These landlords responsibilities are found in s 20(1) of the Residential Tenancies Act (RTA).
20 (1) A landlord is responsible for providing and maintaining a residential complex, including the rental units in it, in a good state of repair and fit for habitation and for complying with health, safety, housing and maintenance standards. .
(2) Subsection (1) applies even if the tenant was aware of a state of non-repair or a contravention of a standard before entering into the tenancy agreement.
The key word in the first of the landlord's responsibilities is "repair". The definition in Black's Law Dictionary, 4th ed., is:
REPAIR. To mend, remedy, restore, renovate, to restore to a sound or good state after decay, injury, dilapidation, or partial destruction. Mozingo v. Wellsburg Electric Light, Heat & Power Co., 131 S.E. 717, 718, 101 W. Va. 79; Board of Education of Hancock County v. Moorehead, 105 Ohio St. 237, 136 N.E. 913, 914; Weiss v. Mitchell, Tex. Civ. App., 58 S.W. 2d 165, 166.
The word "repair" contemplates an existing structure or thing which has become imperfect, and means to supply in the original existing structure that which is lost or destroyed, and thereby restore it to the condition in which it originally existed, as near as may be. Childers v. Speer, 63 Ga. App. 848, 12 S.E. 2d 439, 440.
and in Stroud's Judicial Dictionary, 4th ed., is:
(2) To repair is to remedy defects or to put back into good condition something that, having been in good condition, has fallen into bad condition (Day v. Harland and Wolff  1 W.L.R. 906. (3) "Repair" (as used for instance in s. 53 of the Income Tax and Social Services Contribution Assessment Act 1936-62 (Cth)) involves a restoration of a thing to a condition which it formerly had without changing its character.
and in the Shorter Oxford English Dictionary, 3rd ed.:
1. the act of restoring to a sound or unimpaired condition;
(b) restoration of some material thing or structure by the renewal of decayed or worn out parts.
The second of the landlord's responsibilities is "fit for habitation". The Oxford English Dictionary defines "habitation" as "the action of dwelling in or inhabiting as a place of residence; occupancy by inhabitants" and one of the examples given is "the premises to be closed ... until they were made fit for human habitation", and the word "fit" is defined as "suitable or well adapted for".
It is trite law that in the absence of an express covenant there is no obligation on the part of the landlord of an unfurnished house or apartment to keep it in repair, and there is no implied covenant by the landlord that it is or shall continue to be reasonably fit for occupation: see Woodfall on Landlord and Tenant, 25th ed., p. 772, and Williams, Canadian Law of Landlord and Tenant, 2nd ed., p. 346; see also Manchester v. Dixie Cup Co. (Canada) Ltd.,  1 D.L.R. 19,  O.R. 686, and St. George Mansions Ltd. v. Hetherington (1918), 41 D.L.R. 614, 42 O.L.R. 10; also Parks v. Hammond, , 2 D.L.R. 679, O.W.N. 383.
This does not, in my opinion, bring the case within the rule applied in Davey v. Christo,, 36O.L.14. 123, 28 D.L.R. 447, following Smith v. Marrable, 11 M. & W. 5, and Wilson v. Finch Hatton, 2 Ex. D. 336, 344. The former was the case of the letting of a furnished house. The cases are fully collected and considered in Davey v. Christο ', where the rule was applied to the case οf a furnished theatre.
St. George Mansions Limited v. Hetherington,
The "Residential Tenancies Act" (RTA) at s 20(1) makes a residential landlord responsible for providing and maintaining a residential complex, including the rental units in it, in a good state of repair and fit for habitation and for complying with health, safety, housing and maintenance standards.
An English decision rendered in 1943, "Summers v. Salford Corp". held that fit for habitation meant
if the state of disrepair is such that by ordinary use, damage may naturally be caused to the occupier, either in respect of personal injury to life or limb or injury to health, the house is considered not reasonably fit for habitation.
The responsibility is not however absolute or strict. This means that the landlord is not liable or in breach of this obligation the moment a rental unit becomes unfit for habitation by some development. The situation or development must first be brought to the attention of the landlord. At that moment the landlord is judged by whether they took all reasonable measures to address and remedy the problem. Reasonable steps is measured by an objective standard of what is an appropriate method to remedy the problem. The speed at which the landlord deals with the problem is also a factor. Doing nothing is a breach unless there are valid reasons why they could not do so by reasons beyond their control.
The Ontario Court of Appeal (OCA) made this clear in Onyskiw v. CJM Property Management Ltd. The facts were that the tenants in a residential building sought an abatement of rent based on s. 20 of the RTA. The building was six stories high. The elevator in the building broke down in late November 2012 due to a latent defect in the brake drum. The landlord had had the elevator under a maintenance contract leading to regular and proper repairs being made. The elevator had passed all inspections prior to its breaking down.
The elevator was out of commision for ninety-eight (98) days. This was an obvious inconvenience to the tenants. The elderly tenants and those with mobility issues had great difficulty living in the building. The landlord hired runners to assist them and purchased an evacuation chair in case of emergencies.
A further delay was caused by a strike of elevator technicians.