Modifying Garage Ceiling to Accommodate lift

[GMCGarage]

Had another meeting with the engineer, asking if there was an alternative to the expensive LVL beams. He wouldn’t budge off his design plan. According to a horizontal roof rafter Maximum span calculator I should be fine with 2x12 lumber at 24in spacing ( maximum span is 20ft the length of the rafters in my garage would be 18ft) and this calculation is considering a max live load of 20ft/lbs squared. I think I would be fine with regular #1 2x12 lumber. But to cover myself I’ll go with the advise of the “trained professional”


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Does that span calculator consider shear? What dead load did you use? Can you post both sets of calcs and we will put our propeller hats on and give you a good answer?

Also, based on where your engineer is located, the snow load could vary. The ground snow load values fluctuate from 25 to 55 psf depending what county you live in. PGC is min 30 psf roof snow load plus drift.

Can you give your location too?

 

[GMCGarage]

Your engineer has gone completely conventual on you.
And over specified in the process.
(He isn't paying for material>)
Rafters with collar ties only get you as high as the collar ties.

If you go with a roof BEAM under the roof BOARD that the trusses now give you,
you will have a ceiling that goes to the peak.
But the ends of the beam will need support.
And it will need to be threaded through the existing trusses.
I have seen them threaded through the vents in the gable end walls.
(Do some research. It might need some imagnation.)

The wall end of the beam is easy enough with some extra 2x4's as a support post.
The other in will need a support post or sistered trusses.

Roof beams are often ignored as a roofing support system.
Since WW II rafters and roof boards have become "conventual"
But roof beams are the way log cabins were built.

Not sure the OP would want a column down onto his garage floor.

 

[GMCGarage]

Some other thoughts I had about the design is the LVL's could be used too to prevent some lateral displacement. With your engineer's design, there is nothing resisting the outward push of the rafter, other than the collar tie, but there is still push. The more a rafter deflects, the more it pushes. Since a LVL is much stiffer than 2x12, it could be limiting the push. Any other engineers agree?

 

[LX-Markham]

According to a horizontal roof rafter Maximum span calculator I should be fine with 2x12 lumber at 24in spacing

That's likely simply supported.

Your load case, with the collar tie is more like a cantilever situation. Which is likely why your engineer chose LVL beams over conventional framing lumber.

 

[Speedman87]

Does that span calculator consider shear? What dead load did you use? Can you post both sets of calcs and we will put our propeller hats on and give you a good answer?

Also, based on where your engineer is located, the snow load could vary. The ground snow load values fluctuate from 25 to 55 psf depending what county you live in. PGC is min 30 psf roof snow load plus drift.

Can you give your location too?

Wasn’t my calculations. Was a online calculator. Just plug in your your data and it gives you a figure. Species of wood, size, grade, member type, deflection limit, spacing, live loads (this number I was unsure so I just played around with a few numbers) I live in southern Maryland. Rafter length is 18ft


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[Speedman87]

Some other thoughts I had about the design is the LVL's could be used too to prevent some lateral displacement. With your engineer's design, there is nothing resisting the outward push of the rafter, other than the collar tie, but there is still push. The more a rafter deflects, the more it pushes. Since a LVL is much stiffer than 2x12, it could be limiting the push. Any other engineers agree?

Also this modification is only for 5 truss out of 15. Not the whole garage


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[Falcon67]

Just googling about Maryland snow load I come up with Prince George county at 30 PSI load. Figure 10 PSI dead load, 12" over hang trusses on 24" OC, killing 5 leaving 14' in the breeze, 18' between walls. I figure minimum you are tying to hold up 5040 lbs, or about 360 lb/linear ft along the plates.

Also note that recently I've read that there has been a reduction in the load capability of normal "southern pine". The new rafter tables say my 2x6 rafters (12' span) are now under sized and a do over would require 2x8. That may contribute to the recommendation of the LVLs.

Yes, our old house used 2x4 rafters 16~24" OC (they didn't seem to care that much in 1928) with one layer of cedar and 4 layers of asphalt and the ridge never sagged. Nothing even remotely approaching current code. But I'm kinda glad they don't build them like the used to.

 

[z3speed4me]

So general question as I am assessing doing something similar... building permits required I assume, so does the town typically need legitimate signed/stamped drawings or just a sketch? The cost difference between those is quite significant from the quotes I received.

 

[Matti]

What you could do is replace some trusses or notch and reinforce some existing trusses. This is called a tray or boxed ceiing. What I did is use a plenum/one piece raised center bay truss. Its like a room in ceiling truss except with the center beam cut out. I have 9 foot walls so the roof is 9 foot tall on the outer 4 feet and 11 foot high in the centre 18 feet (its 26 foot wide). Its a custom design that took me along time to find. The trusses are heavy but not overly expensive.
Yours is 90 degrees (I think) so you would have a lower ceiling in the front and back.

 

[Speedman87]

So general question as I am assessing doing something similar... building permits required I assume, so does the town typically need legitimate signed/stamped drawings or just a sketch? The cost difference between those is quite significant from the quotes I received.

Depends on jurisdiction. In my jurisdiction a licensed engineer has to sign off and provide plans for any structural modifications in order to obtain permits. Can not legally modify anything structural without permits.


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[laser3kw]

are scissor trusses out of the question?
Is it possible to have scissor trusses engineered to be placed along side the existing trusses to take over the loads and the remove only the interfering portions of the original trusses?

 

[z3speed4me]

Depends on jurisdiction. In my jurisdiction a licensed engineer has to sign off and provide plans for any structural modifications in order to obtain permits. Can not legally modify anything structural without permits.

Yea figured such for permits, I'll have to inquire with the town as to what level of detail they require so I am not wasting money.

 

[Speedman87]

Pics


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[Speedman87]

Kind of a bummer, construction is almost finished. Went to order the lift I wanted (BendPak Grand Prix Gp7) and it is currently not in production.


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[GMCGarage]

Pics


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So just did your own thing with 2x12's, or the engineer cave?

 

[Falcon67]

Parallel universe LOL

 

[pennsylvaniaboy]

Well $650 for engineering plans that says do exactly what my cousin purposed to do. I guess I’ll sleep better at night knowing for sure it was done right. I will post the plans and updates on the project


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so will the internet experts

 

[Speedman87]

Found another Solution for a lift. The Rotary Ato7n000bbl Which is also designed for narrow bays. I believe this is actually a better solution than the bendpak, alot better quality, but of course with a premium cost. Think ill go this route vs waiting on the bendpak grandprix to go back into production

 

[Speedman87]

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[Speedman87]

Challenger LE10 is on order. expected to arrive next week, will post more pics when installation is complete

 

[firebirdparts]

Not sure the OP would want a column down onto his garage floor.

that's what I did. It came down beside my lift post. You can say "oooh my clear span is so important" but when you put the lift there, it's not a clear floor anymore.

 

[Speedman87]

Finally complete [emoji16]


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[Lucky13driver]

Speedman nice job!

 

[Wes Tex]

In my all metal pole garage I bolted a two post lift into the ceiling supports. With the lift near the center of the building this became a center roof support.

 

[Fish-man]

what happened to the LVLs?

 

[Speedman87]

what happened to the LVLs?

Lvls are Defiantly overkill and not needed. Went into the attic of my house the other day. 2x8 rafters on the same span as the garage. House is build in 1954, no issues. 2x12s will defiantly serve me fine


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[Buddy Jackson Racing]

Nice work. Doing something similar


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