Flat Roof on a concrete garage

Discussion in 'Roofing and Siding' started by chaka, Jul 30, 2019.

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  1. Jul 30, 2019 #1

    chaka

    chaka

    chaka

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    Hello!
    I currently have a concrete roofed garage covered with epdm that is leaking through the roof and into the garage (seam and corner failure from previous installer). It hasn't been much, but it has made it all the way through.

    There is a deck on top of the garage (that sits on parapet walls) that we have removed and are going to replace the roof. I have a couple questions about preparation and materials when we replace the roof. (a deck is going back on top, so It wouldn't be completely accessible after the deck is back on).

    1. Should we put anything on the concrete to fill any gaps, coat, protect, etc?

    2. What is the best material to use for the new roof? I've had a few folks come in to give estimates some folks have suggested epdm again, some have suggested tpo. They will both be going on top of plywood and insulation... so wasn't sure if it made a difference. Many thanks!!
     
  2. Jul 30, 2019 #2

    oldognewtrick

    oldognewtrick

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    If it were mine, I'd insist on TPO. The seams are heat welded together, EPDM seams are glued. Either membrane will require a recover board or an insulation board for it to be adhered to. If you have any structure that will be resting on the roof, have your installer leave extra membrane so you can put a slip sheet between the framing and roof surface. Flashing and drip edge is critical to a proper installation.
     
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  3. Jul 31, 2019 #3

    hornetd

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    And if it were mine I would have the new deck installed on the parapet wall tops again and use drop in flooring section assemblies for the deck flooring in order to facilitate easy removal of the deck flooring to service the roofing. That completely eliminates any chance of finger pointing between the roofers and the carpenters.

    --
    Tom Horne
     
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  4. Aug 1, 2019 #4

    chaka

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    Thanks for the suggestions! So, make sure to use a slip sheet between the decking sleeper system and the roof. I was planning on making sure this happened on the parapet walls (between the flashing and decking, but if there is decking structure between the parapet walls resting on the roof, use slip sheets there as well?

    Also, I'll take a look at the drop in floor assemblies, but have you had any that you have worked with that you like?

    David
     
  5. Aug 1, 2019 #5

    oldognewtrick

    oldognewtrick

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    Yes, use a slip sheet anywhere any object contacts the roof system.
     
  6. Aug 1, 2019 #6

    hornetd

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    David

    Your contractor just builds the floor in sections sized to be lifted out of place on the framing by one person.

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    Tom Horne
     
  7. Aug 5, 2019 #7

    chaka

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    IMG_7896.JPG IMG_7938.JPG IMG_7939.JPG IMG_7943.JPG Thank you Tom! I feel a little foolish...

    So as with all projects, you get one set of questions answered and another crops up... Let me know if this should go in another forum...

    So I'm posting some pictures of the deck with the "walls" installed. I removed these sections with a sawzall, basically just cutting through the nails. What (if any) is the best way to reinstall them? They were originally nailed to the 4x4's you see in the pictures. I"m guessing it would be a pain to nail them again (with the old nails still being in the 4x4s. So any thoughts?

    Also, I was trying to preserve the joists (and possibly the sill plates), but will throw everything else away.(bridging, etc). Does that seem sensible? Or should I just start from brand new with new joists... or new everything? (get rid of cut wall panels)?

    Thank you for your opinions...
     
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  8. Aug 5, 2019 #8

    hornetd

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    Keep your framing! You or your carpenter can make the floor sections. Decide how large they can be by the weight of the materials you need to make one section. I might go 4 feet square so that with the cross pieces it might be only a little heavier than a 4X8 sheet of 3/4 inch plywood so that they can be handled safely when the need to remove them arises. They do not have to be fastened in place unless that is required by your local building code. If fastening is required devise a way to use fewer yet larger fasteners to simplify removal.

    Depending on the spacing of the existing joists you might consider doubling or tripling them on 4 foot centers to make the openings between the joists larger so that the roofers can work more readily. I strongly suspect that they would really hate working through joists on 16 inch centers because of how awkward that would be. They would merely strongly dislike working through 24 inch spaced joist but would put up with it grudgingly. If you use 48 inch centering they will only bitch about their being in the way but would probably cope quite well. Explore the idea of using Stainless or limited rusting steel connectors on all of the permanently fastened structural elements. Do not make the mistake which I have seen of using indoor connectors on outdoor work.

    If you add a ledger board on each side of the doubled or tripled joist then the cross pieces for the 4X4 foot deck sections could sit on the ledgers with only the ends of the decking pieces covering half of the tops of each joist. With each adjacent deck section covering half of the joist tops they would be fully covered. Be aware that this would make a very clear line of decking ends that would be very visible. Make sure that the other members of the household and you will be able to adjust to that visual effect.

    Get someone who knows the structural code and the load factors involved to check the joist dimensions that you will end up with for adequate load bearing capacity.

    Remember that when it comes to architecture, carpentry, and engineering I'm a pretty good electrician. What I'm laying out are mere suggestions based only on things that I have seen in my 50+ years in the electrical craft. That doesn't make me even an apprentice carpenter, let alone an architect or engineer. Make sure you know how much more it will cost you to do the flooring as removable sections before you commit your money and/or effort to that idea. The whole reason that I suggested such an approach is that after the deck has been rebuilt it would be very tough to do repair work on the roofing with a solid fastened floor in place over it. You would also have to remove most or all of the existing joists now just to allow the new roof to proceed. You have to balance how much work is worth doing in order to allow for the future and be practical in the present. It is entirely possible that I have suggested something that is functionally desirable but financially or scheduling wise unfeasible.

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    Tom Horne
     
  9. Aug 7, 2019 #9

    chaka

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    IMG_8342.JPG IMG_8341.JPG IMG_8344.JPG Thanks Tom... I'm including a few more pictures here of the substructure. I was going to use joist hangers when I put this pack together, but curious if I would still need the sleeper in the middle of the roof. In the photos you can see it changes width along the length of the structure to match the pitch change.

    Also, any thoughts on the best way to reattach the fencing modules to the 4x4s?? Brackets?
     
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  10. Aug 7, 2019 #10

    hornetd

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    Those questions involve carpentry knowledge that I don't have. I'm a retired electrician. Electricians believe that they can rebuild the world if you supply enough construction strut and fittings but when you get beyond supporting electrical installations we are out of the scope of our craft. That is why I said that you should "Get someone who knows the structural code and the load factors involved to check the joist dimensions that you will end up with for adequate load bearing capacity" and also "Remember that when it comes to architecture, carpentry, and engineering I'm a pretty good electrician." I didn't mention the sleeper but that is definitely a structural element and will need evaluation by someone who really knows carpentry and maybe even structural engineering. One thing that I would ask about is whether the roof itself is actually adequate in strength to carry the load imposed by the sleeper. As for reattaching the side panels to the uprights that is also outside of my skill set. Don't you just love it when someone suggests all sorts of things that they themselves do not know how to execute? Everything that I suggested is from techniques I saw used not from skills I actually have. Sorry I cannot be of more help on those aspects of the job.

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    Tom Horne
     
  11. Aug 7, 2019 #11

    hornetd

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  12. Aug 7, 2019 #12

    chaka

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    Hi Tom,
    absolutely... I get it. I just really appreciate another brain on this one. I take everything you say with a ton of gratitude while also recognizing you are not a structural engineer or carpenter. Maybe I'll post in the carpentry forum to see if I can't get more eyes on this.

    Thank you so much for your input so far!!!
    David
     
  13. Aug 8, 2019 #13

    mabloodhound

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    Keep the center support. That's too long a span without it. Looks like all the joists are PT so they should be fine with new hangers.
     
  14. Aug 8, 2019 #14

    oldognewtrick

    oldognewtrick

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    If this were my roof, I'd seriously consider decking the structure with advantec plywood, putting a TPO roof on it, lay sleeper 2x over slip sheets, lay your new deck boards on the sleepers. Eliminate the space between the decking and hidden roof. Upgrade your support structure over load points and have a deck with less oppritunity for problems. Over the years I've seen multiple problems with peripet walls.
     
  15. Oct 11, 2019 #15

    chaka

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    IMG_8388.JPG Okay folks, providing an update. We went with TPO, and are now looking at rebuilding the deck. We have a small section that used to be tiled (attached photo) and am now looking at tiles that you can put over a TPO membrane. We would get a slip sheet, and it would likely be a floating system (I'm not sure I'm comfortable with using adhesive as I don't know what that would do to the slip sheet). Has anyone put tiles on a TPO roof? or should I convince my wife not to replace the tile and find a different solution? Many thanks for your thoughts.
     
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