If a governmental entity builds and maintains a structure which is permanent in nature and the maintenance of the structure causes a diminution in value to a person’s real estate, the structure is considered a nuisance and the landowner is entitled to compensation. See Midgett v. Highway Commission, 265 N.C. 373, 144 S.E. 2d 121 (1965); Glace v. Pilot Mountain, 265 N.C. 181, 143 S.E. 2d 78 (1965); Midgett v. Highway Commission, 260 N.C. 241, 132 S.E. 2d 599 (1963); and Clinard v. Kernersville, 215 N.C. 745, 3 S.E. 2d 267 (1939). In this case the evidence when considered most favorably for the plaintiffs is that the defendant’s sewage system as originally constructed did not cause any damage to the plaintiffs property. In 1971 the defendant’s sewage system began to malfunction, causing an intermittent overflow of raw sewage in the plaintiffs’ basement. The defendant attempted to remedy the condition until 2 November 1979, at which time it notified the plaintiffs it would not take any other steps to rectify the condition.
As we understand the law, it is the maintenance of a structure or condition permanent in nature which constitutes a nuisance. The defendant would not be liable for a nuisance if it had negligently maintained or performed some work on a structure which caused some temporary inconvenience to the plaintiffs. We do not believe the defendant was maintaining a nuisance so long as it was attempting to repair or change the sewage system so that it would not overflow on the plaintiffs’ property. When the defendant notified the plaintiffs that it would no longer attempt to correct the problem but would maintain the system in its then existing condition, we believe defendant started to maintain a nuisance.
 Defendant argues that there is not sufficient evidence that the deterioration of its sewage lines caused the overflow for the jury to find this fact. It contends that the affidavits of Mr. Buchanan, the plumber, and Mr. Daniel, the engineer, should not *110be considered because their opinions as to the cause of the overflow were based in part on the information given to them by the plaintiffs and were thus based on “hearsay, speculation and conjecture.” Mr. Buchanan and Mr. Daniel, because of their education and experience, are better qualified than would be a jury to form opinions as to the causes of failures in sewer lines. They qualify as expert witnesses. See 1 Brandis on N.C. Evidence Sec. 133 (1982). The report by the defendant as to its experiments to determine the cause of the problem was in evidence. The expert witnesses may give their opinions as to causation based on the facts obtained in the report. The two cases cited by the defendant, Hubbard v. Oil Co., 268 N.C. 489, 151 S.E. 2d 71 (1966) and Keith v. Gas Co., 266 N.C. 119, 146 S.E. 2d 7 (1965), do not apply. In each of them, an expert witness gave an opinion based on a hypothetical question which assumed facts not in evidence. Our Supreme Court held this was error. In this case, the facts on which the expert witnesses based their opinions were in evidence.
The defendant also argues that the expert witnesses could not testify that the overflow was caused by breaks in the sewer line because there was no evidence of broken or damaged lines. The witnesses’ opinions based on the facts before them were that there were breaks in the line which caused the overflow. The formation of this opinion was within the parameters of the witnesses’ expertise.
The defendant contends further that the overflow could be as well caused by breaks in the plaintiffs’ line or the lines of a neighbor. These are questions for the jury. The defendant argues further that the plaintiffs’ plumbing facilities which overflow are located below the street level; and the North Carolina State Building Code requires a backwater valve for such facilities, which the plaintiffs have not installed. We reiterate that we are passing on a motion for summary judgment. We believe the plaintiffs have presented sufficient evidence of the cause of the overflow to make it a question for the jury. If the jury believes that the overflow was caused by the basement facilities being too low, they may decide the case for the defendant. We cannot make this decision.
The defendant also contends the plaintiffs have not shown they have suffered damage. There is evidence that raw sewage *111was overflowing intermittently in the plaintiffs’ basement. Mr. Hughes testified that the house was not marketable. We believe he was competent to give this testimony. See 1 Brandis on N.C. Evidence Sec. 128 (1982). This establishes damage to the plaintiffs.
The defendant contends that the claim arose in 1971 and it was not filed within the required time. In light of our holding that the plaintiffs did not have a claim based on a nuisance until 2 November 1979, we reject this argument.
We hold that there should be a trial as to whether the defendant is maintaining a nuisance and whether the plaintiffs have been damaged thereby.
Reversed and remanded.
Judges Hedrick and Becton concur.