×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Strengthening attic trusses for light storage

Strengthening attic trusses for light storage

Strengthening attic trusses for light storage

(OP)
.
OK, I've read the excellent thread on this topic several times, but it's now locked.  Like that thread poster, I want to use a small area of my attic for some light storage.
 
http://www.eng-tips.com/viewthread.cfm?qid=261461

I have attached a sketch of my truss configuration.  The house was built in 1982, using pressed metal plate trusses.  

All chords are 2x4 and all webs are 2x3.  The floor will span 4 trusses and an exterior wall made of 24" oc vertical 2x4.  The truss spacing is roughly 24" oc, but the distance between the exterior wall and the first truss is 19".  There is continuous horizontal bracing on only three truss webs, as shown in the drawing by the little blocks at the mid-span of the webs.  

There is a diagonal brace (2x6 - not shown) from the base of the exterior wall to the top  of the fourth truss.  This brace is nailed to each "kingpost" (the centermost and nearly vertical web)

At location AA I have a set of pull-down stairs in the middle of these trusses.  I stacked 2x4's atop the bottom chords the entire distance between the web joints, attaching them with 2.5" screws at an angle into the chords.  I put a 2x6 header between two chords to form the box for the stairs.  I did not cut any truss members, these are 22" wide stairs.  

Location AA will have flooring surrounding the stairs to act as a landing.    

Location BB is the storage area.  The floor here will be approximately 12 x 8 feet.  The flooring will be 5/8" T&G SturdiFloor ply, attached using 2" screws.  I will attach the floor to the exterior wall by scabbing a 2x4 across the vertical supports of the wall.  

In order for the floor to clear a vent pipe and some light cans, and allow for insulation, I am going to need to stack a 2x6 atop the bottom chords.  The first question is how to install this.  My initial thought is to use 8" timberlok through the top of the 2x6 and all the way down into the chord, with an inset drilled in the 2x6 to accomodate the hex head.  Spacing is 12" - 18", and predrilling would be used.

http://www.fastenmaster.com/details/product/timberlok-heavy-duty-wood-screw.html

Then, since I am prone to overkill, I want to use an 8" wide 5/8" thick plywood gusset that is glued and screwed to one side of the 2x6 and then screwed to the side of the chord, using 2" x 10 GRK RSS screws, with a big head that won't pull through the ply.  In addition, the RSS is self tapping, so no predrilling is required, and it's supposed to be hardened for better tensile and shear strength than similar size screws.

 http://www.grkfasteners.com/en/RSS_1_2_information.htm

I was going to use a "W" pattern every 6", so each member will have two rows of screws at 12" OC, in a staggered pattern, at least 3/4" away from the side of the member.  I'd probably use two screws at the end of each ply section.  

Both of these fasteners (timberlok and RSS) are relatively small gauge, which seems to be better for a relatively small chord, especially chords that are very dry and brittle.  Yet the manufacturers claim that these fasteners compete with larger-gauge counterparts.  

My two initial questions are:
(1) is my attachment method sound?  Too much?  Too little?  

(2) is it advisable to glue the 2x6 to the bottom chord?  I am thinking that by gluing the bottom of the 2x6 to the top of the chord and also gluing the chord to the side gusset, I will be spreading the load evenly across the full length of the added 2x6, rather than at the discrete attachment points of the fasteners.  Plus, I'll be making up for all the fasteners weakening the chord by firmly attaching these other members (the 2x6 and the ply) to it.  I'd be using PL Premium, a polyurethane based construction adhesive.  

http://www.loctiteproducts.com/p/pl_ca_prem/overview/Loctite-PL-Premium-Polyurethane-Construction-Adhesive.htm

Then suddenly, I get this vision of Mike Holmes coming to my house.  He says not only did I screw this up, but by gluing it, he can't fix it without completely replacing the entire truss system, so he'll tear off the roof and start rebuilding ....  Then I wake up ...  

So prevent my continuing to wake up in a cold sweat, I'm asking the knowledgeable folks here whether gluing is a sound idea.
  

RE: Strengthening attic trusses for light storage

A 53' truss w/ 2x4 chords is a bit of a stretch - although doable if you have enough interior bearing walls and from your drawing it would appear you do. What part of the country are you in??  Snow??

That said - it would also appear that the 2x4 bottom chord is already spanning some 8 to 10' in places??  That again is not bad.

BUT it will not carry any more load - at least if I remember from days as a truss engineer.  Sorry, but you are out of luck.  Actually, just walking on it may be a bit dubious.  It wasn't until the mid-80's I think that all trusses had to be checked to insure they could carry a 250 lb man.

If you are still interested, contact a local truss engineer or fabricator and maybe they can inspect and offer some help.

But I kind of think you might be maxxed out.

RE: Strengthening attic trusses for light storage

(OP)
Thank you.

RE: Strengthening attic trusses for light storage

I would be concerned about the bottom chord size at the support points B, C and particularly E since the support is not at the panel point.  

It would be interesting to see the truss diagrams from the truss supplier to note what points are the support points.  May only be A, D and F, with B, C and E being non-bearing separation walls.

That being said, adding storage load to the area of "E" will only lake the situation worse if it is a bearing location.  I tend to agree with MtE here.   

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Strengthening attic trusses for light storage

Why not just support your "light storage" area on the partitions rather than worry about the roof trusses?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources