Swamp build - Page 2

Love that open web design.

I've been following this thread with interest as I'm looking at using these open web trusses in my own upcoming new build. My concern is that I've heard mixed reviews about using them from the different builders i'm interviewing. Most don't want to use them. Some say they aren't as safe as I-beams (fire hazard?), or that they have more deflection, which causes bouncy or squeaky floors. Does anyone have any input on pros/cons as to the quality of using these vs traditional methods?

All other things being equal, an open web truss will allow more deflection than a closed web alternative of the same dimensions. The difference, however, is that the designer should take this into account in the design. That is, if the span requires a certain size closed web truss, it will likely require a different size open web truss. You can't just interchange the two like for like. This also limits you with floor designs on upper levels. If you have a weight bearing wall that must be supported mid-span of your floor, then it becomes more difficult to use open web trusses because they are not as "strong." You get to a point where you are size limited. That is, you can probably design an open web truss for any application, but if it needs to be 36", you probably will not be willing to give up that much headroom in your basement. Again, it all comes back to the floor designer understanding the constraints of the problem.

With regard to engineered floors vs traditional (I'm assuming you mean traditional dimensional lumber) then engineered floors will generally result it an a much flatter floor as well as reduced deflection. Our framers said they rarely use traditional floors anymore as they couldn't prevent squeaks with traditional lumber.

EDIT: I should point out that my experience with these products is limited, but I did quite a bit of research when discussing the flooring with my builder. This is the way I understand it, but it's subject to being completely incorrect

obviously i'm not an engineer, but is it possible to mix and match different types of trusses? It looks like a great idea to go with the open web trusses above areas like the home theater, but maybe it would be better to have solid ones everywhere else?

I don't see why not, but you'll have to ask for it specifically. The only problem you might run into is if the entire house, except for the theater room, calls for something like a 16" solid truss, but it would require something like an 18" or 20" in the theater, then you'll have a floor height or ceiling height difference.

As an example, my house uses solid web trusses throughout, except for areas of increased loading (i.e. a load bearing wall supported by the floor above). In those areas, they used LVL's which are solid laminated beams. in some cases these things are 24" deep by 6"-8" thick, compared to the trusses which are 16" deep.

This brings up another point. if you use open web trusses, but you have to have an LVL running through the middle of your theater to support the loading from above, you've defeated the purpose of the open web trusses. It has to be open all the way across to be of any benefit.

Find a good truss designer and they can work magic. If the truss designer knows what your requirements are, they can make it work. Getting all the other trades (especially HVAC and plumbers) coordinated can be a chore though.

One advantage to solid engineered I-joists is that they can be cut to length on site. Actually, that's only an advantage if your builder sucks and can't hit layout on the foundation and stem walls. Otherwise they will have to measure the stem walls and order the trusses to fit. Lead time can run a couple of weeks on trusses and if you don't have floor trusses the day after stem walls are complete your project stops dead.

My family has owned and operated a Truss business for 25+ years. I also contracted out/Project Managed my own house construction about two years ago. A properly engineered floor system will not have sag or appreciable defelction. The engineer has a LOT of leeway in how he engineers the truss layout including truss design, depth, spacing, and interlocking concepts.

Laminated I-beams are actually generally more rigid for a smaller unit area, but do not have open spaces and are generally more expensive than trusses.

Either system could be designed to give substandard results.

Laminated systems are not that popular in my area(Coastal NC). In my experience though contractors/Project Managers who bad mouth trusses are covering their own deficiencies in planning or skill.

+1

It really comes down to your flooring designer knowing what they're doing, and you and your contractor effectively communicating what you want. If you don't specify that you want an open truss design, they will probably design a floor that meets their design criteria for deflection at the lowest cost.

I appreciate the input guys. Sounds like i need to interview some better builders. It's unbelievable what goes into building a new house (especially for the first time). Quite the learning curve. Kudos to rabident for his good looking house, and apologies for using his thread for my own questions...

Sweet

NO, as long as you use the whisper clips, hat channel, double DW and GG that you have pondered using. Fill the stud cavities with pink fluffy.

If the wall had been built on top of the concrete ledge how would the bottom portion of the wall have been attached? You would have needed to fasten whisper clips by using concrete anchors, a very tedious task compared to a deck screw into a stud.

Firemen tend to hate these trusses. They tend to burn up much quicker than conventional lumber and cause collapses. An neighbor of mine is a Captain in Fairfax and he has trusses. That was the first thing he noticed when he visited my build (I have joists that are conventional lumber).

It's going to be a beautiful build too!

Carry on...

Just a related note on open trusses. In my jurisdiction there is a fire/building code of how large (Sq ft) of a ceiling structure can be open. When you reach the limit they will want you to partition off the truss system by covering a face with drywall. This might come up in your framing inspection. Can't remember the limit.

What are those trusses' spec? live/dead load?
Are they 16" deep? And what is your span? 21' 9"

Wow, four pages back..... You've really got to start posting more pictures

I've been thinking about HVAC a lot recently, and it seems to be a popular topic here on the boards. I had forgotten just how big your room is! Those 12' walls really add to the volume. Looks like you're going to have over 7,000 c.f. once you account for risers, soffits, stages, seats, etc. etc. So you're going to need roughly 700 cfm flowing into and out of your space to get the oft-quoted 6 exchanges per hour.

Now, I don't remember how many people this theater is planned to seat, but assuming your shooting for 8, that's going to require 4,000 BTU/hour of heat removal. A rule of thumb for sizing HVAC is 400 cfm/Ton, so you can figure you need about 135 cfm of cooled air from your HVAC to keep the room cool. Another rule of thumb here is 15-17cfm per person to keep the space cool (both rules of the thumb give about the same results )

That's a pretty large discrepancy between the needed cooled air and the amount of air you need to exchange. Here's a chart I found for sizing HVAC lines, and it looks like you could get by with a single 8" supply from the HVAC. Maybe even go up to a 9" to be safe.



With all those open trusses, you could easily add some dead vents to exchange air with the other rooms in the basement. Panasonic makes a 440 cfm inline fan that's supposed to be super quiet. Here's a link if you're interested. If you go with the 9" supply, and add the 440 cfm dead vent, on paper you're at 665 cfm. Obviously the actual installation might be a little lower, but that's pretty dang close.

As far as velocity goes, again, an oft-quoted requirement is 250 fpm. If you go with the 9" supply from the HVAC, you can up the size to a 10" a couple feet before you enter your theater to slow down the air. Note, you can't run a 10" all the way and get the same result. You need a restriction to limit the flow to what you want, and then an expansion in the duct size to slow down the flow. It's still going to be too fast with the 10" duct at around 400 fpm, but you can build a register with a bar diffuser on it to slow it down the rest of the way. The other option would be to use a 12" or 14" going into the theater or hidden in the soffits which should get you right at that 250 fpm mark.

The dead vents would be similar. If you split the 8" from the inline fan into two lines before entering the theater or in your soffits, you'll have about the same flow in each as the HVAC supply.

Sorry for posting the novel here, but I've been reading a lot about this lately, and thought it might help. Feel free to tell me to stop cluttering your thread if you like

Morph1c has two in-line Panasonics in his air exchange design, bottom line is talk to him before going that route. Cooling and noise have plagued his project.

First thing first, when in doubt, I would always defer to Big. He's done this before, I've only built...... Well..... Other stuff

With that out of the way, I actually had Morph1c in mind with my previous post. There are a couple of key differences. Rabident would have a supply capable of cooling the room with all 8 occupants on its own with no aid from the dead vent. Next, the dead vent I mentioned would have 220 cfm flowing through an 8" minimum duct (split the fan duct into two) compared to more than 300 cfm that Morph1c has in a 6" duct.

Again, Big is correct that there are some potential gotcha's to keep in mind, but I think with careful planning, and utilizing previous lessons learned, it can still work. Suggestions?

Just so you know dead vents also apply to a traditional forced system. Running acoustical ducts laterally inside a soffit with soffit and walls and ceiling built with DDW and green glue helps reduce the noise that would escape a theater via a simple typical hole in the ceiling duct work. It also helps to either line such a soffit with Linacoustic or stuff gaps around the duct with loose fluffy.

Why is the conditioned air entering at the rear? The Typical recommendation is for cool air to enter at the front so that you don't have cool air blowing down the back of your neck. I guess we're conditioned to expect the cold air on our face instead of our neck. Also, if you run a supply, you should run a return back to your HVAC if you can. My earlier recommendation for the dead vents was merely to provide additional flow to meet the requirements that the HVAC doesn't meet. Can your HVAC designer meet the flow requirements for six exchanges and the 250 fpm recommendation? With the open joists, you should be able to get the HVAC line wherever you like. On top of that, with 12' ceilings you can add soffits around the perimeter to house them as well. If you do have to add a supplemental dead vent, them you will need both inlets and exhausts capable of handling the required flow.

I'd seen that 15cfm figure before, and I've been curious as to where it came from. However, if you take the 400cfm per ton (1 ton = 12000 BTU/hr) and multiply by 500 BTU per hour per person, you get 16.67 cfm per person. So I wonder if that's the source. Seems reasonable.

You realize this is smaller than a 5 inch round line.

Dude, that's not good

Dude, now that is good! That's gonna be an awesome spot for the morning cup of joe!