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    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #1

    Jun 10, 2010, 12:57 PM
    Roof Loading Question
    I am in the process of fixing up an in-law unit built by the previous owner. Unfortunately, the roof wasn't well constructed. It basically consists of 2x4's running off a ledger attached to the adjacent garage which are then notched and resting on the top plate of the in-law unit (see pictures). Because the wood was notched, it has split from the roof load, so basically I think I have the equivalent 2x2's supporting the roof. Is there any remedy for this short of ripping off the roof and starting over? Maybe steel plates sistered to the 2x4's? You can see from the picture that I attempted a fix with some straps and joists hangers which I'm not that confident with.
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    KBC's Avatar
    KBC Posts: 2,550, Reputation: 487
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    #2

    Jun 10, 2010, 01:09 PM
    They look like 2 X 6's under the roof line.

    The support of the joist hangers can support a lot of weight, I would think this would more than suffice in this situation.Remember,the hangers do support decking boards on very heavy loads.

    If the wood is too dry or rotted,then you might think about more in-depth support,but in my opinion,this should do fine.
    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #3

    Jun 10, 2010, 01:24 PM

    Looking at the way I took the picture, I can see how they look like 2x6's but I'm positive they are 2x4's. That being said, you are right about the hangers -- the manufacturer website confirmed this. Thank you.
    21boat's Avatar
    21boat Posts: 2,441, Reputation: 212
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    #4

    Jun 10, 2010, 03:32 PM

    Nope not hard to figure out a plate is 1 1/2" x 2

    Not being there to see the center roofs deflection and how the 2x4s presently carried the load I come up with two to ways of doing this

    1. Sister up 2x4 1/3 length of the roof and saddle/ Hangers to set in along with notching the ledger part.
    Or
    2. Flush a 2x6 under the top plates between studs. Now Double up all the rafters with 2x6s and joist hangers

    The added 2x6 under plate will drop you 5 1/2" under the bottom of those plates and become a nailer for rafter hangers and also give you a nailer for drywall
    manhattan42's Avatar
    manhattan42 Posts: 143, Reputation: 11
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    #5

    Jun 10, 2010, 04:43 PM

    The joist hangers will not work in this situation because they are not fastened according to the manufacturer's installation instructions.

    You need to have the full hanger fastened solidly to wood with all nail holes filled and attached solidly to wood.

    You do achieve this with your current application.

    Without knowing your location or the total run of these rafters, no one can help you determine what you need to do to correct the problem.

    Presuming you will have at least a 20psf snow load, these (what appear to be 24" on center) rafters can only span a maximum of 7'6" if they are made from #2 SPF lumber.

    I'll wager a guess and bet they span nearly twice that length.

    If so, it is small wonder they cracked considering they are over-notched and are really only 2x2s, not 2x4s for load bearing purposes.

    Unless you can reduce the spans by adding beams to shorten their spans, these rafters will need to be replaced completely with rafters designed for your load conditions.

    (Flat roofs essentially need to be designed as decks to at least 40psf plus snow loads.)

    I'm surprised the roof system hasn't collapsed.

    Tell us your location (county and state is fine) and the overal span of the existing rafters, and we'll be able to tell you what size rafters you need.
    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #6

    Jun 10, 2010, 05:33 PM

    Luckily there is no snow load, as I'm right near Sacramento, CA. I too am surprised that the roof hasn't yet fallen and would have never constructed it like that to begin with. The span is 10 ft. 2 in.. I 'm thinking that using 2x6's will accomplish what I need since I will be able to nail in the hangers using all nail holes.
    manhattan42's Avatar
    manhattan42 Posts: 143, Reputation: 11
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    #7

    Jun 10, 2010, 07:11 PM

    2x6 24" on center will span 11' 9" so you'll be OK structurally.

    But your zone requires a minimum of R-30 ceiling insulation.

    So unless you use expensive foam insulation to fill the 2x6 cavity, you won't be able to properly insulate this roof using conventional insulation.
    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #8

    Jun 10, 2010, 07:18 PM

    Great. I will go with the 2x6's and appropriate hangers then.

    I actually installed 2" polyiso insulation under the roll roofing, so with the addition fiberglass bats in the cavity, I'd expect to be pretty close to R-30.
    21boat's Avatar
    21boat Posts: 2,441, Reputation: 212
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    #9

    Jun 10, 2010, 07:43 PM
    Quote Originally Posted by bergs4 View Post
    Great. I will go with the 2x6's and appropriate hangers then.

    I actually installed 2" polyiso insulation under the roll roofing, so with the addition fiberglass bats in the cavity, I'd expect to be pretty close to R-30.
    I hope these batts will be unfaced. If not the roof insul acts as a vapor barrier. So if ones below and ones above even in the roof a moisture problem will occur. No Mention of venting in that roof. If it were me I would spray foam to stop all possibility s of Moisture in insul Its takes only 5% of moisture in insul for it to lose 95% of its insul properties
    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #10

    Jun 10, 2010, 08:03 PM

    I thought that unfaced polyiso would be fairly vapor permeable.
    21boat's Avatar
    21boat Posts: 2,441, Reputation: 212
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    #11

    Jun 10, 2010, 09:18 PM

    OOPS I whet to quote user and did an "AGREE"

    No the polyiso is not that permeable. See you are fighting by having a flat roof that's NOT vented. That alone causes trouble.

    Read this recent problem similar to this and get back...
    https://www.askmehelpdesk.com/interi...ng-475427.html
    manhattan42's Avatar
    manhattan42 Posts: 143, Reputation: 11
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    #12

    Jun 11, 2010, 03:47 PM

    I thought that unfaced polyiso would be fairly vapor permeable.
    Fairly?
    Unfaced polyisocyanurate insulation is extremely vapor permeable. It has a perm rating of 26 compared with a perm rating of .05 for foil faced polyiso.

    See the table in this link:

    http://www.oregon.gov/ENERGY/CONS/Codes/docs/res15.pdf

    However, you still need ventilation for your rafter cavities even for your region.

    And you aren't providing any.
    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #13

    Jun 11, 2010, 08:18 PM
    I don't understand why that's a requirement. I have gone through all this effort to make the unit air tight yet vapor permeable and by placing ventilation in the rafter bays I'd be creating easy exits or entrances for air (and as a result, a significant decrease in the energy efficiency of the unit).
    21boat's Avatar
    21boat Posts: 2,441, Reputation: 212
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    #14

    Jun 11, 2010, 08:49 PM
    Quote Originally Posted by bergs4 View Post
    I don't understand why that's a requirement. I have gone through all this effort to make the unit air tight yet vapor permeable and by placing ventilation in the rafter bays I'd be creating easy exits or entrances for air (and as a result, a significant decrease in the energy efficiency of the unit).
    Obviously anything no foil is more permeable then foil, I hate to say it but all you needed was a standard roof covering and spray foam insul inside the rafter cavities. Flat roofs are a SOB for insulating properly. The main trouble is getting the proper amount of air flow for moisture to escape the rafters. Air flow is you friend in all roofs I feel your treating your roof as an Airtight house, Yes the rest of the house walls etc. Roofs have different needs. I tell customers this way. A roof of the house is to protect the insulation from getting WET. If no rain, Snow, Wind, We could just lay insul over our heads.

    Your "energy efficiency unit" will be no more if 5% moisture gets in the batts and they lose 95% of its insul properties
    KingsX's Avatar
    KingsX Posts: 231, Reputation: 10
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    #15

    Jun 11, 2010, 08:53 PM

    The spray foam option I like because it acts as a vapour retarder on the underside of the roof sheathing, i.e. plywood or whatever. You couldn't poly that side if your life depended on it, unless you take the sheathing (presumably whatever is on top too, like shingles) and do a proper vapour seal and so on.
    manhattan42's Avatar
    manhattan42 Posts: 143, Reputation: 11
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    #16

    Jun 12, 2010, 12:15 PM
    Quote Originally Posted by bergs4 View Post
    I don't understand why that's a requirement. I have gone through all this effort to make the unit air tight yet vapor permeable and by placing ventilation in the rafter bays I'd be creating easy exits or entrances for air (and as a result, a significant decrease in the energy efficiency of the unit).
    You haven't noticed all the water stains on the underside of the roof sheathing and on the rafters?

    That is from condensing water in these rafter cavities caused in part by the spaces not being ventilated.

    All attics need ventilation to allow mositure to escape to the atmosphere.

    Otherwise the space becomes condensation and mold factory and the roof shingles can have their life spans reduced because of built up heat.

    The moisture comes from the interior of the house and migrates out through the building envelope.

    Only if you have a solidly insulated roof system that uses spray foam can you avoid having to ventilate under any building or energy code.

    And spray foaming the underside of the rafters is still not the fix-all many wrongly believe it is.

    It is the most expensive way to insulate with little return on investment compared to other types insulation.

    That said, the very best solution is this case would have been to demolish the roof system which was designed and built poorly from the beginning, and replace it with a well ventilated gable, shed, or other type roof system.

    Short of that, any remedy you apply is creating and will continue to create other problems.
    bergs4's Avatar
    bergs4 Posts: 107, Reputation: 3
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    #17

    Jun 12, 2010, 09:07 PM

    I appreciate all the advice and information with respect to insulation and potential moisture problems. While I realize there is the "best way" to do things and a range of approaches less than the best way, in this circumstance, the room will be used at most 2 week out of the year, so my approach to this project is necessarily a compromise.
    21boat's Avatar
    21boat Posts: 2,441, Reputation: 212
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    #18

    Jun 12, 2010, 10:29 PM
    Quote Originally Posted by bergs4 View Post
    the room will be used at most 2 week out of the year, so my approach to this project is necessarily a compromise.
    Bergs4. If that's the case then No insulation may be better then Mold Removal later or some urethane foam board against roof sheeting tuck taped and sealed. Not the best R vaule but will work..

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