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-   -   Is it safe to build a roof over my Hawai'i deck? (http://www.diychatroom.com/f19/safe-build-roof-over-my-hawaii-deck-148660/)

ModelM2HB 06-29-2012 11:10 PM

Is it safe to build a roof over my Hawai'i deck?
 
Hello DIY users,

This is my first post. I have built a number of smaller projects including furniture and was a welder for a time, but this deck project has me a little confused. I live in Hawaii and a friend wants to build a roof over his deck. He has a tent-kit built on a hillside that has a partly cantilevered deck, one side is directly supported and the center and other side are not. I've included some pictures of the support structure and posts. He has a farm and I'm helping him with some projects throughout the summer as a trade.

What I know from growing up in the Midwest is that it's not generally a good idea to build a roof on a deck that doesn't have direct support. But in Hawaii we have no snow and since we are on the western side of the big island we get very little strong winds. I'm wondering if we could do a simple continuation of his gable roof to the end of his deck. I'm wondering if we could even support a roof using corrugated metal roofing if we aren't going directly to ground. Will we have to drop two more beams -- one in the center of the deck and one on the far side where it's cantilevered?

I ask all this because the big island is primarily lava rock, and it's hard to dig up.

We were thinking of putting in the deck roof just under the pre-existing gable with enough overhang that water wouldn't come in. Then to put 4x4 posts in on the corners and the center of the deck to fasten the gable to. I'm fairly new to this kind of construction but I'm willing to undertake the project if it's possible. Are there any plans or books that you can recommend for me to grab?

Here are the links to the tent structure: http://www.flickr.com/photos/8154628...n/photostream/

The beams are a little hard to take pictures of since they are surrounded by trees, but I can try and take better pics of them.

Thanks in advance all.

mae-ling 06-29-2012 11:30 PM

Do things shift?

What do others do?

I imagine frost heave is not an issue!

ModelM2HB 06-29-2012 11:37 PM

No, not really. Most of the buildings on the hill side of Mauna Loa use cement blocks poured on top of the rock for support. You can see that general style in the photos if I took them well enough. Yeah, if it gets frosty here good luck to the rest of you.

Bonzai 06-29-2012 11:39 PM

What about some sort of canvas "roof" over the deck ... He's living in a tent after all ;). Light and some sort of tent pole system to keep it up. Just thinking out of the box (or tent).

picflight 06-29-2012 11:56 PM

Post some, lots of pictures.

ModelM2HB 07-02-2012 08:25 PM

Thanks for the feedback. I'm going to take some more pics once it stops raining. Had a long weekend but getting back to making plans for the deck.

Just went and measured things but it started to rain. Rafters would be around 11' and the length of the roof would be right at 10'. It would be at a pretty good pitch as the roof drops 5' over the 11'. He was wanting to do a 2x6 ridge beam then 2x4 rafters with 2x3 purlins at 2 ft intervals. Rafters would be 22" on the center with 4x4 at the corners of the roof to match with the rest of the deck.

Seems like he wants to use translucent plastic for the light since his tent gets a lot of light from his french door onto the deck, so hanging a tarp for a roof doesn't seem like it will fly.

At 22" there would only be 6 rafters per side so I don't think that's a problem, and then there would be a 2" overlap on the corrugated for the roof which I think is fine.

Only worry is about the stress on the support so I'll post shortly with some more pics.

Any ideas? Are 2x4s alright for that distance and pitch?

ModelM2HB 07-02-2012 11:32 PM

Here are more images:

http://flic.kr/p/co7qoJ
http://flic.kr/p/cq1xss
http://flic.kr/p/cq1wj5
http://flic.kr/p/cq1v8U
http://flic.kr/p/cq1u3S
http://flic.kr/p/cq1sE7
http://flic.kr/p/cq1riU
http://flic.kr/p/cq1jqE
http://flic.kr/p/cq1q4N
http://flic.kr/p/cq1oXb
http://flic.kr/p/cq1nqL
http://flic.kr/p/cq1kWw

picflight 07-03-2012 02:43 AM

Thanks to your post, I now know that there is such a thing called "tent-kit."

Shuriko 07-03-2012 02:32 PM

Hi Model:

My initial concern is uplift from wind load. The proposed cover is open. Correct? The proposed cover will be partially supported by posts anchored to the existing deck. Correct? The load path will travel from the cover to the deck and the deck itself is opened so there will be a greater load path to your existing decking posts (which is not tied to the deck beams other than some by nails). The posts are anchored but those concrete pillar blocks will not provide the tied down. You will need to figure out what deadload you have by the decking, posts, etc. weight to help hold down the uplift loads. Remember there is uplift from continuous wind and gusts which can be significant. In Hawaii you are also goverend by hurricane forces so the uplift can be tremondous. If you provide significant anchorage of the proposed cover to your existing house roof be prepared to transfer some of that load to your home, which may not be designed to take on the additional loads.

mae-ling 07-03-2012 03:44 PM

I really know nothing of this type of building, best to talk to someone local.
May need to anchor to the rock?

ModelM2HB 07-03-2012 04:10 PM

Quote:

My initial concern is uplift from wind load. The proposed cover is open. Correct? The proposed cover will be partially supported by posts anchored to the existing deck. Correct? The load path will travel from the cover to the deck and the deck itself is opened so there will be a greater load path to your existing decking posts (which is not tied to the deck beams other than some by nails). The posts are anchored but those concrete pillar blocks will not provide the tied down. You will need to figure out what deadload you have by the decking, posts, etc. weight to help hold down the uplift loads. Remember there is uplift from continuous wind and gusts which can be significant. In Hawaii you are also goverend by hurricane forces so the uplift can be tremondous. If you provide significant anchorage of the proposed cover to your existing house roof be prepared to transfer some of that load to your home, which may not be designed to take on the additional loads.
The cover will be open, and will be partially supported by posts anchored to the existing deck, so you are right on both counts. Could I reinforce some of the deck beams to the support posts with the right hardware to have a better load path? I am currently reading the ASCE 2011 7-05 and doing the calculations for the deadload of the deck. Going through the book might solve some of these questions for me.

Shuriko 07-03-2012 06:22 PM

Quote:

Originally Posted by ModelM2HB (Post 957086)
The cover will be open, and will be partially supported by posts anchored to the existing deck, so you are right on both counts. Could I reinforce some of the deck beams to the support posts with the right hardware to have a better load path? I am currently reading the ASCE 2011 7-05 and doing the calculations for the deadload of the deck. Going through the book might solve some of these questions for me.

Model:
With proper connections the load path does improve but ultimately it has to be tied to some foundation that are capable of resisting the loads. Now all this assumes that the carrying member can also sustain the load. For example if the beam connected to a column/post is not capable of dealing with the shear or bending loads then the connection holds but not the beam. There isn't a simple answer that will make everything clear. My recommendation is to get an engineer to design what you or your friend need. I lived through a hurricane and I know first hand how powerful those wind (uplift) can be.

Another route you can check into is if Hawaii as a typical standard for something similar you want to construct. These standards were created to help typically homeowners so they could avoid the costs of brining in an engineer. These standards cannot be applied to every design situations but when it did apply it reduced the need for running calculations. Your city building department may have such standard.


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