Help Me Convert To Pitched Roofs (Flat Roof Collapse)

[Muckin_Slusher]

I'll be starting a thread in the Garage Gallery section soon, but for now I'd appreciate any suggestions on fixing my failed flat roofs.

I bought a big warehouse (8000ish square feet) in the spring of 2016. I got it for a great price mostly because the roofs were in poor condition, and because the rest was in poor condition.

The building was originally an apartment building that had two warehouse addition added many years ago. First addition was 47x55, second addition was 41x73. Both these additions may have been at the same time. I don't know.

In 2010 the apartment burned down, leaving just the warehouse sections, which is what I bought. It's got a small shop about 33x28 with a concrete roof (used to be apartment floor). Last fall we added some walls above and a truss sloped roof because the floor roof leaked lots. We did a shed roof (single slope) so we'd have the option of sloping the roof behind in the opposite direction (completing a conventional gable end roof).

I was planning on going for a walk on the roof Saturday to check the snowload and shovel off the roof. WIth the other roof I installed I was expecting more snowload/snowdrifts than usual on the back flat roof, and wanted to keep an eye on it.

I ended up home early from work on thursday, and friday's training was cancelled, so I went to check the warehouse. Noticed the drywall near a roof leak was lower than usual. Moved two cars so I could set up a ladder to resecure the drywall and check things out.

Had a peek in the hole that opened up. Black roof joists and mushrooms, which is no surprise as I was planning on replacing this roof soon.

Then I find BROKEN ROOF JOISTS . Great. Now it's time to panic a little and build a 14 foot tall cribbing to hold up a 6x6 beam and some bottle jacks, all while working under an unknown snow load and sagging busted roof. Got it done without dieing. Roof is Steel I beams (you can see them they're red iron, running left to right in the pics), with 2x6 wood every 12 inches for roof joists. Span is 11 feet. I took a couple pics of the part of the roof with no drywall to show the attachment method to the I beams. Condensation in the cavity above drywall is a really common cause of rotten roof joists.

Spent yesterday morning shovelling off the roof. Figure the 47x55 foot roof had an average of 32 inches of snow on it. According to the internet 1 lbs per square foot 1 inch thick is the rule of thumb for snowload. Meaning I had about 80,000 lbs of snow on this old *****.

Edit: And, yes, I am fully, completely, totally aware that I just won the lottery, bigtime. I don't think too many people have ever had this much warning that their roof structure was failing.

Quick picture history of the building:

1. Before the apartments burned.
2. After the apartments burned.
3. New slope roof we constructed to cover the existing flat roof section.
4. Emergency 14 foot tall cribbing to support broken roof joists.
5. Sample of what the roof is made from (2x6 spanning 11 feet between I beams).
6. 41x73 foot warehouse section (24 inch tall steel trusses spaced 9 feet)
7. Pic of the rusted steel roof deck on the steel trusses.

 

[Muckin_Slusher]

I'm really not interested in replacing flat roof stuff, I would much rather build a proper sloped roof, since we get a **** ton of snow here.

These are some potato-CAD drawings of what I'm thinking will be how we add the sloped roofs.

The yellow part is the existing (new) roof we just added. The red and green sections are above the rear warehouse bays (which are 55 feet deep). All the verticle black lines are structural supporting walls. Top in the picture is a straight roof, the most I could get is a 3/12, which I'm not happy with. Middle in the pic is an idea, I'd put EPDM on the section above the red, then shingles above the green. Lower picture I think is the best, conventional truss to span the red section, then flat trusses to cover the green part.

This looks the prettiest (least hack-job).

 

[Muckin_Slusher]

This view shows the whole building. The pink section has the steel trusses. I'm really not sure what my options are for this section.

I'm thinking of ripping off whatever **** is above the steel decking, replacing what needs to be replaced (or laying more steel on top of the existing...??) then insulating and EPDM.

I'd like to do a slop roof here too, but I have no idea how I could do it.

 

[yeldogt]

Are you going to need stamped plans ? Ask the code official if any retired architects working in the area .. that's my typical route. Good bang for the buck ... you also may want raised truss if you can do the height -- gets you full insulation at the edges.

 

[WNYflyer]

Building codes address the need to the account for snow drifting on lower roofs adjacent to the wall common with the high roof. New structures are designed for the additional load caused by drifting snow. That being said you need to be very careful about altering building roof heights relative to each other because of drifting. More often than not around here if a roof collapses on a relatively good shape commercial structure drifting snow is the cause. Seen a few were the stores/owner put big signs over the entrances and the building design never accounted for something there to cause drifting.

 

[Muckin_Slusher]

Building codes address the need to the account for snow drifting on lower roofs adjacent to the wall common with the high roof. New structures are designed for the additional load caused by drifting snow. That being said you need to be very careful about altering building roof heights relative to each other because of drifting. More often than not around here if a roof collapses on a relatively good shape commercial structure drifting snow is the cause. Seen a few were the stores/owner put big signs over the entrances and the building design never accounted for something there to cause drifting.

Right.

So far I've only replaced what was there before. (Where I've added the new roof and walls used to be the 3 storey apartment building). Trouble is years of condensation and leaks have rotted parts of the wooden structure. This section had drywall on the underside of the roof joists which allowed condensation to occur, rotting the wooden bits.

 

[mcbane]

Building code gives credit for roof slopes over 4:12, so you might look at 6:12 or steeper if you need a permit.


Sent from my iPhone using Tapatalk

 

[Muckin_Slusher]

Building code gives credit for roof slopes over 4:12, so you might look at 6:12 or steeper if you need a permit.


Sent from my iPhone using Tapatalk

I do need engineered drawings, and had them done for the first roof. It's a 4:12.

I will have drawings made for whatever I do to correct this.

 

[My Old Tools]

Engineered steel trusses flown in place with a crane would be my first thought. Do the full 73 foot width with matching slopes would look best. Might be able to salvage the material from last year's shed roof. I'm assuming the side walls can support the roof trusses.

 

[NUTTSGT]

Engineered steel trusses flown in place with a crane would be my first thought. Do the full 73 foot width with matching slopes would look best. Might be able to salvage the material from last year's shed roof. I'm assuming the side walls can support the roof trusses.

Kinda what I was thinking along with one other thought. . . . . how is your insurance ?

 

[Muckin_Slusher]

Engineered steel trusses flown in place with a crane would be my first thought. Do the full 73 foot width with matching slopes would look best. Might be able to salvage the material from last year's shed roof. I'm assuming the side walls can support the roof trusses.

I don't follow what you mean about salvaging last years shed roof??? If you mean tear it down, and span everything with 73 foot trusses? I would think that would be far more expensive than handling smaller trusses, expecially since I already have two load bearing walls in the span. Also, the entire building isn't 73 feet deep, one end is only 47 feet.

I'd much prefer to leave the space under the trusses as open as possible to allow access for maintenance.

The existing trusses on the pink section are accross the 41 foot span. I wouldn't trust the end walls to support 73 foot trusses. One has two 12 foot wide doors in it. New trusses would have to sit on the existing trusses.

Kinda what I was thinking along with one other thought. . . . . how is your insurance ?

I'm not calling my insurance company, this is my problem, not theirs. I have a big pet peeve with people not doing building maintenance, then making the insurance company pay for what proper maintenance should have prevented. You didn't change your copper water pipes that are 80 years old but have a 20 year lifespan, now you want your insurance company to replace the interior in most of your house.........

I'm the one who didn't get up there in time to check the snow accumulation, I'm gonna be the guy fixing it.

Anyhooo, to prevent further condensation from forming I'm thinking once the trusses are in place I can put roll insulation on top of the existing torchdown roof. The torchdown would be my vapor barrier, which is in the proper place (between the insulation and the warm part of the building).

Obviously I'll be replacing/repairing what is needed for the roof decking/roof joists.

 

[GMCGarage]

Best bet would be to have the engineer do some prelim design, and you can price it out. Trusses might not be the cheapest option

 

[matt_i]

I think you have to figure out what's intended. I read above about merging epdm and shingles and the very minimum pitches in a high snow area it seems like the cheapest job is the best one. I think its best to define whether the budget is "fix it forever" or just try to upgrade the pieces in the worst shape...

In either case I think its worthwhile to envision in your mind "What would I do if the entire roof was removed and I was looking at the outside walls?" What is the cleanest setup to put it back together? Should the pitch be upgraded to potentially shed snow better and make a stronger truss to boot?

Personally I think shingles are still a very good choice unless you go under 3:12. The architectural versions are very tough, I think you can count on close to 30 years of service which is enough to bridge about 1/2 of a person's adult life.

 

[theoldwizard1]

Building code gives credit for roof slopes over 4:12, so you might look at 6:12 or steeper if you need a permit.

If you get a "**** ton of snow" 6:12 would be the minimum I would build.