Building Society Guarantor & Family Assist Mortgages: UK Options, Eligibility and Risks
A building society guarantor mortgage can help someone buy a home when their income or deposit is not enough to meet ordinary mortgage criteria. A parent, grandparent or another eligible relative may support the application using their income, savings or property equity.
But a guarantor mortgage, Joint Borrower Sole Proprietor (JBSP) mortgage and family-assisted deposit mortgage are not the same thing. The person helping may take on repayment liability, temporarily restrict their savings or put equity in their own home at risk.
This guide explains the differences, identifies current UK lender routes and shows what both the buyer and the supporting family member should check before applying.
Editorial research reviewed: 13 October 2026. UK mortgage products, rates, fees, eligibility rules and lending criteria can change. This website does not provide personalised mortgage or legal advice.
Guarantor & Family Assist Mortgages: Quick Answers
What Is a Building Society Guarantor Mortgage?
A guarantor mortgage is a home loan where another person agrees to support the borrower’s obligations. If the borrower cannot meet the required payments, the guarantor may become responsible under the terms of the guarantee.
Historically, parents often helped younger buyers by guaranteeing part or all of their mortgage. Today, lenders also offer different structures that use family income, savings or property equity without necessarily creating a traditional personal guarantee.
Guarantor vs JBSP vs Family Assist Mortgage
Before comparing mortgage rates, establish the type of family assistance required. Different arrangements solve different problems and expose supporters to different risks.
UK Building Societies Offering Family-Assisted Mortgage Options
Family Building Society currently publishes both a Family Mortgage supported by savings or property security and Joint Borrower Sole Proprietor arrangements. Other lenders may offer related structures with different eligibility and liability rules.
Its Family Mortgage can support qualifying buyers through family savings, property equity or both. The Society also offers JBSP arrangements using eligible family income.
Its published Family Mortgage range includes borrowing up to 100% LTV with qualifying additional security.
Official family-assisted mortgage optionsIts JBSP arrangement can use income from supporting family members while keeping property ownership with the intended owner-occupying borrower.
The Society publishes arrangements involving up to four incomes, subject to its criteria.
Official JBSP mortgage informationAlthough Barclays is a bank rather than a building society, its Family Springboard mortgage provides a useful UK comparison for savings-backed family assistance.
Its published arrangement allows eligible buyers to borrow without their own deposit when a helper provides qualifying savings equal to 10% of the property’s purchase price.
Official Family Springboard detailsOfficial building societyFamily Building Society Family-Assisted Mortgages
After opening this link:
- Find the Family Mortgage and Joint Borrower Sole Proprietor sections.
- Choose whether the intended assistance is a family security contribution or additional qualifying income.
- Read the property, deposit and borrower eligibility information.
- Open the current product details and review the available rates and fees.
- Use the Society’s mortgage adviser or approved intermediary route to check individual circumstances.
Official comparisonBarclays Family Springboard Mortgage
After opening this link:
- Read the separate information for home buyers and family helpers.
- Check the amount of savings the helper must provide.
- Review the restrictions on the linked savings account.
- Check the conditions for receiving savings back.
- Compare this bank product with building society options before deciding which support structure is appropriate.
Family Building Society Family Mortgage: How the Security Works
Family Building Society offers a Family Mortgage intended to help qualifying buyers who have limited savings for a conventional deposit.
Under its current published arrangement, family members can provide qualifying security through savings, equity in their property or a combination. This can allow a buyer to obtain a mortgage without providing a conventional cash deposit.
Example: Buying a £250,000 Home
Suppose an eligible buyer wants to purchase a property costing £250,000 but has no cash deposit. Under an arrangement requiring additional family security equivalent to 20% of the purchase price, the supporting family would need to provide qualifying security of £50,000.
When is family security released?
Family Building Society’s published Family Mortgage terms describe conditions for releasing family security at the end of the relevant fixed-rate arrangement, including payment-history and other requirements.
Do not assume that security will be released automatically after a certain number of years. Check the current mortgage offer, security agreement and release conditions carefully.
Official lender FAQsFamily Building Society Family Mortgage FAQs
After opening this link:
- Read how many family members can provide support.
- Check how savings and property security are treated.
- Find the conditions for releasing family security.
- Read what happens if the borrower misses payments or the property falls in value.
- Review the independent legal advice requirements for each supporter.
Joint Borrower Sole Proprietor Mortgages: Helping With Income
A Joint Borrower Sole Proprietor mortgage allows someone to become a borrower on the mortgage without necessarily becoming a legal owner of the property.
For example, a parent may join a mortgage application so the lender can consider the parent’s income alongside the child’s earnings. The child remains the property owner, while the parent takes on contractual mortgage obligations.
Potential advantages
- Additional eligible family income may improve affordability.
- The intended homeowner can remain the sole property owner.
- It can help when the buyer has a deposit but insufficient qualifying income.
- Some schemes allow several income sources to be considered.
- May avoid making the parent a registered property owner.
Potential disadvantages
- Supporting borrowers may be responsible for the mortgage debt.
- The commitment may reduce the parent’s future borrowing capacity.
- The lender may check the parent’s age, income and credit obligations.
- The parent may remain liable until formally released by the lender.
- A relationship breakdown can make changes more difficult.
What does “sole proprietor” actually mean?
It refers to ownership of the property, not necessarily the number of borrowers responsible for the mortgage.
The legal homeowner and the supporting borrower must understand the difference between mortgage liability and ownership rights. A parent can take on a significant debt obligation without obtaining an ownership share in the child’s home.
Official JBSPFamily Building Society JBSP Mortgage
After opening this link:
- Read how the mortgage separates borrowers from property owners.
- Check which family relationships are accepted.
- Review the maximum number of borrowers and income sources.
- Check how affordability and retirement income are assessed.
- Ask how a supporting borrower can be removed in future and what conditions apply.
Gifted Deposit vs Family Security Savings
Parents who want to help with a first home often assume that giving money for the deposit is the only option. However, some mortgage products allow supporters to retain ownership of savings while making those funds available as security.
Building Society Guarantor Mortgage Eligibility
Neither family support nor substantial savings automatically guarantees approval. The lender must assess the buyer, property and supporting family members under its underwriting criteria.
Can retired parents act as guarantors?
Potentially, but the lender must be satisfied that their financial circumstances meet the relevant criteria.
Retirement income, the supporter’s age, existing borrowing and the product’s maximum mortgage term may all matter. Parents should also consider how supporting a child’s mortgage might affect their own retirement plans and future need for funds.
Family-Assisted Mortgage Examples and Costs
The following calculations show why buyers need to distinguish mortgage affordability from the availability of family security.
Example 1: A Family-Assisted 100% Mortgage
A first-time buyer purchases a £240,000 property. A qualifying family-assisted product allows the buyer to borrow the full purchase price when sufficient additional family security is provided.
The buyer must still qualify for the £240,000 mortgage through the lender’s underwriting process. Additional costs such as conveyancing, surveys, moving expenses and any applicable property purchase taxes also need to be funded.
Example 2: How Monthly Repayments Could Compare
Assume a £240,000 repayment mortgage over 30 years at a hypothetical fixed rate of 5% throughout the period.
Figures are rounded mathematical illustrations using a constant 5% annual rate and standard monthly repayment assumptions. They are not current lender quotations and exclude fees, insurance and future rate changes.
Example 3: What if the Property Falls in Value?
Suppose a buyer has a £240,000 mortgage and the property later falls in value to £210,000. If the outstanding mortgage is still £230,000, the borrower has approximately £20,000 of negative equity.
If the borrower defaults and the property is sold, a lender may seek to recover an eligible shortfall through the agreed family security arrangements. The exact exposure depends on the mortgage contract and security agreement.
Risks for Parents and Family Guarantors
Helping a child onto the property ladder can be valuable, but family-assisted borrowing should be treated as a serious legal and financial commitment.
Documents Needed for a Guarantor or Family-Assisted Mortgage
Lenders and conveyancers commonly require information from both the buyer and the supporting family member.
Documents for the buyer
- Passport or other accepted identification.
- Proof of current address.
- Recent payslips or self-employed income evidence.
- Recent bank statements.
- Deposit and savings evidence.
- Details of existing debts and monthly commitments.
- Property purchase information.
- Gifted-deposit declaration where relevant.
Documents for the supporter
- Identity and address evidence.
- Proof of income if joining the mortgage or acting as guarantor.
- Evidence of savings offered as security.
- Existing mortgage statement where property security is involved.
- Property ownership and valuation information if requested.
- Details of other financial obligations.
- Security and legal documents required by the lender.
- Evidence of independent legal advice where applicable.
Official consumer guidanceMoneyHelper: How to Apply for a Mortgage
After opening this link:
- Read the mortgage application stages.
- Review the list of identity, income and deposit documents.
- Check the guidance for self-employed applicants if applicable.
- Prepare evidence of gifted funds or family assistance.
- Ask the lender or adviser which additional documents the supporting relative must provide.
How to Apply for a Building Society Family-Assisted Mortgage
The correct application process depends on the family support arrangement. Applying for a traditional mortgage before explaining the family contribution can lead to unnecessary delays.
- Identify the problem. Decide whether the buyer needs help with affordability, deposit requirements or both.
- Choose a possible structure. Compare a guarantor arrangement, JBSP, savings-backed security, property-backed support and gifted deposit.
- Discuss the commitment. The family member should decide what level of support they can realistically afford.
- Check eligibility. Review the lender’s income, age, property, deposit and family relationship rules.
- Speak with a regulated adviser. Explain the buyer’s circumstances and the proposed family assistance.
- Prepare documents. Collect the income, deposit, savings, identity and property evidence requested.
- Obtain a Decision in Principle if appropriate. Remember that this is not a guaranteed mortgage offer.
- Review the mortgage illustration. Compare interest rate, APRC, fees, monthly repayments and total borrowing costs.
- Obtain independent legal advice. Each supporting family member should understand their liability and release conditions before signing.
- Complete the lender’s checks. Follow the valuation, underwriting and conveyancing process.
- Keep records. Retain the signed mortgage, security and family support documents.
- Plan for future release. Understand what must happen before the supporter’s obligation ends.
Official FCA verificationCheck Whether a Mortgage Firm or Adviser Is Authorised
After opening this link:
- Use the FCA’s authorised-firm checking service.
- Search for the lender, mortgage broker or advice firm.
- Confirm that the firm has appropriate permissions for the proposed service.
- Check whether the adviser is an appointed representative of another authorised firm.
- Verify contact details independently before submitting sensitive financial information.
Stamp Duty, Ownership and Legal Issues
Family-assisted mortgages can affect legal ownership, tax treatment and inheritance arrangements. These issues depend on the country where the property is located and the exact structure.
Joint Borrower Sole Proprietor and Property Ownership
A supporting parent on a JBSP mortgage is not necessarily a legal owner. This may be significant when considering higher-rate property transaction taxes and first-time buyer relief.
However, avoiding registration on the property title does not automatically settle all legal, tax or beneficial-ownership questions. The solicitor must examine the actual arrangements.
Gifted Deposits
A genuine gifted deposit normally requires confirmation that the giver does not expect repayment and will not acquire an ownership interest through the gift.
If the family expects the money to be repaid, describe it honestly as a proposed loan and check whether the lender accepts that arrangement. A repayable family loan can affect affordability and may not be acceptable as a deposit.
UK Property Tax Differences
Official UK tax sourceGOV.UK Stamp Duty Land Tax Guidance
After opening this link:
- Confirm that the property is in England or Northern Ireland.
- Read the current purchase-price thresholds and reliefs.
- Check whether any buyer owns another residential property.
- Review additional-property rules if applicable.
- Ask the conveyancer to calculate the final SDLT liability using the current rules.
Alternatives to a Guarantor Mortgage
Family members should consider whether they can help without taking on long-term mortgage liability or placing their own home at risk.
Official MoneyHelperMoneyHelper: Understanding 100% Mortgages
After opening this link:
- Read how no-deposit mortgages work.
- Check the differences between family-backed and other eligibility routes.
- Review the negative-equity risks.
- Compare mortgage repayments with your current housing costs.
- Remember to budget separately for legal fees, surveys and moving expenses.
What Happens if the Borrower Cannot Pay?
The outcome depends on the mortgage and security agreement. A payment difficulty does not automatically mean that a family supporter will immediately lose their savings or property, but it may activate contractual rights and obligations.
Before Agreeing to Help: Family Checklist
Related Building-Society.org Guides
For more background on lenders and their mortgage services, use these published guides.
Official Sources and Further Reading
These official resources explain family-assisted lending, guarantor obligations and mortgage applications. Always confirm current product terms with the lender.
Independent Financial Information and Safety Notice
Building-society.org is an independent informational website. It is not Family Building Society, Barclays, a mortgage lender, mortgage intermediary, financial adviser or the Financial Conduct Authority.
This article provides general information about UK mortgage arrangements. It does not assess personal affordability, legal liability, tax circumstances or the suitability of a particular product.
Mortgage rates, lending criteria, fees, deposit requirements, maximum LTV and product availability can change. Any example calculation is illustrative and not a mortgage quotation.
Editorial review: 13 October 2026. The article is based on publicly available lender, MoneyHelper, FCA and government guidance. Confirm all current mortgage terms directly with official sources.
Building Society Guarantor Mortgage FAQs
1. What is a building society guarantor mortgage?
A guarantor mortgage is a home loan supported by another person who agrees to take on specified repayment obligations if the borrower cannot meet them. The exact liability depends on the mortgage agreement.
2. Can my parents help me get a mortgage without giving me money?
Yes. Depending on the lender, parents may support a mortgage through their income, savings pledged as security or equity in their property. The arrangement can involve financial risk even when no money is given away permanently.
3. Which building societies offer family-assisted mortgages?
Family Building Society currently publishes Family Mortgage and Joint Borrower Sole Proprietor arrangements. Other lenders may offer related products, but eligibility, rates and security requirements vary.
4. Can I get a 100% mortgage with family support?
Some specialist products allow eligible borrowers to borrow up to 100% of the property’s purchase price if suitable additional family security is provided. The buyer must still pass affordability and other mortgage checks.
5. Is a guarantor mortgage the same as a JBSP mortgage?
No. A traditional guarantor accepts specified guarantee obligations. Under a Joint Borrower Sole Proprietor mortgage, the supporter becomes a borrower on the mortgage but does not necessarily become a legal owner of the property.
6. Can retired parents act as mortgage guarantors?
Potentially. Lenders may consider their retirement income, age, existing mortgage, financial commitments and the specific support required. Approval is not guaranteed merely because the parents own property.
7. Can parents lose their house if they guarantee a mortgage?
There can be serious financial consequences. Where a parent’s home is used as security, a legal charge may expose that property to enforcement risk. The exact consequences depend on the agreement and the borrower’s mortgage performance.
8. How long are family savings held as mortgage security?
The period depends on the product and its release conditions. Some arrangements are linked to a fixed-rate period or specified repayment history. Savings should not be assumed available for withdrawal until the lender confirms release.
9. Can a parent be removed from a JBSP mortgage later?
Possibly, but the lender must agree. It may reassess whether the remaining borrower can afford the mortgage alone and whether the proposed change meets its underwriting criteria.
10. Do guarantors and supporting family members need legal advice?
Independent legal advice is strongly recommended and can be required by the lender. Supporting relatives should understand their obligations, maximum exposure, enforcement risks and the conditions for ending the arrangement before signing.