How to Estimate a Construction Addition

Create a sketch of your planned addition. This will help you get a better picture of the work involved, and will give your architect an example of what you're looking for.

Estimate the amount of materials involved. Start on the exterior of the house and work in. For example, begin by counting up the total square footage of siding you'll need, followed by wood framing, roofing, drywall, and interior finishes. Create an estimated material count for every product you plan to use in the job.

Get material prices from suppliers. You can get an idea on unit prices for materials by heading to a home improvement store or contacting suppliers. Once you have unit prices, you can multiply these prices by the material counts you estimated in Step 2 to obtain a total material cost.

Calculate labor costs. If you plan to do most of the work yourself, you can plug in an hourly rate of zero for self-performed work. For work you plan to contract out, such as roofing or other projects, call up subcontractors to get bid prices. By getting a few different prices, you can ensure you're getting a good deal. Ask bidders to break out material and labor costs.

Determine sitework costs. Any digging, tree removal , landscaping, or underground work should be bid out to sitework contractors. Again, get several bids so you can determine the range.

Consider architectural fees. To get a permit, you'll likely need plans drawn by an architect. Architectural drawings can be estimated at around 3 percent of total construction costs. Don't forget to plug this number in to your total.

Add up your total costs to get an estimate on the construction addition. Include material costs, labor costs, costs for sitework, and design fees. Include the cost of the permit, which will vary depending on where you live.