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  1. #1
    Join Date
    Dec 2009
    Location
    Bozeman, MT
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    8

    Default adding a second story

    I am considering adding a second story on my personal house. The house is 100 yr old home with a 10/12 pitched roof and a width of 22ft. I would like to add some more square footage and up is one of the few options. I haven't ever done this on a project before so I am looking for the best plan of attack.

    I am looking at having approximately 4 ft side walls for the upstairs. Wondering if I should plan a whole new floor system and than my walls and rafters on top of that? Or should I look at having an attic truss built?

    We are not planning much change to the first floor and am wanting to disturb it as little as possible, but knowing there will definitely be some disturbance.

    I would be open to any advice or direction from anyone who has maybe attack something of this nature.

  2. #2
    Join Date
    Mar 2006
    Location
    Seattle, WA
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    11,339

    Default Re: adding a second story

    First thing you need to know is if your foundation will support it.

    Second is to come up with the design so you know where you will have point loads. The point loads will continue all the way to the foundation. You want the point loads to be in line with walls on the 1st floor to minimize changes there.

    Unless you have height restrictions the 4 foot walls sound good, but wind up with les space and, often, a more complicated roof because you're using dormers to create the rooms. You might find it cheaper in the long run to raise the walls higher (it's essentially the same load, although you wind up with more wind surface area) and go with a simpler roof plan.

    Plan on pulling siding- you will probably be adding shear panels to the 1st floor.

    I have done this adding a second floor above the existing ceiling. I'd set a 2x or 4x on flat directly on the existing ceiling joists and set the new floor on top of that. You may avoid having to move all the wiring and ducting. You will have to install insulation that doubles as fire blocking (well, or should if you aren't under an AHJ).

    And then, of course, it's a good idea to have the design checked by an engineer to ensure proper point loads, foundation, shear, etc., unless you are very comfortable with all of that. And even then- even if you don't need plans & permits, it's still a good idea.
    http://www.lavrans.com

    "He uses statistics as a drunken man uses lamp posts; for support rather than illumination." -Andrew Lang

  3. #3
    Join Date
    Feb 2008
    Location
    North Central Vermont
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    1,866

    Default Re: adding a second story

    Quote Originally Posted by mtcarpenter View Post
    I am looking at having approximately 4 ft side walls for the upstairs. Wondering if I should plan a whole new floor system and than my walls and rafters on top of that? Or should I look at having an attic truss built?
    With a house of that vintage, it's almost certain that the ceiling joists (attic floor) are not sized for the 30 psf live load of a bedroom floor - so you're likely going to have to sister the existing joists with minimum 2x8 16 oc.

    If you decide to use kneewalls, then 5' is considered the minimum height for a usable living space, but then unless you can design a structural ridge you will almost certainly need roof trusses because there'll be no way to incorporate adequate rafter ties to prevent "hinging" of the kneewalls. And make sure that whatever roof system you use has enough room for adequate insulation (and venting).

    [If you complete your user profile, we'll know what part of the universe you're in.]
    Robert Riversong
    Master HouseWright

  4. #4
    Join Date
    Dec 2009
    Location
    Bozeman, MT
    Posts
    8

    Default Re: adding a second story

    Thanks for your reply. The reason for the 4ft walls is because of city restrictions. Otherwise I agree with you about it being easier going up higher. I'm actually looking at no dormers, just windows in the front and back gables and possibly some skylites. The steeper pitch should give enough head room.

    My foundation may be an issue. I had an initial review of it by a structural engineer and we have to look at doing some reinforcing, but we are still looking at it.

    I know my existing ceiling joist will not be sufficient enough to carry the floor load of the second floor. So I will be either running new floor joist maybe along side the existing ceiling joists or this is where I wondered if attic trusses would make sense because they could serve as the floor system and the rafters. Any thoughts on this?

  5. #5
    Join Date
    Mar 2006
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    Seattle, WA
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    Default Re: adding a second story

    I would try to avoid sistering to the existing ceiling joists if you can possibly avoid it. If you can build a second floor diaphragm you won't risk disturbing all the stuff that has been pulled through the old ceiling, and as a second benefit, you have a much better sound separation between floors.

    Re-reading- I should have pointed out that you install the new plates over the perimeter and directly over interior load-bearing walls. That keeps the new floor diaphragm suspended completely above the existing ceiling.

    An alternative is to install a rim board around the perimeter and then use top-flange hangers to install the new floor joists dropped into the bay between the existing ceiling joists a bit.

    It's a nice detail to have 2 floor diaphragms if you can do it. The other good thing is that you have a lot more room for plumbing and any ducting.
    http://www.lavrans.com

    "He uses statistics as a drunken man uses lamp posts; for support rather than illumination." -Andrew Lang

  6. #6
    Join Date
    Dec 2009
    Location
    Bozeman, MT
    Posts
    8

    Default Re: adding a second story

    I just made a post that addressed the ceiling joists. You are right, they aren't adequate. Also because of the "hinging" factor, this is one reason why I wondered about having an attic truss manufactured. Another option might be a manufactured truss that sits on tops of the knee wall. It could maybe have a 2x8 or 10 cord with a collar ties. I'm not sure if this is an option. I have only had a common truss or a scissor truss made before.

  7. #7
    Join Date
    Apr 2009
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    midwestish
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    7,201

    Default Re: adding a second story

    Is there actually anything in the old ceiling worth trying to save? If you can/do save it will doing so benefit you? What is the existing ceiling finish and its condition? Odds are there is only a waste vent stack or two, no duct work and mostly wiring for OH lights that's likely not current code so will need replacing anyways, or should be if not required.

  8. #8
    Join Date
    Feb 2008
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    North Central Vermont
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    Default Re: adding a second story

    Quote Originally Posted by mtcarpenter View Post
    The reason for the 4ft walls is because of city restrictions.
    If you have height restrictions, then it may not make sense to build a new floor deck above the existing one. An attic truss isn't going to raise the roof or give you much usable space (see attachements), but kneewalls and a parallel-chord energy truss will.

    You'll have to figure out the best way to strengthen your floor system without losing usable space.
    Attached Images Attached Images
    Robert Riversong
    Master HouseWright

  9. #9
    Join Date
    Mar 2006
    Location
    Seattle, WA
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    Default Re: adding a second story

    If you have height restrictions, then I'd plan on pulling the old ceiling- the existing will be more of a hastle to work around than they are worth.

    I also would probably stick frame the roof rather than use trusses. It's easier to get more usable space than working around truss designs IMO. (Well, except for thaw parallel chord truss...)

    Come on though... You really don't wand any dormers? Cheaper now than later ;-)
    http://www.lavrans.com

    "He uses statistics as a drunken man uses lamp posts; for support rather than illumination." -Andrew Lang

  10. #10
    Join Date
    Dec 2009
    Location
    Bozeman, MT
    Posts
    8

    Default Re: adding a second story

    the existing ceiling for the is sheetrock and it is in ok condition. One of the main reasons for leaving it is trying not to disturb the main floor that we are living in and will try to stay in for a good part of the time. MarkMc mentioned the electircal and yes most of it need to be rewired anyway due to no grounding currently.

    Lavrans you mentioned the dormers, I am trying to balance the look of the house with the cost of adding dormers, with the fact that we don't need the space, but I agree, "cheaper now than later".

    Another reason for talking truss vs hand framing is in relation to timing of the project. Trying to keep the house below dry while we are working is going to be a challenge. So getting things torn off and new framing up as quick as possible will be important and the use of a few big tarps.

    The existing first floor walls are 2x4 and I know I will proably have to add studs for bearing purposes as well as the foundation may need some reinforcing. I considered running beams along the top of the load bearing walls to carry the load of the new floor system and roof system. I was than thinking of posting these beams down at certain points. Any thoughts on this?

  11. #11
    Join Date
    Jun 2004
    Location
    Martinez, California
    Posts
    14,821

    Default Re: adding a second story

    In Bozeman your going to need an engineer, you should be discussing these things with him/her.
    “It is not an endlessly expanding list of rights —the “right” to an education; the “right” to health care; the “right” to food and housing. That is not freedom. That is dependency. Those are not rights. Those are the rations of slavery – hay and a barn for human cattle.” - Alexis de Tocqueville

  12. #12
    Join Date
    Feb 2008
    Location
    North Central Vermont
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    Default Re: adding a second story

    Quote Originally Posted by mtcarpenter View Post
    Another reason for talking truss vs hand framing is in relation to timing of the project. Trying to keep the house below dry while we are working is going to be a challenge. So getting things torn off and new framing up as quick as possible will be important and the use of a few big tarps.
    When raising the roof, the existing roof can be cut just over the load-bearing walls to allow the new walls to be framed, and a roof can be framed and weathered in on those walls before the old roof is removed.

    This may be complicated by having to improve the existing ceiling first, but it may be a way to minimize exposure.

    I considered running beams along the top of the load bearing walls to carry the load of the new floor system and roof system. I was than thinking of posting these beams down at certain points. Any thoughts on this?
    If there is an existing ceiling band joist over a doubled top plate, that is all the beam you should need.
    Robert Riversong
    Master HouseWright

  13. #13
    Join Date
    Mar 2009
    Location
    Boston
    Posts
    492

    Default Re: adding a second story

    Riversong,

    Do you have any photos or further info regarding cutting the rafters at the top plate and framing new walls while the old roof stays in place?

    Wonder how much it slows things down.

  14. #14
    Join Date
    Jul 2004
    Location
    Southeastern Indiana
    Posts
    204

    Default Re: adding a second story

    10 years ago, wanting to enlarge my 100 yr. old farmhouse, I sawzalled the rafter plate from the 1st floor ceiling joists brought in a crane, lifted the entire roof which is 10/12- (Queen Anne Victorian 2,000sq. ft.) Stood up 7' walls which were laying down inside. the roof structure was cross-braced for both compression and inversion forces. Set the roof structure down, took some come-a-longing to get it right. Bearing walls on top of bearing walls below.
    The ceiling joist were not sufficient for joists so I built laminated beams that went in between them and flat framed over them adding a 2x4 and 3/4" T&G. So the loads are independent.
    Two skateboarding teenagers and no cracked plaster below. The crane was there for 1 day. we never moved out, nothing got wet. I did remove all the shingles beforehand to lighten the load. A crowd of helpers, most of them expecting and hoping for failure watched/helped.
    Except for your height restrictions, I'd recommend it.

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