What is the cost for a rear extension/addition?

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Posted by: from Etobicoke
2/2/2015 at 10:30:29 AM


We live in Scarborough. We have semi detached 2 storey brick home on a 30x145 lot. The house is 20ft wide with a 10 ft driveway.

We are considering a back extension of approximately 208 sqtft. 16ft wide and 13 ft deep. Our kitchen is completely finished (and ends at the back wall of the house) so the idea of the extension is to give us a "walk through kitchen" and more living space on the other side. No plumbing is required, only a pantry cabinet and possibly an island. We would like to also add french glass doors to access a deck which will need to reinstall.

On top of the extension we would like to explore the possibility of having a walk out deck from the spare room.

The house has open access as we are an end unit and our house backs into a park. On the side of our driveway is a walk way to a park and the back yard is surrounded in a hedge which can be removed.

We would like basement under the extension to connect to the current based to allow us to eventually finish the +1 room in the basement. The current basement is finished with a rec room and a 3 piece bathroom.

Just to give you an idea I have added a picture of the back of the living room which shows the dividing wall between the living room and the kitchen.

Essentially we would like toe extension to begin 4 ft in from the adjoining wall. I have also added a picture of the back of the house.

If we can get a rough estimate on the cost of the extension and the impact of adding a walk out deck upstairs on the total cost.

Let me know if you need more info to assist with providing an estimate.

Thank you.

What is the cost for a rear extension/addition?
What is the cost for a rear extension/addition?
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Date/Time2/2/2015 at 1:33:57 PM

Hi Alex,

Sounds like you have given your project a good amount of thought.

Additions like your are approx. $220 per foot for the above ground addition only.

Figure on approx $50,000

Add about $30,000 for the basement

Add about $5,000 for the deck.

Now, the usual add ons or "Mission Creep"

Does the existing heating system have the capacity to handle the added square footage?

Will this drive a change to the existing first floor floors?

Will you have to seek permission from Committee of Adjustment?

Will you have enough back yard left over?

What exterior finishes would you like and how will that effect market value?

There are a great many more questions to be asked and decisions to be made before you get to an accurate quote.

Hire a reputable design/builder to guide you through the process and the journey will be much easier. Insist on getting RECENT references. You need to know if your builder is still performing for his customers, not just 10 years ago.



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Manuel from A.A.U. Construction in Toronto
Date/Time2/2/2015 at 3:25:10 PM

Hello Alex,

I agree with what Andrew had to say about your project. But if you are willing to do some of the leg work yourself, commity of adjustmebts, permits etc.. that can save you alot of money.

I think you can get this project more in the $125/$175 a sqft.

The fact there is no plumbing helps you out cost wise.

Best is to get someone out to have a look at your project first hand.

Good luck with your project.

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Suzanne from Built By Pros Inc. in Toronto
Date/Time2/2/2015 at 3:32:29 PM

The addition will cost $35,000-$45,000 including the openings to structurally connect it to the existing home with a 12- 15' wide beam on the first floor for open concept kitchen/living area, and single door in the existing basement to access the new unfinished basement. This would include one double exterior french door, one medium sized vinyl window on first and one small vinyl window in new basement. This assumes that your existing electrical panel and furnace are sufficient to service the new space.

Add $10-12000 for a flat roof with walk out deck and railings vs a sloped asphalt roof.

Add $5-10,000 for your design/engineering an permit fees.

Add $8-12,000 to finish the new basement space.

You will first need to check with the zoning dept at city hall to see what size addition is allowed to be and how close it can come to the back fence (also called "rear yard setback allowance")

Hope this helps.

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Alex in Etobicoke
Date/Time2/3/2015 at 1:21:36 PM

Thank you all for your great feedback and advice!

We will definitely be engaging a reputable contractor once we are ready to move forward.

All the information shared here has given me some valuable information that will help us with our decision making process.

I may have more questions later but for now, thanks to you all.

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Fiona in Scarborough
Date/Time2/2/2017 at 9:40:55 AM


I have a VERY similar project to have done and was quoted $125k the other day, so was about to throw in the towel (my budget is less than half that!!) Then I saw your post. May I ask if you had the work done and how much it ended up costing you?

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Ganesh in Mississauga
Date/Time4/6/2017 at 2:32:04 PM

Would like to know the quote for a 200 sq feet main floor extension alone in teh backyard. It is a free hold townhome and no need for raising the side walls.

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