Need some advice on fixin my old shop roof

I've got a janky garage/shop roof that I'm trying to get ready for the winter, and need a suggestion for some kind of filler material. The guy who built it was in the military probably in the early 60s and it seems like it was built to the standards of a field manual. The roof is sloped about 3 deg, which when it was new probably performed well, but a number of decades later and it ain't lookin so hot. Everything's under control insofar as major structural integrity is concerned. The problem is with some of the plywood that droops in spots between the joists. I'd like to secure a large tarp up there to give it the best chance possible over the winter, but if these dips aren't filled in before the tarp goes on there's gonna be lots of places that will harbor shallow pools of water weighing on the roof all winter.

What I have are a number of say 3 ft long runs between joists that are sunk about 2", and these are the places I'm trying to fill. My first idea was to use expanding foam but emptying out a can doesn't nearly fill one of these dips. Something with more volume is needed. So then I had the idea of using mulch, but that's got too much potential to absorb moisture and become too heavy. Thought about sawdust, but it's got the same potential to gain weight. And now my last idea is to use shipping peanuts. Although I don't think they'll end up being what I go with because of their cost and anticipated difficulty in working with them, they do happen to be a good example of a material that would fit the requirements of being light and resting absorbing water.

So that's where I'm at with this guys. Any ideas on some kind of filler material I haven't thought of?

Last thing is, I'm trying to figure out a material I could cut to about 3'x5' and use as an outside tabletop, something that rain won't effect. 3/4" melamine would work great insofar as utility is concerned but obviously wouldn't work due to not being weatherproof. Any suggestion for a material here?


Thanks.

I don't understand your band aid approach. Sounds to me like the rood needs to be stripped and rebuilt. Did all the roofers in your area go to Florida?

How big and what shape is your roof? If you could afford a big sheet of TPO roofing or Rubber roofing for a temporary cover the dips might not matter. Getting either one up there, un rolled and secured around the edges will be a big job. Be careful up there those sags could be weak.

At least around here it seems like putting a tarp on the roof is always pointless, as they tear up in the cold wind. If it's leaking now I would try to replace the plywood and roofing at least, before winter comes, and maybe add a bit of height to one end and put on new rafters to give more slope. If it's not leaking now then you could wait and do the job properly in the spring, though sooner is always better for roofs in my experience.

I bought a house last fall that had been abandoned and the back 1 story kitchen was only about a 2.5/12 pitch. It had leaked, then someone put on some really lousy roll roofing that wasn't doubled up or tarred properly, and then someone had nailed a tarp over that at some later point. All of it had failed completely, and I had to replace several rafters and all the decking, as well as all the joists in the floor below. Putting a tarp over the roof is a good strategy for a couple of days during a roofing job if it rains, or after a storm if the roof is damaged till it can be fixed, but all winter is not likely to work.

I would climb around inside with a step ladder and bang on all the joists with a hammer. If they are sound, run PT perlins across the roof and screw on metal roofing. The perlins will also give you something safe to walk on while installing the roofing

tabletop.... solid surface glue up or cast concrete. How about a big solar panel?
Bill D

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Originally Posted by Richard Coers

I don't understand your band aid approach. Sounds to me like the rood needs to be stripped and rebuilt. Did all the roofers in your area go to Florida?

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I agree with Richard here. If the plywood is "dipping" there's likely serious water damage and it needs to be eliminated by re-decking and re-roofing.

A 22 oz vinyl tarp can make a long lasting roof. They cost more than some roofing materials. Steel is a good idea. I cover pressure treated purlins with a strip pf 30 pound tar paper to protect the steel. I have not found roofing screws that are approved for treated wood.

I don't think that regular metal roofing is meant to be used on slopes less than 3/12, if I recall correctly, but that's not to say that it wouldn't work. I shingled the new kitchen roof even though the rest of the house is metal because of the low slope. I don't know about slope requirements for standing seam metal roofing, but it's more expensive anyway.

Sounds like your roof needs an intervention. A bandaid will only make it worse, you'll end up with leaks because something is going to start rotting. Fixing the substructure is the proper first step, then you have other options. Like they said above, sounds like you need some purlins. I would not use pressure treated. However, I'm wondering if you even have safe trusses or if they are something the builder salvaged from something else that are so far out of spec as to be unsafe. Odd to have 3' spacing. If the are adequate, purlins on hangers will fix the sags.

Brad,
You really need a new roof, but I'm not living in your shoes.

If you "just gotta get through the winter", maybe you could jury-rig 2 inch thick closed cell foam sheets to fill your dips. Maybe apply roofing tar to fasten it down and then cover with a well fastened tarp. Here's the foam. A 4 x 8 sheet of 2" thick foam is about $60. LINK

Doing it this way sure seems like a desparate kind of fix, but maybe the foam sheets will give you a better idea.

Let us know what you decide to do and how it works out.
Fred

I fixed a couple of very low pitched porch roofs on an old house that had been added on to it. They are something less than 1 in 12. I pulled all the sheathing off, sistered all the sagging rafters with new wood that had been straightened on a jointer, and carefully made sure the new roof planes were exactly flat with 3/4" plywood sheathing. On top of that, I installed a standing seam roof with all the standing seams sealed with sealant before the joints were snapped together. They also had no ventilation into the roofs, so I extended the overhang a little, and added some continuous vents all around.

They have not leaked since my redo.