Tag Archives: bending lumber

The Dual Splash Plank Dilemma

The Dual Splash Plank Dilemma

I’ve never been a fan of stacking splash planks. Even when they are center matched (think tongue and grooved) the two boards never seem to want to bend, twist, warp and/or cup the same direction leading to gaps. Gaps which lead to water getting through and spoiling an otherwise fun place to hang out doing man stuff (okay, girl stuff too) when the weather outside is frightening.

Mike the Pole Barn Guru responds:

Reader CRAIG in MONTGOMERY was less than enjoying this experience. Craig writes:

“What is the best method to waterproof the skirt boards (I have 2) so that snow melt does not leak into my building and on to the concrete slab. The lower green treat board was used as the concrete form then another was stacked on as the lowest exterior purlin. The seam is above ground and visible below the steel.”

Concrete slab in a pole barnI hate it when this happens – basically the builder used the lower splash plank (aka skirt board) to screed the concrete off from then had to add the upper one in order to have something to attach the siding to. Now you are stuck with the challenge.

I’d look upon this as a multi part solution.

First – seal the leak, a bead of good caulking (check in at the ProDesk of your local The Home Depot for recommendations) placed along the seam will be a beginning. However, this can be seen, so…..

Second – order up some Plasti-skirts (https://www.hansenpolebuildings.com/2017/08/plasti-skirt/) and cut off the inside leg so you have an “L”. Remove the lowest row of screws from the siding and dig away the soil from the base of the lower splash plank so the short leg of the Plasti-skirts can be slid under the bottom and the remaining long leg slipped behind the bottom edge of the siding. Put the screws back in place.

Third – If your building does not have continuous seamless gutters (read more here:  https://www.hansenpolebuildings.com/2012/09/rain-gutters/), invest in them. Make sure the downspouts either go into a drain which takes the runoff away from the building, or have significant extensions at the bottom.

Fourth – If you did number three, add a snow retention system to your roof to keep sliding snow from taking off those brand new gutters. Most gutter companies will not warranty their installs without them.

Fifth – Make sure the grade at the edge of your building is no higher than the bottom of the lower splash plank and slopes away from there at a minimum of a 5% slope.

Do all of these things and the concrete slab inside of your building should be a dry and happy place.


Lumber Bending Stress

The Big Stick is Better than the Little Stick – Right?

Those of you who are regular readers know I am fascinated by all things magical. I don’t know how they do it, but I will watch a good magician over and over.

When I was in architecture school at the University of Idaho – the Amazing Randi (https://en.wikipedia.org/wiki/James_Randi) did a performance there. Asking for a volunteer to give up a piece of their clothing – I handed over my favorite denim sports coat, which he proceeded to cut in half on stage (to my horror). It was returned to me intact and unharmed after the show! To this day I have absolutely no idea how he did it.Lumber Bending

Well – lumber doesn’t come along with magic, but it can do some magical things. One of those is allowing a lesser sized piece of lumber (of an equal grade) to do things a bigger piece can’t do!

Let’s take a look at a 4×6 and a 6×6 of #2 Hem-Fir, both of which are commonly used in pole buildings for columns. For sake of simplicity, we will just examine the lumber bending properties – as the ability to resist wind loads is the primary function of a column.

As either piece, when incised, has the strength in lumber bending value decreased by 20%, I will leave it out of the discussion as well.

The 4×6 – has a base Fb (fiberstress in bending) value of 850 psi. Lumber which has a least dimension of four inches or less has a width adjustment factor (Cf) of 1.3, making the size adjusted value 1105 psi. As the size adjusted bending value is not over 1150 psi, no adjustment for wet use is needed. When used with the wide face towards the wind a flatwise use factor (Cfu) is applied of 1.05 for a Fb of 1160.25.

Used with four inches to the wind the Section Modulus (Sm) of the 4×6 is 17.65 inches, as a 6×4 11.23. Multiplying the Sm values by Fb, gives a moment resisting value of 19,503.25 in-lb for the 4×6 and 13,029.6 for the 6×4.

Now on to the bigger piece. The 6×6 has a Fb value of 575 psi. Posts and timbers (smallest dimension five inches or larger) do not get a size adjustment. The Sm of the 6×6 is 27.73. Multiplying by Fb gives a value of 15,944.3.

Looking strictly at lumber bending the 4×6 is 22.3% stronger than the 6×6, while the 6×6 is 22.4% stronger than the 6×4.

In many cases, as if by magic, the smaller piece of lumber will outperform the larger piece! Plus the side bonuses – the smaller piece of lumber has smaller (and fewer) allowable defects (https://www.hansenpolebuildings.com/blog/2013/12/lumber-defects/) and it will be about 1/3 lighter in weight!

Even the Amazing Randi can’t debunk this one!

For more reading on lumber bending: https://www.hansenpolebuildings.com/blog/2012/09/bending-moment/