Costs are very location specific. In fact, most of your questions are very location specific, plan specific, or site specific and cannot readily be answered in any accuracy on the internet. What costs 20K in one place may cost 10K in another or 30K in yet another location. You need an architect to finalize your plans for you and a builder to give you a price estimate on those particular plans. You could start by interviewing builders in your location on their general costs to build and look at specific homes that they built with their costs.

We DIY built our 30x60 shop/garage 15 years ago. However, we still spent 40K on materials, with no labor. It would probably cost at least 70K in materials to replace what's there, and that's with no labor to pay. If we had to pay to have it constructed, it would top 100K easily, and we're in a very cheap labor market. Admittedly, it's a very well built and insulated garage, with HVAC, but it has zero decorative finishes.

Live-wire-oak, thank you for the reply. I understand your point, but can we hypothesize to use the same materials and methods to either build an extra attached garage or a detached garage with the same size in mind, disregard the difference in location for the costs?

I am not trying to have an exact figure but only comparing the cost-wise between an extra detached and attached garage.

Thanks

Are you talking about adding to it before the house is constructed or after. I would think that adding it before the house is built could be cheaper. It would all just depend on how that extension affected the rest of the plan like the foundation and roof.

However, if the house were already built, you would have additional costs like how to join the foundation, how to tie into the exterior of the house, load bearing walls , joining the roof, etc. and I think it would be cheaper to built a separate unit.

The house is not built yet. My husband wants a 4 car-garage, which is hard to be found on small foorprint/sq footage house plans. We would like to plan building a 4-car, instead of 2 car garage

We are currently building a 4 car attached garage. I decided to add it to the budget when my husband told me he would forgo a seperate garage later if we did a 4 car now. As far as the addition to cost, it was somewhere around 3,000-5,000 per space. We have unsuitable soil(clay that is expansive) so we had to have the slab engineered with post tensioning, which in turn required us to pour the slab twice as thick as it would be under normal circumstances etc. We also have an all brick home, so when you add the cost of each brick (.38 per brick and .30 for labor plus the grout, that add up in a hurry!)

To build a seperate garage would have been well over 30,000. When you are already building, the contractors are there anyway so doing a little more work is less expensive then them having to ''re-mobilize''

My 2 cents

Slab should be equal
Roofing materials close to equal (unless local code requires some exotic roof that you wouldn't match on detached garage)
Framing - more with detached (unless local code requires something expensive on attached - ie high wind zone)
Doors - same unless local code .....
Siding/brick - more with detached unless you plan on vinyl on detached and brick the house
Electricity - more with detached unless you didn't plan on having outlets in a detached garage. Code requires so little of attached garages that the cost of getting electricity to detached would certainly be more expensive.
Gutters - detached may not need so you might save a few hundred here.

So there are a lot of local variables. In my inland area, if the siding was the same, then attached would surely be significantly cheaper. That being said, it is hard to picture a small house looking good with 4 attached garages.

For comparison sake...our plan originally had a 2 stall attached garage, during the drafting phase we added a 3rd stall. Our contractor only added $2500 to our estimate to add that 3rd stall. It would cost WAY more than $2500 to build a detached garage later on.

With the extra concrete, walls, ceiling, and garage door for this stall, plus the floor, walls, and roof it added to the bonus room above, I don't think $2500 was unreasonable at all.

LOL at "it is hard to picture a small house looking good with 4 attached garages." quoted from david's 2 cents.

I know, but that's my husband's request. It told him that, yet he does not care the look at all!!!

Thank you for your analysis; it's very helpful

We were quoted about 30k-40k for a separate 2 car garage to match the house (hardi and stone). I can't remember how much more we paid for adding a 3rd garage to the 2 car plan, but it wasn't anything close to 30k.

If your husband is insistent on a 4 car garage, then look at making the garage rear entry instead of front or side entry. It wouldn't look like a commercial auto repair place with a small house attached then. It would also give you the turnaround space as a private "party" patio without having to construct an extra patio. It will only be minimally more expensive for your driveway paving to construct it like that and it keeps the facade looking like a house at least. You will have to have a large enough lot for this, but if you're looking at a 4 car, you're not looking at 50 foot wide lots.

Our workshop/garage is side entry and the single and double doors are basically in line with the house's side entry garage. Like all side entries, it's at least only partially visible to the street. We've had the "auto shop attached to the house" comments, even though the house is in front and they are separate structures. We had to do the shop in the rear because of codes, but we have a great view to the rear of the property, so building it in a "L" orientation to the house was our compromise to keep as much of the view as possible and still have the shop. I only wish we had had other more aesthetically pleasing options. Starting from scratch gives you a lot more options.