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Old 01-21-2013, 08:20 AM   #1
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Garage ceiling joist, bracing, and insulation


Hello all,

Norther VA.

I have a finished 20x24 garage. I am in the process of doctoring it up, painting and installing cabinets.

The ceiling joist are 2x4 - 24"oc. When in the attic the ceiling is a bit bouncy. I have a few minor things in the attic such as spare moldings for my kitchen cabinets and florescent light tube.

The space above the garage door is wasted space. I have seen some recommendations to put up a rail type system and slide storage boxes up there like here.

I am a little reluctant to do that with my current joist because it seems too flimsy.

The question:

If I were to put blocking in between the joints at 16"oc would it help strength the ceiling enough to do something like this? I have even though to use 3/8" plywood triangles to reinforce the trusses.

As a side question:
If I put blocking in the ceiling joist, then install no backing fiberglass insulation and throw down 3/8" decking would garage be any warmer and the attic more usable?

Thank you,
Fred

PS: Now is the time to do the attic, it is cold outside.

Last edited by ACR_SCOUT; 01-21-2013 at 08:21 AM. Reason: No change.
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Old 01-21-2013, 08:35 AM   #2
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Garage ceiling joist, bracing, and insulation


Got a picture?
You can not store anything up there with just 2 X 4 bottom cords.
You run the risk of them failing by trying to do so.
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Old 01-21-2013, 12:22 PM   #3
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What do you want a picture of?
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Old 01-21-2013, 01:14 PM   #4
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Garage ceiling joist, bracing, and insulation


if you are planning on using the attic space I would use 20 pounds per square foot live load at minimum. of course you could use less if a permit is not required for your work, and you're not concerned about sag.

check out these ceiling joist spans based upon size and species of lumber. this is from the 2009 International Residential Code.

I believe what you have are rafter ties and not ceiling joists. The 2x4's do not meet the span requirements for ceiling joists. They are installed to keep rafter thrust from pushing out the tops of the load bearing walls.
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Old 01-21-2013, 01:22 PM   #5
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Rafter ties. I think I just learned something. I guess this means they are not worth anything to support other than the drywall ceiling.

Thanks.
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Old 01-21-2013, 02:10 PM   #6
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Garage ceiling joist, bracing, and insulation


in my area rafter ties are commonly used in garages unless the homeowner wants storage above the garage. In this case floor joists and beams are installed to support those loads. This of course increases cost.

from the 2009 International Residential Code:

R802.3 Framing details. Rafters shall be framed to ridge board or to each other with a gusset plate as a tie. Ridge board shall be at least 1-inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter. At all valleys and hips there shall be a valley or hip rafter not less than 2-inch (51 mm) nominal thickness and not less in depth than the cut end of the rafter. Hip and valley rafters shall be supported at the ridge by a brace to a bearing partition or be designed to carry and distribute the specific load at that point. Where the roof pitch is less than three units vertical in 12 units horizontal (25-percent slope), structural members that support rafters and ceiling joists, such as ridge beams, hips and valleys, shall be designed as beams.

R802.3.1 Ceiling joist and rafter connections. Ceiling joists and rafters shall be nailed to each other in accordance with Table R802.5.1(9), and the rafter shall be nailed to the top wall plate in accordance with Table R602.3(1). Ceiling joists shall be continuous or securely joined in accordance with Table R802.5.1(9) where they meet over interior partitions and are nailed to adjacent rafters to provide a continuous tie across the building when such joists are parallel to the rafters.

Where ceiling joists are not connected to the rafters at the top wall plate, joists connected higher in the
attic shall be installed as rafter ties, or rafter ties shall be installed to provide a continuous tie. Where ceiling joists are not parallel to rafters, rafter ties shall be installed. Rafter ties shall be a minimum of 2-inch by 4-inch (51 mm by 102 mm) (nominal), installed in accordance with the connection requirements in Table R802.5.1(9), or connections of equivalent capacities shall be provided. Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice.

Collar ties or ridge straps to resist wind uplift shall be connected in the upper third of the
attic space in accordance with Table R602.3(1).

Collar ties shall be a minimum of 1-inch by 4-inch (25 mm by 102 mm) (nominal), spaced not more than 4 feet (1219 mm) on center.
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Old 01-21-2013, 02:14 PM   #7
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Garage ceiling joist, bracing, and insulation


check out this post Rafter Ties
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Old 01-21-2013, 03:34 PM   #8
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Here is a link pictures of the attic. I couldn't figure out how to embed them.
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Old 01-21-2013, 03:55 PM   #9
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Garage ceiling joist, bracing, and insulation


Keep in mind you are dealing with roof trusses are expected to be minimal as fat a strength and "bounce" based on expected loads.

When you try to modify the truss OR the load distribution everything goes out the window since it upsets the balance of a structure that was designed for specific loads since the builder wanted the minimum cost for trusses and erection/framing. It doubtful everything was designed for the loads you want to put there plus trusses arenot really designed for "bounce" or accurate deflection to prevent too many drywall cracks. - Keep in mind that "rafter ties" depending on the location do not eliminate loads, bur move it around where they were not designed for.

Look for a tag on the trusses to determine the manufacturer to try and find a solution for what you want to do now and in the future, since odd loadings can cause BIG problems down the road, even with high winds. The manufacture knows more than anybody, especially with pressed plates on one or two sides of the truss. A truss is usually used because it is cheaper, either for common applications or for complex roofing shapes that may require more labor to work.

Dick
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Old 01-21-2013, 04:57 PM   #10
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There is no reason to look for a manufacturer. I just will not restructure or worry about putting a load up there. I hope it will hold up florescent lights. Do you think I will need to brace the rafter ties to hang lights?

Will rafter ties support insulation?
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Old 01-21-2013, 05:59 PM   #11
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Garage ceiling joist, bracing, and insulation


I am a structural engineer that worked as part owner in a truss plant. - Do the trusses have plates on both sides or just one? I have seen many "after the fact/situations" that did not work out well a few years later.

The added loads will have an effect since you were not the owner at he time and no one knew what would be up there and if the Christmas Santas stored there with the lights were hollow plastic or concrete. Insulation is a minor concern if you are storing things in an area not intended for storage.

What you do is up to your judgement and the results you have inherited.

Dick
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Old 01-21-2013, 06:05 PM   #12
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Quote:
Originally Posted by concretemasonry View Post
I am a structural engineer that worked as part owner in a truss plant. - Do the trusses have plates on both sides or just one? I have seen many "after the fact/situations" that did not work out well a few years later.

The added loads will have an effect since you were not the owner at he time and no one knew what would be up there and if the Christmas Santas stored there with the lights were hollow plastic or concrete. Insulation is a minor concern if you are storing things in an area not intended for storage.

What you do is up to your judgement and the results you have inherited.

Dick
I am really not sure what you are talking about here. If you are talking about the plates on the joint they are on both sides but I thought about reinforcing them with plywood triangles.

As far as I know nothing was stored up there because I am the one that cut the hole up there.
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