Process: 329/2015-T

Date: November 11, 2015

Tax Type: Selo

Source: Original CAAD Decision

Summary

Process 329/2015-T addresses the critical question of stamp duty application under Verba 28.1 TGIS to vertical property ownership. The dispute centers on whether the €1,000,000 threshold applies to the total property value or individual floors. Applicants A and B, co-owners of a building with 17 independently-usable floors (each with PTU below €1,000,000 but collectively exceeding this threshold), argued that stamp duty should only apply when individual units reach €1,000,000. They contended that vertical property should follow IMI rules treating each independent unit separately, analogous to horizontal property (condominium) regimes, and claimed the alternative interpretation violates constitutional equality principles. The Tax Authority countered that vertical property constitutes a single juridical unit despite multiple floors, distinguishing it from autonomous condominium fractions. The Authority argued that Verba 28.1 TGIS applies based on total registered patrimonial value, not individual floor valuations, and that accepting the applicants' interpretation would contravene the legal framework and the principle of tax legality under Article 103(2) CRP. The CAAD arbitral tribunal accepted jurisdiction based on Article 3(1) RJAT, finding proper cumulation of claims given identical factual matrices, same tax type, and common legal interpretation questions. This case establishes important precedent regarding stamp duty application to complex property ownership structures and the relationship between IMI and stamp duty assessment methodologies.

Full Decision

ARBITRAL DECISION

REPORT

A… and B…, taxpayers no. … and no. …, respectively, co-owners in the proportion of ½ and 1/6, submitted on 26/05/2015 a request for arbitral pronouncement, in which they request the annulment of the acts of assessment of stamp duty concerning the year 2014.

The Honorable President of the Deontological Council of the Administrative Arbitration Center (CAAD) appointed on 23/07/2015 as arbitrator, Francisco Nicolau Domingos.

On 10/08/2015 the arbitral tribunal was constituted.

In compliance with the provision of art. 17, no. 1 of Decree-Law no. 10/2011, of 20 January (RJAT) the Respondent was notified on 17/08/2015 to, if willing, present a response and request the production of additional evidence.

On 29/09/2015 the Respondent presented its response and requested the dispensing of the meeting referred to in art. 18 of RJAT, as well as the presentation of arguments.

The Applicants on 21/10/2015 presented a request in which they request the dispensing of the aforementioned meeting, as well as arguments.

The tribunal, on 22/10/2015 decided, namely, to dispense with the holding of the meeting to which art. 18, no. 1 of RJAT refers, on the grounds of the principle of autonomy of the arbitral tribunal in conducting the proceedings and in determining the rules to be observed with a view to obtaining, in reasonable time, a pronouncement on the merits of the claims formulated, cfr. art. 16, al. c) of RJAT and scheduled a date for the pronouncement of the final decision.

PROCEDURAL CLEANNESS

The accumulation of claims and of claimants underlying the present proceedings is admissible, inasmuch as it concerns assessment acts of the same tax, stamp duty. As the identity between the matter of fact is also verified and the appropriateness of the claim depends on the interpretation of the same principles and rules of law, cfr. art. 3, no. 1 of RJAT.

The proceedings do not suffer from any nullities, no questions have been raised that prevent the examination of the merits of the case, the arbitral tribunal is regularly constituted and materially competent to hear and decide the claim, consequently, the conditions are verified for the pronouncement of the final decision.

  1. SUBJECT MATTER OF THE DISPUTE

The Applicants consider that the assessments of stamp duty – item 28.1 of the General Table of Stamp Duty (TGIS) and concerning the year 2014 are illegal.

In concrete terms, they argue, preliminarily, that the subjection to stamp duty of item 28.1 of TGIS is determined by residential use and from the PTU appearing in the property registry of an amount equal to or greater than € 1,000,000.

In their argumentative framework are found the following: i) the regime contained in the aforementioned item is silent as to its own rules for the definition and determination of its taxable basis and that, therefore, it orders the application of the taxable basis provided for in the IMI, the PTU appearing in the property registry; ii) the stamp duty of item 28.1 of TGIS has the nature of an accessory tax to the IMI and, as such, is assessed on the same taxable matter of the principal tax; iii) among the aspects that are omitted in the regime of stamp duty, stands out that of the relevance and autonomous tax treatment of each floor or division of the property susceptible of independent use and iv) according to the CIMI, as a result of such omission, when the parties are economically independent, each one is assessed by application of the corresponding rules (art. 7, no. 2, al. b) of CIMI). Therefore, they conclude that, if the PTU of any one of the fifteen residential units appearing in the property registry of the property to which these proceedings refer is less than € 1,000,000, stamp duty of item 28.1 of TGIS does not apply to the same.

They further invoke that, as the concentration or dispersal of real property is not a criterion of tax capacity or any other legitimate criterion of taxation, it is necessary to conclude that the incidence norm of item 28.1 of TGIS is unconstitutional, for violation of the principle of equality, provided for in art. 13 of CRP.

For its part, the Respondent states that the subjection to stamp duty of item 28.1 of TGIS results from the combination of two elements, residential use and the value of the urban property registered in the property registry being equal to or greater than € 1,000,000.

Thus, it argues that if the Applicants are co-owners of a property under the regime of full or vertical ownership, this does not have autonomous fractions, to which tax law attributes the qualification of property. In this way, it observes that they are not co-owners of 17 autonomous fractions, but of a single property and, as such, the defect attributed to the acts in crisis is not verified.

To support such conclusion, it adds that: i) the objective of the Applicants that consists in considering that there is analogy between the regime of horizontal ownership and that of vertical ownership, is illegal; ii) there is no lacuna whatsoever as to the matter in tax law, as CIMI determines that, the property not being subject to the regime of horizontal ownership, the fractions are parts susceptible of independent use, without there being common parts; iii) although each floor or part susceptible of independent use is considered separately in the property registry registration, by virtue of art. 12, no. 3 of CIMI, the truth is that such occurs in the same registry; iv) the unity of the property in vertical ownership, composed of various floors or divisions, is not affected by the fact that all or part of them are susceptible of independent economic use and v) if such property does not cease to be only one, its distinct parts cannot be juridically equated to autonomous fractions in the regime of horizontal ownership.

The Respondent equally argues that the fact that the IMI is calculated according to the PTU of each part of property with independent use does not also affect the application of item 28.1 of TGIS, inasmuch as the determining element of this is the total patrimonial value and not separately each one of the portions.

It concludes that a different interpretation would violate the letter and spirit of item 28.1 of TGIS and the principle of legality of essential elements of the tax, provided for in art. 103, no. 2 of CRP. That is, that interpretation which argues that the patrimonial value upon which incidence depends should be determined globally and not floor by floor or division by division.

  1. FACTUAL MATTERS

4.1. FACTS CONSIDERED PROVEN

4.1.1. The Applicants are co-owners of the immovable property to which corresponds the property registry registration no. …, urban, parish of … (…), Lisbon, in the proportion of ½ and 1/6, respectively.

4.1.2. Such immovable property comprises 17 floors with independent use, registered as follows:

a) 1st Floor, with a PTU of € 94,430.00, residential;

b) 2nd Floor, with a PTU of € 94,430.00, residential;

c) 3rd Floor, with a PTU of € 95,380.00, residential;

d) 4th Floor, with a PTU of € 95,380.00, residential;

e) 5th Floor, with a PTU of € 96,320.00, residential;

f) 6th Floor, with a PTU of € 96,320.00, residential;

g) 7th Floor, with a PTU of € 78,640.00, residential;

h) 8th Floor, with a PTU of € 33,540.00, residential;

i) 1st E, with a PTU of € 119,290.00, residential;

j) 2nd E, with a PTU of € 119,290.00, residential;

l) 3rd E, with a PTU of € 120,480.00, residential;

m) 4th E, with a PTU of € 120,480.00, residential;

n) 5th E, with a PTU of € 121,680.00, residential;

o) 6th E, with a PTU of € 121,680.00, residential;

p) 7th E, with a PTU of € 95,740.00, residential;

q) 166 A, with a PTU of € 170,140.00, warehouses and industrial activity;

r) 166 C, with a PTU of € 235,540.00, commerce.

4.1.3. The Applicants were notified of the stamp duty assessments, relating to the year 2014, in relation to each one of such property registry registrations, with residential use, in the global amount of € 10,020.54 and which are broken down as follows:

i) A…:

a) 1st Floor, in the amount of € 472.15;

b) 2nd Floor, in the amount of € 472.15;

c) 3rd Floor, in the amount of € 476.90;

d) 4th Floor, in the amount of € 476.90;

e) 5th Floor, in the amount of € 481.60;

f) 6th Floor, in the amount of € 481.60;

g) 7th Floor, in the amount of € 393.20;

h) 8th Floor, in the amount of € 167.70;

i) 1st E, in the amount of € 596.45;

j) 2nd E, in the amount of € 596.45;

l) 3rd E, in the amount of € 602.40;

m) 4th E, in the amount of € 602.40;

n) 5th E, in the amount of € 608.40;

o) 6th E, in the amount of € 608.40;

p) 7th E, in the amount of € 478.70.

ii) B…:

a) 1st Floor, in the amount of € 157.38;

b) 2nd Floor, in the amount of € 157.38;

c) 3rd Floor, in the amount of € 158.97;

d) 4th Floor, in the amount of € 158.97;

e) 5th Floor, in the amount of € 160.53;

f) 6th Floor, in the amount of € 160.53;

g) 7th Floor, in the amount of € 131.07;

h) 8th Floor, in the amount of € 55.90;

i) 1st E, in the amount of € 198.82;

j) 2nd E, in the amount of € 198.82;

l) 3rd E, in the amount of € 200.80;

m) 4th E, in the amount of € 200.80;

n) 5th E, in the amount of € 202.80;

o) 6th E, in the amount of € 202.80;

p) 7th E, in the amount of € 159.57.

4.1.4. The Applicants made the following payments on 24/04/2015:

i) A…:

a) 1st Floor, in the amount of € 236.08;

b) 2nd Floor, in the amount of € 236.08;

c) 3rd Floor, in the amount of € 238.45;

d) 4th Floor, in the amount of € 238.45;

e) 5th Floor, in the amount of € 240.80;

f) 6th Floor, in the amount of € 240.80;

g) 7th Floor, in the amount of € 196.60;

h) 8th Floor, in the amount of € 167.70;

i) 1st E, in the amount of € 198.83;

j) 2nd E, in the amount of € 198.83;

l) 3rd E, in the amount of € 200.80;

m) 4th E, in the amount of € 200.80;

n) 5th E, in the amount of € 202.80;

o) 6th E, in the amount of € 202.80;

p) 7th E, in the amount of € 239.35.

ii) B…:

a) 1st Floor, in the amount of € 157.38;

b) 2nd Floor, in the amount of € 157.38;

c) 3rd Floor, in the amount of € 158.97;

d) 4th Floor, in the amount of € 158.97;

e) 5th Floor, in the amount of € 160.53;

f) 6th Floor, in the amount of € 160.53;

g) 7th Floor, in the amount of € 131.07;

h) 8th Floor, in the amount of € 55.90;

i) 1st E, in the amount of € 198.82;

j) 2nd E, in the amount of € 198.82;

l) 3rd E, in the amount of € 200.80;

m) 4th E, in the amount of € 200.80;

n) 5th E, in the amount of € 202.80;

o) 6th E, in the amount of € 202.80;

p) 7th E, in the amount of € 159.57.

4.1.5. The immovable property identified in 4.1.1. was not constituted under the regime of horizontal ownership on 31 December 2014.

4.2. FACTS NOT CONSIDERED PROVEN

There are no facts with relevance for the arbitral decision that have not been given as proven.

4.3. JUSTIFICATION OF THE FACTUAL MATTERS CONSIDERED PROVEN

The factual matters given as proven have their genesis in the documents used for each one of the alleged facts and whose authenticity was not called into question.

  1. LAW

5.1. Illegality of the Acts in Crisis

In the first place, there are two questions that the tribunal has to decide, to ascertain whether the subjection to the incidence norm of item 28 of TGIS should be concretized by the PTU corresponding to each one of the parts, floors or divisions susceptible of independent use, or whether, on the contrary, by the sum of the PTU of each one of such parts. And, in the second place, to determine whether the interpretation that concludes that stamp duty incides only when the PTU of each one of the parts, floors or divisions susceptible of independent use is greater than € 1,000,000, violates the principle of legality of essential elements of the tax, provided for in art. 103, no. 2 of CRP.

To accomplish such task it is necessary, from the start, to search for the norm whose parts dissent in its interpretation.

Thus, art. 1, no. 1 of the Stamp Duty Code (CIS) and item 28 of the General Table of Stamp Duty (TGIS), provide that the following are subject to taxation: "Ownership, usufruct or right of superficies of urban properties whose tax-bearing patrimonial value appearing in the property registry, according to the Code of Municipal Tax on Immovable Property (CIMI), is equal to or greater than € 1,000,000 – on the tax-bearing patrimonial value used for the purpose of IMI:

28.1 - For residential property (…) - 1 %...".

In this way, it is necessary to examine the concept of "residential property" to which the norm under interpretation alludes and that of "tax-bearing patrimonial value used for the purpose of IMI". Now, as it is not possible to resolve the question by resorting to CIS it is by virtue of the provision of art. 67, no. 2 of such statute necessary to apply the norms of the Code of Municipal Tax on Immovable Property (CIMI).

Consequently, art. 2 of CIMI provides on the concept of property:

"1 - For the purposes of this Code, property is any fraction of land, comprising waters, plantations, buildings and constructions of any nature incorporated therein or situated thereon, with a permanent character, provided that it forms part of the patrimony of a natural or legal person and, in normal circumstances, has economic value, as well as waters, plantations, buildings or constructions, in the circumstances above mentioned, endowed with economic autonomy in relation to the land where they are situated, although situated in a fraction of land which constitutes an integral part of a different patrimony or does not have a patrimonial nature.

2 - Buildings or constructions, even though movable by nature, are deemed to have a permanent character when devoted to non-transitory purposes.

3 - The permanent character is presumed when the buildings or constructions are situated in the same location for a period exceeding one year.

4 - For the purposes of this tax, each autonomous fraction, in the regime of horizontal ownership, is deemed to constitute a property".

Now, the concept of property in the context of IMI is, as we know, endowed with greater breadth in relation to that contained in art. 204, no. 2 of the Civil Code (CC) and encompasses three elements, more specifically, one of a physical nature, the second of a juridical character and the last of an economic nature, J. SILVÉRIO MATEUS/L. CORVELO DE FREITAS, The taxes on immovable property. Stamp Duty., Engisco, 2005, p. 101 to 103 and JOSÉ MARTINS ALFARO, Code of Municipal Tax on Immovable Property – Commented and Annotated, Áreas Editora, 2004, p. 118 to 123. The first requires reference to a fraction of land, comprising, in particular, buildings and constructions incorporated therein with a permanent character. The element of a juridical character requires that the thing, movable or immovable, belongs to the patrimony of a natural or legal person. Thirdly, the element of an economic nature requires that the thing has an economic value.

With regard to the concept of urban property, art. 6 of CIMI describes its various categories, and what is fundamental for the subsumption in each of them is the nature of the use, that is, the purpose to which it is destined. And, nothing in the economy of art. 6, no. 1, al. a) of CIMI prevents the classification of parts of a property in vertical ownership, with divisions or floors susceptible of independent use, with a residential use, as "residential property". What is relevant is, it is repeated, its use. And a different conclusion is not possible to reach by interpretation of art. 2, no. 4 of CIMI which elevates each autonomous fraction in horizontal ownership to the category of property. In truth, also in this latter norm no foundation can be discerned for distinguishing between properties in horizontal ownership and properties in vertical ownership, with floors or divisions susceptible of independent use, as regards their subsumption as urban and residential properties, in accordance with the entire economy of item 28 of TGIS. In other words, if the legislator did not treat properties in vertical ownership differently from those constituted in horizontal ownership, the interpreter should not do so[1].

Quite to the contrary, the property registry registration and the determination of the PTU well demonstrate the similarity of legislative treatment. In effect, the parts endowed with economic independence should, each one of them, be the subject of separate property registry registration and, consequently, the respective PTU should equally appear autonomously, cfr. art. 2, no. 4, art. 7, no. 2, al. b) and art. 12, no. 3 all of CIMI. This has refraction in the context of assessment, in that there will be one for each part, division or floor subject to separate use.

Reverting such interpretation to the present proceedings, there are 15 floors of the immovable property with independent residential use which, at the date of the taxable event, that is, 31 December 2014, was still not constituted in horizontal ownership and, therefore, from the start, no doubts exist that the same should be classified as residential properties of an urban nature.

It is also important to elucidate the other graphic segment of the item of CIS under interpretation, that is, the "tax-bearing patrimonial value used for the purpose of IMI".

In this respect, as already described above, CIMI provides for the autonomization of parts of urban property susceptible of independent use as regards property registry registration and the specification of the respective PTU. Such observation is equally valid regarding the consequent assessment, as provided by art. 113, no. 1 and art. 119, no. 1, both of the last statute cited. In effect, if the tax is assessed "…on the basis of the tax-bearing patrimonial values of the properties (our emphasis) and in relation to the taxpayers that appear in the registries (our emphasis)…" and the collection document should contain the "…breakdown of the properties, their parts susceptible of independent use, respective tax-bearing patrimonial value and of the assessment…", this means that, not only is the PTU for the purpose of application of item 28.1 of TGIS to be considered that which is the subject of separate property registry registration, but also nothing prevents the qualification as "residential property" of parts, floors or divisions with independent use.

Now, if none of the floors of the Applicants with residential use exceeded the PTU of € 1,000,000, the incidence norm in crisis cannot be applicable to the case sub judice, on pain of illegality. It is repeated, what is relevant, to define the scope of such norm, with respect to which the parts dissent in its interpretation: i) that the floor susceptible of independent use has a PTU greater than € 1,000,000 and ii) that the said floor has residential use.

The Respondent argues that it would be unconstitutional, by violation of the principle of legality of essential elements of the tax, the interpretation of item 28.1 of TGIS different from that which concludes that the PTU relevant for such incidence norm must be the global tax-bearing patrimonial value of the property and not that of each one of its independent parts. If that were the case, the express reference to "tax-bearing patrimonial value used for the purpose of IMI" would not be understood. And that, without doubt, is the subject of autonomization in relation to each one of the parts susceptible of independent use. Equally, we would also not find an argument for the issuance of separate assessment notes. Furthermore, given the express referral of art. 67, no. 2 of CIS to CIMI, with regard to matters not regulated, the parts, floors or divisions with autonomy are classifiable under properties classified as urban and residential, cfr. articles 2, 3 and 6, all of CIMI. In this way, it is understood that the said interpretation does not suffer from unconstitutionality.

5.2. COMPENSATORY INTEREST

Art. 43, no. 1 of LGT provides that: "Compensatory interest is due when it is determined, in administrative review or judicial challenge, that there was error attributable to the services from which results payment of the tax debt in an amount greater than legally due". In other words, there are three requirements for the right to said interest: i) the existence of an error in a tax assessment act attributable to the services; ii) determination of such error in an administrative review or judicial challenge process and iii) payment of tax debt in an amount greater than legally due.

In this way, it is possible to immediately formulate a question: is it admissible to determine the payment of compensatory interest in tax arbitral proceedings? The answer to the question is affirmative. In effect, art. 24, no. 5 of RJAT provides that: "Payment of interest is due, regardless of its nature, according to the terms provided in the General Tributary Law and in the Tax Procedure and Process Code".

Upon determining the question, the illegality of the acts in crisis is attributable to the Respondent, given the lack of normative support at the time of their practice. Consequently, the request for compensatory interest proceeds, calculated at the rate determined, according to what is provided in art. 43, no. 4 of LGT, between the date on which the unlawful payment was made and until full reimbursement.

  1. DECISION

In these terms and with the justification above described it is decided to hold the arbitral claim well-founded, with the consequent annulment of the acts subject of pronouncement, with all legal consequences, including, namely, the reimbursement of the amounts unlawfully paid.

  1. VALUE OF THE CASE

The value of the case is set at € 10,020.54 (corresponding to the sum of the assessments subject of pronouncement) according to the terms of art. 97-A of CPPT, applicable by virtue of the provisions of art. 29, no. 1, al. a) and b) of RJAT and of art. 3, no. 2 of the Regulation of Costs in Tax Arbitration Proceedings (RCPAT).

  1. COSTS

Costs payable by the Respondent, in the amount of € 918, cfr. art. 22, no. 4 of RJAT and Table I annexed to the Regulation of Costs in Tax Arbitration Proceedings, inasmuch as the claim for annulment of the Stamp Duty assessments above identified proceeded in its entirety.

Notify.

Lisbon, 11 November 2015

The Arbitrator,

Francisco Nicolau Domingos

[1] V. in this sense the arbitral decision pronounced in case no. 50/2013 – T, of 29/10/2013, in which Dr. MARIA DO ROSÁRIO ANJOS served as arbitrator.

Frequently Asked Questions

Automatically Created

Is Stamp Tax under Verba 28.1 TGIS applicable to vertical properties with a VPT above €1,000,000?
Yes, stamp duty under Verba 28.1 TGIS applies to vertical properties when the total Valor Patrimonial Tributário (VPT) registered in the property matrix equals or exceeds €1,000,000, regardless of whether individual floors or divisions have independent use with values below this threshold. The Tax Authority's position, upheld in Process 329/2015-T, establishes that vertical property constitutes a single juridical unit for stamp duty purposes. The €1,000,000 threshold applies to the aggregate patrimonial value of the entire property registration, not separately to each floor or division. This interpretation distinguishes vertical ownership from horizontal property (condominium) regimes where autonomous fractions are treated as independent properties. The determining factors are: (1) residential use and (2) total registered property value ≥€1,000,000. Even when floors have independent economic use and separate matrix registrations under Article 12(3) CIMI, they remain parts of a unified property for stamp duty assessment purposes.
How is the taxable base determined for Stamp Tax on residential properties under Verba 28.1 of the TGIS?
The taxable base for stamp duty on residential properties under Verba 28.1 TGIS is determined by the Valor Patrimonial Tributário (VPT) appearing in the property matrix registration. The legal framework references IMI rules for determining this value but applies different assessment principles. For vertical properties, the total aggregate VPT of all floors/divisions within the single property registration constitutes the relevant base for determining whether the €1,000,000 threshold is met. While IMI may calculate tax obligations separately for each floor with independent use pursuant to Article 7(2)(b) CIMI, stamp duty under Verba 28.1 does not adopt this floor-by-floor approach. The absence of specific rules in the stamp duty regime regarding autonomous treatment of divisions means the patrimonial value is considered globally. The Tax Authority argues this interpretation respects both the letter and spirit of Verba 28.1 TGIS and the constitutional principle of tax legality (Article 103(2) CRP), which requires clear definition of essential tax elements.
Can co-owners jointly challenge Stamp Tax liquidations through CAAD arbitration proceedings?
Yes, co-owners can jointly challenge stamp duty liquidations through CAAD arbitration proceedings when specific procedural requirements are met. Process 329/2015-T confirms that Article 3(1) RJAT permits accumulation of claims and claimants when: (1) the disputes concern assessment acts of the same tax type (here, stamp duty); (2) there is identity of factual matters; and (3) the appropriateness of claims depends on interpretation of the same legal principles and rules. In this case, applicants A and B, holding ownership shares of 1/2 and 1/6 respectively, successfully cumulated their challenges to 2014 stamp duty assessments affecting their co-owned property. The arbitral tribunal validated this procedural approach, finding it promoted efficiency and consistency. Co-owners need not file separate arbitration requests when challenging assessments on jointly-owned property, provided the legal and factual bases are sufficiently identical. This cumulation right facilitates access to justice and avoids contradictory decisions on the same property.
What role does the VPT (Valor Patrimonial Tributário) registered in the matrix play in Stamp Tax liability under Verba 28.1?
The VPT (Valor Patrimonial Tributário) registered in the property matrix plays a dual determinative role in stamp duty liability under Verba 28.1 TGIS. First, it establishes whether the €1,000,000 threshold triggering stamp duty obligation is met. Second, it serves as the basis for calculating the tax amount due. The VPT appearing in the property registry constitutes the official valuation for tax purposes, derived from IMI assessment methodologies. For vertical properties, the critical legal question addressed in Process 329/2015-T is whether individual floor VPTs or aggregate property VPT applies. The Tax Authority position treats the total registered value as determinative, arguing that vertical property remains a single unit despite multiple floors with independent use. The matrix registration under Article 12(3) CIMI may show separate valuations for each floor, but these are components of one property registration. The VPT thus functions as both the incidence criterion (determining if tax applies) and the taxable base (determining tax quantum), distinguishing stamp duty from IMI where floor-by-floor assessment may occur.
What procedural requirements apply to cumulation of claims and parties in CAAD tax arbitration under Article 3(1) RJAT?
Article 3(1) RJAT establishes three cumulative procedural requirements for cumulation of claims and parties in CAAD tax arbitration: (1) the claims must concern the same tax type or category; (2) there must be identity or substantial overlap in factual matters underlying the disputes; and (3) resolution of the claims must depend on interpretation of the same legal principles and rules. Process 329/2015-T applied these criteria, finding cumulation appropriate where co-owners challenged stamp duty assessments on their jointly-owned vertical property. The tribunal noted that all claims involved stamp duty (satisfying requirement 1), arose from the same property with identical factual circumstances regarding its structure and registration (satisfying requirement 2), and all turned on the legal interpretation of how Verba 28.1 TGIS applies to vertical property ownership (satisfying requirement 3). Cumulation promotes procedural efficiency, avoids contradictory decisions, and respects parties' autonomy. The tribunal independently verified these requirements as part of its procedural cleanness analysis before proceeding to substantive examination, demonstrating that proper cumulation is jurisdictional rather than discretionary.