that they enable rightsizing. The government defines rightsizing homes as “smaller dwellings designed to meet the needs of older people.” Ireland needs a rightsizing strategy. The Department for Housing, Local Government, and Heritage estimates that 150,000 rightsizing homes will be required by 2031.

A survey of 554 adults aged 55 and over by the Housing Agency and Ireland’s Smart Ageing Exchange showed that the majority of older people cared more about staying in their area rather than their particular dwelling. A strong seomraí policy would allow older people to rightsize, without leaving the communities that they call home. That is one of the reasons why the Royal Institute of the Architects (RIAI) and the Association of Occupational Therapists of Ireland (AOTI) support “the provision of accommodation that reflects the identified demographic and support needs of the population of Ireland and acknowledges the right of people to choose to remain in place.” The provision, they note, should include both attached and detached granny flats.

According to the CSO, the population of over sixty-fives is projected to reach about 1.5 million by 2051. To accommodate this demographic change, there will be a growing need to build smaller homes. This is a point recognised by the Department of Housing, Local Government, and Heritage. Meeting the challenge of an ageing population head-on means creating more housing options for every stage of life. Seomraí are one tool among many to meet this challenge. 

The second benefit of Seomraí is the "cascade effect" – the extra housing that is unlocked when people downsize into a smaller home.

There is a mismatch between the existing housing stock and the preferred household size in Ireland. While our homes are too big for us, our families are getting smaller. Household sizes are tending toward the EU average of 2.3. The average household size in Ireland is 2.74, down from 3.34 in 1991. As a result, there are too few small homes, for one to two people, on the market.

Seomraí will help connect people’s preferred household size with the types of housing available. This will free up larger family homes. Homes more appropriate for families are misallocated to two groups: older people seeking to rightsize, as discussed, and younger crammers.

Young people are ‘crammed’ into homes which are shared with friends or strangers. One measure of this phenomena is the ratio between single person households and households containing unrelated persons. The higher the number of single family homes, the more housing options for those wishing to form their own household. The lower the number, the more people are ‘crammed’ together. In the Netherlands, the ration is 20:1, there are 20 times the number of single person households than crammer households. The average number across eight European countries measured was 8:1. Ireland only has two single person households for every one crammer home.

A seomraí policy may see a cascade of family homes coming onto the market. Matching smaller homes with smaller households will free up larger homes rented by groups of single people for families. With a strong market for smaller homes, so-called ‘crammer homes’, where young people are often living with groups of strangers, will revert to the market for families. Similarly, rightsizing will continue the cascade of family homes to the market.

A third benefit of seomraí is that they help homeowners pay the bills. In Vancouver, renting out an ADU is so common partly because it helps ease the burden of a mortgage. They call them ‘mortgage helpers.’ Enabling homeowners to meet the growing cost of living while providing a home to the market is a win-win. 

A fourth benefit of seomraí is that they can help cut carbon emissions. Seomraí are one tool among many to help curb our carbon emissions. Areas with higher densities are the most environmentally friendly. A strong seomraí policy would allow an increase in the supply of homes in the areas with the highest demand. Restrictions on building in the areas with the highest demand leads to dispersed development and higher emissions. 

That is why the Climate Action Plan 2024 is informing the revision of compact growth goals in the National Planning Framework. Seomraí are one powerful means to achieve compact growth, helping Ireland deliver homes where they are needed most.

Seomraí could be fitted with a ‘green roof’, contributing to biodiversity. Typical suburban gardens usually contain monocultural grass. Unused sheds or underused structures such as gyms could be replaced with a home which contributes to biodiversity in the area by its green design.   

A fifth benefit of seomraí is that their benefits are targeted at groups who are feeling the housing shortage most acutely. Seomraí could provide additional housing options for students and young professionals currently priced out of the market and low down on housing lists. Young people are staying in the family home far longer than they would like. Between 2011 and 2022, the number of adults living with their parents rose by 19 per cent. That’s a change of 83,008. Irish people between the ages of 25 and 34 are over 3 times more likely to live with their parents than Germans of the same age. Seomraí could help our young people get their start by providing affordable accommodation.

A sixth benefit of seomraí is that they can help accommodate carers. A seomraí policy could enable the implementation of the National Housing Strategy for Disabled People 2022-2027. That strategy highlights the goal that people with disabilities should be enabled to live independently. According to a 2018 study, 84 per cent of families with a disabled relative in the United States would consider building an ADU. A RIAI and AOTI report sketches out how detached or attached granny flats could be used to enable people with disabilities to live independently here in Ireland.  

Affordable housing for carers is increasingly necessary as the population ages. Seomraí can provide cost-effective living spaces for carers, supporting the essential role they play in our society.

A sixth benefit of seomraí is that they can help accommodate carers. A seomraí policy could enable the implementation of the National Housing Strategy for Disabled People 2022-2027. That strategy highlights the goal that people with disabilities should be enabled to live independently. According to a 2018 study, 84 per cent of families with a disabled relative in the United States would consider building an ADU. A RIAI and AOTI reportsketches out how detached or attached granny flats could be used to enable people with disabilities to live independently here in Ireland.  

Affordable housing for carers is increasingly necessary as the population ages. Seomraí can provide cost-effective living spaces for carers, supporting the essential role they play in our society.