Tag Archives: truss loads

Roof Trusses 4′ o.c., Condensation Issues, and a Sliding Door

This Monday the Pole Barn Guru answers questions about roof trusses at 4′ o.c., ways to solve condensation issues, and sliding door options.

DEAR POLE BARN GURU: My question is I just purchased some roof trusses that are 32 feet long heel to heel they are constructed with 2 by 4s can I put these on 4 foot centers? Thanks. CRAIG in BELVIDERE

DEAR CRAIG: You can if you want your building to collapse in a moderate snow event. Along with your trusses, you should have received an engineer sealed truss drawing with all specifics as to what can be carried by it and spacing. If you did not, and they are prefabricated metal connector plated wood trusses, there should be a manufacturer’s stamp somewhere on truss bottom chords. You could then contact them and give them truss specifics (and probably a few photos showing lumber grades, web configuration and steel connector plate sizes. From this, they may be able to determine what you have actually spent your hard earned money on.

If you are unable to determine where they came from, another alternative would be to take their information to a Registered Professional Engineer with roof truss experience. For a few hundred dollars, you may be able to get an opinion as to their strength.

 

DEAR POLE BARN GURU: Hello, I have a 30x46x16 all steel pole barn that I am having condensation problems with. My question is what is the best thing I can install or do to help the problem? I have been told by others to install a ventilation exhaust fan controlled by an thermostat. I do have electricity in barn. I also have a wind turbine I haven’t installed yet too? Should I put both of these items in or one of them? And if so, do you guys install these items? Please help, its rusting all my tools and growing mildew in my RV!! Thanks ALYSSA in LEWIS CENTER

DEAR ALYSSA: You have found a challenge (one of many actually) Quonset steel building providers never seem to mention – condensation (read about other Quonset issues here: https://www.hansenpolebuildings.com/2011/07/quonset-huts/).

The two best things you can do are to seal your concrete floor (https://www.hansenpolebuildings.com/2019/02/how-to-properly-apply-post-frame-concrete-sealant/) and have two or more inches of closed cell spray foam insulation applied to the inside of your steel building shell. An exhaust fan might help, provided it can adequately move enough air (need to move between 3000 and 4000 CFM – cubic feet per minute) and it will require an air inlet of similar dimensions. We are not contractors, so we won’t be able to assist you with any installations.

 

Figure 27-5

DEAR POLE BARN GURU: Hi. Not really looking for a whole building. What I am looking for is an exterior sliding door to install onto a shop wall. The Shop is a timber frame unit. The opening is roughly 6 feet wide by 7 – 7.5 feet tall. I have not yet taken exact measurements. I will as soon as I can find a vendor within my price range.

I was very intrigued by your video presentation describing the “nail on” round track system. Also, this shop is in an odd location. It is a basement shop under my house, the house is built on a slope, so the wall I want to put the door onto is at ground level, but the opposite wall is fully underground. Since it is an exterior door to my basement any info on weather sealing for the cold Vt. Winters would be greatly appreciated. ANDREW in WESTMINSTER

DEAR ANDREW: Whilst I can appreciate you thinking a sliding “barn style” door might be a solution, I am doubtful as to it truly being a viable design solution. At best a sliding door will be a challenge to insulate beyond a bare minimal R value. A bigger concern is you are not going to achieve a tight air seal.

A design solution I can recommend (although it may stretch your budget) would be to go with an insulated commercial steel double entry door (six feet wide) in steel jambs. These doors will afford a secure access to your shop, are insulated and can seal air tight.

Although we typically only provide doors with our complete third-party engineered post frame building kit packages, you can message Materials@HansenPoleBuildings.com for a delivered price.

 

Alternative Siding, Building on Slab, and Ceiling Liner Loading

Today’s Pole Barn Guru answers questions about alternative siding and roofing, whether one can build on an existing slab, and if a ceiling liner can hold insulation.

DEAR POLE BARN GURU: Can you build me a steel wall inside and vinyl siding on the outside with asphalt shingles? PAUL in BLUE GRASS

DEAR PAUL: A beauty of post-frame construction is we can design for virtually any combination of roofing and siding materials you may desire. While I am not a huge fan of steel liner panels, yes – your building can have them along with your vinyl siding. Steel liner panels end up posing challenges with trying to attach things to them, like work benches, cabinets, shelves, etc. Gypsum wallboard (sheet rock) is generally far more affordable as well as easier to make attachments to. And, if 5/8” Type X is used, affords some fire protection.

 

DEAR POLE BARN GURU: Can Hansen build the barn on top of an existing slab? CLYDE in BELLVILLE

DEAR CLYDE: Yes, we can design a complete post frame building kit package to be attached to your existing concrete slab. https://www.hansenpolebuildings.com/2014/12/dry-set-column-anchors/

 

DEAR POLE BARN GURU: My trusses are 8 feet on center will the metal ceiling liner span that 8 feet without sagging if I blow in fiberglass insulation? RODNEY in LAKE ELMO

DEAR RODNEY: No, steel liner panels will sag across an eight foot span. If your building’s roof trusses are not designed to support weight of a ceiling load, then they will sag as well – and, in combination with a snow load, may fail.

 

 

 

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”.