I have a 2x4 truss ceiling in my garage spanning 21 feet. The ceiling joist portion of the truss seem very weak. I am concerned about adding insulation with such weakness. I'm considering spray foam but blown cellulose insulation is not out of the question.

I am concerned the ceiling will not hold the weight.

I have thought about block bracing (making a grid) the ceiling joist but I am not sure that will help the span wise strength of the joist.

 

What say you? 

When I built our dining room addition, I used 2 x 4 trusses, too. The width wasn't quite that far- more like 18'. I used 2 x 4's perpendicular to the ceiling joists, down the center, to add stiffness. The interior ceiling was dry walled. I added pink fiberglass above the drywall. There's been no problems.

@lew I forgot to mention the ceiling my garage is 1/2" drywall.

 

That does make it a little more difficult. If you can get into the "attic", using plywood sheets for support, you could probably still add the fiberglass- or some other form of insulation. The plywood sheets, as a working platform, should spread out the load enough to allow for a safe installation.

I am less concerned about the installation and more about the static load of the insulation up there.

 

Will it be strong enough to support foam or cellulose insulation ?

I'm not an expert on this. Maybe one of the other members, with more construction experience, can give you a definitive answer.

 

My guess is yes, but please don't take that as gospel.

1 hour ago, lew said:

I'm not an expert on this. Maybe one of the other members, with more construction experience, can give you a definitive answer.

 

My guess is yes, but please don't take that as gospel.

2X4 trusses are super strong. Do you have the "W" webs that supports the bottom cord or the King post, a 2X4 that is fastened to the peak and again straight down to the bottom cord.?  Either one will support you and the insulation. However don't stand on the sheetrock it will give way. My guess is that bat insulation weighs less than blow -in. and blow-in packs over time and looses some of its insulating properties.

 

http://www.locketruss.com/roofspan.pdf

 

This show the king post truss:       http://www.vermonttimberworks.com/blog/timber-truss-designs/

 

Herb

Edited December 11, 20169 yr by Dadio

My trusses are definitely not the 4x4 deal. As I recall you can easily maneuver down the center so I don't remember any kind of vertical post in the center.

 

I've scheduled a few estimates for insulation so I don't know if they will blow in or bat. I know the soffit needs to remain open. It's only thirty degrees outside so I'm guessing it's not too warm up there.

 

1 hour ago, ACR_SCOUT said:

It's only thirty degrees outside so I'm guessing it's not too warm up there.

 

Best time to do insulation!  When I was in high school I worked for a contractor. When it got too hot to put on shingles, he'd have us put insulation in the attics, or put up hay in his barn!

1 hour ago, lew said:

Best time to do insulation!  When I was in high school I worked for a contractor. When it got too hot to put on shingles, he'd have us put insulation in the attics, or put up hay in his barn!

Thats like jumping from the pot into the fire.

herb

If those are engineered trusses, they are plenty strong.  I believe mine are 2x6's with a 24' span and I have two rooms upstairs.

If they were so weak that insulation would cause failure, they would not stand up to wind, snow, or bird droppings!

Cal

It's what Cal said, if those are engineered trusses you have nothing to worry about, even with drywall hanging on them. Engineered trusses (at least the ones I've seen) are all printed on the side with the manufacturers name and other pertinent info. They won't necessarily have a center support, most of them have just the W shaped webbing.

Many homes these days are built with 2x4 truss systems. Insulation is no problem. Usually they are on two foot centers.  Truss lift is a big problem but not for you since you not dealing with an interior wall.

Worried ? Screw 2x6 along side of the 2x4's....