What type of home addition can we afford?

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Estimating the general cost of home additions is like finding a needle in a haystack. There are so many variables involved that it is impossible to predict without getting down to the detailed cost of using 2x4's or 2x6's. Yet, we all need to have a general idea of the cost before we can realistically decide whether to seriously consider doing a home addition.

If you go to the bank and discover that your budget for the home addition is $80,000, how will you know if it will cover the type of addition that you want?

Read on to determine what kind of home addition your budget will allow. If you already know this, go to Step 7 where we give you a breakdown for the detailed cost of home additions.

General Rule of Thumb

If you are thinking about a multi-story addition at the back, but discover that your budget is only $80,000, you may want to change it to a second-storey build-over, or increase your budget. Knowing the type of home addition you can build based on your budget is great information to have before you start getting quotes.

A general rule of thumb is:

Contractors will usually give you a range of $80-$250 per sq. ft. for the cost of home additions.

But how do you know whether you will be paying $80 per sq. ft. or $250? And if you have a budget of $80,000, what kind of addition can you have?

A basic calculation that will give you a very general idea is:

Budget / price per sq. ft = size of home addition you can build for that budget.

For example,

If I have an $80,000 budget, and I decide to build it at the low end of $80 per sq. ft, I divide $80,000 by $80 ..... I can build a 1,000 sq. ft home addition, quite a substantial size.

If I have an $80,000 budget, and I decide to build a high-end home addition at $250 per sq. ft, I divide $80,000 by $250 ..... I can build a 320 sq. ft. addition, the size of three 10ft. x 10ft. rooms.

This calculation seems simple enough, and gives a very general indication. However, there are many other factors that affect the price per square footage that you should consider, including: who does the work, the size, your location, degree of completion, type of construction and choice of finishing materials.

One other rule of thumb - additions with bathrooms and kitchens add a lot more to the price per square foot.

In the example above, a budget of $80,000 for a high-end addition will give me a 320 sq. ft. addition, but if one of the rooms is to be a kitchen, I can likely only build a one-room addition for $80,000.

General Cost Estimate Range

Many websites and contractors give you a ballpark cost estimate for different types of home additions. There are even some general online cost estimate calculators that give you a ballpark estimate.

JUST REMEMBER that unless the estimator asks for your location and some specific design and construction details (see below), the estimate will be very GENERAL.

After scouting a number of websites and from our own experience with contractors and home additions, we have put together the following range of general cost estimates for home additions.

Please feel free to save or print out the PDF, and you can click on the links to give you more information about the type of home addition.

You can use this chart to give you a budget for your home addition, and to narrow down the type of home addition you can afford. Keep in mind that it gives a general estimate only.

Detailed Cost Estimates for Home Additions

To calculate a detailed cost estimate, you will have to decide on the following:

Who Does the Work

A DIY home addition is much cheaper than hiring a design-build contractor because there is no markup on materials and no charge for labor. If you decide to DIY, your costs may be closer to $80 per sq. ft., or even below, but of course that depends on the other factors as well.

Hiring a design-build contractor can be as much as 2.5 times the material cost of a DIY project, however, there are underlying costs of a DIY project that should be considered, such as the income lost while you are constructing the home addition and not at your regular job.

A midrange option is to become the general contractor and hire out the different trades to complete the jobs you cannot do yourself. An underlying cost here is that you should have insurance to cover any accidents that may happen at the workplace, your home.

Bottom line: much cheaper to DIY. However, many people choose to hire a design-build contractor or become the general contractor for a host of other reasons. See Step 3 for an explanation.


The larger the home addition, the more expensive the overall cost. However, the cost per sq. ft. decreases as the size of the home addition increases. Therefore, a large, multi-story, high-end addition may be built by a contractor at $150 per sq. ft., whereas a one room high-end addition may be $200 per sq. ft.

Oversized rooms will obviously increase the cost, so add on up to 25% more if you anticipate large room sizes. See Step 6 to determine the size of home addition that you need.


Location matters. For our own home remodel, we built a multi-story home addition for $125 per sq. ft., but in other locations such as the midwest, costs may be considerably cheaper. The best way to determine if you are in a high or low end home addition cost zone, before determining actual construction pricing, is to compare the cost of buying a home in your area compared to other regions in the country. The cost of building materials generally follows economic trends, unless you are situated right next to cheap building supply companies.

If you know you are in a location where building materials are low cost and easy to get, you will be closer to $80 per sq. ft for a low-end DIY project. If you live on the east or west coast in the U.S., the cost for home additions may be double. In Canada, the cost of home additions is greater in Ontario, mid-range in B.C, Alberta and Quebec, and low end elsewhere.

Online home addition cost calculators (see sidebar) provide detailed estimates and often take the location into account before providing an estimate.

Type of Construction

Modular vs. Traditional Framing - pre-fab and modular built homes are generally much cheaper to buy and install than starting from scratch, see Step 5 should we do pre-fab, modular, or traditional construction?. Traditional wood framing is much cheaper than metal framing.

Type of Foundation - Small additions in warm climates that require at-grade footings are much less expensive than larger additions with a full basement that must extend a minimum of 4 ft. below the frost line in cold climates.

Degree of Completion

If you want to do part of the contstruction yourself, you can decide to have the contractor complete the foundation, framing and exterior cladding only. Then you can save considerable money by doing the interior of the work yourself or hiring part of it out to the trades. A project that is fully completed by the contractor is much more expensive than one only partially completed.

Finishing Details

Granite countertop, concrete or laminate? An estimate for the cost of a home addition is not accurate without knowing the finishing details for kitchens (cabinet doors, countertops, appliance models, lighting), bathrooms (single or double vanity, regular bathtub or separate shower), wall coverings, window type and size, window trim and much more.

When you know the answers to the questions above, you will be ready for a detailed cost estimate that we cover in Step 7.

For now, let's take one last look at how you can determine a general budget for a home addition:

Are you on the low, medium, or high end of the home addition cost spectrum ?

Here is a method for determining a general cost estimate for your home addition. If you prefer to use an online cost estimate calculator, see the sidebar.

To determine whether your home addition will be closer to the low end or high end cost, do the following:

  1. Identify the price range for the type of home addition you have. Click on the thumbnail below, which is the same as the General Ballpark Estimate Chart shown above:

  2. Now determine if you are on the low, medium or high end of the above price ranges by clicking on the thumbnail below and filling out the chart.

    chart listing the factors affecting the cost of a home addition

  3. Now go back to the price ranges listed above in #1. If you identified your home addition to be on the high end (by filling out the chart in #2), then choose the high end of the price range in the chart on #1.

    For example, you want to build an addition for a 1-room addition, which is listed above as having a medium price range of $50,000 - $100,000. From the chart in #2, you determine that your price will be on the low end of the scale because the addition will be a small size, you will be the General Contractor, you will use standard finishing materials, and you live in the midwest. Going back to the price ranges in #1, you estimate the cost of the one-room addition to be on the lower end of the price range, $50,000 - $70,000.

You can use the above method to predict an estimate for any type of home addition, but remember that it is a very general estimate.

Your general estimate can be further refined by doing a detailed home addition cost estimate as outlined in Step 7. But first, you will want to decide on two important design considerations -

  1. type of construction - click on Step 5

  2. size - click on Step 6

After going through these two steps, you will be able to put together a more realistic construction budget.

One room addition at side of house

Another way to determine the cost of a home addition is to use an online calculator.

The following cost estimate calculators and spreadsheets are available online:

Contractor online cost estimators
Many contractor websites will offer you a detailed quote for your home addition project, and there a few general ones as well.

Building supplier online cost estimators
Many building supply places such as Home Depot provide detailed calculators for flooring, drywall, insulation, paint, roofing, etc.

Directory websites with online calculators
Directory websites offer general and specific online calculators with links to contractors and building suppliers.

When you are ready to have a detailed cost estimate (down to the last 2x4 and box of nails), bidsheets can provide detailed cost estimates. You may want to review Step 7 - How much will my home addition cost? before clicking here.

For our own home renovation, we used some of the online calculators to give us a general estimate, then put together our own Home Additions Cost Estimate Worksheet once we were sure about the type of construction and the size we wanted.

Professional Cost Estimation Software
A number of websites sell cost estimation software programs geared toward design professionals and contractors, that are very detailed and cover every forseeable cost.