# Lag screw size/load



## fireguy (Jul 11, 2014)

Next week we install a 4 foot type I hood, 450 pounds with the fire system. The kitchen is in a daylight basement.  The GC will drill a hole in the concrete wall, and dig a trench for the  for the horizontal duct.   The exhaust duct will exit the hood at the back of the plenum, not the top. The duct will be 4 feet horizontal and either 6 feet or 10 feet vertical, with a sidewall fan. At present I am expecting to use use uni-strut fastened to the 2 inch x ??  trusses that support the floor above the hood.    Is there a chart that tells me the size of fasteners to secure the uni-strut to the trusses?  Captive Aire specifies 1/2 Inch redi-bolt to the uni-strut.  But they do not specify the lag screws to secure the uni-strut.

Next week we will start a job.  Our responsibility will be to supply the hood, install the fire system, gas valve and the duct insulation.  That is easy.  But I am also to be involved in overseeing the GC install the hood, and the sheet metal shop installing the duct.

The hood is 4 feet, about 450 pounds.  The duct will exit the hood at the back of the plenum, 30 inches  through a concrete wall, (the kitchen is in a daylight basement), up the exterior  sidewall either 6 feet or 10 feet to the sidewall fan.  I will supply the uni-strut and 1/2 inch bolts to hang the hood.  Is there a chart that tells me the size of lag screw

to secure the uni-strut to the 2 x 6 framing above the hood?

Are there any suggestions about protecting the horizontal duct through the concrete wall and the dirt?  Do I need to use duct wrap through the concrete and dirt?  What about supporting the horizontal duct?   We will use 3M 15A insulation for the vertical duct and it will be enclosed in wood framing.

And of course there is no hurry for the information.  We don't start until Monday.


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## TheCommish (Jul 11, 2014)

Do you have a drawing?

Who is the RDP responsible for the building design? he should be answer this question or the SRE of record

Is the supporting structure (floor truss) designed for the load you intend to hang off of it? is the load concreted or uniform?

the NDS has holding power for lags bolts provide you can get a decent lag screw no the off the shelf junk a the home store.

it seems that you may not need duct wrap intil you go up the building since concrete in non combustible, you can contact the manufacture they are geet help for the duct wrap install

good luck


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## Mark K (Jul 11, 2014)

Lag screws are for wood not concrete or steel.

To get an intelligent answer to your question you need a professional engineer who has access to more complete information such as any existing drawings of the building.


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## ICE (Jul 13, 2014)

Is there a permit with approved plans?  If not I suppose 1/2" lag bolts into the bottom chord of floor trusses is a-okay.

On the other hand, there might be the potential for an inspector to see that.

Right or wrong, I would question hanging from the bottom chord....especially with lag bolts.


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## Frank (Jul 14, 2014)

Most any threaded rod screw into the wood on all 4 corners with 1/4 or 3/8 rod will work  450# hood over 12 sq ft is not that much

1/4" x 2" screw vertical in pine is good for 1000# ultimate load

http://www.powers.com/pdfs/catalogs/49053_vertigoplus_lo.pdf


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## Mark K (Jul 14, 2014)

If you are talking about a 450# load on a wood truss I would suggest that you may have a bigger question regarding the adequacy of the truss itself.  These trusses are often very tightly designed.  Was the truss designed for this piece of equipment.

The problem with simplistic answers is that they often ignore issues such as edge distance which can significantly impact the capacity of the fastener.   In addition eccentricities in the mounting can increase the loads on individual fasterners.


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