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Forum topic by hpw posted 08-08-2015 03:14 PM 925 views 0 times favorited 11 replies Add to Favorites Watch
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hpw

2 posts in 488 days


08-08-2015 03:14 PM

I’m going to be building a 14’ x 20’ single car garage in my backyard. I have a 14’-8” ridge height restriction because that is what my existing ridge height is on my house. I will be using a Gambrel Roof that will have a 7’
ridge height. Trying to maximize the height of 1st floor so that I can get a 7’ tall garage door in.

I will be using the attic for storage and am looking for an alternative to 2×8’s for ceiling joist. There are no span charts for doubling(tripling?) 2×6’s on 12”o.c. spacing. Even thought about going solid 2×4’s glued and screwed the entire 20’, like a glue-lam beam. That would be $1000.00 in just the 160 2”x4”x14’, not counting glue and screws. And I don’t even know if it would work.

Am I crazy?
I realize I am only talking inches here in an effort to gain in interior height,

so is there anyone that can give me some ideas/alternatives for a thin structurally sound 2nd floor?


11 replies so far

View BurlyBob's profile

BurlyBob

3695 posts in 1731 days


#1 posted 08-08-2015 03:59 PM

I used TGI beams and Simpson hangers for my living room ceiling. I tore out the old ceiling and vaulted it to 13 Feet. Another alternative might be a steel building. I’ve got a 30’ x 30’ steel building with a second floor. the joist and rafters are all steel. It’s really quite strong.

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Ghidrah

667 posts in 688 days


#2 posted 08-08-2015 04:05 PM

1st you need to talk to your local Building Dept. for design plan suggestions, (minimums for structural integrity) The IRC has minimums for truss material dimensions, which are the only things I can think of where any dim under 2X10 are allowed for rafters.

A bit of perspective, a true gambrel is based on the circle; that said a 14’ wide building has a 7’ radius which is what the roof height would be if the rafters had no tails. Add tails and the gambrel is now higher and wider than the width of the building.

If you use 7’4” 2X4 studs with double top plates and single bottom plus a 2X PT sill you’re already at 94”, (7’10”) above grade. Will you be building the garage on the ground or will there be a foundation with a minimum rise of 8” or 1 cinder block above grade? Now you’re 102”, (8’6”) from grade to top plate, leaving you with 74”, (6’2”) remaining for the roof. This pretty much kills the gambrel idea.

-- I meant to do that!

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crank49

3981 posts in 2437 days


#3 posted 08-08-2015 04:26 PM

My shop is similar. Rooof height is 14’-6”. My floor is 16’ x 24’ and I have 9 ft ceiling height.
My roof framing was what are called storage trusses. They are made of 2X4 lumber, gambrel shape, with a 10’ wide attic space down the center that has a 4’ ceiling height.

I elected to come in and redesign 1/3 of the space by building a 16” high truss across the width with a bottom chord of 2X6. This truss is 8 ft from the back wall. Then I built a tripled 2×6 center beam from the truss to the back wall. and ceiling joists from the center beam to the outside walls. All the joists are 2×6 and none are longer than 8 ft. The main floor ceiling height in the back 1/3 is now just over 7 ft and the attic height is just over 6 ft down the center. I then removed the bottom chord of the back original trusses. This gave me a space to go up to the attic on stairs and to have a small office and still have a 16 ft x 10 ft storage attic.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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hpw

2 posts in 488 days


#4 posted 08-08-2015 04:34 PM

thanks for the reply


1st you need to talk to your local Building Dept. for design plan suggestions, (minimums for structural integrity) The IRC has minimums for truss material dimensions, which are the only things I can think of where any dim under 2X10 are allowed for rafters.

A bit of perspective, a true gambrel is based on the circle; that said a 14 wide building has a 7 radius which is what the roof height would be if the rafters had no tails. Add tails and the gambrel is now higher and wider than the width of the building.

If you use 7 4” 2X4 studs with double top plates and single bottom plus a 2X PT sill you re already at 94”, (7 10”) above grade. Will you be building the garage on the ground or will there be a foundation with a minimum rise of 8” or 1 cinder block above grade? Now you re 102”, (8 6”) from grade to top plate, leaving you with 74”, (6 2”) remaining for the roof. This pretty much kills the gambrel idea.

- Ghidrah

I will use a 5-1/2” wide x 7” tall stem wall for the exterior walls with the interior slab poured(monolithic) 1”-2” above grade for increased ceiling height. I will do a kick tail at the outside wall to get a overhang(eyebrow?)
I guess my ? is where do I get info. for what kinda of floor would I get with doubled/tripled 2×6’s on 12” centers

I will check with the building inspector monday
Span would be 13’-5” with 3-1/2” bearing on each end.

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Ghidrah

667 posts in 688 days


#5 posted 08-09-2015 03:53 PM

In our area, the design you show is called a Dutch hat because the radii aren’t equidistant.

-- I meant to do that!

View sras's profile

sras

4392 posts in 2595 days


#6 posted 08-09-2015 04:14 PM

A 2×8 (I’m assuming 7.5 inch actual dimension) is 2.5 times stiffer than a 2×6 (again assuming 5.5 inches actual).

ASSUMING your current design is acceptable, you would need 2 1/2 times as many 2×6 joists for the same stiffness.

-- Steve - Impatience is Expensive

View crank49's profile

crank49

3981 posts in 2437 days


#7 posted 08-10-2015 02:37 AM



A 2×8 (I m assuming 7.5 inch actual dimension) is 2.5 times stiffer than a 2×6 (again assuming 5.5 inches actual).

ASSUMING your current design is acceptable, you would need 2 1/2 times as many 2×6 joists for the same stiffness.

- sras


A 2X8 is 7 1/4” by 1 1/2”

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View Ghidrah's profile

Ghidrah

667 posts in 688 days


#8 posted 08-10-2015 03:26 PM

That would depend on the mill the lumber came from 7 1/4” is the most common but I have seen 7.5 and 7.625

-- I meant to do that!

View canadianchips's profile

canadianchips

2358 posts in 2463 days


#9 posted 08-10-2015 04:10 PM

I wouldn’t sacrifice headroom in work area for storage. Chances are you will store CRAP that you may never use again.
Go for maximum headroom on main floor. Later when you think you may need storage up, add it on later. That Gambriel roof will allow you to do that LATER.

-- "My mission in life - make everyone smile !"

View DrDirt's profile

DrDirt

4169 posts in 3208 days


#10 posted 08-10-2015 04:32 PM

+1 Canadianchips.

I would perhaps even go for a vaulted ceiling (no attic)... and add skylights.
For storage maybe a “Loft area” at one end of the shop, perhaps over your workbench, so that you can then have additional lighting mounted beneath the loft to light that space more brightly

The loft can hold materials, but perhaps other items like your dust collector or Air Compressor to free up floor space.

My shop is 14X21… and it is tight for big equipment and still being able to assemble things.

-- 'Political correctness is fascism pretending to be manners' ~George Carlin

View buildingmonkey's profile

buildingmonkey

242 posts in 1013 days


#11 posted 09-16-2015 05:47 PM

If you have room, I’d probably go with a lean to for storage. And to put your dust collector and air compressor in.

-- Jim from Kansas

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