Ask us: How can I add a roof deck to a 2-unit building?

Where readers ask and we (the community) try to answer:

Firstly, thanks for such a great site! It has really given me some amazing insight into the San Francisco market. One item I’ve been trying to research to no avail, is just how hard it is to add a roof deck to a two unit building. Specifically, are the permits easily obtained? How long would such a project usually take to construct? Estimated costs etc? I’m not looking to do this without professional help, so if anyone has any recommendations of an architect and/or contractor who has any experience with roof deck design/construction it would be greatly appreciated.


Unfortunately this came to us anonymously so we can’t thank the reader or direct any experts to them directly, and that, in turn, opens the door for you to plug the hell out of your (or anybody you know) services in the comments. Just answer the question first, so we all benefit. ;-)

27 thoughts on “Ask us: How can I add a roof deck to a 2-unit building?

  1. Yes, it’s possible to add a roof deck to your building. With restrictions, codes and safety requirements. Here are a few basics to start:

    1. Hire an architect to review the building and planning code requirements; height limits, setbacks, allowable area of deck, exiting.

    2. You will most likely need a structural engineer to also review the roof loading requirements. Most existing roof loads are NOT designed for live loads of people. Most likely you will need additional joists, columns, beams added to support your new roof deck.

    3. The architect can then develop the right drawings for permit approvals and submittals. You may need to do 311 notification for neighbors. The architects drawings and specs will be also used for getting bids from contractors. Without drawings, you really have no way of getting accurate pricing for your new deck.

    The architect can also help you select the right contractors and get several bids for construction.

    So, yes. You may be able to build a new roof deck on your 2 unit building. Following a clear process will make it go easier, resulting in the right project for you.

  2. When you say you may need additional joists, columns, beams, etc. Is this all added in the basement/garage?

    Will the structure engineer also look at your foundation to see if it should be enforced to handle the additional live loads?

  3. Yes, essentially the engineer will look at your foundations to see what upgrades may be needed to support the new roof loads. For the new roof deck you may need additional joists installed at the roof level, some beams to support the joists and columns under the beams. those new loads all must be carried down vertically to the foundations. If you don’t have stair access now to the roof, you will need to add the stair, per code, and the required stair penthouse. This will all come out of the initial review your architect can perform for you.

    Hope this helps.

  4. a side note regarding structural engineers.

    Do NOT, NEVER, accept to work with any engineer who REFUSES to * come * take photos *get his suit dirty crawling under/above/behind etc * have a very strict contract of what/where/how * to submit his drawings to YOU FIRST for discussion and approval before anything leaks to the all mighty DBI.

    Structural engineers can be either good or dumber than my 6yo son. DO NOT, NEVER get side tracked because of incompetence, ghost work at a big company (read me? bozo, you know I’m talking about you!), or simple stupidity.

    Any structural work can be done at least 6 different ways, each with pros and cons (including differences in costs, materials, time, damage to living space etc) – and ANY structural engineer who does not offer at least THREE reasonable options is not worth your time or your money. (those 3 options might not go as far as structural drawings that you would need to pay, but they should be explained in writing and ask for your permission to follow any/YOUR CHOICE of those 3 options).


    Repeat after me: a beam split in 2 at its midpoint is STRONGER that the same beam doubled. Any bozo knows that – except the kiddy who did our plans…

  5. wow. such emotional turmoil! sounds like you have had some bad experiences with an engineer. sorry about that.

    The engineers I work with would NEVER perform the way you have mentioned. But I suppose there may be some unprofessional ones out there. That’s why I recommend the client start with a licensed architect, such as myself, to begin the process of designing the project, and assembling the right professional team. Even a roof deck, perhaps seeming like a simple project, involves architectural and structural work to make it conform to the building and planning code.

    The health, safety and welfare of the public is one aspect of the architect and engineers responsibility to all clients.

  6. urban, you would be shocked if I was telling you the name (like one of the names that everybody knows in the city) … seriously.

    And to be honest, I would not have typed my note if it was not for 4 projects I know where homeowners sold their house because the structural report was so butchered than a “simple” project such as above was hammered into a “the only way you can do this is with a 1.5 MILLION dollars remodel of the house”.

    I guess the problem is always the same “your project is too small – either you accept to spend over a million in remodeling and upgrading cost, or we wont work with you”.

    I met that wall of “minimum size” in 2001, while researching my first homeimprovment (I guess 2001 was a bad year for tiny projects anyway), but it seems that there is SO MUCH money keeping flowing into the city that many contractors, architects, subs etc… can indeed afford to ignore “mr normal” with his “normal size project”. There are so many “down to the studs” projects around the city that the building world seems to forget what is a non-intrusive improvment.

  7. @sophie:

    sorry you’ve had such a bad experience with certain engineers. but don’t write off the whole profession because of one bad apple. there are good people and I’m sure some not so good.

    I would say that those homeowners probably picked the wrong team in the first place. If the budget is firmly established by the Owner, up front initially, then no one can really “force” a client to spend more. they need to assume some responsibility.

    Most of my projects would fall in the “small” category; from $100k to $500k, and that can cover a lot of construction. I only had one last year in the $1m range for a full house remodel, and that budget was set at the very beginning by the client.

  8. major issue: you will definitely need to do a 3.11 notification. that means you must declare, via legal process, to all the neighbors around you of your intended roof deck.

    bottom line: if you reside in an uppidy, persnickety neighborhood, chances are pretty damn good at least one of your neighbors will put you through the meat grinder with appeals to the city. it’s hard to argue that a roof deck is necessary living space; your neighbors may be jealous; or they may have a valid claim- as you’ll probably be higher than most folks, and privacy becomes an issue. (you have an uphill battle!)

    now assuming god’s grace is with you and you pass the 3.11 process, if you need to do foundation/structural upgrades, this roof deck can quickly become one expensive-ass proposition.

    you may want to consider meeting up with an experienced general contractor, to see if you can do this on the sly w/o permits. as long as you have reasonable access to the roof (perhaps via a rear deck.) and as long as you don’t plan a rave up there, building a small platform for a few folding chairs, etc. may be your cheapest/easiest option. (but remember, no raves!)

  9. may I kindly say that small should be UNDER 100K, and not up to half a million?

    consider the sunset. Many of those houses could benefit, and many owners could spend up to 100K in improvments, and some require a nice structural analysis. think the deck at the back, the deck on the roof, opening the wall between the 2 front rooms (the living and the dining), closing/modifying the courtyard/kitchen etc. and OF COURSE, a simple “remove this @#$! post in the garage to add one more parking space – whose costs is – plans, permits, a couple thousand in material (a couple beams, a dozen sheets of sheetrock) and labor.

    with half a million, you can have a WAY beyond small project that includes raising the house, new foundations/basement, new roofline etc – check our house, you cant even recognize the building between before and after! and we didnt spend “that much” money compared to the glamour of the result (and the amazing extend of the structural upgrade)

    Also, I want to point that I’ve rarely seen any project (construction or otherwise) stay on budget. Halfway thru construction, we were the target of some ridiculous pressure to use the equity created by the first half of the project to pay for additional parts and costs we didnt plan for and didnt want. Yes you say “was set at the very beginning by the client” – but considering that everybody EVERYBODY lies to their teeth, I want to speak for people who might not have the patience or strength to hold their ground.

    If you tell your RE agent that you want a condo between 800 and 1200 – chances are that the agent will show you only condos in the 1100-1300 range.

    If you tell your architect that you want to remodel your house and that your budget is 1M, guess what, the project will with certainty end at and beyond the million target.

    Should you have annonced a budget of 750K, guess what, the SAME project might go slower, maybe with some cost control, but will still be finished, up to code, and be nice and stay under the million, and maybe (let’s dream) not go over 900K.

    so what’s your take on that?

    when a client annonce the budget is 800, are you planning a 400, 600, 800, 1M, 1.2M project? Do you even check the financing for the first 400K? do you google the owner and plan to spend his million and a half you know he has in cash?

    I’m not saying you are not ethical (the “you” is a simple general address with no fingerpointing to anybody). I’m just saying that because everybody lies, the spender always add 10, 30% or even 80% to the numbers annonced – just to be safe, and the biller – depending on his ethics – might annonce a price tag of 70%, 100% or 130% depending on what he wants from the spender!

    to go back on the question raised here, I think there are TWO approaches to the idea of adding a deck to a house. And BOTH approaches should be persued with great attention and detail.

    The first lead is to tell your builder that you have so much cash in the bank, and what is the best use of that money if your dream is a deck.

    The second lead is to tell your architect that you want a deck and that you have no set budget and want to know how much it would cost.

    Then, with those contradicting (or not) informations, you start negotiating adding the structural needs (source = the architect) into your talk to the builder, and you start negotiating simplifying the blue prints to reduce the costs (source = the builder) to your architect. And dont settle till the architect and the builder are on the same page, yours.

    I believe this is the only way to take away the frustration of doing too much, or too little, for too much, or too little money, and have the dreadfull feeling that the project went of the tracks (while the project itself can be very well wrapped and budgeted)

    So back to the deck on the roof. Unless you have an architect check (with a structural engineer) your building (each building is different, zoning, age of the building, structure, naighbors, etc) you wont have an idea of what is involved and which grandfathered code you can use or need to fight – and unless you have a contractor check your building, you wont have an idea of specifics that can unbalance greatly your budget (like historic parts hard to match, storage, parking/unloading of material, general access, etc).

    And altho it’s a safe bet to shut your ears to any sentence starting with “while you’re at it…” having your builder state those sentences BEFORE the project start might help you decide to finaly spend the money in a more urgent matter. (such as: the roof is in bad shape and would need some serious TLC in the next 5 years.)

    Dear Anonymous, let us know how your deck project is doing, and please invite Alex for a margarita to inaugurate it!

  10. Some valid comments , perhaps; but, unfortunately the underlying tone is some bad experiences you have had, or others have had. I sense frustration, anger and much mis-trust.

    I can’t really help with those issues, but I will say this and keep it brief:

    1. not EVERYBODY lies. there are good professionals out there.

    2. $100k is considered a small remodel project in San Francisco.

    3. $500k will start to bring you full new foundations, a kitchen remodel, perhaps 2 bath remodels, some rear addition, some exterior improvements.

    4. my $1m budget project of last year is now 100% complete and occupied. The final, real cost of construction was $895k. It is absolutely possible to come in UNDER a proposed budget with careful planning, design and a good team.

    5. no one can be the “target of some ridiculous pressure..” unless they choose to be.

    best of luck.

  11. Lot’s of good comments but clearly, a lot of people need that Thursday, no B&T people around drink. Damn. Aside from that, I have one piece to add.

    Two unit buildings under the current code require only one exit per floor in some situations. Under the old code, you needed two. Yet many in the building dept. still do not get this. So you need to find an architect who is able to get the correct interpretation for you. The SF building dept. has yet to issue an official interpretation. Additionally, if the roof deck is shared space, you need to be very very concerned about occupant load and exiting. And if its a condo or TIC project, you’ll have to be concerned about noise coming from the roof into the space below. Your architect can help you with that. If it is private space for one unit, it is much, much easier to deal with.

    Lastly, if you find yourself tight on budget, one technique often used is plan value. I mean if you want a hot tub and gas grill on the roof but can afford it all, at least put in the utilities in the walls etc. to be connected later. And have your architect and engineer design for it. In the industry this is called roughing-in for future work.

    So to echo, find a good architect and engineer who understand the cost, design, planning, and structural issues involved with your particular type and scale of project.

  12. nice catch kenny!

    the general rule of thumb for avoiding ‘sophie’s choice’ is to interview some contractors who have installed some roof decks in the city. with their free bid you’ll get a MUCH more realistic idea of what its going to cost. you will also benefit from their knowledge without having to pay some (potentially) self-important architect. that way you go directly to the engineer who can draw up the plans.

  13. Paco,

    There are some real changes to the building code for two unit buildings that not even the SF building department really understands. These changes generally make it much easier and cheaper to build two unit buildings, but not three or more. Most inspectors and plan checkers are still thinking old code even though its almost 1 year old. This is one time where I would disagree with you (as both a former architect and more recently general contractor). This is one scenario where somebody (architect, engineer, contractor, building official) not knowing what they are doing can cost an owner a hell of a lot of money because they are thinking old code not new. Imagine building a three story fire rated exit stair that is not the least bit necessary because the roof deck might constitute an assembly are. That’s a lot of wasted money.

  14. Unfortunately, there are some comments here that are simply reactionary and WRONG.

    Securing a building permit is not based on instant answers, or a one time review with the Building Dept. or the plan checkers. Getting a building permit for any work other than simple “over the counter” work requires a serious and thorough review process to address life safety, structural and architectural issues.

    It’s a PROCESS, people. Yes, the code is complex. Yes, the code changed on Jan 1 of this year. Yes, there are still many interpretations being sorted out. There is simply no evidence that the code has suddenly made it “cheaper and easier” to build a 2 unit building. It depends on many factors, including the size of the building, the location, the construction type and other important issues.

    The plan checkers and inspectors are NOT thinking old code. That’s just false.

    And to assume that someone (architect, engineer, etc.) would get plans approved for a hypothetical 3 story exit stair for a roof deck, when that stair MAY NOT be required is just ludicrous. The approval process would determine LONG BEFORE construction even starts as to whether or not that stair is required. That comment is just plain wrong.

    My overriding sense here is that many people just want construction to be cheaper than what it really is. We all agree that it’s costly and tough to build here. That’s the reality of San Francisco construction in 2008. But I never hear anybody complain when it comes time to selling their house that they sold it for 10 times what they paid for it in 1995.

  15. urbanSF7- I agree with you that no one is thinking old code and consistenly getting it wrong. All the plan checkers currently have some old code and some new code on there desk, so some oversite is possible. But you can get it fixed quick. Everybody in the business should have the new code books (your architect, engineer, and contractor) so it gets fixed quick. Plus, if there is one commen knowledge thing about the new code, it’s the 1 flight of stairs.

    Roof deck permits are not that hard to optain, and don’t require notification. In fact a small enclosed access room complete with doors, windows and a wet bar doesn’t even need notification. You’ve got to carry the weight down, that’s where the money is spent.

  16. Why do you need to hire an architect to design a roof deck? How much of it needs to be designed? You aren’t designing or building the Taj Mahal.

    Jeez, I would think that a structural engineer and a contractor w/extensive experience building roof decks are sufficient — the structural engineer tells you what needs to be done and the limits of what can be done while the contractor can give you options according to your budget.

    There are design/build firms in SF who can provide one price to do it all, including gutting and rebuilding 2 unit flats and cut out the middleman. Seems like you should get also get a bid from these folks to get an idea of costs.

    A very simple analogy: I needed my standard 40 gallon gas water heater replaced. Called several plumbers (some “hi-end,” some not) who quoted me a price from $500 to $1,600 for identical work. I gave the job to the plumber for $500 and have no problems. Goes to show the huge variances in construction costs.

  17. sparky- no disrespect, but I disagree with you on a couple of points.

    1. Your reference to “1 flight of stairs” probably means one means of egress. That DEPENDS on several factors. For most single family homes, one means of egress is enough, except for large floor areas. In some cases, yes, you may need 2 means of egress. Each case is individual. For 2 unit buildings, meaning 2 floors of living area over a garage level, you will need 2 means of egress. That’s the code. There are conditions and other issues if you choose to sprinkler the building. (I’m talking new construction here only.) I doubt if we could find a pair of flats with NO stair at the rear of the units leading to the rear yard, (except for completely unpermitted and illegal construction).

    2. As for roof decks, depending on many factors, the permit can be easy or challenging to obtain. In many cases you WILL need 311 notification. In some you wont. The planning dept. is pretty clear on those issues. And yes, you are correct about structural costs. As I mentioned previously, for any new live loads you MUST carry the new loads completely down to the foundation.

  18. urbanSF7,

    “Two means of egress” meaning 1 for each unit; of course you need that. If you mean 2-units need 2 each that is not true. The new code is 1. Have I submitted and approved this with the new code; Yes. But anyway we are talking about the egress from the deck, and that would be one. Either from the private unit or from the comman stairs. Have I submitted and approved this: yes.

    Do you need rear stairs to the back yard anymore; NO.

    LiveSmart, What you described is what my company does; Design/Build. But most generals do not, and since engineers won’t do the architectural drawings, and city needs them, an architect is required. So it’s not really like the water heater scenario.

  19. @urbanSF,

    I watched somebody at the building dept. this very week, a licensed architect, try to negotiate with a plan checker about a second exit requirement when all the conditions (height, area, occupant load, occupancy, etc) called for just a single exit for one unit in a two unit building – and I watched them loose. The plan checker said two exits are always required from each unit in two unit buildings. Somebody who doesn’t fully understand the issues would not continue the fight – and in this case they didn’t. So I stand my comments.

    You are absolutely correct in stating that it is a process – and you need somebody who understands the process working for you in making sure your interests are protected.

  20. Interesting conversation. I had a similar question, but my home is a two story SFR in the sunset. I’m interested in a roof deck too. My questions are:

    Can i get away with one egress from the roof, that goes to the 2nd floor deck?

    Also – if i’m not buidling a stairwell penthouse, just a deck with transparent windscreens, and some railings, do i need a 311?

    Thanks for any help!


  21. Mark – Did you end up buiding a roof deck? I was just starting research on this as I am interested in putting roof deck on my home in the sunset also.

  22. Samantha/Mark,

    I am in the sunset and want to build a simple deck too… did you succeed? Did you have to do a 311? Cost? Architect’s name?

  23. Samantha / Mark / Steve:

    I am in the Inner Sunset and I too want to build a simple roof deck. Any successes to share?

  24. Roof deck is great in the city.
    I’m doing architectural plans for two roof deck projects. One is 4 story 3 units building by Telegraph Hill and the other one is 17 story high rise in Union Square. SF planning department can approve the roof deck over the counter as long as the roof is maintain within allowable built area with railing or parapet not more than 48″. If the proposed roof deck that encroaches on a yard or setback, then all railings are limited to 42 inches tall a notice will be required for immediate neighbors only not the 311 long process. Make sure to read the SF bldg. code Amendment – section 1511.5 about the roof deck requirement, one of the require is that decking material must be fire retardant treated wood such as Ipe wood or 2″ nominal thick redwood.
    Lastly make sure that the roof decking system is allowed for roof maintenance or repair. Bison pedestal decking support system & 2×2 ipe wood tile work great to allow flexibility to remove portion of decking for repair.

    Check out the deck handout from SF planning website.


    Email me [email protected] if you need more info.

  25. Well, I’m not the only one with a very late reply.
    FYI, residential and commercial structural engineering are pretty different animals. You could hire someone brilliant moonlighting from one of the “big” structural firms downtown (actually, they are small businesses) and they won’t know the pitfalls of existing local construction.
    Adding a roof deck can be a very complicated and expensive project in SF. Many folks want to add a hot tub to their 4th floor Russian Hill condo on brick foundations and are upset when I tell them what is involved.

  26. We just finished the roof deck project in the Crown Towers Penthouse on 666 post street in SF. The new roof deck becomes a great feature for the penthouse.

    We were able to get the permit over the counter and the roofer finished the roof deck in a week.

    Attached the link of the project.

    Charles Chan
    [email protected]

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