Need some advice on fixin my old shop roof

[Brad Hays]

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.

 

[Tom Gall]

Not exactly sure I understand your problem ... or your budget. Rigid foam insulation comes in various thicknesses and sizes. Very light and easy to work. Cost is considerably more than the last time I purchased some. Also useful around the shop.

https://www.lowes.com/search?searchTerm=foam%20board%20insulation

Search Results for rigid foam insulation at The Home Depot

Search Results for rigid foam insulation at The Home Depot

www.homedepot.com

 

[Kevin Jenness]

Sounds like you need a new, thicker deck, which ideally would involve stripping and replacing the roofing material. If your rafters are stout enough you could go over the existing buildup with another layer of sheathing plus asphalt roll roofing. Trying to level out the dips in the existing deck seems like a sketchy stopgap.

For a relatively cheap water resistant work surface you could use MDO or Medex, or go to the junkyard and look for some sheet steel..

 

[Lou Jacobs]

I’d first explore (unless you already have) adding rafters to narrow the span the decking has to cover. Even if it’s hard to access full length there are ways to splice together two pieces to make one rafter. Once you’ve done that you’ll have a sound basis for figuring out the best way to cover and waterproof your roof.

 

[Mike Johnson]

There are companies that can spray a clear sealer over the existing shingles that will extend the life of the roof.
Not sure how large a roof you have but you could try securing some corrugated metal roofing panels over the shingles.
With the price of lumber and plywood being what it is you could sell one of your kidneys and maybe pay for new materials
to re-deck and re-shingle the roof.
When a roof gets old and "janky", sooner or later you will need to replace it, you are better off fixing it right the first time
and not waste time and money on half-ass temporary fixes. The old saying throwing good money after bad.
If your funds are tight because of the economy and inflation it is understandable, you could try stretching some chicken
wire across the roof and stapling it to the high ridge points, this might provide enough support for a lightweight tarp
stretched across the roof. Hopefully in your region of the country you won't get hit with a snowstorm. The weight of the
snow would most likely weigh the tarp down into the low spots.

 

[robo hippy]

What kind of building? Pole barn/agricultural type building? What type of roof? Composition or metal? Lots of options. As for insulating, I priced insulation for my old shop, then on a whim called an insulation company. They put the insulation in, and added a white reflective type cover over the insulation for $50 more than I could have bought the materials for. You might call a roofing company to look at it, since they are experts. 3 feet in between joists is too much, especially if you are using anything other than about 1 inch thick plywood. If it is a metal building and the joists run length wise, I think they call those 'perlins'. Most of the time they will have a metal roof on them because it 'spans' the 3 foot better than plywood and comp roofing. It might be a pain, but putting in individual 2 by 4s in between them on 2 foot centers would help the sagging. Hopefully it won't come down to having to replace the whole roof.

robo hippy