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Sagging shed roof

winwood111's picture

My wife and I are in the process of finalizing the financing on our current land contract for our house with attached workshop. My interest in this place of course was primarily the shop. It is basically a 50' x 100' concrete and stucco building with post and beam supported roof system. The general shape is just a low sloped gable (about 3/12) building with a "doghouse" section at the middle leaving two shed type roofs running the whole 100'. The problem that I am trying to solve is that the roof is currently covered with roll roofing that has a number of minor leaks and worst of all has some substantial sag in some areas (3-4"). My idea was to double up the 2x8 joists which are 24" on center and obviously under sized. I felt that I could add full length joists to each one to eliminate any further sag. (I don't have any hopes of actually removing the dips. The building has been standing since 1920.) The whole roof is covered on the inside with 1x8 T&G pine boards that I plan to remove so that I can get a good evaluation of the roof deck condition from inside.  For roofing I would like to run 1x wood strips along the length of the roof and shim them level as I go to bring the roof surface basically back to level. On top of this I would like to put either a corrugated metal or asphalt panel roof. Any advice would be appreciated. Thank you.

(post #94446, reply #1 of 12)

hate to say this, rip it off and trusses..


 


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(post #94446, reply #2 of 12)

Ripping it off and putting up trusses sounds good, but would be awfully expensive.

But adding new overspanned rafters alongside old overspanned rafters doesn't sound like much of a solution either.

A couple of pictures of the framing would help us out a great deal in coming up with a solution.

Sounds like a nice sized shop, though.



Q: What's the difference between Michael Jackson and a grocery bag?

A: One is white, made out of plastic, and dangerous for kids to play with and the other you carry your groceries in.

(post #94446, reply #11 of 12)

I'm still figuring out how to navigate this site but I have some pictures on the web of my House/Workshop. http://www.imagestation.com/picture/sraid102/p4ade27375d3bb73c3a3dc522ded57610/f9bf469d.jpg

(post #94446, reply #12 of 12)

(post #94446, reply #3 of 12)

This is drastically overspanned. I would recommend that you be very careful about tearing down the pine inside on the ceiling. It could be acting to help spread loads. The whole assembly could be weakened further by removing the ceiling material.

how many layers of roll roofing are on this beast of a shop?

90# times once overy ten years is about 540# or 54#/sq ft possible. I wager that you are in the south, perhaps Arkansas and that it was only intended to handle 15#. Getting some of that weight off before adding any more will help.

Also, A roof that low slope and that old wioll surelyhave a little rot here and there.

If you can tolerate the cost, i would vote for tearing it all off to truss it. But I can't see it from here.

.

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(post #94446, reply #6 of 12)

I agree about the ceiling boards. I began to tear a few off and then got the idea that they may be helping to spread load and prevent twisting of the joists.


I believe that there is about 3/4-1" of roofing material all though I am not sure of that. We are actually in Northeast Ohio near the snow belt but that still doesn't mean that they figured for accurate snow load in 1920. I am pretty sur that there will be some rot but I was hoping to kind of eliminate the function of most of the existing roof deck by adding the new joists and purlins for the corrugated.


Unfortunately I think the cost of a total tearoff would be very costly on a 5000' S.F. roof and I will need to do most of the work myself so doing it witthout tearoff and in stages will make it possible for me.


Thanks for your advice. 

(post #94446, reply #10 of 12)

The reason I figured down south is that land contract deals are more common there than in the north and that this structure is no way designed for heavy snow loads of the north. That is why it is in failure now. The porevious post points out what you actions will be.

.

Welcome to the

Taunton University of Knowledge

FHB Campus at Breaktime.

where

Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #94446, reply #4 of 12)

Winwood,


I can't quite decipher your post.  What is the max. span of the rafters in question?


 


Jon Blakemore

 

Jon Blakemore

RappahannockINC.com

Fredericksburg, VA

(post #94446, reply #7 of 12)

The length of each rafter is about 18'.

(post #94446, reply #5 of 12)

winwood,

Why not add some beams like gluelams to decrease the span. Seems easy from here. :)

KK

(post #94446, reply #8 of 12)

I have considered this idea but I don't want to add any posts in the shop if I can help it. One idea that I have considered is to bring posts down onto the 8 x 8 posts that run from each main post about 8' off the floor to the outside walls. This would keep the added posts oout of the main space but I am afraid that over time the wight of thwe roof would settle down on to these beams and be too much. Some of these cross beams are also questionable where they sit on the wall because of the moisture that they wick out of the walls.


Thanks for your reply.

(post #94446, reply #9 of 12)

Winwood,


What is your goal?  To get a few more years out of that structure?......Or to make it right?  Two differrent ends, with two different solutions.


Jon