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I am looking to install an 18’ by 18’ shade sail. 2 corners I am planning on putting in 6 x 6 posts cemented into the ground. I’m having trouble with the other 2 corners that need to be safely attached to my house. I am unable to get to the rafters or fascia to tie them in.

It will be about 8’ off the ground and the post ends will be near our fence so there won’t be a ton of wind from the west side.

Would it be ok to attach to the studs of the outer wall, Or the header above the window?

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  • two story? And your connecting about mid height of this wall?
    – Ack
    Commented Apr 12, 2020 at 21:40
  • It’s a single story and about 8 feet from patio to the bottom of the soffit there. Commented Apr 12, 2020 at 22:05

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Lag eye bolts into solid framing members is fine for this. But any time you drill through an exterior wall into the interior structure, you are providing an access point for pests and water. So make sure whatever you do has easy access for you to do periodic inspection and maintenance, and use plenty of sealant, even putting some on the lag screw threads before putting them in.

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Wall studs and the header have strength out of plane but not enough against the wind force of the sail you want to install. I even doubt that the 6x6 posts are enough.

Consider a 10 psf wind load, that you have 18x18=324 sf ft = 3230 lbs, with 4 connections that is roughly 810 lbs per connection. Now consider the real design wind load is more than that (10 psf is code minimum), a typical wind load for your condition can easily get up to 40 psf for this situation (gusts) and even more if your building site is more exposed or on the coast, etc.

Don't let the thought that wind is horizontal and the wind load on the sail will be vertical rule anything out. That's because the house changes the air flow and causes uplift, in fact, the highest wind force on a house is on the eaves.

Note too that because this is not a rigid surface like a roof, it move around a lot and will have much, much higher forces as it 'snaps' full of air. For anecdotal reference, consider the power of wind on a sail boat, or a holding an umbrella in a wind storm.

You can mitigate the impact force of the snap by using sometime to ease the force such as a strong spring at the attachment point.

If you provide a way to ensure that the house studs and header will not receive too much wind force then there isn't an issue. This could be done with some sort of breakaway device which can be as simple as a properly size cord between the sail and the connection at the house that will break free before damage is done to the house. This is not needed at the 6x6 posts as once the connection is broken at the house then the sail becomes a flag. The sail would be damaged in the wind but at least your house would not be damaged.

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    I’ve been doing a lot of research and I thought I was seeing that a 6 x 6 post cemented 4 feet into the ground would be enough on that end for anchors. The house is my issue. It seems like a common place for anchor points but your information makes it sound like it wouldn’t be and I believe you have more knowledge about it than I do or I wouldn’t be asking. Where on the house would be the best bet as an anchor spot in this case? Commented Apr 12, 2020 at 21:28
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    The post will be 'strong'. Is it strong enough for the worst case? That is an engineering design question. For your question, the best location is the top plate of the wall but the roof overhang is probably in the way. Next is to the wall studs. This assumes a single story house
    – Ack
    Commented Apr 12, 2020 at 21:39
  • From what I gathered from what I could find, I assumed the top plate would’ve been in that small space right above the window in that photo. Commented Apr 12, 2020 at 22:06
  • Unfortunately it's probably not in view due to the soffit added to the roof overhang. Even the window header is mostly hidden. Something like: cdnassets.hw.net/dims4/GG/a8cf430/2147483647/resize/876x%3E/…
    – Ack
    Commented Apr 12, 2020 at 22:42
  • Yea that makes sense. So if I can figure out a way to tie in the rafters to the fascia board would that be the best way to go? I just don’t know if I have enough room to get them attached. So my options would be tie those in or use the studs correct? Commented Apr 12, 2020 at 22:53

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