Cost for Rear Two Storey Addition

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Posted by: from Etobicoke
2/2/2020 at 11:20:35 AM

I would like to add a rear addition of 14 x 30, with basement, main floor and second floor. I am located in Mississauga. Any ideas on cost? Would it be cheaper to do a 1000 sqft second storey addition on my current footprint instead?

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Date/Time2/2/2020 at 3:28:45 PM

Hi there,

In general, it is less expensive to build up than out, but that comes with a lot of caveats. According to HomeAdvisor, the average cost for building additions is between $110 to $250 per square foot without regard to whether it is up or out.

While it is usually cheaper to build up than out, that's just the actual construction expense. When you add another story to your home, you will probably have to relocate until the work is complete, as the contractor must remove the roof.

Unless you have friends or family willing to put you and yours up for a while, you'll have to rent another dwelling or stay in a hotel during this period, and those costs are considerable.

If you're building out, you will have to deal with the dirt and disruption of construction, but you can generally stay in place.

Costs also vary depending on exactly what the contractor must do. An addition usually costs more because the builder must perform excavation work and install a new foundation.

When construction is near completion, the contractor must open up the exterior wall of your home so the old and new are joined together.

However, if you decide to build up, you have to make sure your current foundation is strong enough to support another story.

If the foundation requires retrofitting, the expense includes removing your existing walls, which will raise your costs substantially.

Keep in mind that adding another story means adding a staircase, which will take up precious floor space on your first floor.

Remember this will impact power and plumbing either way, but if going up, you remain in the existing envelope.

We are not located in your area, but would be happy to at least help you make sound decisions with whomever you contract, if that would be of help to you.


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Date/Time2/2/2020 at 3:30:40 PM

I don't give ballparks for projects this size there's too many variables! I do know it would be less expensive to build up on existing than it would to be building an addition

I strongly recommend you contact a trusted Pro contractor in your local area to get a firm quote with all details.

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Date/Time2/2/2020 at 8:22:15 PM

Hi Christine, I hope you had a great weekend.

My name is Marko Furlani, president/creative director of Urbanest Construction.

Normally there is a higher cost when increasing the footprint of your home, such as excavation, forming, footings and engineering. Not to mention the additional permit and architectural work involved. When adding an additional story, you avoid most of those items, but are limited to the size of the addition.

Its very difficult to provide a pricing for a project such as an addition, but you should consider increasing the footprint could cost up to 50% more than an additional story.

Thank you,

Marko Furlani

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Christine in Etobicoke
Date/Time2/3/2020 at 8:06:58 AM

Thank you all for your replys! I am leaning away from a second storey as I would like as little disruption to the current space as possible. The main floor has already been renovated by the previous owner. Here is my next Q:

Would it be more cost effective to build a main floor 700 sqft rear addition or a 450 sqft rear two storey addition? Thanks in advance!

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Date/Time2/3/2020 at 8:16:05 AM

Ultimately, both reno projects would cost about the same. It really comes down to the final details. Exterior fa ade can greatly increase the cost of an addition so keeping that in mind, the more exterior wall you have to finish, the more you could be spending.


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Date/Time2/3/2020 at 8:21:24 AM

You should also keep in mind the city will have some restrictions and limitations as to how you construct your addition.


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Christine in Etobicoke
Date/Time2/4/2020 at 6:38:56 PM

Can a rear addition be safely built on "slab on grade" in Ontario?

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Date/Time2/4/2020 at 6:40:40 PM

No, it cannot. It will require a footing between 4'& 5'min.

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