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Engineered Wood I-Joists Used for Exterior Deck

jar546

jar546

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I was just at the New Jersey Motorsports Park outside of Millville, NJ, and noticed the following that made me think. To get out of the rain, I was standing under a deck on a heavy steel frame that was self supporting. It was not attached to the structure it served. The top of the deck was waterproofed, but all of the joists on the steel frame were engineered wood I-Joists. I did not notice any water damage or leaks onto the I-Joists but it made me wonder if these I-joists are even rated or designed to be used in this type of environment.

My initial answer is going to be no, they are not and I am wondering how this was approved. Does anyone have experience with the use of engineered wood I-joists used on an exterior-only project? I forgot to take a picture.
 
I have seen them used in that type of structure, but the design called for the joists to be fully encapsulated/enclosed/weathered-in.
 
jar546 said:
Well, according to that. If these are the same manufacturer, then no way would this be allowed.
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Why do you say that? You indicated that the deck was waterproofed, so the I-joists would not be subject to rain from above. If the rim joists/fascia are similarly waterproofed, that would satisfy the "open, protected" criterion specified.

Cheers, Wayne
 
wwhitney said:
Why do you say that? You indicated that the deck was waterproofed, so the I-joists would not be subject to rain from above. If the rim joists/fascia are similarly waterproofed, that would satisfy the "open, protected" criterion specified.

Cheers, Wayne
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The manufacturers are very clear about having them not being exposed to moisture. Outside is considered a damp environment.
 
jar546 said:
The manufacturers are very clear about having them not being exposed to moisture. Outside is considered a damp environment.
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Did you read the document from Boise Cascade? That's not what it says. Exposure to outside air is fine as long as they are not exposed to rain.

Cheers, Wayne
 
wwhitney said:
Did you read the document from Boise Cascade? That's not what it says. Exposure to outside air is fine as long as they are not exposed to rain.

Cheers, Wayne
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I read this part: The devil is in the details. I would think that KD19 would be sufficient but BC knows better and limits their definition of dry use to less than 16% WME. This is an area where I have quite a bit of experience with multiple different moisture meters and thousands of houses checked. Unless you are in an arid environment, it is nearly impossible for any unpainted, exterior wood to maintain such a low moisture content.

This is also where manufacturers use language such as this to deny warranty claims. On one end, they tell you it is OK and on the other, they give you more restrictive definitions that they will hang their hat on when they deny the claim. Just like window manufacturers void warranties because the installation instructions were not carried out to the T.

Exterior, untreated lumber, even when not exposed directly to the rain, acts like a sponge in the face of humidity. Installing these i-joists without any priming and protection with paint and/or sealant will do nothing more than guarantee the early demise of the product itself.

Screen Shot 2023-09-26 at 00.11.02.png
 
Yes, but earlier it says "Open, protected applications can be defined as areas where members are exposed to outside air but typically do not have contact with moisture when it rains." And the part you quoted says that "Products used in . . . open, protected applications qualify as conditions of dry use."

So if your deck framing was open to outside air underneath, but was protected from rain from above and the sides, per the document it qualifies as an open, protected application and dry use.

Cut and dried, so to speak.

Cheers, Wayne
 
jar546 said:
It also needs proof the wood will stay at less than 16%WME
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You would think that is true, yet the document takes a clear position that an "open, protected application" is a "dry use". See the last sentence of paragraph 2. The rest of the document is elaborating on that and some details.

As a matter of science, wood equilibrium moisture content (EMC) when exposed to air of constant temperature and relative humidity doesn't depend much on the temperature, just the relative humidity. 16% EMC corresponds to a relative humidity of about 85%. https://en.wikipedia.org/wiki/Equilibrium_moisture_content

So if you have an environment with a continuous relative humidity above 85%, then it is worth being concerned the wood EMC will be too high. Hence the example in the document of an indoor pool with open framing above--if the space is poorly ventilated, the relative humidity could be constantly above 85%.

But even in Florida, I don't think you get continuous outdoor relative humidity above 85% for the several months it would take for the EMC to rise above 16%. E.g. this source gives monthly averages of twice daily relative humidity measurements for various locations in Florida (it would be better to get averages over the whole month for say hourly data, but this is what a quick search turned up):

Relative Humidity - Florida Climate Center

climatecenter.fsu.edu climatecenter.fsu.edu

I didn't go through the whole chart, but on the basis of the annual numbers, Key West is one of the most humid locations. And the worst case monthly average of the morning and afternoon average humidities is 77% for Key West.

Cheers, Wayne
 
wwhitney said:
I didn't go through the whole chart, but on the basis of the annual numbers, Key West is one of the most humid locations. And the worst case monthly average of the morning and afternoon average humidities is 77% for Key West.
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There is the internet and there is real world, actual experience in a given area based on actual circumstances.
 
jar546 said:
There is the internet and there is real world, actual experience in a given area based on actual circumstances.
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OK, so when you find some installed I-joists that are protected from rain from above and the sides, but open to outdoor air from below and well ventilated, and you stick a calibrated moisture meter in them and get a moisture content above 16%, you can let me and Boise Cascade know that we're wrong to consider "open, protected applications" as "conditions of dry use."

Until then, I'll stick with the theory and the manufacturer's recommendation.

To switch to a related and hopefully more productive conversation, is it common practice for an inspector to use a moisture meter at the rough framing inspection to ensure the framing lumber is below 16% moisture content before it is closed up?

Cheers, Wayne
 
wwhitney said:
To switch to a related and hopefully more productive conversation, is it common practice for an inspector to use a moisture meter at the rough framing inspection to ensure the framing lumber is below 16% moisture content before it is closed up?
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In Pennsylvania I used a moisture meter frequently. In Florida, not at all because no one knows what wood is down here. Everything is CMU and metal studs, although some SFRs have wood roof trusses, most new construction is modern with a poured flat, concrete roof.
 
I lived in Daytona Beach ... experienced plenty of the wild life.
 
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