Turning a SFH into a duplex- estimating cost

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I hate to ask for help, but am having one heck of a time figuring out an estimated cost for renovation on a property I will be closing on at the end of the month. It's 1,344 finished single family manufactured house built 2005 over a 1,344 sqft basement with 9' ceilings (2,688 total sqft.) The pluming is roughly in as well as loads of building materials. The problem is that it is Aurora, CO- one block outside of Denver and all licensed contractors are booked out for months and charging what I consider outrageous prices per books/online estimates I've came across. 

The previous owner was passed away in beginning phases of turning it into a duplex; its is zoned R2. The city does not have any duplex related permits. I would like a separation of gas and electric, framing, dry wall and doors. I can then complete the rest myself and/or sub out the remaining work. I've contacted 9 licensed contractors and have only received two estimate of 30k-50k or 80k-100k for full reno. One said the pricing it's due to the height of the ceilings (9') and that since it's below manufactured home it will require "specialty" framing work. 

I would think that the materials, age or the property (2005) and rough pluming would save me quite a bit?? lol I'll get multiple itemized estimates after closing, but would like to get finances in order prior. Any insight?? These guys just taking me for a ride?

@Chelsea Mastin Not being familiar with CO pricing, my idea on pricing may be off a bit.  But with that being said, sounds like your looking at finishing 1344 ft2 for the second basement unit. You would save on the foundation, exterior, roof, but you have almost everything else left.  My guess would be in the $50-65/ft2 cost range (this is based on my local costs of about $90-100/ft2 for new construction). Then there is some added cost for splitting the services like water, electricity, HVAC.  There is no way your going to finish 1344 ft2 for $30k, not even $50k, unless you try and do most of the work yourself.  All of the above assumes that the original house needs little renovation work.

Before committing with a contractor, make sure that you get with the local town to make sure that you are allowed to split the house and there are no issues that would prevent it (like egress, unit separation, etc).  Your local building department should be able to help.

Thanks Mike! 

I called city today and it sounds like there is some "red tape" to get through, but it is doable. Many of the little things that are required are already in place. I will follow up with them after purchase and ask to have an inspector come out to examine property with us. Really appreciate the help.

@Chelsea Mastin and @Al Williamson You could split with town/municipal approval without condo-ing.

With basement units egress windows are usually an issue.  Those are larger windows big enough for a fire fighter to enter with full gear including an air tank and for occupants to exit in case of fire or other major problem.  This would apply to either establishing a second unit or condo-ing.  Egress windows are expensive and if below grade you need window wells, there are precast concrete versions as well as large metal versions maybe even vinyl or PVC versions.  If below grade you will need to factor excavation costs also.  And fire, smoke and carbon monoxide detectors.  Some codes require interlocking units which set off alarm in all units for smoke or fire in one unit.

Usually the next hurdle is off street parking, around here 2 off street parking per unit is common though some places are requiring 2.5 or 3 per unit.

Next is code issues including fire separation;  the 2 units need to be separated with a fire barrier, usually they will accept 5/8 or 3/4 inch drywall; or double layer of 1/2 drywall.  All penetrations for pipes, duct work, wiring or anything else much be caulked with fire retardant material.

In many areas a condo separation will require a subdivision plan, with engineering, blue prints and municipal/county review and approval.  In some areas subdivision can take 1 year to get all approvals.

Even condo documents, must be drawn by an attorney and recorded at the courthouse can cost $5,000 to $10,000 themselves.

Before we did out first condo conversion, we had experience in land subdivision and development which aided us in understanding and expediting the process.  We've done subdivision work in different states and the rules are different everywhere.  One interesting project we did was the condo conversion of a 1902 build Victorian building.

hth

FYI it is my understanding that you can not do a "condo" for two units in Colorado. @Chelsea Mastin so your charge to contractors is a bit like. How much does it cost to build a house. The person that gave you the $30-$50k bid has no idea what they are doing. Years ago (~10) the going price for a basement finish started at $30 per sq ft. On top of that, you want to do separate systems (electric, gas, which means a furnace and water heater. To get real bids, you need a detailed written scope of work that includes finishes and a list of materials you will be supplying. It sounds like you are trying to do this on the cheap. To do so, you need way more knowledge than your post demonstrates. My advise would be to find a basement finish contractor and work with them. Also what you are proposing is not a "full reno" but more like a basement finish with some modifications. I would be floored if you could get the project done for less than $80k based on the picture.