Wood Truss for Car Wash 1

[Brad805]

I have been asked by a client to design a truck/car wash using wood trusses over the bays. I am not a fan of this at all, and I sketched out a precast alternate. The precast roof leads to more steps to create the roof finish they desire, and they are adamant about using wood trusses. The owner of the property has another car wash that used wood trusses, so they are not receptive to our concerns. At this point, I have not committed to complete the project, but I indicated we would investigate the solution briefly before stepping away from the project.

The general arch section is not any different than any typical residential application at this point. I have sketched the basics below.

Below is Technical bulletin from the Truss Plate Industry of Canada that discusses the use of wood trusses in a corrosive environment.
TPIC Bulletin

Wet v. dry moisture.

Currently they have not retained a mechanical engineer since that is not required due to the building size. I am not sure the air handling system will be stellar. I am trying to persuade them to add a mech eng since having a plan will be very helpful for the precast concrete aspects.

Questions:
1. Would you consider the attic space a moist environment and use the additional steps to protect the wood trusses? If so, I can probably just walk away at this point and save myself the headache.
2. Any experience with this? I found some discussions of others doing this, and a few plan submissions where they were doing so. The plans I found did not indicate anything special.

 

[RontheRedneck]

phamENG - We do very few jobs for corrosive environments. But they do come up.

For such applications the engineers sometimes require plates to be quoted with something like coal tar epoxy.

I have done trusses with stainless steel plates in the past. But our plate supplier no longer makes them.

They do have an option to use metal that has a thicker galvanized coating when they make the plates. Off the top of my head I don't recall the name of it.

As far as cost - I think it tripled the plate cost. Right now plates are maybe 7% of the cost of a truss. So figuring in some added overhead, maybe a 20 to 25% upcharge would be a reasonable guess.


I've done trusses for car washes before. I have never heard any feedback about truss-related problems down the road.

In a residence, you have the stack effect due to heated air. That obviously helps move warm, moist air into a cold attic during cold weather.

You don't have that with a car wash. (Unless it's heated) So as long as the roof is properly vented I don't see an issue.

 

[Brad805]

Thanks Ron. The building is heated since it is located in a climate where the temps will drop as low as -30deg C in winter. It is in operation at those low temps, but business is very slow.

 

[dik]

The old adage, "Just because you can do something, doesn't mean that you should."

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[MotorCity]

I would walk away from the project. Not because its not possible to use wood trusses in a wet environment. There is a precedence for wood trusses being used in countless outdoor projects subject to weather. I would walk away because the proper engineers have not been engaged to protect my design. If the moisture and humidity is not properly mitigated and issues develop with the trusses, it will all come back to you.

 

[Brad805]

Thanks Motorcity. That is what I plan to do at this point.

 

[dik]

coal tar epoxy will not likely help... the plates will still work free... In addition, many coal tar epoxies are carcinogenic... From my project notes:

-EOR/ARCH SHALL CONFIRM ALL BITUMINOUS COATINGS ARE NON-CARCINOGENIC.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[XR250]

EOR/ARCH SHALL CONFIRM ALL BITUMINOUS COATINGS ARE NON-CARCINOGENIC.

Dik,
Exactly how many pages of notes does one of your drawing sets contain?

 

[dik]

For a large project, there may be 5 or 6. My notes are very detailed and take the place of a 3 part spec.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[Brad805]

I hope you take the time to read them to each of the trades.

 

[dik]

They are updated for each project and standard references are updated. I leave it up to the trades to read... I've encountered too many older projects where drawings are available and specs aren't.

Also about 10 years back, I was questioned about the length of my notes for a large federal project in Winnipeg. The Project management firm, forgot to include the specifications for the contract documents... I was happy I had my notes. Kaka happens...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik