Patio Cover Rebuild

Discussion in 'Remodel Forum & Blog' started by Jeff1, Oct 27, 2009.

  1. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    I'm going to rebuild a patio cover that my contractor used the cheapest materials possible on. It passed inspection but looked cheap and didn't hold up. I'm planning on replacing the 2x6 beams with 4x6. They have a 10 foot span from header to outside frame. My question is: do the new beams have to have the same spacing or can they be placed farther apart? Is there an online calculator to determine the proper spacing?

    Thanks for your help and suggestions.

    Jeff
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,184
    Location:
    New England
    The goal is to minimize deflection. There are two components of that, along the joist and for the flooring, inbetween the joists. It depends on the strength of the flooring material you choose whether you can extend the spacing. You wouldn't want to stand in the middle of the joists and have the flooring sag. this is especially important when using one of the man-made materials like Trex (just one example). Thicker materials can support larger spans, both for the joists and the floor. Doubling the joists and using a double joist hanger may be less expensive than the thicker material. You wouldn't want to set something heavy inbetween a large joist spacing and have it sag, say a big barbeque or the weighted base of a table umbrella.
  3. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    That's what I'm concerned about. The cover will only be a roof and will only have an extra load on it while its being built. The beams will be exposed which is why I'm looking at 4x6. There will be a decorative cut on the overhanging part as well.

    Is there a way to determine maximum spacing? I don't want to push the envelope and really want it to remain intact.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,184
    Location:
    New England
    You'd need to know the design load requirements for your area. This accounts for things like wind, snow, etc. Then, once you know what load it must carry, you can look up load tables, sometimes called span tables, that would show how strong various materials are over a specified length and spacing.
  5. sjsmithjr

    sjsmithjr Geologist

    Messages:
    295
    Location:
    Knoxville, Tennessee
    There sure is. Some questions first - what species and grade of wood are you working with? Is it incised? What are the live and dead loads? (you can always call your local building dept for this). From your description, you will have also consider that the wood will be exposed. Lastly, I'm a little fuzzy on what exactly you're building. Are you building a covered pergola over a patio or something else? What will the roofing material be?
  6. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    This is a roofed patio cover. I'm not sure how else to describe it. The old one had rolled roofing and I'll probably have to use that too - the slope is very shallow. I haven't decided if I'm using a plywood or ship lap for the top yet. The beams I'm looking at are standard 4x6 from the lumber yard. I'll have to verify the type of wood. We don't get much rain, but wind is huge in my area (40 mph at times).
  7. sjsmithjr

    sjsmithjr Geologist

    Messages:
    295
    Location:
    Knoxville, Tennessee
    You have to know the species and grade and load because it can make a big difference. A No. 2 Douglas Fir Larch 2x6 used as an exposed rafter could span 10'4" assuming a 20lb live/10lb dead load while a No. 3 could only span 9'1", both on 24-inch spacing.

    Remember that your sheathing may require that you space the rafters closer together than the maximum allowed.

    Once you get all the info together, google "AWC Maximum Span Caluculator for Joists and Rafters". Use member type rafter and for exterior exposure select yes. Many lumber yards can help you figure this out as well.
  8. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    Great info. Thanks. Looks like I'll be spending some time at the local lumber yard - not big box.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,882
    Location:
    Cave Creek, Arizona
    beams

    What are you calling "beams"? Beams are usually support items and as such they are attached to something, such as columns, which means they cannot be "respaced".
  10. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    I guess they would be joists.
  11. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    I think you're referring to rafters if they're in the ceiling.

    You may want to consider using a gable roof rather than a shed roof. More expensive, tougher to build but it typically looks better.
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,882
    Location:
    Cave Creek, Arizona
    rafters

    Typically for rafters/joists you change the spacing of the 2x6 rather than the size of the member. But depending on the type of wood, a 2x6 at 10' span with 16" centers will carry a 40#/sq.ft. load and at 12" it will support 60#, either of which should be well beyond your design loads.
  13. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    The original cover was built with 2x6 at a 10' span and 24" on center. I'm changing to 4x6 to match another patio cover on a different side of my house. The new one was built with 4x6 about 32" on center. I won't be changing the overall design of the old cover, just the materials. The original builder used the cheapest 2x6 and plywood possible. The joists/rafters are twisted and the plywood warped allowing moisture damage. I'm going to use Doug Fir for the 4x6. I'd like to space them 32" to match. Does this sound reasonable?

    Thanks
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,184
    Location:
    New England
    It depends on the roof loading required in your area. Being SoCal, you probably don't have to worry about snow load. But, if anyone ever is walking around up there, 32" is a huge width to span with plywood. Somebody needs to install it from up there and probably put down some roofing materials. It will be bouncy...

    Also, you may not have enough fasteners to meet the required wind loading if things are 32" apart.
  15. Jeff1

    Jeff1 New Member

    Messages:
    102
    Location:
    So Cal
    I'm going to talk to building and safety to make sure before i start this project. I'd kind of like it to stay standing and not take the wall of my house down if it goes.

    Thanks for all the inputs.
  16. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,882
    Location:
    Cave Creek, Arizona
    roof

    The 4x's on 32" center would be adequate to support the load, BUT will the roofing material be stable with that spacing under it? Most would not, since the normal spacing is usually 24" or less, NOT 32". With that spacing you will need a fairly substantial roofing material to avoid flexing when walking on it.
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