Adjusting comps for older builds with only new built comps

[Robin Muthomi]

I am looking to put this 3 bed 3 bath bungalow into contract but i am having trouble finding comps because majority of the sold comps in the area are new builds while my property was built in the 80s. How do i go about calculating the ARV i can trust?

If I could be more detailed the subject property was valued at 280k by insurance the average size footage of the neighborhood (mostly new builds) is 2500 sq feet on 1/4 acre the subject property is at 2000 sq feet the cost of rehab including new roof, floor, kitchen and bathroom update and adding square feet to 2500 will be approximately 68 k. My issue is with comps the closest i have are new builds 4 bed 4 baths maisonette on a 1/4 acre