In his assignments of error, plaintiff contends that the trial court’s conclusions are unsupported by the evidence, unsupported by the findings, contrary to law and seek to vary the terms of the written instruments. Defendant contends that the written language of the contract is clear and that the trial court properly concluded that the transfer entitled defendant to a 12% interest rate.
“When the language of a contract is plain and unambiguous, the construction thereof is a matter of law . . . and it is the duty of the court to construe the contract as written.” Ins. Co. of North America v. Aetna Life & Casualty Co., 88 N.C. App. 236, 362 S.E.2d 836 (1987) (citations omitted). The contract between plaintiff and defendant is unambiguous. The deed of trust clearly states in its due on sale clause:
17. Transfer of the Property: Assumption. If all or any part of the Property or an interest therein is sold or transferred by Borrower without Lender’s prior written consent, *556. . . Lender may at Lender’s option, declare all the sums secured by this Deed of Trust to be immediately due and payable.
*See Assumption Rider attached hereto.
However, the assumption rider provides a means for the borrower to avoid the harsh reality of the due on sale clause by increasing the interest rate to 12% on the remaining balance:
ASSUMPTION Rider (Section 17 cont’d). Provided, however, that in the event the sale or other transfer on any interest in the Property . . . the Lender shall permit assumption of the obligations under the Note and this Deed of Trust under the following conditions:
a) the interest rate shall be increased to ... twelve percent (12%). . . .
In this case, while the transfer was between tenants in common, according to the clear language of the contract, such a transfer invokes the due on sale clause which in turn provides for an increased interest rate of 12%. Plaintiff does not argue and we find no authority supporting such argument that transfers between cotenants do not trigger due on sale clauses.
Instead, plaintiff contends that a distinction at law exists between property conveyances where the borrower “assumes” an existing deed of trust and where the borrower takes property “subject to” an existing deed of trust. Plaintiff further contends the due on sale clause is not triggered because he did not “assume” the deed of trust but only took the property “subject to” the existing deed of trust. We agree with plaintiff that the law recognizes a distinction between deeds of trust “assumed” and property taken “subject to” an existing deed of trust. See Driftwood Manor Investors v. City Federal Savings & Loan Association, 63 N.C. App. 459, 305 S.E.2d 204 (1983). However, the distinction is irrelevant to the issue at hand. The unambiguous deed of trust language states “If all or any part of the Property or an interest therein is sold or transferred by Borrower. . . .” The due on sale clause language does not limit itself to “assumption” transfers and this court is prohibited from reading such limitation into the otherwise clear language. Isby v. Crews, 55 N.C. App. 47, 284 S.E.2d 534 (1981).
*557Affirmed.
Judges JOHNSON and COZORT concur.