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Thread: Attaching a patio cover to house

  1. Default Attaching a patio cover to house

    Im in PA where we do get some snow, they require a 30lb load bearing. In Texas I added a small awning/patio cover to my house by attaching directly to the fascia board. I gather that is not acceptable here.

    I am thinking about 13' by 20' foot, preferably polycarbonate? plexiglass smoked translucent roof. I have a 16" soffit.

    I dont want to put a ledger under the soffit, because a door opening is only 6 inches below the soffit.

    I dont like going back on the roof, and putting it on the shingles, as that would probably mean greater than 12' roofing sheets.

    I don't like just using asphalt shinges everywhere because I want more light.

    I thought about bolting the 2x8 patio joists to the 2x8 roof joists (16" OC) that angle down and connect to the soffit. That is, I remove the fascia board, and either attach a ledger board to the end of the roof joists and the patio joists on the other side, or by simply bolting the two joists together. However I read that that is not ideal as the wall top plate becomes a teeter totter and can break the joists.

    Another option, is to cut back the roof and run the patio joists to lay on top of the house band joist top plate, or attach the joists to the house band or to a ledger attached to the house band. That would mean removing some of the existing roof, making the project hard to undo, and I am concerned about
    the patio roof being too thick, or thicker than the ashalt shingles, and how to accommodate that.

    I had originally wanted one of the flat metal, built-in gutter type of roofs that my parents had in Virginia, but I have not found them, and I don't know if I could just attach them to the fascia board like my parents house, as if the codes have changed in 40 years for that.

    And the last option I have thought of is to add three support posts with a beam/ledger next to the house so to make it free standing, but attached to the roof? And I dont like the extra holes to make and the appearance of these additional posts.

    Any suggestions? Am I overlooking something?

  2. #2
    Join Date
    Oct 2003
    Living in, not from North Carolina


    To span the 13' your going to need to use 2x8's select, (2x6 can span it with snow load but you would need to make them on 12" centers.). The best option would be to use 2x8's on 16" ctrs and span them all the way to sit on the existing homes top plate (what size are the existing homes rafters ?) The max. span of 2x8 SS with a 30 snow load is 13'10" on 16" ctrs and 15'3" on 12" ctrs. The problem you have is your deck is to be 13" wide add to that the 16" soffit and your at 14 1/2'.
    If it were me I'd use 2x8's sitting on the top plate, this would also allow you to use a shingle to corrugated transition flashing for the polycarbonate roofing material.

  3. Default clarification

    Just to clarify, I was planning on 12' 8" total from top plate to the patio beam, inside measurements. however that is a horizontal distance, when in fact it will be pitched somewhat and a little longer therefore.

    The existing roof has 2x6s under the plywood sheathing under the shingles, on 16" centers, and there are 2x8s ceiling joists that also rest on the top plate.

    So I guess I am thinking of doing that, putting 2x8s patio joists on the top plate, but leaving the existing sheathing and shingles to extend their same 16" past the top plate, and then join that to the polycarbonate, 12' panels. That way I get my 13' plus 6" overhang.

    That might mean changing the slope of the shingles for those 16" (as they change from a regular roof slope to a patio flat slope, and using blocking under the sheathing on top of the joist
    to provide solid support for this changed slope (curved?). Or should I forget about that and just go with overlapping the polycarbonate to make them run whatever I need, 13.5' ??

  4. #4
    Join Date
    Oct 2003
    Living in, not from North Carolina


    It is common to see the roof slope remain the same and have a new roof (patio) come off that on a different slope. You can buy flashing that is specifically made for shingle to corrugated (or three or four other materials/profiles), this flashing is slid in under the shingles and laid on top of the polycarbonate.

    Changing the roof slope/pitch to be the same as the patio is a much bigger job, either you need to remove the lower 16" of sheathing, install your new patio rafters then install new sheathing and shingles or cut slots in the sheathing to allow the new rafters to slide in then add new sheathing.

    and always install new tar paper with an overlap of at least 12" .

  5. Default A ledger on the roof and not top plate?

    From the top plate to the end of the beam would be 12'8". So I can be safe with 2x8s and a 30 lb load.

    However, I dont like the idea of cutting the roof off above my sofits in order to run the 2x8s to the top plate. That seems more work and less reversible, but maybe reversibility should not be an issue. But it does sound the most stable.

    Can I attach a ledger to the roof right above the top plate? I think it is a 5:12 roof, its not a 45 degree, but it is a bit steeper than many (made in 1960). If I do that, would l then cut out the shingles and paper under where the ledger would go, and nail it into the rafters (through the plywood sheathing) and with some sort of flashing? And then would I use some sort of joist hanger with an angle on it.

    And, by the way, can I use joist hangers to butt my joists on the other end right into the beam? I want to maximize the height of the beam at that end of the porch.


  6. #6
    Join Date
    Oct 2003
    Living in, not from North Carolina


    If you don't want to cut into the roof, you could always put the porch rafters on top of the roof, this would mean though that you will have a significant amount of extra flashing and finish work.
    Simply remove the shingles (not felt paper) add your 2x8 nailed down into the rafters, you then need to cut your new rafters over the deck on an angle to suit. You would not use joist hangers for this, just nail the angle cut rafters straight into the roof deck ledger.
    The angle from the roof deck to the porch deck bearer would most likely stop you from being able to use standard joist hangers, unless the lumber sits directly on the bottom of the hanger they kinda are useless.
    You could use adjustable hangers (about $5 a piece) they are diamond shaped with a nailing flange that you bend up (or down) to meet the lumber.
    If you wanted to maximize the height , sit the new rafters on top of the beam notched to suit, you will need to use "Hurricane Clips" for each rafter.

  7. Default not maximizing heights

    On th outside beam, I dont want to maximize height so much as to minimize vertical width of blindness. For example, if I use 10" beam plus 8" joists and they sit on top, that means 18" of non-visibility.

    Notching the joists and using hurricane clips will help, how much could/should I notch them? Can I use joist hangers on the other side of the beam?

    I was thinking if I butted them into the beam with joist hangers, then I would only have the 10" of vertical blindness.

    And now I am thinking of attaching a gutter to the beam, so an inch of overhang would be sufficient.

    Thanks much for your help! You helped me a lot with my bathroom 2 years ago, and that project turned out well. I will try to post pics of that sometime.

  8. #8
    Join Date
    Oct 2003
    Living in, not from North Carolina


    If you butt the deck rafters to the beam you need to use the adjustable hangers.
    You could toe nail two nails either side of the rafter into the beam and for good measure two nails in from the beam side into the end of the rafter and use small Simpson 90 degree anchor plates on either side of the rafters to beam connection.
    If you stop the rafters level with the top of the beam (make sure you allow for the angle of the rafter coming down to the front edge of the beam, don't make it flush with the inside edge of the beam) your roofing material could stick out the 1" ( 1 1/2" would be better) you want for the gutter.

  9. Default trimming the bottom edge of the joist

    Good poiint about the flushness.

    To simplify, and reduce cost of the adjustable joist hangers, why not just
    trim the bottom edge of the joist ( at a 1.5 to 12 pitch) to make if flat,
    and then use a regular joist hanger, since the angle is relatively small? Or
    also putting a 2x4 bottom plate (is that what you call it) under the beam
    and setting it on top of that?


  10. Default Sopn table calculator?

    SPAN Table calcualtor

    I cant find the right span table or calculator for my joists. I guess
    they are roof joists, or are they trusses? And all I know from the
    inspector is that they need to support 30psf. I dont know if that
    is the snow load, dead load, live loadand would I be getting select, no 1,
    or no 2, at Home Depot? I do know that they will be 16" OC

    At www.awc there is a calculator but I dont know how to specify
    the rafter type or deflection, and I would prefer to just print out
    a sheet that is appropriate for my situation, but I havent found it
    yet. Incised lumber??

    My inspector was kind of vague when I last talked with him, I could
    ask to see his charts, but it would be nice if I knew what charts
    that might be, for Penn. (We do have some snow.)

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