Extending thje back wall of a brownstone
I live in a 20-ft wide brownstone with a 9’x10′ single story extension in the back. The garden floor is an apartment in need of renovation. As part of the renovation we are thinking about extending the back wall of the house so that the extension spans the full width of the house (20’x10′) .
Has anyone done this type of project? We have heard that we will need to dig out the basement under the extended wall to allow for the construction of a foundation. I assume we will also need to provide additional support for the bearing wall along the back of the house. What are the other issues/problems we might encounter? Any ball part estimates of the cost of doing this type of work?
dianeg
in Renovation 8 years and 4 months ago
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16 replies
CarmenR | 8 years and 3 months ago
We just finished a major gut reno and a 3-story 21X10′ extension. Our project sounds like it was bigger than yours, but if you want to chat, feel free to drop me a line at greenwoodframed at gmail.
dianeg | 8 years and 3 months ago
Thanks so much to the recommendation and all your information. Very helpful.
DanWilson | 8 years and 3 months ago
The architect for my project is Nicholas Wilder, WM Architecture DPC. He’s really great to work with and he has been a very helpful navigating the DOB filing process. Tell him kquock sent you. Price wise I would say he is about average from other quotes I’ve seen. Most of the cost for my design (about 50%) was the structural engineer. The other cost is the Expediter, soil testers, Asbestos tester (I forgot to mention that in my last post. You must do an asbestos test for your filing, but it is not a big deal, recommend QualTechNY) Many contractors also provide architecture and DOB filing services or they have an architect that they typically work with. It’s up to you to if you want to just go with a one stop Contractor. I like that Nick is not tied to a contractor so I have the flexibility to manage my project and hire whoever. But if you just want to hand everything over to a one stop shop that works as well. As far as contractors I have not settled on who will be doing my project yet but I am looking at two potential companies Sienia Construction INC who did the reno on my friend’s South Slope condo. They do larger jobs like mine as well. I would say that Sienia is your typical contractor where if you can get them on contract and scheduled, your are good to go. But if your project is further out like mine is, they can be very non-committal until you are ready to pull the trigger. The second is Azad Waterproofing who is a small local contractor who does a lot of masonry work in my neighborhood of South Slope. He did some other work for me a few months ago and I was very happy with it. He also does complete interior renovations as well. Since he is a small shop he can be competitive with his bids and is very reliable. (Fair warning…he can be a hard to understand, but if you’re patient and work with him in person, he grows on you). Lozano Construction is doing a gut reno on a 3-story brick townhouse on my block. From what I can see they look like they are doing good work. I’ll probably get an estimate from them as well. Anyway recommend sifting through several contractors until you find the right one for you.
Also, a basic subscription to Angie’s list is now free so you can join and look through some of their listings, which is another good resource.
imgrant2020 | 8 years and 3 months ago
Kquock – would also appreciate some recommendations for architects and contracts…looking to do something similar.
rodneyanonymous | 8 years and 3 months ago
Dianeng. We are considering the same work. Love to hear how yours go so please keep us posted! Thanks.
dianeg | 8 years and 3 months ago
Kquock – thanks for the excellent information. Very helpful. I would love to get a recommendation for an architect and/or contractor. Thank you.
DanWilson | 8 years and 3 months ago
We are doing a two-story (16’x14′) extension on our house this coming year so we have spent the last 6 months or so doing all the planning, designing and filing.
So some recommended steps/suggestions
1.) Check your Zoning and your FAR (Floor Area Ratio) which will tell you if you can build more enclosed square footage onto your house. NYC DOB website will have all this info for you neighborhood.
2.) If you have the extra FAR then recommend you first bring in a few contractors to get some free opinions and some ballpark estimates. (I estimate somewhere in the $50-80k range for the construction and about $20k for the architect and structural engineer). As mentioned Landmarked areas are an issue.
3.) If you make it through steps 1 and 2 and you want to go through with it then get an architect (I have a great one doing my project if you want a recommendation) The architect will do the design, contract the structural eng, expediter for the DOB filing, etc….
4.) Depending on when your existing extension was built and if it was filed with the city (probably not) you may b e required to demo the existing structure. I would highly recommend just demo-ing the existing structure and starting from scratch. Demo and concrete are cheap. You will also need to have a company come in to do soil testing so the structural engineer can design the foundation properly. Your architect will help coordinate this.
5.) You will need to do some digging as mentioned by others in this post to pour a foundation for the perimeter walls (probably at least 5 ft deep). The floor will be on a 4″ concrete slab and be level with the existing floor. All of this will be spec’d out by the Structural Eng.
6.) Structural steel beams will be used if you plan to blow out the back wall into the extension. If you only plan to do a standard doorway into the extension with no major demo of the back wall, then only minor structural framing will be needed if any at all.
7.) Agree with slopefarm on the insulation since you will now have three walls exposed in the extension. However, your architect will ensure that the new construction meets thermal building code so they will work to ensure proper insulation, windows, waterproofing, etc…. Depending on what type of heat you have now (probably steam/hydronic heating) you will need a plumber to extend a heat pipe into the new extension. Or you can install a split air-conditioning/heating system and kill two birds with one stone. Another alternative is to do Hydronic Radiant floor heating which you would install when you pour your concrete slab.
Also look at the cost differential of doing an even larger extension (go as big as you can). You will find the cost difference to do a larger extension is pretty minimal. To give you an idea, for us to knock down and rebuild a small half width extension (9’x9′) would have cost around $50k To do a full width two story extension (16’x14′) is only about $80k. You are already paying for all the engineering work so the biggest delta is the extra material and some labor (Disclaimer: I’m doing most of the interior finish work to keep the cost down so my numbers may seem like a pretty good deal. But relatively speaking its a small delta to get over 3x the sq footage of what we were originally going to do)
Believe it or not this whole process is quite involved for something that seems so small. Anyway start with steps 1 and 2 above and then go from there! Good luck. Let me know if you need an architect.
nfkswcrae | 8 years and 3 months ago
Make sure you have your site survey then find an architect, I can recommend if you’d like. A simple, quick and free review if the site survey will let you know what you can and can not do on the lot.
Good luck
dianeg | 8 years and 4 months ago
Thanks for the guesstimate and the detailed response from slopefarm. This is the type of information I was seeking. I understand we need to check the FAR allowance and zoning restrictions. I am somewhat confident we are ok since others on the block have made similiar changes to their brownstones.
jimhillra | 8 years and 4 months ago
EJR – That was never allowed in residential zoning districts. The closest one might be able to get to that would be on a lot within 100′ of a corner, in which a rear yard is not required. However, lot coverage would still apply, and that’s typically 80% max at a corner, so you’d have to have a big front yard to be able to build to the rear property line.
EJR | 8 years and 4 months ago
> @jimhillra
> Arkady – What do you mean “no longer allow property line to property line”?
I think he means in the rear of the buildings, not on the sides.
jimhillra | 8 years and 4 months ago
Arkady – What do you mean “no longer allow property line to property line”? Aside from areas in which side yards are required (usually not brownstone areas) it is actually harder NOT to build to the property line.
Arkady | 8 years and 4 months ago
If you’re in a landmark area, you will have to get permission. I’m pretty sure that most areas, landmark or not, no longer allow property line to property line. You should also be looking at your FAR allowance.
EJR | 8 years and 4 months ago
All good advice above. This is really the type of question that requires consultation with an architect and structural engineer. Every house will have different quirks that require house-specific solutions. Before proceeding too far with this plan, you should get a sense of whether this fits in your budget. While this is a guesstimate, I could see a project like this running $50-$100k.
slopefarm | 8 years and 4 months ago
We had a partial extension on our frame that we tore down in favor of a full width extension that uses the full depth allowable with the setback. We also put a deck on top accessible from the parlor floor DR/K. We did a full foundation for it, down to the proper depth below the frost line, with a slab for under the floor. We did not extend the cellar underneath the extension. A few considerations, though your architect will know this better. You will need to support the current rear wall and redistribute the weight (probably a steel beam) because you are removing support when you open it up. The extension will be cold in the winter, with more exposed walls. You will want to insulate more heavily than you would the front and rear walls of an attached house, and you will want to bring heat all the way into the new space. Also, you want your architect and contractor to be attentive to how the extension is attached to the house, waterproofing the extension roof etc. You are creating new points of vulnerability, so do it right the first time. Finally, if you are d ecking over the extension roof, make sure it is relatively easy to remove and put back in case you need to access the roof for leaks etc.
agdipierro
in Renovation 8 years and 4 months ago
First, ascertain if the work is permissible according to the NYC Zoning Resolution and the building code. Do you have the available square footage? How about the rear yard setbacks?
You may not need to fully excavate the basement if you just have a crawl space or a slab on grade for the addition.