Tag Archives: open web floor trusses

Open Web Wood Floor Trusses

Prefabricated Open-Web Wood Floor Trusses in Your Future?

Use of open-web floor trusses has steadily increased over this past decade, but there’s a lot of room to grow. Ed Huston from Home Innovation Research Labs (HIRL) recently shared some results from their April 2021 Builder Best Practice Reports on Structural Systems, containing survey results from over 1500 homebuilder participants. 

If a picture speaks a thousand words, the chart below neatly summarizes more than ten thousand words regarding building code impacts. Chart’s green line represents wood I-joists, clearly preferred framing product for non-slab-on-grade first floors and floors above grade.  Market share was actually increasing until 2015, when most states updated to 2012 versions of model code.  In IRC (International Residential Code), Section R501.3 (R 503.1 in later versions of the code), gypsum sheathing was now required on all unprotected wood structural framing unless it was constructed using dimensional lumber.

This code change had an immediate impact on builder preference, with I-joists and dimensional lumber market share moving in opposite directions. Curiously, over time this code change may have actually prompted some builders to finish off basements and use open-web floor trusses to more easily run all MEP (mechanical, electrical, plumbing) in the floor cavity.  Benefits of easier MEP installation in floor trusses is efficiently illustrated in builder-preference in multi-family construction, where market share has also increased over time, as chart below shows.

Since 2017, slab-on-grade single-family construction has surged. While this has taken relative market share from both dimensional and EWP joists,  open-web floor truss share has continued to increase (albeit, slightly). Given dramatic shifts in market share, this national market resiliency of floor trusses suggests in non-slab markets, floor truss market share has increased in recent years.  Chart below shows there is currently significant regional preference for floor trusses.

All of this data suggests there is an opportunity for significant market share growth for floor trusses, given they offer an incredibly efficient and accurate floor framing system utilizing less lumber and easing labor burden for all MEP trades. 

Personally, our now 16 year old post frame shouse (shop/house) utilizes floor trusses to give a 48 foot clearspan over our basketball half-court and provides a comfortable structural system for our second floor living space. All of our plumbing, electrical and HVAC is run through our floor truss system, providing an unobstructed ceiling downstairs.

Planning upon a multi-story post frame building? Open-web wood floor trusses might very well be an excellent design solution.

Door Facing North, Optimizing Space, and Remodel?

DEAR POLE BARN GURU: I have a (about) 40×24 pole building that faces north. I have a regular door that faces west. The wind and any accompanying rain typically blows directly against that west facing door. The building was built in 1996 by the original owner of the house. I’ve only lived in the house for 3 years and when we bought the house the moulding and threshold were starting to deteriorate. I would like to add an awning over the door to stop the rain from pounding against it. Is it as simple as attaching a ledger board, building off it, and adding a roof? CHRIS in SEAFORD

DEAR CHRIS: You sadly have a very common problem – people all too often end up with exterior people doors which are sadly inadequate for long term use. Most often they have wood jambs which have been left exposed to the weather and not kept painted or otherwise protected.

As to your solution – just adding a roof off the existing building may very well be problematic, as the footings of the existing building are probably inadequate to support the added weight from the added roof (awning).
What I would do – I would replace the troubled entry door with an insulated commercial steel door with steel jambs which is factory finish painted (I actually have recently done this with three of my own doors).
If you do want to build a permanent roof over the door, you should hire a competent registered design professional (architect or engineer) to inspect your present building and design a solution for you which will not compromise the integrity of your existing structure. It will be money well invested.

DEAR POLE BARN GURU: Hello I am wanting to build a 40x104x18 pole barn, my dad will have his living quarters and a wood shop on the main level, the second level will be my living quarters and an exercise room. The top level will be 40’—40 feet. What kind of beam or footing do you recommend? Also if you would like to quote me for this building package that would be great. Thank you, SHAWN in WRIGHT CITY

DEAR SHAWN: Lots of ways you can go with supporting your second floor, and how you design the floor will determine the size (diameter) of the concrete footings needed beneath the individual columns.

Least expensive will place a literal forest of columns below the floor – on 40 foot square, most probably every 10 feet in both directions. Whilst this might be dandy for the pocket book, it could cause challenges with the use of the space below.

As columns become spaced further apart, the beams necessary to support the floor joists and possibly the floor joists themselves are going to become larger in dimension and their cost will not be offset by the savings of a few columns.

I recently designed a floor for a 40 foot by 40 foot residence which had only a single column dead in the center. The LVLs (https://www.hansenpolebuildings.com/2013/01/lvl/) necessary to carry the floor joists were 20 inches in depth! The floor joists were 2×12 at 12 inches on center. Not a low budget investment, but it did provide far greater flexibility downstairs.

Another option is to go to prefabricated wood floor trusses. In our own home we have a 48 foot wide clearspan floor – it is also four feet deep! A floor this thick requires a taller eave height to allow adequate headroom. And yes, it is expensive!

Regardless of which of these options works best for your internal layout it will behoove you to look at the ultimate stiffness of the floor in regards to deflection. Some extended reading on floor deflection and vibration can be found at: https://www.hansenpolebuildings.com/2015/12/wood-floors-deflection-and-vibration/.

DEAR POLE BARN GURU: I currently have a 30×40 pole barn. I want to install a post lift and would need to remove one bottom chord on a truss. The trusses are 4ft on center. Is this possible and how would I do such a thing? The pole barn is also insulated and closed in with 5/8 osb. Except for the one 8 ft span. DUSTIN in NESCOPECK

DUSTIN: Given enough time and money, anything is possible, although probably not practical. Your situation is one of my “case in points” as to why post frame buildings with trusses placed every four feet on top of truss carriers is not the most flexible design solution when it comes to having to remodel.

Should you pursue a remodel, it should ultimately involve a registered design professional (architect or engineer) as what you are looking at doing is not going to be a simple task.

I’d probably follow a path such as this – adding a new extra truss to the single truss at each side of the eight foot area. Temporarily supporting the flat purlins over the middle truss whilst removing it, then adding purlins on edge between the two new trusses (and either under or next to the existing purlins). Keep in mind, this is a highly simplistic outline and the actual fix will be far more complicated.

A less expensive solution – add a 12 foot bay onto one end of the building with a truss on each side of the 12 feet and purlins spanning from truss to truss.


Open Web Wood Floor Trusses

Most of us don’t think too much about the floors we walk upon – unless they are not level, squeak when we walk on them, or are too bouncy.

open web trussesTraditionally wood floors have been framed with dimensional lumber (2×6, 2×8, etc.), usually spaced 16 inches on center. Often floor joist span limitations are not based upon the strength of the lumber (the ability to carry a load), but upon deflection criteria. Building codes limit floor deflection to L/360, where “L” is the length of the span, in inches.

The “stiffest” (by MOE – Modulus of Elasticity values) commonly used framing lumber is Douglas Fir. A #2 grade Douglas-Fir 2×12, 16 inches on center will span 18’1” when carrying standard residential loads. An L/360 deflection event, would cause the center of one of these floor joists to deflect as much as 6/10ths of an inch!

Lumber is organic, so it varies in consistency from one board to the next. It also varies in size, and it is not unusual for a dimensional variance of over ¼ inch, from one end of a board to another. Combine this with the probability some of the boards will be crowned the wrong way, and it means an uneven floor will result.

One of our friends lives in a fairly new home. In the hallway between her kitchen and the sleeping areas, there is a good ½ inch dip in the floor – more than noticeable when walking across it!

I first used floor trusses in my own pole building almost 20 years ago. My trusses were designed so they were only 1-1/2” thick, but the 30 foot span trusses are only 24 inches in depth. They allowed me to create some unique interior areas, without the need for columns inside the building.

When we built our home in South Dakota, we utilized floor trusses again – here to span 48’ (yes 48 feet)! We live upstairs in a gambrel building, with a clearspan ½ court basketball court size garage downstairs!

A few years ago, my oldest son Jake needed a new garage – his mom convinced him the design would be so much better with a mother-in-law apartment upstairs. We used 4×2 (2x4s turned flat) floor trusses to span the 24 foot width!

I’d forgotten how fast a trussed floor can be done – until Jake used them for the support of the second floor in the addition he is now putting on his home. In a matter of just a couple of hours, the entire 24 by 32 floor was framed and ready for sheathing. All of the ductwork can be run through the open truss webs, making for nice clean ceilings downstairs.

Considering a second floor loft in a pole building? Don’t want posts down below to get in the way of full space utilization? Then floor trusses may be the answer.

Make sure to allow adequate height for the thickness of the trusses. As a rough rule-of-thumb, I plan upon one inch of thickness, for every foot of span. While it will nearly always be less, it is better to design for having a couple of extra inches, than not enough.