Cost of rear addition to a brownstone
Is there a general rule of thumb for adding a rear addition to a brownstone (i.e. cost / foot) , and does that estimated price fluctuate based on the number of floors that are added? (i.e. would it just be a multiple or would higher floors be more expensive?)
My goal here is just to get a very rough ballpark figure so that I know what is and isn’t possible. Depending on cost/feasibility, we could be looking to add 5-10 ft to the back of a 17 foot wide building on the garden (partially underground), parlor, and potentially 3rd floors.
ssuarez
in Construction 12 years and 11 months ago
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7 replies
brucef | 12 years and 11 months ago
Bond, Great tip on the ceiling heights. Structurals called for doubled 10″ 12 gauge C-joists, but that doesn’t work to line up with building floors that are built with old 3X8″‘s. So we managed to get engineering to agree to 10 gauge doubled 8″ C-joists.
AnArchitect | 12 years and 11 months ago
Plan on @$300 per square foot and then slowly back into a budget once some of the critical issues above (FAR, Geotech Report, and Program) are resolved. We’re architects and engineers and have done this a number of times: www.agenciegroup.com
Bond | 12 years and 11 months ago
Some good advice here, I’ll add my two cents worth. Figure on 20K just for start up cost, architect, soil load test, asbestos, architectural survey, exhibits, etc. Then depending on what the soil test comes up with, you may or may not have to go down past five feet to hit good soil (there are lots of former swamps in Brooklyn which won’t pass inspection, so you have to excavate to good soil) and then you’re talking about shoring, which if you don’t have easy access to the back for an excavotor is a big pain in the butt. Bottom line is that anyone giving you costs without the soil test is either planning for a worst case scenario and adding in a large cushion, or is going to give you a price subject to change, or has no idea what they are doing. So the dilema is that if you have to excate to the point that you need shoring, you may as well add full cellar space, so then you’ll end up a big cost. If you have to do it by hand, it’s probably in the 30-40K range to get the foundation in. Once you have the soil test, everything else should be pretty straightforward with pricing. CMU side walls with standard bond beams, ladder wire, etc. runs about $15 a square foot, but don’t again, if I’m you’re GC, I’m adding my cut to that. Then you have to figure how you want to cover the block, or even if you want to cover them, you may choose to go with simple waterproofing. Going up won’t significantly add to the cost, the minimum foundation you can build will be code for six stories, so other than scaffolding, you’re not talking about any additional costs. If you’re going all the way to the roofline, you may have a problem in that most Brooklyn roofs that I have seen slope to the point that the cockloft has disappeared by the time it hits the rear wall, so in order to meet code on ceiling heights, you may have to raise the roof, another expensive proposition. Last but not least, a lot of joists in older homes are undersized, so matching ceiling heights on one level and floor heights on the one above is problematic, so make keep that in mind when planning. If you go with a different ceiling height, it can be a problem if it’s on a typical garden level with low ceilings to begin with. Different floor levels, well, who wants that??? Obviously this is all rough estimates, but it may help to give you some idea of some of the pricing or potential problems, other than that, it’s a piece of cake.
Augustiner | 12 years and 11 months ago
I had a quote from a good GC for a 2 story 40 ft (!) extension – it was roughly 200 k, which is surely reasonable for an additional 1800 sqf.
This is just the shell with foundation and opening up the back plus lighting and electric wiring, not including finishes, windows, planning, expediting.
brucef | 12 years and 11 months ago
We are adding a few additions, in our case we don’t have the FAR to go up higher than 1 story. For example we have 350 ft available, so we will be going out 15′ on a 22′ wide building. If we had split that into a two story addition each could be only 7′ deep each. Our single story addition only requires a 4′ deep foundation with one gotcha. The 4 ‘ foundation has to be faired down to 10′ deep where it meets the cellars foundation. I would think that 5 ft wouldn’t be worth the expense. Figure our 15’X22’ single story additions will be 50K each for the shell, not including guts. The two buildings share a wall and we will be building up the walls with CMU (not frame, too tacky). That is hard cost not including architect, Structural engineer, permits, expediting. Bear in mind that you are not allowed to make existing rear space with windows into an interior “dark” space. If you are “heading out” the rear wall and just extending the same rooms with same usage, you would be OK.
jparnass | 12 years and 11 months ago
The basic cost of the foundation (expensive part) plus block or steel framing (less expensive part) and roof is going to be fairly similar from project to project, but what’s really going to affect the price is what you plan on doing with the extra space you create. Adding additional floors makes sense since the incremental cost is small relative to the base excavation, concrete and wall construction you will have to do in all cases. Beyond materials and finishes, elements such as number, type and size of windows, heating tie-ins, plumbing, electric and all the necessary infrastructural work will add significantly to the cost. Following this logic, adding bedroom or living space is much cheaper than new bathrooms or kitchens (as in any renovation). The first step should definitely be a calculation of setbacks and FAR to determine exactly the footprint and amount of square footage you can legally build. Combining that figure with a rough program for the use of the new spaces a ballpark scope budget can be generated.
widthom | 12 years and 11 months ago
Will be following this thread with interest as I am in virtually the same situation. I know what we’d like to do but have no concept of what it might cost. Perhaps we can compare notes at some point!