Saltbox Machine Shed Framing

[msterner]

Hi!

I purchased a plan for a 24x48' post and stick frame "machine shed" with 3 sides and open stalls on the front. It is a saltbox style roof so that most of the snow sheds to the back.

Here's what it looks like:


I've installed post footings with permacolumn brackets instead of a slab (gravel floor), so the footings are complete. As I start building I am concerned that it only has a ridge board and collar ties (relatively high up). There are also no central posts supporting a ridge beam. Obviously, this is acceptable in many situations but with a 24' span and no front to back connections beyond the collar ties, it just doesn't seem like enough.

To make myself feel better about our high snowload in Northern Wisconsin (I've seen many buildings collapse these last few years), I am considering adding a load bearing ridge beam and 3 additional footings. Can you take a look and tell me if there is any reason I should not do this or anything I am not understand about the roof load that makes this not work? Aside from the interior not being wide open (which I can live with since this is for parking machines), this seems all around more of a safe bet... Load support in the center, better tying the front and back, etc.

I would very much appreciate your opinions! Thank you.

 

[Wolley]

I'd say move the collar tie down to the top of the front wall and call it good. They probably have it higher because some customers want a overly tall ceiling and to advertise a cheaper build cost using shorter lumber. If you have a steel roof the pitch look sufficient to slide snow before it build up to much. You can also beef it up by adding your own truss chords once you get it framed.

 

[Sumboodie]

Why not beef up the ridge board to the beam instead of both?

 

[msterner]

I'd say move the collar tie down to the top of the front wall and call it good. They probably have it higher because some customers want a overly tall ceiling and to advertise a cheaper build cost using shorter lumber. If you have a steel roof the pitch look sufficient to slide snow before it build up to much. You can also beef it up by adding your own truss chords once you get it framed.

Hey Wolley,
Thanks! I could do that with 22' collar ties. So, you think it's unnecessary to add a centerline of footings, posts and a beam if I move the collar ties down?

Why not beef up the ridge board to the beam instead of both?

Hey Sumboodie,
If I am understanding you, the main reason is because I already have the footings in place and they're in the center of the 24' span. I could center a ridge beam over those and have no ridge board, but I'd have to do a gable roof.

 

[Sumboodie]

Hey Wolley,
Thanks! I could do that with 22' collar ties. So, you think it's unnecessary to add a centerline of footings, posts and a beam if I move the collar ties down?

Hey Sumboodie,
If I am understanding you, the main reason is because I already have the footings in place and they're in the center of the 24' span. I could center a ridge beam over those and have no ridge board, but I'd have to do a gable roof.

Instead of the ridge board, use the beam is what I'm saying. Use metal roofing to help shed snow as well.

 

[mike93lx]

I'd say move the collar tie down to the top of the front wall and call it good. They probably have it higher because some customers want a overly tall ceiling and to advertise a cheaper build cost using shorter lumber. If you have a steel roof the pitch look sufficient to slide snow before it build up to much. You can also beef it up by adding your own truss chords once you get it framed.

That makes it not a collar tie then.

Collar ties are to prevent uplift at the ridge and are placed in the top third of the roof.

Rafter ties prevent the walls from bowing out and go in the bottom third.

They serve completely different purposes.

 

[msterner]

That makes it not a collar tie then.

Collar ties are to prevent uplift at the ridge and are placed in the top third of the roof.

Rafter ties prevent the walls from bowing out and go in the bottom third.

They serve completely different purposes.

Mike, given that, what would you suggest doing? Using the original design but keep collar ties AND add rafter ties to keep walls from splaying out?

Or would you suggest moving to interior footings and a load bearing beam to support the load in the center of the building?

Thanks!

 

[CraigStu]

I am with you on your concern. I have never understood how people can take a triangle which we know is super strong and convert it to a small triangle w/ long legs hanging off the bottom? What exactly do they think is keeping the ends of those legs from expanding? What height clearance do you need for the machines? Do you need that height for just one machine and not the others? I ask because I like Wolley's idea. Heck I'd move those boards to the top of both front and rear walls. But there are a lot of them so w/o counting they must be on maybe 2ft centers so your height would be gone. If you need the height, then your idea of a somewhat offset ridge beam looks good to me.

 

[mike93lx]

Mike, given that, what would you suggest doing? Using the original design but keep collar ties AND add rafter ties to keep walls from splaying out?

Or would you suggest moving to interior footings and a load bearing beam to support the load in the center of the building?

Thanks!

Have you reached out to the plan designer for load specs? I would not reengineer anything without that first.

 

[K'ledgeBldr]

Have you reached out to the plan designer for load specs? I would not reengineer anything without that first.

I would not “change” the plan. Who you need to be talking to is your AHJ.

Regardless, of what, or who says this or that- the only voice you have to answer to is your AHJ! Find out what they’re looking for/accepting then go in that direction… regardless of the suggestions here.

 

[mike93lx]

I would not “change” the plan. Who you need to be talking to is your AHJ.

Regardless, of what, or who says this or that- the only voice you have to answer to is your AHJ! Find out what they’re looking for/accepting then go in that direction… regardless of the suggestions here.

The ahj isn't going to offer suggestions on design changes. That's for an engineer.

The ahj will accept the engineered plans or not.

I am getting the feeling that these plans may not be engineered and that there aren't permits involved here , though

 

[Sumboodie]

I would not “change” the plan. Who you need to be talking to is your AHJ.

Regardless, of what, or who says this or that- the only voice you have to answer to is your AHJ! Find out what they’re looking for/accepting then go in that direction… regardless of the suggestions here.

What's an AHJ?

 

[msterner]

I am with you on your concern. I have never understood how people can take a triangle which we know is super strong and convert it to a small triangle w/ long legs hanging off the bottom? What exactly do they think is keeping the ends of those legs from expanding? What height clearance do you need for the machines? Do you need that height for just one machine and not the others? I ask because I like Wolley's idea. Heck I'd move those boards to the top of both front and rear walls. But there are a lot of them so w/o counting they must be on maybe 2ft centers so your height would be gone. If you need the height, then your idea of a somewhat offset ridge beam looks good to me.

Hi CraigStu,
Agreed. That's how I feel about it as well. I have seen plenty of older buildings around here with a collar tie in the top 1/3rd and then something like a cable running front to back that was clearly added later in the building's lift to ensure the front and rear walls didn't splay out.

I only need 10' height inside. More is better but I can live with it being low. The front door clearance is 9', so this isn't an overly tall building. Yes, 24" on center was the plan.

If I put rafter ties down towards the top of the back wall not only would the ceiling be angled, but it would become very low. Take a look at my updated drawing here and you'll see because it is a saltbox the rear wall is quite low. My 9' machines are only a max of 20' long so I have full clearance back to that depth. Thanks!

 

[K'ledgeBldr]

The ahj isn't going to offer suggestions on design changes. That's for an engineer.

The ahj will accept the engineered plans or not.

Exactly! That’s why I suggest talking with the AHJ- they will tell the “permit applicant” what is needed, required, and/or documented to build the structure.

I f the OP wants to build w/o a permit (good luck on resale), or doesn’t require a permit/inspections, I think it behooves him/her to hire a PE. Why take the chance with your own or family members lives? Or for that matter- the next owner’s? People are quite sue-happy these days!

 

[msterner]

Have you reached out to the plan designer for load specs? I would not reengineer anything without that first.

I did some time ago and they said:
- Wind load of the building is 80mph
- Snow load of 80lbs per sq ft (which does meet needs in our area)

They also said "If you require engineered calculations they can be provided by our sales staff for an additional fee."

That would suggest that it was engineered.

I am not suggesting that I know more than engineers but I've also seen engineered buildings collapse here and would like to make sure that doesn't happen. I just don't like those front and rear walls not having front-to-back support of any kind.

I would assume that adding rafter ties every other rafter would not have any negative effect?

I would not “change” the plan. Who you need to be talking to is your AHJ.

Regardless, of what, or who says this or that- the only voice you have to answer to is your AHJ! Find out what they’re looking for/accepting then go in that direction… regardless of the suggestions here.

I don't know what an AHJ is but there's not anybody overseeing machine shed projects around here.

The ahj isn't going to offer suggestions on design changes. That's for an engineer.

The ahj will accept the engineered plans or not.

I am getting the feeling that these plans may not be engineered and that there aren't permits involved here , though

That's correct, no "AHJ" and plans don't need to be accepted/rejected. There is a permit but it is pretty much just get a permit for the size building you want to build and go for it. As long as it doesn't have plumbing, there are no follow up measures.

I could hire an engineer to review these plans but that seems excessive seeming that I already purchased "engineered" plans and am just looking to beef it up even more to make myself feel confident I am not going to be panicking during the winter when an early freezing rain sticks to the metal roof and makes the snow cling until mid-winter...

 

[mike93lx]

AHJ is Authority Having Jurisdiction. So whomever inspects for the permit.

Adding rafter ties will not hurt. May not help either, but if you will sleep better and can give up the headroom, go for it.

It would also give you a place for a ceiling and insulation, if so desired

 

[mike93lx]

Exactly! That’s why I suggest talking with the AHJ- they will tell the “permit applicant” what is needed, required, and/or documented to build the structure.

I f the OP wants to build w/o a permit (good luck on resale), or doesn’t require a permit/inspections, I think it behooves him/her to hire a PE. Why take the chance with your own or family members lives? Or for that matter- the next owner’s? People are quite sue-happy these days!

Doom and gloom doesn't help. Stuff is sold all the time with unpermitted work...I have a long list of disclosures with my last house and it still sold for an inappropriately high amount.

Sheds can be built that won't kill anyone without engineers, too

 

[Daniel Dudley]

I built something much like that a couple of years ago. It was engineer spec, and it had 2x4 rafters and ties. We used 5/16" high shear construction screws in the ties instead of nails, which pull them very tight.

24' is not particularly deep for that kind of structure. FWIW, I always use Doug Fir for all framing except for the occasional closet. I generally hand pick all my joists and rafters, particularly long ones. I tend to trust engineers as well, but I have never told anyone not to make something stronger than it needs to be.

 

[msterner]

I built something much like that a couple of years ago. It was engineer spec, and it had 2x4 rafters and ties. We used 5/16" high shear construction screws in the ties instead of nails, which pull them very tight.

24' is not particularly deep for that kind of structure. FWIW, I always use Doug Fir for all framing except for the occasional closet. I generally hand pick all my joists and rafters, particularly long ones. I tend to trust engineers as well, but I have never told anyone not to make something stronger than it needs to be.

Hi Daniel, Thanks for the feedback.

In your build was it a saltbox roof? Did the rafter ties go from the front wall to the back wall or stop short as mine are shown?

To my mind, adding the rafter ties (as shown here) takes care of the walls splaying out. Then you just have to have the right roof load and rafter calculation... and ensure that your connections are good for shear, which, as you suggest, using he construction screws would be good for.

 

[Daniel Dudley]

The one I built was very similar to your picture in post #19, with the tie sitting right on the header. The header was a lot taller and longer, as it sat on shear walls at each end. It was a big header spanning a single wide opening. Part of the reason the header was so high was because the roof ran out more than three feet past the front wall, so there was a dry area in front of the building as wide as a sidewalk. the ties and top of the header were somewhere around 9 or 10 feet up.

When I initially spoke with the owner about this building, there were discussions about a structural ridge, but the engineer said it was redundant. What he did want was a steel strap going over the ridge, tying the two rafters together, or a short tie directly under the ridge. He also wanted structural sheathing to make all of the walls shear walls. The siding went on over that, and was nailed directly to the studs. There were also hurricane ties on all of the rafters tying them to the walls. We built the lower walls first, and made masts to help support the end rafters and ridge beam. We built up the ridge beam out of 1x12 pine and supported it in four places, to get and keep it straight.

I know it seems important that the ties sit straight on the framing, but I have seen it done both ways. The headers will all be flagged with studs on their ends, so they will not be twisting. The sheathing on the walls and roof keep all of the framing locked in place, and you will gave temporary cross bracing until the roof is sheathed. The most important thing isn't where the tie is placed, it is the sizing of the ties and rafters, and the quality and quantity of fasteners that you use to hold them together. Putting the tie directly onto the header does however make it a lot easier to assemble in place. It seems like I also put both the steel strap over the ridge and the short tie under it. We were there anyway. If you have the stuff and you are on a roll, keep on rolling. I predrilled for the 5/16" fasteners going into the ties. Might as well.

In an industrial building that could potentially house cars, I would always assume that you should have enough headroom to put in a lift later, which top out at about 12 feet. This almost always becomes a factor to someone down the road, and if is never a good idea to shut out that option, even if you are sure you will never need one. No one was ever sorry they put in too much head room. At least 80% of the time, it is the other way around.

BTW, regardless as to where the tie ties in to the short front rafter, it is the stronger rafter. If the rear rafter is particularly long, and the tie is far from the end wall, it is common to put a support beam under the end of the tie where it hits the rafter, and posts corresponding to the front framing or a known span. Real Colonial salt boxes were built like that, and lots of tractor sheds are too. It makes more sense than putting in a structural ridge when you look at the structure.

 

[matt_i]

This doesn't address your original question but just something i noted: with a building where wind can "enter" needs extra detail as to reinforcing the "uplift" load bearing path from roof to ground.

In an enclosed building, essentially the only way to create pressure differential to "lift" off the roof is the accumulated area under the soffit and eave overhangs. But, when the entire underside of the roof is in play, there's a heck of a lot more area that the pressure differential can act against.

Also a plan to exclude birds would be great. There would be a lot of competition for that beautiful "birdhouse" in my area

 

[CraigStu]

Hi Daniel, Thanks for the feedback.

In your build was it a saltbox roof? Did the rafter ties go from the front wall to the back wall or stop short as mine are shown?

To my mind, adding the rafter ties (as shown here) takes care of the walls splaying out. Then you just have to have the right roof load and rafter calculation... and ensure that your connections are good for shear, which, as you suggest, using he construction screws would be good for.

That looks good to me too. At least now the tail hanging off the bottom of the triangle is only 4-5ft long which to my eye seems acceptable. Also perhaps you could run a cable from top of front wall to top of back wall in line w/ the support posts between your front 'door' openings. That way, as long as your taller machine is backed into the building in line w/ the 'door' openings, the cable will not be in the way.