Building a carport

[apease]

The Kubota just plays a supporting role in this story, but I thought folks
might be interested just the same. Carport Construction

 

[ultrarunner]

Well Documented... thanks for posting!!!

 

[mcnitt]

Wow! That was about the best "how to" I have ever seen. I learned a lot. Thank you for posting it. You did a very nice job.

 

[dave1949]

Holy cow those are some big piers!

I wonder if the county inspectors would have okayed those 'big-foot' plastic pier forms? They incorporate the base and pier into one pour. You stick the rebar inside and back-fill before pouring.

I haven't tried them, but have thought if I had such a project, I would certainly consider using them.

Nice work!

 

[apease]

Pier forms are a good idea. I wish I had known about them before doing the project. A friend had mentioned them to me after the engineering was already done. One lesson I learned from the project is that engineering really messes things up. An engineer makes a profit on small jobs by recycling previous project. So you don't get the best/easiest/strongest/cheapest design for you, but just what was done for the last guy. You can pay a lot for custom engineering but then you've transfered a pot of money from the building cost bucket to the engineering cost bucket. The two best alternatives I think are either find a way to avoid any requirement for engineering, or learn how to do all your own engineering and then take it to a compliant engineering who just checks your calculations and stamps your drawings (usually not practical).

 

[dave1949]

Pier forms are a good idea. I wish I had known about them before doing the project. A friend had mentioned them to me after the engineering was already done. One lesson I learned from the project is that engineering really messes things up. An engineer makes a profit on small jobs by recycling previous project. So you don't get the best/easiest/strongest/cheapest design for you, but just what was done for the last guy. You can pay a lot for custom engineering but then you've transfered a pot of money from the building cost bucket to the engineering cost bucket. The two best alternatives I think are either find a way to avoid any requirement for engineering, or learn how to do all your own engineering and then take it to a compliant engineering who just checks your calculations and stamps your drawings (usually not practical).

Well, you ended up with a very nice carport - no matter.

This is just a comment - not a criticism:

Seeing the wealth of experience on TBN, I think it is smart to do your homework first, then ask for ideas/sanity checks from members.

The combined knowledge and experience is mind boggling.

Dave.

 

[nhkabotab7800]

plus the engineers on the site will comment...they always do

 

[dfkrug]

One lesson I learned from the project is that engineering really messes things up. An engineer makes a profit on small jobs by recycling previous project. So you don't get the best/easiest/strongest/cheapest design for you, but just what was done for the last guy. You can pay a lot for custom engineering but then you've transfered a pot of money from the building cost bucket to the engineering cost bucket. The two best alternatives I think are either find a way to avoid any requirement for engineering, or learn how to do all your own engineering and then take it to a compliant engineering who just checks your calculations and stamps your drawings (usually not practical).

Yes, I would agree with that.

I enjoyed your build website....especially the nice roof material.

I am in the process of building a carport structure (all steel) and there is a lot
of engineering you can do yourself, if you are not forced by the permitting
authorities to hire an engineer. One is buy something pre-engineered.
Trusses are sold this way. Another is to use the span tables for wood or
steel that are published in the code book or at a manufacturer's website.

With respect to piers, you can calculate your building weight and use the
soil bearing capacity you might have paid for when you built your house
and were forced to get a soils report. Or you can use 1500psf, which is
a fallback number for poor soils. Going deep like you did may be required
to get below the frost line. Otherwise, the piers can be quite small....I
used 8" cardboard tubes and they only go about a foot deep.

(I used to be an engineer, but now I get to build things.)

 

[apease]

Hi dfkrug - Actually, where my place is in northern CA there's no frost consideration. Soil bearing also wasn't an issue. The issue apparently was wind uplift, and I wasn't able to find any guidelines for how to calculate the capacity of a foundation to hold down the structure. I did use beam span tables, and the truss fabricator did the roof engineering as part of their truss bid. I'll try to dig up the beam span tables I used and link to them. One of my goals also is to go back through the engineer's calculations and make sure I can understand them all. It's all simple arithmetic. The challenge for the layperson seems to be knowing which calculations are needed, and finding the formulas and coefficients that are appropriate.

 

[BeezFun]

Beautiful work. I believe the truss that is hanging from the outriggers was intended to be the gable end truss. It should be setting on the top plate of the wall. It has the additional structural element under the top chord and the vertical elements to help carry the additional cantilevered load and to compensate for the notch in the top chord. The "normal" truss that is now sitting on the end wall would then be used as the overhung truss, which would be called a barge rafter if this had been stick built. Also if you live in a high wind area it's required to strap down the outriggers at the gable end truss.

I mention this to suggest that you consider strengthening that gable end truss, particularly if you live in a snow area. I would add vertical elements around the notches, just like the vertical elements that are built into the truss hanging from the outriggers.

 

[apease]

Many thanks for the advice BeezFun. I'll have to check on that. I don't want someone to get the wrong advice from my page. Fortunately, there doesn't seem to be any snow accumulation in my area, although the country requires structures to handle a 35# snow load. It's a hilly area, so it's probably a result of having map segments that cover areas that have much higher elevation.

 

[NIdaho]

I think you will find that the truss with the verticals was meant for the end, as the verticals are for attaching the gable siding or metal in your case.

I personally have never seen it done quite the way you did (hang a gable truss as a barge rafter/truss). in this part of the country. I would have expected to see the gable truss on top of the end wall. The barge rafters (typically a 2x6) are attached to the outriggers. The barge rafters are then covered with your fascia material/trim and the underside of the outriggers (between the gable siding and the fascia) would be covered with soffit material.

 

[apease]

Hi NIdaho, Yes, I thought I did it right, given that one has to have the verticals on the gable end to which the siding is nailed. But I think maybe what BeezFun is getting at is the need for reinforcement in the last supported truss to handle the stress from supporting a cantilevered gable end. My plans from the truss company do mention that, calling for a 1x4 reinforcement to be sistered to the top chord. I was just lazy and didn't do that. I should go back and add that after the fact. I was thinking about whether I should close in the roof structure with a soffit. Without that I suppose I run the risk that birds will nest in the truss structure. The county prohibits combustible soffits. Maybe I could just pre-prime some 1/4" gypsum and use that. What do you think?

 

[dfkrug]

The county prohibits combustible soffits.

Interesting. Combustible soffits not allowed, but open soffits ARE? Where
is that? Soffits on a carport are pretty unusual, but non-combustible
soffits are a good idea (fire protection) on a house with overhanging eaves.

On my workshop building, I used galvanized sheet metal (26 guage) for
the unvented soffits....I have yet to paint them.

 

[apease]

I know, it doesn't make sense to me either, but that's Shasta county, CA for you. Using metal for the soffits sounds like it would give a nice result, but I'd be concerned about the cost, since I have to enclose not only the soffits but the entire underside of the trusses, which would be about 600 square feet.