The landlord does not contest, and in his brief implicitly concedes, the right of the board to condition rent entitlement on habitability. See Flynn v. Cambridge, 383 Mass. 152 (1981); Altschuler v. Boston Rent Bd., 12 Mass. App. Ct. 452. Instead, he advocates a narrow reading of the term “during the time in question” to limit abatements based *221upon code violations to the period during which rent was unpaid.9 This reading not only fails to accord to the board’s interpretation of its own regulations the substantial deference to which it is entitled, absent arbitrary or unreasonable construction, see H. N. Gorin & Leeder Mgmt. Co. v. Rent Control Bd. of Cambridge, 18 Mass. App. Ct. 272, 276 (1984), but it also disregards other provisions in the regulatory scheme. Regulation 61-03 requires the board to order the tenant to pay rent determined on a fair value basis “during the time such condition existed” if it finds that “the landlord has made reasonable efforts to repair such condition.” The previous relevant reference to “such condition” appears in regulation 61-02(b), which predicates the denial of a certificate of eviction on a landlord’s knowing “of such condition prior to the tenant being in arrears in rent” (emphasis supplied). This regulation presumes the existence of the offending condition during a period preceding the rental nonpayment. Moreover, our reading is consonant with the general principle that a tenant is entitled to a rental abatement from the time when a landlord first learns of substandard conditions. See McKenna v. Begin, 5 Mass. App. Ct. 304, 306 (1977). Certainly a tenant is not to be denied the full amount of such abatement by reason of her having paid rent to which the landlord may not have been entitled during part of the period in which substandard conditions existed. That the determination of an abatement entitlement might result in a tenant receiving a credit against future rental obligations to the landlord does not offend any accepted concept of fairness or the policy objective of the rent control statute of reg*222ulating and controlling eviction of tenants. See St. 1976, c. 36, § 1.