Can you claim Multiple Dwellings Relief on a Welsh home purchase with an attached flat?

Introduction

Buyers often ask whether Land Transaction Tax relief is available when they are buying a main home in Wales that includes a separate flat or annexe. This question commonly arises where the main house will be occupied by the buyer, while the additional unit is self-contained or already let to a tenant.

The difficulty is that Welsh rules on Multiple Dwellings Relief (MDR) changed in 2025. In some cases, a buyer who might previously have expected to claim MDR may now need to consider the Subsidiary Dwellings Exception (SDE) instead. The two reliefs no longer work together, so the tax result depends on which set of rules applies and which produces the lower charge.

The Question

A buyer is moving to Wales and purchasing a property consisting of a main house and a separate attached flat. The house will be the buyer’s only or main residence, and the flat will have a sitting tenant at completion. The buyer wants to know whether MDR can be claimed and, if so, how the Land Transaction Tax should be calculated.

Nick’s Explanation

Nick’s explanation was that the buyer needs to be careful because the Welsh rules changed in 2025. He noted that where the Subsidiary Dwellings Exception applies, MDR is no longer available for the same transaction.

In anonymised form, his key point was:

“As of 2025, the Welsh Government has changed the rules regarding MDR. Under the new regulations, MDR can no longer be claimed at the same time as the Subsidiary Dwellings Exception. This means that if the purchase qualifies for SDE, you will not be able to claim MDR. You will need to decide which option provides the better tax outcome.”

He then illustrated the point with an example using a total purchase price of £500,000, split between a main house worth £375,000 and a flat worth £125,000.

On that example:

• if MDR were used and the higher residential rates applied, the tax would be £29,900; and
• if SDE applied so that the purchase was taxed at the main residential rates, the tax would be £18,000.

The example shows why the interaction between MDR and SDE matters in Wales. Even where there are two dwellings, MDR is not automatically the best or available route.

The Law

Land Transaction Tax in Wales is charged under the Land Transaction Tax and Anti-avoidance of Devolved Taxes (Wales) Act 2017.

MDR is a relief that can apply where a transaction includes more than one dwelling. Broadly, the total consideration is divided by the number of dwellings, tax is calculated on that average price, and the result is then multiplied back up. Historically, this could reduce the overall tax bill.

Separate rules deal with the purchase of a main dwelling that also includes a subsidiary dwelling, such as a granny annexe or attached flat. Where the conditions for the Subsidiary Dwellings Exception are met, the transaction may be treated more favourably for higher-rates purposes.

In Wales, the rules were modified so that MDR and SDE cannot both be claimed on the same transaction. That means a buyer must first consider whether the purchase falls within the subsidiary dwelling rules and then compare the available tax treatment under the current Welsh legislation.

Whether there are genuinely two dwellings is a factual and legal question. A unit normally needs sufficient facilities for independent residential use, such as sleeping, washing and cooking accommodation, and a degree of physical and functional separation.

If a buyer argues that part of a property was uninhabitable or not suitable for use as a dwelling, it is important to note that the threshold is now relatively high following Amarjeet and Tajinder Mudan v The Commissioners for HMRC [2025] EWCA Civ 799. Mere disrepair, dated condition, or a need for improvement will often not be enough.

Analysis

The analysis usually involves four steps.

1. First, identify whether the property contains more than one dwelling.

   An attached flat with its own facilities and a sitting tenant will often point strongly towards there being a separate dwelling. The exact facts still matter, including layout, access and the degree of independence.

2. Second, consider whether the subsidiary dwelling rules apply.

   Where a buyer is acquiring a main residence together with a smaller additional dwelling, the SDE may be relevant. This can be especially important where the buyer is not purchasing an additional property as an investment or second home, but a single overall property that includes a subsidiary unit.

3. Third, apply the Welsh 2025 rule change.

   If SDE applies, MDR is no longer available for that same purchase. So the question is not simply whether there are two dwellings, but whether the transaction falls into the SDE regime instead.

4. Fourth, calculate the tax under the correct route.

   Using Nick’s example figures:

   • Total price: £500,000
   • Main house: £375,000
   • Flat: £125,000

   If MDR were available and the higher residential rates applied, the average price per dwelling would be £250,000. Tax on £250,000 at the higher residential rates would be £14,950, and multiplied by two dwellings gives £29,900.

   If SDE applied, the transaction would instead be taxed as a single purchase at the main residential rates. On £500,000, that gives £18,000.

   On those figures, SDE produces the lower tax result.

This means that a buyer in this type of situation should not assume that claiming MDR is the correct answer merely because the property includes a separate flat.

Outcome

For a Welsh purchase of a main home with an attached flat, the buyer may well be dealing with the Subsidiary Dwellings Exception rather than MDR. Since the Welsh changes in 2025, MDR and SDE cannot be used together. If SDE applies, MDR is not available.

In a case like the example given, SDE can produce a significantly lower Land Transaction Tax charge than MDR.

Practical Steps

A buyer should take the following steps before the return is filed:

• confirm whether the attached unit is genuinely a separate dwelling in law and fact;
• check whether the transaction falls within the subsidiary dwelling rules;
• compare the tax position under the current Welsh rules rather than assuming MDR is available;
• give full details of the layout, facilities, occupation and value split to the conveyancer preparing the Land Transaction Tax return;
• keep evidence such as floor plans, tenancy documents, sales particulars and any valuation material showing the relative value of each unit; and
• if any argument is being made that part of the property is not suitable for use as a dwelling, test that carefully against the high threshold confirmed in Amarjeet and Tajinder Mudan v The Commissioners for HMRC [2025] EWCA Civ 799.

Conclusion

Where a buyer in Wales is purchasing a main residence with an attached flat, the key issue is no longer simply whether there are two dwellings. The buyer must also consider whether the Subsidiary Dwellings Exception applies, because under the 2025 Welsh changes that will prevent a simultaneous MDR claim. In many cases, SDE may be the more favourable result.

Legal References Used

• Land Transaction Tax and Anti-avoidance of Devolved Taxes (Wales) Act 2017
• Welsh rules modifying Multiple Dwellings Relief and the Subsidiary Dwellings Exception from 2025
• Amarjeet and Tajinder Mudan v The Commissioners for HMRC [2025] EWCA Civ 799

This page was last updated on 22 March 2026.

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