0

I have an aging cedar deck I'd like to add a small pergola to for use this summer, maybe next, before I replace the deck with something new (probably composite Trex).

I think I have a simple design I like but I am a little baffled on how to safely attach new posts to the existing deck. I believe what I need to use are post anchors but can they be safely attached to the cedar planks near the joists or do they have to go into the existing posts?

Also, is there a major difference in post anchors? Prices seem to be all over the place. Is something like this https://www.thedeckstore.com/tisan-aluminum-post-anchor.html what I want? I like that it is nearly invisible. Or do I need something like this? https://www.homedepot.com/p/Simpson-Strong-Tie-E-Z-Base-Black-Powder-Coated-Post-Base-for-4x4-Nominal-Lumber-FPBB44/100655350

Or am I just looking at the wrong thing entirely?

mikeds
  • 3
  • 1
  • 2

1 Answers1

0

There are four issues: 1) Holding the pergola up, 2) Holding the pergola down, 3) adequate attachment to the pergola and deck , and 4) appearance.

  1. Establishing the weight of the pergola is key to this step. You indicated it is a “small pergola”. So, I’ll assume it’s about 8’ x 8’ x 8’ high. Depending on materials used, this would translate into about 700 lbs. if there is no floor in the pergola. That weight distributed to four posts equals about 175 lbs. to each post.

2x decking cannot support such a load. The posts must be anchored to beams or footings below the decking.

  1. Uplift is determined by calculating the wind uplift minus the weight of the pergola. Uplift is about 25 psf where you live. So, net uplift is 25 psf x 8 x 8 = 1600 lbs. - 700 lbs. (weight of pergola) = 900 lbs.

Again, 2x decking cannot support such a load. The posts must be anchored to beams or footings below the decking.

  1. An adequate post support might look like this: Simpson PA strap tie, because it’s strong enough and long enough to extend down to a concrete anchor ( 150 psf x 1’ deep x 3’ x 3’) sufficient to hold it down and adding a post under each leg could hold it up…but it looks industrial.

https://www.buildsite.com/pdf/simpsonstrongtie/PA-Strap-Tie-Holdowns-Product-Data-1462031.pdf

  1. Having a minimal looking connection will enhance the appearance like this: Simpson CPTZ.

https://www.amazon.com/Simpson-Strong-CPT66Z-Galvanized-Concealed/dp/B00KYVWQNY/ref=asc_df_B00KYVWQNY/?tag=hyprod-20&linkCode=df0&hvadid=198090962560&hvpos=&hvnetw=g&hvrand=8722853821112891294&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9033035&hvtargid=pla-542057085992&psc=1

It is a concealed anchor and will look better. However, it needs the same post extension under the deck and concrete anchor in order for it to work.

Lee Sam
  • 3,836
  • 1
  • 6
  • 14