In my profession as an Architect, many of my clients underestimate the cost of construction. Builders will have to guesstimate their cost unless they have a complete set of drawings.
It is very important to get a well detailed set of construction drawings in order to obtain a realistic bid which will prevent misunderstandings and additional hidden costs. Drawings that are very well detailed will also help to avoid catastrophic mistakes.
For example, a builder called today and invited me to see a house on which he was in the process of demolishing many interior walls. Good thing I stopped him and advised him to get the original drawings of the house. Sure enough, the old blueprints revealed that there were a few bearing walls. I pointed them out to the builder, preventing a major disaster from occurring for both the builder and the homeowner.
The use of the area to be renovated is another factor to be considered in determining the realistic cost of any home improvement. SF by SF, the cost of a kitchen or bath remodel can be five times more than the cost of an open, large living room or garage.
In conclusion, when getting an estimate make sure the builder does not use a standard average price per square foot but provides a cost breakdown item by item. It is better to get an allowance for kitchen appliances, cabinets, plumbing fixtures, flooring and finishes if you are comparing competing bids from more than one builder.
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