Roof pitch

[MF294-4]

I want to get a couple of tractors out of my shop. A lean-to on the north side of my shop will be the best solution and cheapest. Shop is 40x64 and will be putting this on the 64 side. 12 ft sides now. Would like to go at least 16 ft out. Should I continue with the roof line which is 4-12 I think. Or could I flatten it out to keep the hight up. South central IL. Was going to use 2x12s on 8 ft centers for the rafters. Maybe add some to them to strengthen them up or get some half trusses.

 

[IOWA NORTHEAST]

3/12 is usualy the min alowed with a steel roof, and even then you should calk the seams / lap. On a 3/12 you would loose 4 ft.

A one sloped lean to drops alot faster than you would guess it too.

A 4/12 makes it drop 64 inches.

 

[woodbutcher]

I'm considering doing something similar with my shop building. I extended the roof with a 16' shed on the south side, and kept the 5 in 12 pitch which has only 8' clearance from the ground on that side now. On the north side I want to extend it only 12' and keep the same pitch.
Butch

 

[RwEny]

I don't have my load tables with me but I think 2x12's 4' on center would be a little lite.

 

[Bspauld]

I went out 16 ft on mine ,The load table said I could go 2X10 24in on center,4-12 pitch.Thats the least I can do in Mi.

 

[JDemaris]

The roof pitch has nothing to do with rafter-strength. But, you do have to anticipate possible snow load if the roof can't shed itself clean. Are you always going to be there to clear snow off it when it builds up? That's what takes a lot building down in my area. Second home owners not around to clear snow off roofs.

A roof with a 16 foot span and able to handle a light snow (30 psf) load needs 2" X 10"s spaced 24" apart. And that's with high-strength wood.

Single 2" X 12"s on 8 foot centers isn't adequate for any sort of snow loading at 16 feet of span. My area would require, at the minimum, triple 2" X 12"s nailed together if spaced 8 feet apart.

Here in central NY, 2" X 12" on 16" centers for a 16 foot span is the minimum allowed (40 psf).

Just out of my own curiousity, if you want your rafters 8 feet apart, what are you going to lay across them for purlins? Here you'd need a minimum of 2" X 8"s laid on end and spaced 24" apart. In the end, it would be easier to just space the rafters closer to each other.

 

[VADAVE]

IA Northeast has it about right. At 4X12 losing 64 inches means that 12 foot wall goes to 7 foot. Are your tractors that short?
Yes you could lower the roof pitch some--2 to 2.5 X12 maybe but not on 8 foot centers. If you put those 2X12's on 1 foot or at most 16 inch centers then it'll work. I'd use 1 foot centers with 1X6 boards on 12 inch centers for purlins.
Eastern Virginia doesn't get your snow and i built a shed that had 2.5 or 3X12 pitch using 2X6 rafters on 12 inch centers with 1X6 boards on 12 inch centers for purlins. Shed the 3 foot snow we had last year just fine. And it's low, maybe 7 foot at the outside, so I don't park tractors in it, just trailers.

 

[redtom]

I was going to go out at least that far on mine but my shed is 14 high. If you are going in and out one or both of the ends 7ft high at the eave isn't a big deal unless you have big farm equipment. If you are using the ends for entering a low eave provides storage for shorter clutter items. In my dads pole barn we went out and down to 5ft at the eve. It works out good in the shop part because you never walk by the wall any way and in the storeage are of his shed any smal tractor will fit because you don't drive in by the eave you go in the end. We have a JD H, W-12, and 340 Farmall all in there with plenty height.

 

[Anonymous-0]

I built a 16' wide leat-to aside my shop with 2x12 spf rafters on 24" centers. Roof decking is 3/4" boards with three tab shingles. Just under 3/12 pitch. As a safety precaution I scabbed a 12' long 2/6' to each rafter. We live in NE WI.

Another precaution I took was to spread a 1" line of additional roofing tar across the standard tabs, (7 gallons in all). I don't have a building background and just built what I thought would work. The now 15-year-old building is a 100% success.


Glenn F.

 

[Anonymous-0]

Oops, I meant to put this at the top of the thread.

Glenn F.

 

[Leroy]

Never had any problems with a 2.1 to 12" pitch, building is over 30 years old now and this is in Ohio and around here you would never get on a roof to clear it. Same pitch I use on a shingle roof as well.

 

[Stuart]

What is your average yearly snow fall in inches. So in your area what would a 66ft wide shed need if the rafters are on 8ft centers?

 

[jrh009]

You need to find out what the ground snow loads are for your local area, for small buildings you multiply the ground snow load by .6 to obtain your live load. Apply this to a roof joist span chart. You will find yourself in the 2x12@16" o.c. size range if you have live loads in 40psf range. At a 16' span live load deflections often control the design.

You also need to review your foundation conditions on the common wall, as you may be overloading the footings. Also do not consider a ledger board nailed onto the existing wall to support the new roof members. This will not be adequate.

As far as addressing the roof slope you can go with a commercial steel roof profile, use a high rib of 1.25" high at 12" on centre, use proper a proper butyl sealer tape on the lap joints, not caulking, nylon headed screws (designed for this use) and install at a slope of 1 ft in 12 feet. With this type of steel roofing matl you would strap the joists at four foot centers.


Dropping the new roof down 12" or so at the common wall allows different roofing profiles to be used. Counter flashing this section is fairly simple

Alternately you could use a plywood deck and install a single ply TPO roof membrane, this would be beyond do it yourself, but you could decrease the slope even more, to 1" in 12' or flat if you wished (not recommended)

 

[JDemaris]

We get 120" in a good year. But yearly averages don't mean as much as those rare events that DO happen now and then. I was a 100 miles north three years ago in Owesgo when they got 12 feet of snow in a storm that lasted over a week, non-stop. Lake effect from Lake Ontario.

What does the 66 foot width have to do with roof-load and rafter size/spacing? The horizontal-run (not length) of the rafter is what has to be determined. I assume your rafters run across the depth of your building, not the width. There is no way any wood rafter can support anything at 66 feet.

In my area, a 60 PSF roof is the minimum except for certain types of farm buildings that can be excluded. Some places further up north require an 80 PSF roof minimum. To meet a 60 PSF load, 2" X 12"s spaced 1 foot apart can be run a 24 foot span. If spaced 2 feet apart the max run is 16 feet. If an 80 PSF is required, 2" X 12"s spaced one foot apart can run a mex span of 17 feet (if high strength #1 wood).

 

[Stuart]

I have a shed that is 66 ft by 168 feet, so my rafters or trusses are 66 ft wide.

 

[Stuart]

Some times the terms rafter and truss are used as one in the same. Wider buildings have to have a heavier truss. Wider buildings are usually built on 8 ft pole centers or 6 ft . narrower buildings can go with 9 or 10ft pole spacings.

 

[IOWA NORTHEAST]

There isn't a shingle company or steel company that will alow that pitch that I have ever in 45 years in business heard of. There could be one, but we can not find them in our area.

In fact anyone with a steel roof and problems will soon learn that they are selling you a chunk of steel---nothing more than it will not chip or flake the paint. If it does, the company will have a new name, and tough luck on any claims.

We had a round rafter building 80 x 160 w/ 20 ft eves. The local lumber yard contacted the company and they returned the ok that their super industrial steel would work. It was I think the cost was four or five times the price of regular ag steel.

We had major issues with, and after the field man and I climbed up on the roof, he said you know we don't guarentee it not to leak.........

I then told him his engineer gave the go ahead. What was his name?????? Was the next question, we have several of them.........You should probably ordered a different configuration that we have......

 

[JDemaris]

You may know people that swap the terms "rafter" and "truss", but that doesn't make it correct and they don't mean the same thing. There is a "trussed rafter" which is not just a "rafter."

And yes, American English is a "living language", so if words get misused often enough, that misuse becomes accepted. Hasn't happened yet with "rafter", "truss", "trussed rafter", "engineered beam", "girder", "purlin", etc.