What Percentage of New Builds Have to Be Social Housing?

The question “what percentage of new builds have to be social housing?” sounds simple, but the real answer is more complex. There is usually no single national percentage that applies to every new development. Instead, social and affordable housing numbers are set through planning policy, local targets, and site-by-site negotiations.

This guide explains how those percentages are decided, why they differ between places, and what you should look at if you are a developer, landowner, housing provider, or interested resident.

Why there is no single fixed percentage for social housing

Many people expect a clear rule, such as “30% of all new homes must be social housing.” In most countries, that kind of simple national rule does not exist. Even where national guidance exists, local planning authorities usually set their own targets based on local need and viability.

Percentages also change over time. Governments revise planning rules, local plans are updated, and housing markets rise and fall. A figure you read in a news article may only apply to one city, one policy period, or one type of site.

To understand what percentage of new builds have to be social housing in a specific case, you need to look at three layers: national policy, local planning policy, and the details of the individual site.

How planning policy shapes social housing percentages

Social and affordable housing on new sites is usually secured through the planning system. The key idea is that developers get permission to build more valuable private homes, and in return must include some homes that are affordable or social rent.

Governments often set broad rules or expectations in national planning frameworks. These rules may define what counts as “affordable,” encourage mixed communities, and say that local authorities should set clear targets.

Local authorities then translate those expectations into their own local plans. A local plan might say that “major” developments should provide a set percentage of affordable housing, subject to viability and other planning considerations.

What “social housing” means in percentages and policies

Before asking what percentage of new builds have to be social housing, it helps to understand how housing types are grouped in policy language. Many policies use the wider term “affordable housing,” which can include several tenures, not just classic social rent.

Common categories include:

• Social rent: usually the lowest rent level, managed by councils or non-profit landlords.
• Affordable rent: rent set below market, but often higher than social rent.
• Intermediate housing: for example shared ownership or discounted market sale.
• Low-cost market products: homes sold at a discount to local buyers, subject to rules.

When a policy says “40% affordable housing,” that 40% might be a mix of these types. Only part of that 40% may be true social housing. The exact mix is usually set in the local plan or negotiated on each site.

Key factors that decide the percentage on a specific site

The percentage of new builds that must be social or affordable housing is rarely a simple yes/no rule. Planners and developers look at a set of factors, then agree a level that is policy-compliant and financially workable.

The main drivers are usually:

Local housing need, land values, build costs, site conditions, and policy priorities all interact. A high-need, high-value city might push for a higher percentage, while a lower-value area may set a lower target so schemes remain viable.

Typical policy targets and why they vary so widely

Because I cannot give live or exact figures for every country or city, think of social and affordable housing percentages as lying on a spectrum. At one end, some places have no set percentage at all, relying on case-by-case deals. At the other, some cities or regions set strong targets for large sites.

In practice, local targets can differ based on:

Some areas also set different targets for different kinds of sites. For example, higher percentages on greenfield extensions and lower percentages on small brownfield infill sites, where costs are higher or risks are greater.

How “viability” can change the required percentage

Even where a local plan sets a clear percentage, the final number of social or affordable homes can change after a viability assessment. Viability is the test of whether a development can still go ahead with the required contributions.

Developers often provide a financial model showing expected costs and revenues. This model includes land value, construction costs, finance, planning obligations, and expected sales prices or rents. If the model shows that the policy percentage would make the scheme unbuildable, the developer may ask for a lower share of affordable or social housing.

Planners then review that evidence. Sometimes they accept a lower percentage, sometimes they challenge the assumptions, or ask for different forms of contribution, such as off-site homes or payments in lieu.

Answering the core question: what percentage of new builds have to be social housing?

For search purposes, many people want one short line that answers “what percentage of new builds have to be social housing?” In reality, the honest answer is: there is usually no single fixed percentage that applies everywhere, and the share of social housing within any affordable housing requirement can vary even more.

However, you can still get a clear answer for a specific place and site by following a simple process. The steps below will help you find the relevant percentage in your area and check how much of that might be true social housing.

Practical steps to find the percentage in your area

If you are a developer, resident, or student, you can work out the likely percentage for a given site by checking a few core documents. This ordered list gives a simple process you can follow.

1. Identify the planning authority: Find which local council or planning body covers the site or area you care about.
2. Read the local plan policy on affordable housing: Search the local plan or development plan for “affordable housing” or “housing mix” to see any stated percentage targets.
3. Check if the policy distinguishes social rent: Look for text that splits the affordable requirement into social rent, affordable rent, and intermediate products.
4. Look for thresholds and site types: See whether the percentage only applies above a certain number of homes, or whether different zones have different targets.
5. Review any supplementary guidance: Some authorities publish extra guidance that explains how they will apply the policy in practice.
6. Search for recent committee reports: Planning committee reports for similar nearby schemes can show how the policy has been applied and negotiated.
7. Check for viability caveats: Note any policy wording such as “subject to viability” or “unless demonstrated to be unviable,” which signals that the percentage can change.
8. Contact the planning officer if needed: For a live project, speak to the case officer or pre-application team to confirm how they interpret the policy.

By following these steps, you move from a vague national question to a clear, local, and site-specific answer that reflects real planning practice.

Why some developments provide no social housing at all

People are often surprised to see new blocks of flats or estates with no visible social housing element. This can happen even where a local plan has clear percentage targets for affordable homes.

Common reasons include small schemes that fall below the threshold for contributions, viability arguments that reduce the requirement to zero, or off-site provision where the affordable homes are built on a different site. In some planning systems, developers can also pay a sum of money instead of building affordable units on the main site.

Policy makers debate these approaches. Some argue that flexibility keeps development going and still funds some social housing. Others argue that too much flexibility weakens mixed communities and fails to meet local need.

How future policy changes could affect percentages

Housing policy is politically sensitive, so rules around social and affordable housing on new builds can change. Governments can adjust definitions, introduce new products, or change how viability is tested.

Local authorities also update their plans on multi-year cycles. A new local plan may raise or lower the target percentage, or change the balance between social rent, affordable rent, and intermediate homes.

If you work on long projects, such as large sites built in phases, you should track these policy changes. A scheme agreed under one policy framework may face new expectations if later phases need fresh planning permissions.

Using the question well: from headline percentage to real impact

Asking “what percentage of new builds have to be social housing” is a useful starting point, but the headline figure tells only part of the story. The social impact depends on how much of the affordable share is true social rent, who can access the homes, and whether they are integrated on site.

For campaigners and residents, understanding the policy detail helps you ask better questions and respond effectively to consultations. For developers and landowners, early clarity on affordable housing expectations helps you price land, plan design, and avoid late surprises.

The key is to move from the idea of one national rule to a clear grasp of local policy, viability, and tenure mix. Once you do that, the percentage of new builds that have to be social housing in your specific context becomes much easier to understand and to explain.