Tag Archives: truss loads

Condensation Solutions, A Ceiling the Right Way, and Timing

Advice about condensation, ceilings done right, and the timing of questions

DEAR POLE BARN GURU: My deck roof is metal panels on 2×4 purlins, rafters are 2×6, like a pole barn. I am enclosing it, and need to stop the condensation. I spray foamed it with closed cell, but there is some condensation on the foam in a few places. It will be covered with drywall. Would a 6 mil plastic vapor barrier on the conditioned side work? MICHAEL in FRAZIER’S BOTTOM

DEAR MICHAEL: Provided you are able to reduce the moisture content within the building so as no vapor is being trapped between the vapor barrier and the foam, it should take care of the problem. In all reality, as long as you have no holes in the gypsum drywall, once it is painted you should have eliminated the problem of condensation against the insulation.

Now getting to the real problem – you have too much moisture in your building. If you did not place a well sealed vapor barrier under your concrete slab floor, you need to seal it. Walls also need a vapor barrier (without holes) on the conditioned side to prevent moisture from passing through.

 

DEAR POLE BARN GURU: I have a 40 x 80 pole barn with 8 foot truss spacing. I will be installing faced rolled insulation between each truss. What is the recommended ceiling product to install on the inside? Wood, metal, that will be lightweight and easy to install?? Thanks JEFF in SYCAMORE

DEAR JEFF: I see problems in your future….

Faced insulation is the absolute wrong product to use for insulating your ceiling. Any insulation placed at the truss bottom chord level should be unfaced. The best bet would be to blow insulation in above the finished ceiling.

In any case, you must adequately vent the attic space.

Now, on to the ceiling.

 

I am hopeful you have trusses designed with a minimum of a five psf (pounds per square foot) ceiling load, with 10 psf being even better. Confirm with your RDP (Registered Design Professional – architect or engineer) who designed your building, however 2×4 #2 ceiling joists at 24 inches on center between the bottom chords with joist hangers should adequately support a ceiling.

My choice of ceiling product?

5/8” Type X gypsum wallboard. It is affordable, weighs under three psf and provides fire resistance.

 

DEAR POLE BARN GURU: I’m putting up a building with a 3/12 pitch single sloped roof. radiant reflective polyethylene, vapor barrier insulation between the purlins and the metal roof sheathing. Probably rock wool batts under the 1-3″ draped barrier. Do you think the roof has to be vented, and how would this work? CHRIS in BROOKLINE

DEAR CHRIS: Yes, it would need to be vented and it is my feeling you are going about this entirely in the wrong direction. Your question is well timed, as I have just written an article on how to properly insulate between purlins, which will be posted soon. The basic gist is your best solution is to use closed cell spray foam applied directly to the underside of the roof steel.

 

Ceiling Loads

Ceiling Loads

Considering a new pole building? An important question to ask is, “What will the cost be to upgrade the roof trusses to support the weight of a ceiling”?

Most post frame (pole) building trusses are not designed to support the dead weight (things which are permanently attached to the building) of anything other than the trusses themselves, required bracing and minimal wiring and lighting. In most cases, the necessary load carrying capacity on the bottom chord of the trusses is one psf (pounds per square foot).

Ceiling LoadBut – isn’t a ceiling fairly light? It will depend upon what the ceiling is going to be constructed of.

In the case of probably the lightest assembly – steel liner panels, the weight of the liner needs to be accounted for. A cubic foot of steel weighs 489.024 pounds. The thinnest 29 gauge steel measures .0142” thick. If the panels were totally flat, they would then weigh 0.58 psf (pounds per square foot). But liner panels are roll formed, with a 36 inch net coverage coming out of a coil which is typically about 40 inches in width. Figure a minimum thickness 29 gauge panel at about 0.65 psf.

Unless trusses are very close together (say four foot spacing or less), framing will need to be added to support the steel. Dry (19% maximum moisture content) 2×4 Hem-Fir weighs 0.98 plf (pounds per lineal foot), 2×6 1.54 plf. In case a heavier species or damp lumber is used, it is generally accepted to use 0.37 psf for 2×4, or 0.57 psf for 2×6 spaced every four feet.

Insulation is fairly light, but still must be accounted for. Fiberglass adds 0.04 psf per inch of thickness, cellulose 0.14 psf per inch.

This gives the weight added for a steel ceiling with 16 inches of cellulose blown in above at 3.26 psf (1.66 psf for fiberglass).

With the assumption fiberglass insulation will be blown in, I would normally recommend the bottom chord loading be increased to three psf for a 29 gauge steel liner.

How about other materials?

5/8” thick gypsum drywall weighs 2.2 psf, 7/16” osb (oriented strand board) 1.47 psf. Both will often require 2×6 supports every two feet for 1.14 psf. To handle 16 inches of fiberglass insulation, add four psf.

But what if the trusses were NOT designed to support ceiling loads?

Trusses engineered to support ceiling loads are going to be more expensive than those which do not. Depending upon the span of the truss and the applicable snow loads, the cost could be minimal, to very expensive.

With trusses of large spans, it may prove impossible or impractical to upgrade them to support the added ceiling loads.

Repairs (when they can be done) typically include doing one or more of the following:

  1. adding scabs along some or all of the top and bottom chords. Scabs typically are going to be equal to or larger in size, as well as grade of the original truss material. As truss chords are often high grade materials (msr, mel, #1 or Select Structural), it is rarely lumber which can be purchased from anyone except a truss manufacturer.
  2. Adding internal web members is rarely a “fix”. The same goes with flat steel plates.  If the steel connector plates are inadequately sized for the larger loads, structurally rated plywood (usually 5/8″ or 3/4″) “plates” can be added, usually by both glue (not the “off the shelf” construction adhesive) and nailing in a prescribed pattern.

Any truss repair (such as increasing load carrying capacity) should always be designed by a registered design professional (an engineer), and a sealed drawing provided by the engineer.

It is always easier, and less expensive, to pay for the ceiling load to begin with.

Truss Repair? Don’t Skip this Step

A client writes:

“I recently purchased one of your pole barn kits to use as my home garage.  We have begun construction and have all the framing and the roof on.  I recently contacted my building designer about potentially getting the metal lining material for the ceiling and walls.  My designer told me that I can’t put a ceiling in because my trusses weren’t designed to handle the extra 5lbs per sq ft required.  This has got me a little confused and puts me in a bit of a jam.  If I can’t insulate and install a ceiling in my garage it doesn’t do me any good.  I’m just curious if this information is correct and if so what are my options at this point to ensure I can finish the ceiling of my garage??”

Pole Barn Ceiling Load TrussesTypically pole building trusses are NOT designed (by any provider or contractor) to support a ceiling load. The price to upgrade to ceiling loaded trusses is generally offered as an option on our quotes, and is typically fairly inexpensive. All too often, it is a case of a client trying to shave a few dollars and ends up being a case of “penny wise, pound foolish”. We do make every concerted effort to prevent truss repair issues, such as this client is now confronted with, from occurring.

It is important enough so as we specifically mention it in the terms and conditions of every purchase:

“Dead loads specified on engineered roof truss drawings include the weight of the roof truss. Roof trusses are NOT designed to support ANY hanging loads or ceiling loads other than those specified as special truss loads in the Agreement. In the case of design roof truss bottom chord loads of less than five (5) psf (pounds per square foot) the bottom chord dead load may be sufficient only to cover the truss weight itself and may not allow for any additional load to be added to the bottom chord.”

In many cases it may be possible for an engineered truss repair to be made, to upgrade the load carrying capacity of the bottom chord of the trusses to 5 psf. I’m sorry to say, this is not free. The truss company’s engineer will need to put his license on the line in designing a “fix” for trusses which were designed for a load other than is now intended.  It’s not the same as designing the original trusses.  If you think about it, redesigning and augmenting something you have built, is always more time consuming (and brain challenging!) than the first time around. His time and expertise are not without a charge.  It’s not usually “much”, like a couple hundred dollars.  Then there is our time, as changes like this are not included in the basic cost of your building kit.  Again, we don’t charge “much”, but our time is worth something as well. The cost of materials to fix it…one last cost if you are doing the truss repair yourself.  If not, a contractor’s charge must be added.  All totaled, it could run you anywhere from a couple hundred dollars to over a thousand or more, so you can see why we diligently try to get folks to “do it right the first time”.

When ordering a building from anyone, if there is a suspicion anyone might ever consider putting a ceiling in – it is always prudent to err on the side of caution, and spend the extra few dollars to include the load carrying ability in the original design. Truss repair is not my idea of “fun”.