Pergola sizing question

Hi all,

I want to build a 12x12 square pergola using redwood over a concrete slab (using posts metal anchors) with the following details:

I will use 4 4x4 redwood posts spaced 10ft apart as pictured here (sorry for the bad drawing):



The particularity of this pergola is that I live in California and since it can get pretty hot, I want full shade under the pergola. In order to do that, I am planning to fully cover the pergola with a roof and I was planning to use 12 2x12x12 redwood boards laid perpendicularly to the joists.

My question is the following: Will the 4 4x4 be enough to hold the weight of the roof or do I need to add 2 more posts?

Any help will be greatly appreciated.
Thank you for your help.
Regards,
John

 

AFAIK, 4 4x4s will support the structure but footings are required. You can't set the posts on the patio & call it a day. Check your local codes.

 

Hi Pulpo,

I plan to use those to anchor the posts to the concrete.

Shop USP 4-in x 4-in Steel G185 Post Base at Lowes.com

 

I understood what you meant. I don't think that they meet code any more, especially in earthquake land. That's why I suggested that you check your local codes.

 

I have to ask--why such heavy members for the roof planks? Are you in a mountainous region of California, and expecting heavy snow loads? Also, are you content to not being able to use the space under the roof during rainy weather? I suspect the gaps between planks will be constantly leaking, unless you install impervious roofing material on top of them.

 

Hi,

I am not expecting any snow (San Francisco bay area) but I want real shade (This is why I won't use lattice)

2x12x12 may be a bit overkill and I could have used 3/4 inch plywood but since the pergola will be using redwood, I want to keep the same wood for aesthetics reason. Also a 1.5 inch board will provide more shade since it can get pretty hot here.

Concerning the leaking I was planning to use either a white corrugated roof (metal or plastic) on top of the redwood boards or even better put a waterproofing membrane (I want this part to be as discrete as possible).

Thanks to the waterproof roof, the furniture under the pergola will also be protected from the rain

 

A potential drawback to using 2x roofing material is the fact that it will absorb (and retain) much more heat than thinner members will. Along with the cost factor, which will be several times that of using thinner redwood boards would be.

 

Concerning the price, I agree, the redwood roof by itself will be almost half the price of the pergola.
The thing is that I can't find 1x12x12 redwood boards, and approaching 1x size boards are almost the same price as the 2x12x12 boards anyway.

I thought that 2x boards being bigger, it would isolate twice as much from the sun heat + having a white impervious covering on top would reflect more the sun and provide better shade.