Saturday, February 16, 2008

Screws VS Nails for Deck Framing.

While watching one of those TV Hero-Competition Bashing Contractor screwing a deck frame together the other day it illuminated a contentious debate in the Deck Business. Which is stronger… Nails or Screws for decks?

Nails have a much greater sheer strength, while for a short time in a deck application screws may hold tighter. If this surprises you, try this experiment. Put a screw in a nice big block of wood about 1.5” deep…could be firewood, the type doesn’t matter.

Now, hit the screw with a hammer.

It sheers off clean.

Try the same thing with a nail.

You would have to bend the nail back and forth 50 times for it to snap off.

This is why we use Nails for framing.

If it is in the budget to use a joist gasket and stainless screws, we will use them. Or in the case of Pressure Treated, at request of the client, we will use ACQ Screws. However we do let them know that when it comes time to refinish the deck, you may end up changing a number of broken screws even taking these precautions.

When the boards are swelling from moisture it can cause the screws to tear out of the joists leaving a void for moisture to cause premature rot. If the finish was damaged during installation it can corrode. Often the screws will simply not hold beyond a couple of years.

When you refinish a deck typically we set all the nails a quarter inch deep, then sand the deck with a large machine….

If the deck is screwed down, you have to set the screws. This means that roughly half the screws will strip within the joist, or break or the head will strip at the bit. That exposed steel will react with Red Cedar causing black streaks.

Now, In California did you know that it is illegal to assemble your deck with Screws?

Due to earthquakes, screwed frames have collapsed causing injury and damages in several locations. Many things are discovered in California first…

Build Safe gang—Don’t believe what you see on TV when it comes to woodwork.



Anonymous said...

How strong are hidden deck fasteners compared to nails like the Tiger CLaw, EB-ty or LumberLoc? It seems they should not have a problem from sheering because of their design.

bkwrd_dog said...

I don't completely disagree with what you've said but I'm not sure that it matters what you use. If you nail or screw a couple 2x4s together and then use hammer strikes to break them apart at the fastener, the wood always fails before the fastener does. I've done this experiment multiple times and it always happens that way.
Also, I've had warped boards pull out nails enough that I just got sick of it and screwed them down.

dan said...

My background is Industrial cabinetmaking and we use screws extensively . I prefer to use screws in exterior framing/decks because if you make.a Mistake it is faster and easier to correct . (reverse ). also I have had situations where spikes have not 'pulled' material together, And screws have. The shear factor is discussed alot in Canada. Companies that make joist hangers only recommend nails .... But I still prefer to use quality screws. The ones that cost more.

dhellew3 said...

As a contractor I have been using screws for more than 35-years. I use them for everything. Sure they cost more but they don't work their way out like nails do.

The only reason nails don't shear off like screws is because they are soft and pull out instead.

Pre-drill the holes in the deck boards and they will not split. Use good quality deck screws and you will never be sorry.

Unknown said...

Dan-- for exterior framing it isn't just shear strength that is the consideration. Deck frames are made of wet lumber and you are screwing into the end grains. A screw is larger than a nail so what happens is the lumber splits as it dries and knots will break out as well.

They have banned screws for framing in many areas due to FAILURE. It is not a good practice to use screws for framing.

Countersinking the screws to hold decking down will help--especially when it comes time to refinish and the screws don't have to be removed, countersunk and re-installed.

We have found that you don't have nails popping out if you countersink them in the first place. If you stain the deck, the stain locks the nail into the board.


dhellew3 said...

Lawrence, did you notice that I said it was necessary to pre-drill the holes?

Without a pilot hole the screws will shear off when the wood expands and contracts due to moisture changes.

The screws shear, the nails bend and pull out.

If you have ever made a table or edged boards you know the various parts must be fastened in such a way as to allow for wood movement.

For most deck screws drill a 3/16" hole through the deck boards. When screwing into end grain also drill a 1/8" hole in the end grain and use 3-1/2" or 4" screws.

A properly installed screw will keep the boards tight and outlast nails 10-1. Screws will help prevent boards from warping where nails just pull out.


Unknown said...

Yes Dale... Pre-Drill (Countersink).

We normally use 3/8" bit, and 3/16 pilot, then we use a tapered plug cutter to make plugs that we glue in with marine adhesive...

Still, no good for framing. Has to do with seismic. Decks framed with screws fall apart during earthquakes.

Most of our decks are nailed...and we countersink the nails with a center punch 1/4".

Much easier to countersink nails 7 years down the road using a punch...than removing screws and countersinking deeper for sanding.

Inside is much different than outside!


B Mathew said...

For fence pickets, I think the argument aboue shearing of screws is a red herring. The pickets are next to each other, so there is little concern about movement of the pickets parallel to the fence line. The issue is movement in the perpendicular direction relative to the fence line.

Nails pull out easily. Screws hold the pickets in for years. I've done spot repairs with both. The screws hold for much longer.

Yes, they are much more labor intensive to install, which is the other factor to consider.

Unknown said...

Hi B-- Less about shearing when it comes to fence planks and more about a screw causing splits everywhere they are installed. Best to pre-drill the boards if you are using them.