How to estimate a building extension

Written by billy ray
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How to estimate a building extension
Construction projects must begin with a thorough understanding of the plans. (New Home Construction 3 image by JJAVA from

Adding on to a building can be a difficult task. With the necessary building knowledge, such as carpentry, plumbing and electrical skills, you can accomplish it yourself safely and according to local codes. You also have to read the building plans to properly calculate the types and quantity of construction materials you will need. Estimating the cost of a DIY extension on your own home involves determining the costs of building supplies and the costs of required fees, permits and inspections.

Skill level:

Things you need

  • Building plans for new extension
  • Phone
  • Pad and paper
  • Calculator

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    Estimate the costs

  1. 1

    Study the building plan and determine the quantity of each construction material the plan calls for. Make a list of all these supplies and call the contractors department of your building supply company to get the price for all these materials. Materials can include lumber, concrete, drywall, plumbing, electrical components, nails, screws, drywall mud, paint, insulation, roofing materials, guttering, and the cost of transporting all the supplies. You should also calculate the anticipated electricity use for the project. Add 10 per cent to the total of these amounts as a precaution to get the total cost of materials.

    How to estimate a building extension
    Make a list of materials needed (Brand X Pictures/Stockbyte/Getty Images)
  2. 2

    Call your local authority and find out what permits and inspections are needed and the cost involved in each instance. Find out all applicable rules and regulations so the project can be completed legally. Rates and regulations vary from area to area. Determine the costs involved with all necessary permits and inspections for your specific building extension and add all of these figures together.

    How to estimate a building extension
    Find out the legalities and required permits (Photodisc/Photodisc/Getty Images)
  3. 3

    Add the cost of your building supplies to the cost of the permits and other fees. This is the figure you will need to estimate the cost of your DIY building extension. A free building cost calculator may also be useful to see if you have estimated correctly.

    How to estimate a building extension
    Add the cost of the supplies to the cost of the permits (Stockbyte/Stockbyte/Getty Images)

Tips and warnings

  • If the work is to be contracted out, get multiple bids from licensed contractors familiar with your area. Adding in the cost of lost productivity for the time you have spent on the project that could have been used to create income is often a wise move and can help determine how much of the project you may wish to contract out.

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