Cost of a Home Addition
Costing out a Home Addition Requires Attention
to Detail and Time
By: Mark J. Donovan
Calculating the cost of a home
addition can be a little complicated, but with accurate home addition plans and
a little time and effort you can cost out your own home addition fairly
The cost of a home addition has many
variable factors. Home addition costs are a function of the size and type of the
home addition, the materials used in its construction, housing market conditions
and local contractor labor rates.
As a result, there is no simple
formula that can accurately project home addition costs. There is however a
simple process that will allow you to calculate the cost of your home
Over the years I have built my
fair share of home additions and in each case I developed my own set of
construction plans and calculated the costs of the home addition.
Building Material List
The first step in the process of
costing out a home addition requires creating a building material list from
the home addition plans.
The more thorough your building material list, the more accurate you will be
in determining the cost of your home addition. Every board, door, window and
nail should be included in your material list.
I find by breaking the material list
up into the major home addition construction tasks makes creating the building
material list easier and more thorough. For example, start from the ground up.
This means start at the excavation and foundation phases. From there move on to
the rough framing of the home addition.
Next, move on to the siding and
roofing of the home addition. Once the home addition is buttoned up with walls,
roof, doors and windows, move on to the inside of the home addition and address
electric, plumbing, insulation, drywall, trim work, cabinetry, and flooring. For
each phase specify the exact set of materials that will be used.
For tasks such as electrical and
plumbing where most likely you will subcontract out the work, use the
subcontractor quotes for each of these cost items. Likewise use subcontractor
quotes for other tasks that you are not specifically performing. If the
subcontractor quotes do not include specific costs for certain key items,
include these items separately in your home addition cost estimates. For
example, if the plumbing subcontractor quote does not include the cost of the
Jacuzzi tub you want to install in the home addition then make sure you account
for it in your building material list.
Cost of Home
Additions and Use of Contractor Allowances
When it comes to items like flooring,
lighting and cabinetry contractors frequently like to give you a cost allowance
for these items. Do not use cost allowances when attempting to accurately cost
out a home addition. Visit your local home improvement store or building supply
store to get specific costs for each of these items.
Do not be surprised to see
significant variations in contractor quotes for the same task. The variations
can be due to many reasons, including how accurate the quote is, and the labor
rates charged for performing the work. Make sure you carefully study each quote
to understand what you are and are not getting for your money.
The state of the home building
industry in your local area can also affect the cost of the quotes you receive.
If the home building industry is booming, expect higher quotes. Itís just the
simple law of supply and demand, as well as a little greed. If the home building
industry is slow the quotes may be a little more reasonable. In either case,
donít hesitate to question the quotes and ask the subcontractors to sharpen
their pencils a little. Sometimes it works and other times it does not.
Once you have created a comprehensive building material list, and know what
items you are contracting out you can then seek subcontractor quotes to fill in
the costs for those particular items.
Photo by Mark Donovan
Addition Costs for Building Materials
For the items on your home addition
building material list that you plan on tackling yourself, you need to next
obtain material costs for each one of these items.
If for example you plan on rough
framing the home addition yourself, take the portion of your building material
list that relates to lumber, doors and windows, siding, and roofing to a few
local home improvement centers. Visit their contractor desk and ask them to
provide you with costs for each line item in your material list. Alternatively
you can also walk down the aisles of the building supply store and obtain your
own material costs, however I find using the contractor desk much more
efficient. The other advantage of going to the contractor desk is that you can
occasionally convince them to give you a discount.
With your building material list
complete, and costs determined for each phase of the home addition project you
can now accurately calculate the cost of your home addition.
and Home Addition Finance Charges
When calculating the cost of a home
addition do not forget to include building permits costs and financing charges.
Building permit costs are relatively low, however they are real costs. Likewise,
if you are using a home equity loan you should also include any costs for
obtaining the loan and the finance charges that come with it.
So with a solid set of home addition
plans and a building material list you should be able to accurately calculate
the cost of your home addition. It just takes attention to detail and some time.
For more help on calculating the cost of a home addition, see HomeAdditionPlus.com's
Addition Bid Sheets.
Addition Bid Sheets
provide you with the knowledge and information on how to plan a home addition project,
and what to look for when hiring contractors. They
also include detailed cost breakdown tables and spreadsheets for estimating
your own new home addition building costs.
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