The traditional way to attach a deck ledger board to the house is either with lag screws or carriage bolts. Both offer incredible strength, ensuring your ledger board will be able to support your deck for years. But they also take a lot of work to install.
You have to tack the ledger board in place, predrill the ledger screw holes, put washers on the bolts, fumble through your sockets set to then ratchet in the screw. Then repeat this process all over again.
This is what I love about GRK structural screws. They are easy to drive with an impact driver, can support the weight of the deck and hold the ledger tight to the house.
They are so easy and fun to install that I swear that sometimes I add “another one” just for the pleasure of it, not because the ledger needs additional strength.
Yes, the strength thing is true and the reason I reinforce ledgers before building the deck even when it’s already been nailed in place by the builder. Unlike regular screws, GRK structural screws will make the deck stronger.
GRK 14225 5/16 in. x 4 in. Star Drive Washer Head Coated Steel RSS Structural Screws, 25/Box
Enough ranting about how much I love GRK screws lets get to the specific reasons.
Advantages of GRK Structural Screws Over Lag Screws
The advantage of GRK screws over lag screws can be summarized in one word.
“Easy”
GRK screws are easy to install with similar holding power as lag screws but let’s break that down.
RECESSED STAR DRIVE
I am a Canadian, so I have enjoyed the advantages of Robison, square head, which is predominant with construction screws in Canada.
But GRK screws with their 6-point star drive take it to a whole new level. With the advantages of a Philips combined with a Robinson.
The screw easily clips into place for easy setup and then holds the screws with minimal slipping while sucking the ledger board tight to the wall. Don’t, but you could torque a GRK screw right through the wood without it slipping. It holds that well and drives that easy.
W-CUT™
The ease of installation is partially due to the W-CUT™. The screw threads are designed to cut into the wood with minimal difficulty.
Which makes driving the screws easer and faster. The real reason to use GRK screws. Speed of installation.
CEE THREAD™
I have skipped this step before, but you should always enlarge the hole in the ledger so the wood can expand and contract with the seasons without splitting the wood. But as I said, I have skipped this stage before because of the extra time drilling your holes twice.
- Drill for the screw.
- Then redrill the ledger to allow movement.
- Then finally driving the screw.
GRK combines these three steps into one without compromising performance.
The cee thread built right into the screw cuts a larger hole for the last section of the screw to enlarge the hole for movement without requiring additional drilling.
Saving you time. Getting you onto your deck quicker.
ZIP-TIP™
This one is just icing on the cake. Not only do GRK screws take less work (no predrilling) to install, but the screws drive faster than lag screws. Like twice as fast. Now that is impressive.
But all this speed doesn’t compromise performance.
Performance of GRK Screws Compared to Lag Screws
Unlike other screws, which are often brittle, breaking under shear load, GRK screws will not.
Case Hardened Steel
Makes the screws less brittle, increasing their bearing strength by creating a hard shell for the threads to cut into the wood while leaving the inner core soft to resist load fatigue.
High Tensile, Torque and Shear Strength
GRK screws have your back or at least your deck ledger with a high tensile strength.
“Tensile strength is the amount of load or stress that can be handled by a material before it stretches and breaks.”
There is no need to worry about ledger failures when properly installed and correctly spaced.
Climatek™ Coating is AC257 Code
One of the shortcomings of current pressure-treated wood is how corrosive it is to metals. No need to worry with GRK screws. They arecoated to not react with the copper in pressure-treated wood.
Code Approved for Structural Application
All this is to say that GRK is approved for structural application
.
Meaning you can build with confidence. Not only is your deck stronger with GRK screws, but it is approved by the law of the land for construction.
Which is probably why, even beyond decks, engineers will often call for GRK screws to be installed for structural applications.
Ledger Board Fastener Spacing Schedule
Screws should be installed in a “W” pattern on the ledger.
Image of Ledger Screws
The spacing of lag and GRK screws are based on the span of the joists being supported and the strength of the wood. Douglas fir, for example, is denser and therefore stronger than spruce therefore able to hold more weight with fewer screws. Of course, the longer the joists, the more weight the ledger needs to be designed for.
Roughly every 1’ (0.3m) of joist at 16” (400mm) on centre spacing needs to be able to support a minimum (1.33 sq’ x 50lbs) 66.5lbs. The minimum for residential deck construction. Again, minimum, often decks are built to support 60lbs live weight per square foot.
RSS 5/16 x 4″
| Live load (psf) | Wood Species | 6 ft Joist Span | 8 ft Joist Span | 10 ft Joist Span | 12 ft Joist Span | 14 ft Joist Span |
| 40 | G= 0.42 / SPF | 14” | 10” | 8” | 7” | 6” |
| 40 | G = 0.50 / DF-PSL-LVL-LSV | 17” | 12” | 10” | 8” | 7” |
| 40 | G = 0.55 / SP | 20” | 15” | 12” | 10” | 8” |
| 60 | G= 0.42 / SPF | 10” | 7” | 6” | 5” | 4” |
| 60 | G = 0.50 / DF-PSL-LVL-LSV | 12” | 9” | 7” | 6” | 5” |
| 60 | G = 0.55 / SP | 14” | 10” | 8” | 7” | 6” |
Source GRK Fasteners
If you have a unique design or engineering, I highly recommend you go directly to GRK fasteners chart.
But I largely work with SPF pressure-treated when building deck substructures. Which happens to be the weakest available wood but in my market is the most readily available.
Here is a quick chart for SPF ledgers and the number of GRK screws required. To make ordering easier.
“Width before Depth”
| Size of Deck | Number of 5/16” GRK Screws Required |
| 12’ x 10’ | 19 |
| 12’ x 12’ | 22 |
| 12’ x 14’ | 25 |
So, if the deck is 12’ wide and 12’ deep, you will need to order 22 5/16” GRK screws. The 25-count pack is excellent, with a few extras just for fun. They also make great screws for aluminum railing posts.
| Size of Deck | Number of 5/16” GRK Screws Required |
| 16’ x 10’ | 25 |
| 16’ x 12’ | 29 |
| 16’ x 14’ | 33 |
Often a bigger deck is more advantageous. So, the above chart is for a deck with a ledger 16’ long.
If you haven’t figured out your size of your deck yet you should check out How to Figure Out the Right Size Deck for Lounging, Dining or Grilling. Often you will want a deck with a minimum of 12’x12,’ but 16’x12 is generally better.
For decks deeper than 14’ will beam placement will impact design. Placing more of the total weight on the beam than the ledger. So, in those cases, you can still use 14’ depth.
Of course, you can always upgrade to 3/8” GRK with greater shear strength. Less likely to break off.
Compare the price surprisingly often they will cost you no more for the bigger size.
GRK Have Greater Shear Strength Than Lag Screws
This is actually a little bit of a mixed bag.
When comparing traditional 3/8” lag screws with the equivalent RSS GRK screws, they are roughly 45% stronger. Meaning GRK screws are less likely to break off than lag screws. Which is good when having a dance party on your deck.
On the flip side, lag screws are harder to pull out. Roughly 20% more. But from my experience, the wood is more likely to split before either one is pulled out. Just saying the ledger may be the weaker link in both cases.
To see a fuller comparison of lag screws sizes, check out GRK Conversion Guide.
Economical Alternative to GRK Screws
If the price of GRK is a little too much for you, here are a few cheaper alternatives.
FastenMaster FMTLOK04-50 TimberLOK Heavy-Duty Wood Screw, 4 Inches, 50-Count, Black
The top 2 differences from GRK screws are.
- Socket drive
- Fewer Threads
If these don’t matter to you, or you even prefer, check out their current price. They will often cost less than GRK lag screws.
Not me, but some deck contractors prefer the socket drive and the longer smooth shaft for improved pulling together of material.
SPAX lag-screws, 5/16 x 4”
They look the same as GRK at a quick glance except for colour. Spax are green. But after closer examination, you will notice they are missing some of the finer patent parts of GRK screws. But if you are looking for self-drilling lag screws at a lower price. Check out Spax. It may be the answer.
But if you are like me. For all the reasons we have gone over. If you still want the original and the best lag screw alternative. Order GRK. You will not be disappointed.
GRK 14225 5/16 in. x 4 in. Star Drive Washer Head Coated Steel RSS Structural Screws, 25/Box
If you are a professional and have a whole season of decks coming up, they also have a larger case. Giving you plenty of screws to get you through the summer. But you may love them so much that you will need two.
