Concurrent estate

In property law, a concurrent estate or co-tenancy is any of various ways in which property is owned by more than one person at a time. If more than one person owns the same property, they are commonly referred to as co-owners. Legal terminology for co-owners of real estate is either co-tenants or joint tenants, with the latter phrase signifying a right of survivorship. Most common law jurisdictions recognize tenancies in common and joint tenancies, and many also recognise tenancy by the entirety as a distinct form of co-ownership.
Many jurisdictions also recognize tenancies by the entirety, which is effectively a joint tenancy between married persons. Many jurisdictions refer to a joint tenancy as a joint tenancy with right of survivorship, but they are the same, as every joint tenancy includes a right of survivorship. In contrast, a tenancy in common does not include a right of survivorship.
The type of co-ownership does not affect the right of co-owners to sell their fractional interest in the property to others during their lifetimes, but it does affect their power to will the property upon death to their devisees in the case of joint tenants. However, any joint tenant can change this by severing the joint tenancy. This occurs whenever a joint tenant transfers their fractional interest in the property.
The terminology of concurrent estates is characteristic of common-law systems. Civil-law jurisdictions typically organise co-ownership under different categories, such as ownership in indivision or other forms of undivided co-ownership, which are functionally similar to tenancy in common but based on distinct doctrinal frameworks.
Laws can vary from place to place, and the following general discussion will not be applicable in its entirety to all jurisdictions.

Rights and duties of co-owners (general)

Under the common law, co-owners share a number of rights by default:

Each owner has an unrestricted right of access to the property. When one co-owner wrongfully excludes another from using the shared property, the excluded co-owner can bring a cause of action for ouster. As a remedy, the court may grant the wronged co-owner the fair rental value of the property for the time that they were ousted.
Each owner has a right to an accounting of profits made from the property. If the property generates any income each owner is entitled to a pro-rata share of that income.
Each owner has a right of contribution for the costs of owning the property. Co-owners can be forced to contribute to the payment of expenses such as property taxes, necessary maintenance and repairs, or mortgages for the entire property.
Contribution and improvements

Co-owners generally do not have any obligation to contribute to any costs of improving the property. If one co-owner adds a feature that enhances the value of the property, that co-owner has no right to demand that any others share the cost of adding that feature even if other co-owners reap greater profits from the property because of it. However, at partition, a co-owner is entitled to recover the value added by their improvements of the property if the "improvements" resulted in an increase in property value. Conversely, if the co-owner's "improvements" decrease the value of the property, the co-owner is responsible for the decrease. In an Australian case, the High Court said that the costs of repairing by one co-owner must be taken into account on the partition or final distribution of the property.

Mortgages

Each co-owner can independently encumber the co-owner's own share in the property by taking out a mortgage using fractional financing on that share. Other co-owners have no obligation to help pay a mortgage that only runs to another owner's share of the property, and the mortgagee can only foreclose on that mortgagor's share.

Tenancy in common

Tenancy in common is a form of concurrent estate in which each owner, referred to as a tenant in common, is regarded by the law as owning a separate and distinct share of the same property. By default, all co-owners own equal shares, but their interests may differ in size.
TIC owners own percentages in an undivided property rather than particular units or apartments, and their deeds show only their ownership percentages. In some jurisdictions, the detailed use rights of a particular TIC owner in relation to a particular dwelling or unit come from a written contract signed by all co-owners, rather than from the deed, map, or other recorded instrument. This form of ownership is common where the co-owners are not married or have contributed different amounts to the purchase of the property. The assets of a joint commercial partnership might be held as a tenancy in common.
Tenants in common have no right of survivorship, meaning that if one tenant in common dies, that tenant's interest in the property will be part of their estate and pass by inheritance to that owner's devisees or heirs, either by will, or by intestate succession. Also, as each tenant in common has an interest in the property, they may, in the absence of any restriction agreed to between all the tenants in common, sell or otherwise deal with the interest in the property during their lifetime, like any other property interest.

Destruction of tenancy in common

Where any party to a tenancy in common wishes to terminate the joint interest, he or she may obtain a partition of the property. This is a division of the land into distinctly owned lots, if such division is legally permitted under zoning and other local land-use restrictions. Where such division is not permitted, a forced sale of the property is the only alternative, followed by a division of the proceeds.
If the parties are unable to agree to a partition, any or all of them may seek the ruling of a court to determine how the land should be divided physical division between the joint owners, leaving each with ownership of a portion of the property representing their share. Courts may also order a partition by sale in which the property is sold and the proceeds are distributed to the owners. Where local law does not permit physical division, the court must order a partition by sale.
Each co-owner is entitled to partition as a matter of right, meaning that the court will order a partition at the request of any of the co-owners. The only exception to this general rule is where the co-owners have agreed, either expressly or impliedly, to waive the right of partition. The right may be waived either permanently, for a specific period of time, or under certain conditions. The court, however, will likely not enforce this waiver because it is a restraint on the alienability of property.

Joint tenancy

A joint tenancy or joint tenancy with right of survivorship is a type of concurrent estate in which co-owners have a right of survivorship, meaning that if one owner dies, that owner's interest in the property will pass to the surviving owner or owners by operation of law, usually avoiding probate. Under this type of ownership, the last owner living owns all the property, and on their death the property will form part of their estate. Unlike a tenancy in common, where co-owners may have unequal interests in a property, joint co-owners have an equal share in the property.
Creditors' claims against the deceased owner's estate may, under certain circumstances, be satisfied by the portion of ownership previously owned by the deceased, but now owned by the survivor or survivors. In other words, the deceased's liabilities can sometimes remain attached to the property.
This form of ownership is common between spouses, parent and child, and in any other situation where parties want ownership to pass immediately and automatically to the survivor. For bank and brokerage accounts held in this fashion, the acronym JTWROS is commonly appended to the account name as evidence of the owners' intent.
To create a joint tenancy, clear language indicating that intent must be used e.g. "to AB and CD as joint tenants with right of survivorship, and not as tenants in common". This long form of wording may be especially appropriate in those jurisdictions which use the phrase "joint tenancy" as synonymous with a tenancy in common. Shorter forms such as "to AB and CD as joint tenants" or "to AB and CD jointly" can be used in most jurisdictions. Words to that effect may be used by the parties in the deed of conveyance or other instrument of transfer of title, or by a testator in a will, or in an inter vivos trust deed.
If a testator leaves property in a will to several beneficiaries "jointly" and one or more of those named beneficiaries dies before the will takes effect, then the survivors of those named beneficiaries will inherit the whole property on a joint tenancy basis. But if these named beneficiaries had been bequeathed the property on a tenancy in common basis, but died before the will took effect, then those beneficiaries' heirs would in turn inherit their share immediately.

Four unities of a joint tenancy

To create a joint tenancy, the co-owners must share "four unities":

Time – the co-owners must acquire the property at the same time. So, for example, if a piece of land was vested to ABCD as co-owners on 1 January 2018 and ‘A’ died before the date leaving ‘K’ to succeed him for, as between K on the one hand and BCD on the other hand, there is no unity of time. K becomes a tenant in common, while BCD are joint tenants.
Title – the co-owners must have the same title to the property. If a condition applies to one owner and not another, there is no unity of title. Also, there must be unity in the sense that title must emanate from the same grantor. Thus, in the hypothetical example above, there is no unity of title between ‘K’ on the one hand and ‘BCD’ on the other hand because K derives his title from a distinct individual, that is; A.
Interest – each co-owner owns an equal share of the property; for example, if three co-owners are on the deed, then each co-owner owns a one-third interest in the property regardless of the amount each co-owner contributed to the purchase price
Possession – the co-owners must have an equal right to possess the whole property.

If any of these elements is missing, the joint tenancy is ineffective, and the joint tenancy will be treated as a tenancy in common in equal shares.