Wood shed roof strength

[Oldtoolsnewproblems]

Hopefully this is the right forum.
Title hopefully says it all. I'm building two lean-tos for drying wood. One for firewood and one for drying lumber. The one for lumber is gonna be 7ft by 18 or 20ft. Steep slope to shed snow since I'm in new England and we get a fair bit. I know I'll be to put some anchors in the ground to deal with wind loads, even though it's in fairly shaded woods so it won't get nailed.
My big issue is I want to minimize the number of posts to make getting long lengths in and out easier. Was hoping to get away with only one in each corner in the open side, but I could be convinced to add one 5ft from one end for extra support.

Normal roof guidelines are not very helpful when you're only spanning 7ft, way less load than usual. Was hoping to get away with sistering a 2x4 to a 2x6 because that's what I have left in my scrap pile. Just looking at it it almost feels like a 4x4 would even be enough, but I could be wildly wrong

 

[tomalophicon]

Hopefully this is the right forum.
Title hopefully says it all. I'm building two lean-tos for drying wood. One for firewood and one for drying lumber. The one for lumber is gonna be 7ft by 18 or 20ft. Steep slope to shed snow since I'm in new England and we get a fair bit. I know I'll be to put some anchors in the ground to deal with wind loads, even though it's in fairly shaded woods so it won't get nailed.
My big issue is I want to minimize the number of posts to make getting long lengths in and out easier. Was hoping to get away with only one in each corner in the open side, but I could be convinced to add one 5ft from one end for extra support.

Normal roof guidelines are not very helpful when you're only spanning 7ft, way less load than usual. Was hoping to get away with sistering a 2x4 to a 2x6 because that's what I have left in my scrap pile. Just looking at it it almost feels like a 4x4 would even be enough, but I could be wildly wrong

I know it's not the same but over here there are pergola and verandah guidelines which were very helpful when I decided how to build my woodshed.
If you can find span tables for outdoor structures like that I would follow those, as they usually account for smaller spans.

Failing that, I'd go the biggest timber I could with a continuous span (where possible).

 

[esshup]

Ditto on the span tables. You can also look for span tables for floor joists to give you some idea. A 2x8 will give you more "support" for a given span than a 4x4.

Calculate your snow load and transfer that to a pounds per square foot load to calculate the length of span for the size of wood you have.

If you put snow stops on it to hold the snow on the roof vs. letting it slide off that increases the joist size requirement.

 

[CaseyForrest]

You can also not place them at the corners, set them in a few feet so you have overhangs.

 

[Oldtoolsnewproblems]

That makes sense, gonna try to find those specialized tables

 

[sand sock]

i dont know alot about lumber strengths. but for steel screws. the GRK screws 5/16 have roughly the same breaking strength as !/2 '' bolts, is what i was told. we had a peaked barn roof collapse in early 2020 , from the snow load/ we ended up jacking the barn roof up and sistering 2x6 to 2x12. depending on the beam. but teh screws did wonderfully. did things with them, that normal screws would of just sheared off.

 

[Bearcreek]

Hopefully this is the right forum.
Title hopefully says it all. I'm building two lean-tos for drying wood. One for firewood and one for drying lumber. The one for lumber is gonna be 7ft by 18 or 20ft. Steep slope to shed snow since I'm in new England and we get a fair bit. I know I'll be to put some anchors in the ground to deal with wind loads, even though it's in fairly shaded woods so it won't get nailed.
My big issue is I want to minimize the number of posts to make getting long lengths in and out easier. Was hoping to get away with only one in each corner in the open side, but I could be convinced to add one 5ft from one end for extra support.

Normal roof guidelines are not very helpful when you're only spanning 7ft, way less load than usual. Was hoping to get away with sistering a 2x4 to a 2x6 because that's what I have left in my scrap pile. Just looking at it it almost feels like a 4x4 would even be enough, but I could be wildly wrong

Are you saying you want to span 18-20 feet, or 7 feet? Which is the open side? Typical wood shed design would have the long side open, but I have to think you're not trying to span 20 ft. with a 2x6.

 

[WoodyGuy]

Same question as Bearcreek ... your note sounds like you're talking about spanning the full open
front of the shed - 20 feet. that kinda span is gonna need a beam in the depth range of 14" to 18"
depending on how much sag you can live with .... a good rule of thumb for sizing floor joist depth
is half the span + 2 .... for a 7 foot span, that'd be 3-1/2 + 2 = 5-1/2 ... 2X6's would do fine.
BTW - if you figure a snow load of 40 lbs per s/f, and a dead load of 10 lbs s/f, your roof load
is 50/sq-ft ... that front open beam would be holding half the roof load (20 X 3.5) X 50 ... a
design load of 3,500 pounds.

 

[Oldtoolsnewproblems]

So the plan is to use 8ft roof panels at a step enough slope to shed snow, so it will probably be 6-7 feet deep, then maximum possible open front span to make it easy to bring in some long lumber I cut. Figure less than 20, more than 15 would be ideal. I know it will be a pretty large beam but I'd rather not manhandle large boards thru a small opening.

This is for drying lumber, not firewood. Also some tool storage

 

[CUCV]

So your looking for a 20' opening on the front face and the roof would slope to the back 8'. Going to a span of 20' for the supporting beam your really hard pressed to even with multiple 2X12's Most likely you would have to go with an LVL to not worry about snow load. The roof rafters in the 8' direction most likely only need to be 2x6's. What is the code snow load rating in your area?

 

[ChasSC]

Normal roof guidelines are not very helpful when you're only spanning 7ft, way less load than usual. Was hoping to get away with sistering a 2x4 to a 2x6 because that's what I have left in my scrap pile. Just looking at it it almost feels like a 4x4 would even be enough, but I could be wildly wrong

Consider using an I-Joist across the front, but I wouldn't build it with particle board since it's going to be exposed to the elements. Depending on how it's built, can meet the same specs as a steel I-beam.

https://www.apawood.org/i-joist

 

[holeycow]

Make a removeable or swing-up post mid-span. Or somewhere near midspan.

just a thought..

 

[CUCV]

With some 2x4's ,nails, glue and plywood you could make a 2' tall truss to span that length too.

 

[holeycow]

Possibly even with a strategically placed cable... I've built log bridges over creeks for equipment crossings with cables installed to increase the load bearing capacity of undersized stringers.

personally, I would just use a keyed-in removable post. Or even bolted-in finger tight.

 

[kuhndog]

Or build it with 1 or 2 removable posts for loading it ?

 

[John Stryker]

This is the woodshed I built (overbuilt) last year. It is 12' x 30'. I used 16' 6x6 posts, triple 2x10 beams, and 16' 2x8" rafters on 2' centres. The wood piles are over 7' tall. The roof is 4/12 pitch and the snow comes off the steel roof real easy, never any sag in the roof. Material cost was under $4,000.

 

[Oldtoolsnewproblems]

Ok honestly I had thought a lot about a removable post and I think I'll go back to just doing that, keep it simple etc.

 

[Bearcreek]

Ok honestly I had thought a lot about a removable post and I think I'll go back to just doing that, keep it simple etc.

It's not more simple, just cheaper. It'd actually be more complicated to build and potentially far more of a hassle to use.

 

[Winn R]

18 to 20 foot length at seven feet width, With object of minimizing the number of posts /columns, instead of putting your columns at corners cantilever the ends 5 feet with a 10 foot girder span at center. If you want 7 feet of coverage, place columns in 1 foot on the high side and low side which leaves you only a 5 foot span for the roof joists with 1.5 foot cantilever. Girders would be two 16 foot and two 8 foot with 4 foot overlap alternated between column lines. With adequate slope, metal roof, and a bit of heat tape plugged in prior to a storm; this should do ya.

 

[holeycow]

Object is not to eliminate posts as much as maximize clear span.