Framehouse extension: how to build a 3rd floor
Thanks very much for the comments. It was a pleasure discussing the project with you. Jim
dazednconfused2
in Construction 9 years and 11 months ago
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okreitz | 10 years and 4 months ago
We want to build an extension on top of our semi-detached frame house in East Flatbush (R6). We have ~ 550 sf FAR left, the footprint of the house is 16 x 62 (~1000sf). Our plan was to build a 3rd floor master suite of ~ 500sf and a rooftop patio (also ~500sf). The problem is, according to 1938 building code, you can’t have a 3rd story on a frame house (if it is a 2 family which we have and want to keep that way). It looks like according to 1968 or newer BC you might be able to if the house meets certain fire standards (e.g. adding sprinklers). Does anyone have done this before or know someone who has built a 3rd floor on top of a 2 story 2-family frame house? BTW, the dividing wall between the 2 buildings of our semi-detached is brick, all other walls are wood frames with drywall. Any hint or recommendation of a good expeditor appreciated. Thanks!
resident2 | 10 years and 4 months ago
Yes, you will most likely need to add a sprinkler system. Consult an “old code” architect, if you call it an attic storage space etc you may be able to get an addition without a fire-escape or sprinkler. But also keep in mind that when you add additional space and make all of these additions, improvements etc to your house; approximately two years after you have finished and it is all signed off etc, you will get a huge Real Estate tax increase. If you want a bigger house it is often better in the long run to just sell the current house and buy a bigger one.
dazednconfused2 | 10 years and 4 months ago
We recently completed a rear extension and additional floor on top of a three story frame row-house. It required a steel frame for the top floor, with columns going down through the frame walls to the foundation. In the end, it wasn’t as bad as it sounds. The one or two family restriction applies only if you are trying to maintain the same type of construction. So if you are willing to entertain the thought of adding some steel, then you’re changing the new construction class, and it is then permissible. The section of the 38 code to which you refer also states the following:
> c. Any wood frame structure erected before January first, nineteen hundred thirty-eight, may be enlarged provided the new extensions are all Class 1, 2 or 3 construction, and provided further that the structures after alteration are within the limits of height and area prescribed in section C26-254.0, for Class 1, 2 or 3 structures, respectively. d. Nothing in this section shall be construed to permit the enlargement of any wood frame structure erected before January first, nineteen hundred thirty-eight within the fire limits, occupied exclusively as a private dwelling, to exceed the limits authorized as follows: 1\. For the purpose of erecting a flat roof thereon, any structure already exceeding twenty-five feet in height may be raised to a height of thirty-five feet or less.
Jim Hill RA, LEED AP **Urban Pioneering Architecture, DPC**
okreitz | 10 years and 4 months ago
Thanks for your input, Jim! I went through the 1938 Building Code and found the same encouraging passage. But then it refers to section C26-254.0 which again refers to the table on the following page. According to the table, a Class 4 Wood Frame has the following height limitation:
> 35 feet 2-story and attic without human occupancy, except that single family dwellings may be forty feet, three stories and except as otherwise provided in section C26-248.0
The experts we talked to so far believe that we could only build an attic which means no bathroom and limited to 8ft. Are you saying that through the extension the building changes it’s building classification (to Class 3, I assume) which then allows a 3rd story? That sounds fantastic albeit costly. Would you disclose how much more (in %) you would calculate for the extension of steal beams all the way through to the foundation (for the sake of adding value to this forum – I will reach out to you directly to continue the conversation)?
dazednconfused2 | 10 years and 4 months ago
It was our experience in this project, that the additional structure was accepted as a different construction class, Class 1 Fireproof according to that table, because it was all steel beams, joists, studs, etc. In that table, that construction class is unlimited in terms of height and area. This does not mean that the construction classification for the whole building changed, just the top floor. The rear extension was also non-combustible being steel joists and concrete block walls. As for the additional cost, I’m really not at liberty to say, especially on an open forum like this. Please feel free to call to discuss this further, specific to your home. Jim Hill, RA, LEED AP **Urban Pioneering Architecture, DPC**
riva | 10 years and 3 months ago
Happy to help estimate cost: Find me here: http://brownstoner.staging.wpengine.com/hxaw
greatwindowsss | 10 years and 2 months ago
elm_bk | 9 years and 11 months ago
Hi I’m interested in what you learned – do you mind updating us? I’m trying to come up with some estimates for demoing my cockloft or raising the roof on my third floor to max height/FAR . . . thanks for any info!
okreitz | 9 years and 11 months ago
Here a project update (by popular demand): We ended up not moving forward with the project. Jim Hill (see above) was very kind to give additional input (offline) and we ended up finding other folks who had very similar challenges. Bottom line: if you have a 2 family frame house of 2 stories, you can’t build a third story unless you make the entire house “non-combustible” in some way according to the 1968 BC. The easiest way seems to be to add sprinklers to the entire house but we didn’t want to make that investment on top of the building cost. There are exceptions if it’s a 1 family (you can base of 1938 BC in that case) or if it already has 3 stories. But this particular constellation it’s either sprinklers or only building an attic which has some height limitations and also can’t be livable space. I recommend getting in touch with Jim if you need further help.