How to Install Deck Guardrail Posts | Trex Academy

Installing guardrail posts are essential in creating a safe and functional outdoor space. Learn more about guardrail post installation and spacing with Trex® Academy's step-by-step video instructions.
To learn more about deck guardrail posts, installation, and the deck building process, visit: cur.lt/jxneurigx and start building your dream deck.
Key moments in this video:
00:00 Intro
1:04 Corner Post Install
6:53 Front Rim Joist Line / Intermediate Post Install
9:42 Side Rim Joist Line / Intermediate Posts

[@SeanInAlaska]

I am at the point of installing railing and this is by far the best video I have seen on the subject. Thank you!

[@eugeneanderson8884]

One of the best videos out there! Waiting on my Trex decking to arrive as I finish my build. Needed this information. Excellent tutorial

[@lancomedic]

Takes forever to get here doesn't it? I'm still waiting for my square deck boards.

[@joeburrier2273]

I used this method and the posts are far more secure than I expected. Fantastic video.

[@TheTrexCo]

Hi Joe. Thank you for taking the time to share your experience with us. Thank you for choosing Trex. Kind Regards, - Trex Customer Care Team

[@hiebiz]

Excellent instructions, very clear and easy to follow. Thank you.

[@TheTrexCo]

Thank you for your feedback! We're so glad the instructions were easy to understand and we hope it makes for a simple installation. Have a great day! -Trex Customer Care

[@eriks1206]

I've watched a lot of deck construction videos. This is, without question, the best guide for rail post installation. Looking forward to installing my new Trex composite deck!

[@GeraldTheMaker]

cannot thanks more for this information! this is the best deck post tutorial you can get on youtube!

[@TheTrexCo]

Thank you! We truly appreciate you taking the time to share your feedback on our installation. We hope you have a great day! -Trex Customer Care

[@GeraldTheMaker]

@@TheTrexCo i just add a part of guardrail for one of my friend yesterday, followed the video. turns out so good!

[@prhapsisuppose]

This video is exactly what i was searching for. thanks so much!

[@bjrnarvaland5100]

Very detailed and good decriptions. Thanks.

[@TheTrexCo]

Hi Bjørnar. Thank you so much for your positive feedback. We are happy to hear that the information provided in the video is helpful to you. We look forward to serving you in the future. Kind Regards. -Trex Customer Care

[@glarios5839]

I learned a lot from your video! Thank you 😊

[@EverythingHasAStory]

very good information and very clear illustration. will follow it. thank you very much.

[@johnblandy8268]

Excellent video. It would be nice to know how you block the post next to the the ledger

[@mrrutledge1967]

One heck of a fastener commercial. I'm thinking the fastners would cost as much if not more than the lumber. Was all that really needed or was it just a clever way to sell multiple sizes of screws? What good are the 8" screws with 2 inches of thread on the corner? Doesn't hurt to over build but this was over kill on the fastener sales. Pretty entertaining though.

[@garrystacey3816]

😮ky to

[@alv9815]

1/2 “ Through Bolts with washers and nuts

[@ThatGuy-zu7ze]

I get a kick out of this obsession with "center to center". it makes it easier to line up the next one by corner without having to trying to find the "center" of the next post... But I will say these videos are pretty well done.

[@vidwithg]

When you did the corner post with the blocking, do you think I can use this method to build the post for pergola? My deck is already built and was thinking how to attached 6x6 post to my deck. I don’t want to dig into the ground, i woukd rather attach it to my deck joist if possible. Thanks

[@terryjones8360]

Excellent! The only thing I'd do differently is turn your clamps around so you don't run your leg, (or something else) into them... LOL. You might also mention that different configurations may require you to double your rim joists as well.

[@onetwothree4148]

I've seen this structural screw method becoming more popular. However, I'd note that it is not the strongest blocking method. I'd guess the structural screw manufacturers are suggesting this method because it uses more of their screws. A better blocking method would use butt the 2x8 end grains up against the post, instead of butting your post up against the weak, flexible sides of the 2x8s. Also, a 4x4 with structural screws is not going to be as strong as two 2x8s (laminated or not) with 6 normal screws perpendicular to the force they are resisting. Through bolts would be ideal for these installations, but regardless the blocking would be less likely to fail with a larger number of smaller screws, installed only in the direction of shear forces... Which is possible if you butt the ends of 2x8's into each side of the post (and add blocking to the next joist bay too if you're not in a corner)

[@POLOLOUS3]

I agree also I like using tension ties also on guard rail posts. Especially with cable rail installs. These structural screw methods are ok for a traditional bottom/top rail methods cause it helps stiffen the posts but they stiff aren’t as strong as through bolts with tension ties.

[@mikemcdermott1026]

Would sinking. Your posts in the ground be stronger

[@Pepe-dq2ib]

@@mikemcdermott1026 helical pile post 20ft into the ground and welded up the deck as rail post is slightly stronger. You would secure the steel post to the joist by four DDT tension ties by welding directly to the steel post and 4x4 blockings.

[@chuckhall5347]

@@Pepe-dq2ib Then I could park a dump truck on my deck.

[@spelunkerd]

What do you think about the rigidity of surface mount aluminum railing, with no 4X4 posts? If well secured below, do they hold up as well over time?

[@mrtaktiks]

I have to install railing posts on the inside or outside of a beam-if I go with flush joists. I assume posts would be installed on the outside otherwise wouldn't the posts be inset too far inward on the inside of double 2x12 beams?

[@WildGoose_F12]

If making modifications for a pergola type structure at the corners and center, would you consider adding footings instead of attaching to the rail for structural support? Maybe use bolts instead of timber screws? Excellent video btw!

[@TheTrexCo]

Hello! We would reccomend reaching out to a code official for the correct mounting hardware. If you have any other questions, please feel free to call us at 1.800.289.8739

[@chris19567]

Absolutely great video! I feel like it should have 10x the number of views. I do have another pre-drill question for you. I have looked at the literature Simpson Strong tie has for the Timber screw series and they keep repeating that the design eliminates the need for pre-drilling in most applications. There are certain scenarios where they discuss the use of a 5/32" drill bit, but only in very specific instances. Can you confirm if you used a 5/32" bit and if there was something that specifically made you lean towards pre-drilling or if it is just a general practice you follow on longer length screws? Again, really appreciate this video and really the whole series of videos you put out.

[@TheTrexCo]

Hi Chris! Thank you so much for your interest in our videos. For this installation we utilized a 5/32" drill bit to predrill for the 8" Simpson SDWS Timber Screw. We elected not to pre-drill for the shorter Timber Screws as the pressure-treated wood was quite wet, and we didn't feel it was necessary. If you think of any additional questions, please let us know! Thank you, Trex Customer Care Team

[@onetwothree4148]

Pre drilling always makes your wood less likely to split. Ideally, every screw would be predrilled. That's not necessary with small screws, but the larger the diameter, and longer the screw, the more necessary it becomes to avoid splitting or weakening your wood. It's a judgement call, and if you don't have enough experience to know, just predrill.

[@patty109109]

@@onetwothree4148 also can greatly help with guiding the screw; it is easier to drill a straight hole that small printer put a large screw in straight and the screw will happily follow where the drill bit went.

[@allencolvin4320]

My guess is to prevent splitting in the blocking, and to make a pilot hole so the longer screws do not blow out the side

[@TheTrexCo]

Hi Allen, thank you for reaching out and for taking the time to watch our videos. We chose to use the installation method by Simpson Strong Tie to keep a code compliant guardrail application. This installation is backed by Simpson Strong Tie reports. Installation reports provided by Simpson Strong Tie can be found on their website: www.strongtie.com/search?v=%3Arelevance&tab=literature If you have any additional questions, please let us know. Thank you, Trex Customer Care Team

[@Dydeeo]

If 2x10s are being used for the joists and rim band, are these same screws ok to use at 2 per joist and band connection? Thanks

[@sponce500]

Thanks for the video , how is the best solution for installing railings ,if you have bracket in the corner, because it is obstacles for the post .. thank you

[@SteveK99Sub]

Thanks for the video. What size bit are you using to predrill for those 8" timber locks.? Thanks

[@TheTrexCo]

Hi Steve, the screws are SDWS made by Simpson Strong Tie. We used a 5/32 drill bit. Thank you, Trex Customer Care Team

[@adamhall4236]

Can you please explain how the corner post at the ledger board was attached? I've seen diagrams from Simpson, but they don't address this scenario. Thank for for the excellent videos!

[@TheTrexCo]

Hi Adam! In this instance we did a combination of the corner post assembly and the side rim post assembly. We spaced the post off of the ledger just enough to allow for the post sleeve and post cap so that it would not hit the wall of the house. We then cut a spacer out of 2x material and put it between the post and the ledger. We then installed 2 2x blocks like the corner post, just on the other side away from the ledger board. We used the post and a post block just like the corner post. We used all the same fasteners and just went through the blocking and post into the ledger. We then added two fasteners through the side rim joist like is done in the side rim attachment.

[@davidhoy2250]

Hello Trex, please note that the 2022 version of the Simpson "Deck Connection and Fastening Guide" no longer supports the use of 8" long Simpson SDS screws to connect deck post bases. It was shown in the 2020 version of the guide but was removed in the 2022 version. The 2022 Guide shows only through-bolts with DTT2 type tension ties. Not sure why this change occurred. This video is informative and helpful, but the guardrail post base attachment details used in it are no longer current, and I'm not sure if they would be accepted by a code official at this time. Suggest everyone use the through-bolt details that the latest Guide shows.

[@davidhoy2250]

Actually I am wrong, the 2022 Simpson Guide does show a post base connection option using just their screws, rather than with 1/2" diameter through bolts, on a separate page. Sorry I missed that initially. However, still have a question. A quick calc of the withdrawal force on an 8" screw (say SDWS22800DB) at the post base resulting from the lever action of an out-of-plane code load of 200# on a 36" high post, results in a withdrawal load way higher than the allowable resistance values for the 8" screws as shown in UES ER 192 (table 15 on page 16 shows an allowable resistance max of 590# for SP timber). With a load duration factor of 1.6 the allowable withdrawal would bump up to 1.6X590#=944#, but this is still far too low. So I am unfortunately confused. The numbers don't seem to work. Perhaps Simpson tested real post assemblies to see if the screws held, but I dont see any evidence or discussion of such testing in the ER 192. I will ask this question of them as well. Can you shed any light on this question?

[@ADVENTUREKM]

Would be nice if these deck videos were numbered to show progress. Seems hard to find the next video. Good videos cheers.

[@TheTrexCo]

On this deck our top rail height was 36” above the finished decking surface. Our rail post sleeves were 40” above the finished deck surface and the pressure treated posts were 39” above the finished deck surface. The overall length of all pressure treated posts on the main deck surface on camera was: 7-1/2” joist height (nominal 2x8 joists) 1” deck board thickness 39” above finished deck height 47-1/2” pressure treated post length For a 36” rail height it is most common to have the rail post sleeves either 39” or 40” above the finished deck height. The pressure treated post inside the sleeve should be at least 37”, allowing for plenty of post area to hold the railing support bracket screws below the top rail, but does not have to extend the full height of the post sleeve. Kindly, Trex Customer Care

[@meganfox5516]

This comment from Trex is gold.. I was looking everywhere for info on the length of the rail posts used in the video, they never mentioned it in the video!

[@chrism9976]

It's not necessary to predrill for the 8" screws and impossible to do it level between the joists. It's also important to ensure that the 4x4 blocking is flush with top of the joist if you plan on picture framing.

[@grizthedog]

Best video I've seen. But one question.. I'm not sure why 4x4 blocking was not used on the 2nd post (intermediate) post but was required on the next 3 posts (the ones at 52 7/8 on center). Help? Thanks.

[@TheTrexCo]

Hello Michael, This is a good question. With codes being a little different all over the country we wanted to use a method that had a code report behind it. The details we show here are from Simpson Strong Tie which is a very well trusted company. If you have any other questions, please feel free to give us a call at 1.800.289.8739. Thank you, Trex Customer Care

[@davidgoldsmith2904]

@grizthedog. I think you are talking about the intermediate post on the front rim board. They don't need the short post block because the two layers of 2x blocking is acting as the equivalent resistance against the post torquing out if you fall against the railing. On the side rails, the 2x blocking parallels the post, so the extra post block behind it helps pin the post so it can't rotate out and down.

[@lancomedic]

What size drill bit are you using for those timber screw pilot holes?

[@TheTrexCo]

Hi Fred! Thank you so much for your interest in our videos. For this installation we utilized a 5/32" drill bit to predrill for the 8" Simpson SDWS Timber Screw! Thank you, Trex Customer Care Team

[@realjackbronco]

What did you do for the post at the ledger board???

[@TheTrexCo]

In this instance we did a combination of the corner post assembly and the side rim post assembly. We spaced the post off of the ledger just enough to allow for the post sleeve and post cap so that it would not hit the wall of the house. We then cut a spacer out of 2x material and put it between the post and the ledger. We then installed 2 2x blocks like the corner post, just on the other side away from the ledger board. We used the post and a post block just like the corner post. We used all the same fasteners and just went through the blocking and post into the ledger. We then added two fasteners through the side rim joist like is done in the side rim attachment.

[@spelunkerd]

I get the idea of back blocking, to increase the surface area of contact with the post. However over time we all expect that post to shrink, and as it does the secure clamping force disappears. In the past all one had to do was retighten the back nuts on the mounting carriage bolts, but in this case the back blocks are themselves screwed into joists. So to retighten the post connection you'd have to remove those mounting screws to the backblocks before retightening. Why do you even need to fix backblocks with screws into the joists? Aren't they simply acting as a big washer, to increase the surface area of the connection?

[@TheTrexCo]

Hello. Thank you so much for reaching out with your inquiry and interest in Trex. In building railings for decks, we examined numerous instances and concluded that a system based on documented reports would be optimal. We utilized Simpson Strong-Tie SDWS screws, and attached is their report detailing how posts should be secured. While other installation methods exist, we did not find corresponding supporting documentation for them. You may visit this link for more information, www.strongtie.com/solutions/deckcenter/deck-code-compliance Please feel free to reach back out with any further questions or concerns. Someone from our Customer Care Team will be more than happy to assist. Kind Regards, Trex Customer Care 1.800.289.8739 | [e-mail]

[@geraldwhite8301]

how high is the recommendation for the 4x4 post to be from the top of the decking? 40"

[@TheTrexCo]

Hi Gerald. If you are installing a 36" rail height the recommended height for the posts are 40", however we do recommend to confirm with your local code that this is accurate for your location.

[@markd.6364]

Jeez what town and what country . I find that if you make a simple box using the frame material one piece each side for corners and 2 to 3 on the straits. Use the 4in GRK screws about 3 to 4 work. They have great holding power. Most railings need to be strong enough to hold a 250lb person if they fall against it. 8in screws are little excessive and will most likely go the materials and loose holding power.

[@yamaguy9846]

Any idea why not use std. Practise of lag bolts instead of timber screws? Also much stronger.

[@TheTrexCo]

Hello, Thank you for reaching out. We've sent your request to the appropriate parties and will get back to you as soon as possible. Kindly, Trex Customer Care Team

[@TheTrexCo]

Good morning, We used timber screws in our videos specifically because they had a code report to verify their installation. These screws were Simpson Strong SDWS Timber screws. Simpson Strong Tie has a specific installation report that verifies these attachments. Lag bolts on guardrail posts is not listed in many of the code books such as DCA6 or IRC and that is why we did not show them being used. Thank you for choosing Trex, Trex Customer Care Team. 1-800-289-8739

[@775aure]

Hello, how much was the total cost of this job including materials and labor?

[@alanhertrick4073]

Who is the publisher of the evaluation report referred to in the video, and is it available for download somewhere?

[@TheTrexCo]

Hi Alan, the evaluation report referenced is published by UES and can be downloaded from the Simpson Strong-Tie website. In addition, we used Simpson's brochure for the SDS Timber Screws. The testing method and evaluation report are referenced on page 1 of the brochure. If you have any additional questions, feel free to give us a call! 1-800-289-8739 Thank you, Trex Customer Care Team.

[@jeffhaman9010]

What did you use to seal up the ends of the 2x blocking?

[@TheTrexCo]

Hello Mr. Haman, thank you for reaching out to us! In this video, the double blocking should be coated with a wood preservative before installing the blocking to the joists. If you have any additional questions, please call us at 1-800-289-8739. Thanks - Paul, Trex Customer Care

[@ADVENTUREKM]

How high are your corner post from the deck.

[@highertiercarpentry]

40 inches off framing

[@chrissling4191]

What is the size of the drill bit used to pre-drill those 8 inch screws?

[@TheTrexCo]

Hello Chris, we reccomend that you reach out to the screw manufacture, which is Simpson and you can reach them at [phone]. If you have any other questions please feel free to give us a call at 1(800) 289-8739 as we would be happy to help.-Thank you, Trex Customer Care

[@cmil8191]

@@TheTrexCo I reached out and they do not have any idea or any recommendation. I think what would be helpful is to actually post a material and tool list all the time in all your videos.

[@glendavis1266]

Very helpful video but I did not see yo address the length of the post and to include the calculations for the deck thickness and height above the top rail reveal!

[@TheTrexCo]

Hi Glen, thank you for reaching out and for your interest in our videos. The height of the post, deck thickness and the height above the top rail reveal will all be independent variables depending on your installation. For this installation, we have used the following: - A 36" railing height kit was used. - The post sleeve is our standard 40” height. The post sleeve goes on after the decking so the finished height is 40” from the top of the deck surface to the top of the sleeve. - The post is 39” above decking. This gives one inch of space at the top of the post for wiring of lights if needed. - The decking is a nominal 1” (actual .94"). So the post would stick up 40” above the top of the frame. - With the post cap would come down 1” over the top of the post sleeve these measurements would give approximately 3” of post sleeve showing above the top of the railing to the bottom of the post sleeve cap. - Then there is the width of the frame material. In this deck we used a 2x8 joist so that measurement would be 7 ¼”. So with the post being 40” above the framing plus 7 ¼” of the joist this would give a total post length of 47 ¼”. If you have any additional questions, please give us a call 1-800-289-8739. Thank you, Trex Customer Care Team

[@michaelwong9192]

How are you connecting the corner post near the house with the gap?

[@TheTrexCo]

Hello Mr. Wong, thank you for your interest in Trex! This post was installed like the side rim post. A 2x on each side of the post, SDWS screws through the side rim joist into the post and screws through the block going into the post. The blocks are attached the same as the side rim post blocks are, by putting a 2x against the ledger it held and keeping the post away from the house enough to be able to put the sleeve and the post cap on. If you have any further questions, please feel free to call us at 1-800-289-8739. Thanks - Trex Customer Care Team

[@troyturner6498]

12 8" timber screws per post...what!?

[@troyturner-ve1zj]

Hey

[@bolawdean]

Video definitely sponsored by Simpson 😂

[@danielking3611]

I’m not sure it’s really solid … I think he should about 16 ounces of Gorilla glue to each post.

[@tomconley6163]

How do you determine where your intermediate posts are to go?

[@tomconley6163]

Never mind. I asked the question before the video was through.

[@chandana56]

Question: The inside dimension of the sleeve is 95 mm ( rib to rib) and the 4x4 post size is 89 mm (3 1/2” x 3 1/2”). Once you insert the sleeve on to the post, there is a gap of 3 mm [(95 - 89)/2 = 3] all around between the sleeve and the treated wood post. When you attach the RSB to the post, the sleeve has to compress that 3 mm in order to touch the post (from both sides, if brackets are attached on both sides of the post). In my opinion compressing composite sleeve by a total of 6 mm (3 mm on each side) is not good. Don’t you have to put 3 mm shims between the sleeve and the post before you attach the RSB to the post?

[@TheTrexCo]

Hello and thank you for reaching out to us. Our post sleeves have notches on the inside to make them fit snug around the wood 4x4. Sometimes the pressure treated posts may be uneven or twist so shimming would be recommended if you find it is wobbly. Our sleeves will measure 93.726 mm ( 3.69") from notch to notch. If you have any additional questions please let us know. We are here to help! Kindly, - Trex Customer Care Team

[@chandana56]

@@TheTrexCo Thank you very much for the prompt reply. The dimension you gave from notch to notch is 93.726 mm. That seems to be the "nominal" dimension. What are the upper and lower control limits of this dimension? I measured just one sleeve all 4 dimensions with a digital caliper and I measured 94.25, 93.89, 94.98 and 95.00 mm. This is not a big enough sample size for me to calculate your 3 sigma control limits. But all 4 dimensions are larger than your nominal. Also I measured one of the 4 x 4 my contractor has installed and it measures 86.36 and 88.28 mm side to side. Based on these dimensions it is definitely required to have shims. Otherwise there is a lot of compression the sleeve has to go through when tightening the screws. I do not recall that this precaution is mentioned in anyone of your videos. Even my "Platinum" Level contractor did not use any shims at all unfortunately. In my opinion, it is an important factor to remind the contractors to do it. Specially for DIYs. Because this situation does not happen just once in a while.

[@chandana56]

@@TheTrexCoHello, I am still waiting for your answer to my question posted 5 days ago.

[@chandana56]

Why Trex is NOT replying to my question I asked a month ago????

[@TheTrexCo]

Hello Chandana, We hope you're doing well. We'd like to learn more information regarding your inquiry. If you wouldn’t mind giving us a call directly at 1-800-289-8739 any of our Customer Loyalty Advocates would be happy to further assist M-F 9 am to 5 pm EST. We look forward to speaking with you!

[@michaelrobling9636]

What is the length of the 4x4 posts

[@TheTrexCo]

Hi Michael. Thank you so much for reaching out to Trex with your question. There are a lot of variables that go into that question. Starting point is, the rail needs to be 36” high, some local codes require 42" rail height. That means that the post needs to be more than 36”. The post height is a personal aesthetic preference. However, a typical height is 3" above the top rail. Then the post cap will be 1” down and leave 2” of post showing. If you would like more post showing, you can always modify more in height. At this stage the length is 39” above the decking, and that would be 40” above the framing as the decking is 1” thick. Then the post needs to go to the bottom of the frame. If the frame is made of 2x10 material then the 40” needs to add 9 ¼” (always measure the 2x10 to make sure) this would give a total length of 49 ¼”. If the frame is made out of 2x8 or 2x12 then that measurement will be different. You will adjust and modify to the conditions on site. If you do need further assistance, please feel free to reach back out to Trex. Someone from our Customer Care Team will be more than happy to assist. Thank you for choosing Trex. Kind Regards. -Trex Customer Care 1.800.289.8739 | [e-mail]

[@journeymusic]

13:05 recap you said 3 equal railing sections of 58 7/8 instead of 52 7/8

[@allencolvin4320]

The 8 inch screws going through the double blocking behind the corner post make no sense....wouldn't those larger screws, placed so close together weaken the blocking???

[@daleon96]

Nope

[@greenlanebandit8136]

Why wasnt your band board doubled?

[@TheTrexCo]

Unfortunately, It is not required for this installation, but I would always check with your local code officiant to see exactly what is required in your area. - Trex customer care

[@adamblumke2478]

That’s $50 in screws per post. What a tool!

[@peterferry5559]

They're like a dollar each

[@DC-ct8tv]

They're 59 dollars for a box of 50

[@wayneguy6043]

The deck posts will rot before the railing post

[@peterjohnson617]

since when has a balustrade been called a guardrail ?

[@martinmcfly3433]

Devon sounded like he had dip in his lip in this video. Good video though

[@shaunburke]

Do you really need to mark the lines? You can easily see where they need to go

[@ajpieri]

If you need a nailer board where he is using the 4x4, do not use the 4x4 like this! You deck board screws will not bite into the end cut of the 4x4!!!

[@totalpkg6912]

over build will cause premature failure

[@thomaskehoe1473]

descent info, but way too much effort spent with the "temp supports/marker blocks" wasting time and money. Mark it, plumb it attach it.

[@warrengauthier4699]

Lmao...talk about overkill...what do you have a herd of Rhinos running around on that deck? You need how many screws to secure the post???