Insulation help on trussed roof/ceiling

[ottoemezzo]

Hi all,

Any suggestions on the right way approach insulating this ceiling (please see link below)? The trusses make it a little complicated. For example, should I insulate just the underside -- the ceiling of the garage? Or do I need something above, in the rafters, as it were?

The garage will be heated (forced air, electric) and cooled. FWIW, I live in Nashville - hot summers and cool winters.

The link below goes to my shutterfly site, with photos that should help clarify.

http://garagetrusses.shutterfly.com/pictures/9#12

Thanks!
-Bob

 

[NUTTSGT]

If it were mine, I would insulate across the bottom/between the trusses. I prefer to create an attic space for the hot air in the summer and cool air in the winter.

 

[porschedude996TT]

^^^^^what he says!

I have R30 at the ceiling joist of the trusses un-backed fiberglass bats.

 

[bczygan]

A couple of things.
Were those trusses designed for the extra load of the OSB deck that is on the bottom chord, as well as any things you might store there?
That deck limits the amount of insulation you can use to an inadequate amount.
You also didn't get energy trusses. These are trusses with enough depth designed into them at the haunch, where the truss meets the wall, so that you get full depth of insulation all the way to the outside face of the wall studs. Example:

These two situations can be partly overcome.
First, use unfaced batt insulation between all the truss bottom chords. Make it full depth of the chords. Hold it in place with wires.
Then to make up for the lack of total insulation depth and R value, install 2" foam insulation panels across the bottom face of the truss bottom chords. They may require some rows of 2x nailers to be installed perpendicular to the trusses for the edges of the foam panels.Tape the joints to create a vapor barrier. This is more expensive than deeper batt or loose fill insulation, but will achieve the same result. Then you can drywall over this. Were the trusses designed for DW and lighting too?

Object lesson for others. If you want deep insulation AND attic storage, get your trusses designed to accommodate both with a deeper bottom chord and adequate depth at the wall.

 

[ottoemezzo]

Thanks for the replies, guys.

A couple of things.
Were those trusses designed for the extra load of the OSB deck that is on the bottom chord, as well as any things you might store there?

I hope so. I specifically asked the builder for storage in the trusses.

Were the trusses designed for DW and lighting too?

Again, I hope so, and they'd better be! Do you have any reason to suspect otherwise? I told the builder I'd be finishing off the inside w/ drywall.

Thanks for your help. Much appreciated. I guess there's a reason this guy came in at a much lower price than the other builders

 

[bczygan]

BTW, welcome to GJ!

Get a copy of the truss engineering drawings from your builders truss supplier. They should be sealed by an engineer and will tell you what they were designed to do. Live loads and dead loads will be listed.

And that is the problem with building projects. You, the owner don't know all the myriad choices to be made for all the details of a building. You are doing this once. The builder has done it dozens or hundreds of times and knows where to make choices that save money.

He gives you a price, and makes the building match it.

Pulte Homes, for instance, didn't install a sill plate on top their foundation walls unless required. Saves a lot of money over hundreds of homes.

My advice to owners is a complete and detailed set of construction drawings, a complete and detailed set of specifications with very specific language and selections that are nailed completely down before signing of a contract. How can you have a "meeting of the minds" that a contract requires, if everything isn't defined and understood by both parties?

The best contractors divulge everything, ad infinitum. But many just don't tell you anything, so they have a lot of wiggle room to save money on the job where they need to.

 

[Kels]

Curious to know if you don't know where your trusses came from is there a way to find out what they are able to do?

 

[bczygan]

Curious to know if you don't know where your trusses came from is there a way to find out what they are able to do?

There may be some truss experts on here.

My experience as a builder is that it is all about minimizing cost and maximizing profit.

The truss companies have a program they run, that selects truss configuration, member sizes, species and strength characteristics, along with availability and cost factors. You might be able to get close by reverse engineering from the configuration and member sizing. Connectors have a role too.

New homes have paperwork from the truss company. Reputable builders should give a copy of the truss engineering diagram to the new owners. This would be in the owners package that includes a set of the plans, lot survey, appliance warranties and care instructions. In fact, I believe all homes should have a data plate, with all load factors plainly imprinted on it. This information would be useful to make homeowners aware of the loads their structures were designed to accommodate. This is especially needed for things like decks, which can sometimes be overloaded at parties.
We don't do this because our structures have such a large safety factor built into them.

 

[Cemoto]

This is very timely for me. Thanks for the question and responses.

Regards,

 

[ottoemezzo]

BTW, welcome to GJ!

And that is the problem with building projects. You, the owner don't know all the myriad choices to be made for all the details of a building. You are doing this once. The builder has done it dozens or hundreds of times and knows where to make choices that save money.

He gives you a price, and makes the building match it.

Thanks again. Glad to be here . I've asked for a copy of the engineering drawings. The thing is, I didn't ask him to build to a price, or to match what someone else quoted me. I just told him what I wanted. He didn't have to go the cheap-o route. All it would've taken was a two minute lesson on trusses. Maybe it's just SOP for them to do it as cheaply as possible.....

(BTW, I don't blame him for wanting to maximize his profits. I'm a capitalist through and through! If one option costs more than another, tell me why it's worth it. You may be able to convince me! In this case, he could have.)

 

[ottoemezzo]

BTW, welcome to GJ!

Get a copy of the truss engineering drawings from your builders truss supplier. They should be sealed by an engineer and will tell you what they were designed to do. Live loads and dead loads will be listed.

Got it! My builder may have taken a few shortcuts for the sake of cost, but I have to say he's been super helpful whenever I have a question.

The engineering drawing says: "This truss has been designed for a 10.0 psf bottom chord live load nonconcurrent with any other live loads."

I'm not sure of the conversion formula from 10.0 psf to 'how much **** can I store up there?' . Any thoughts? Once again, thanks for your help.

(here is the actual drawing if anyone is interested: http://garagetrusses.shutterfly.com/pictures/15)

 

[Kels]

There may be some truss experts on here.

My experience as a builder is that it is all about minimizing cost and maximizing profit.

The truss companies have a program they run, that selects truss configuration, member sizes, species and strength characteristics, along with availability and cost factors. You might be able to get close by reverse engineering from the configuration and member sizing. Connectors have a role too.

New homes have paperwork from the truss company. Reputable builders should give a copy of the truss engineering diagram to the new owners. This would be in the owners package that includes a set of the plans, lot survey, appliance warranties and care instructions. In fact, I believe all homes should have a data plate, with all load factors plainly imprinted on it. This information would be useful to make homeowners aware of the loads their structures were designed to accommodate. This is especially needed for things like decks, which can sometimes be overloaded at parties.
We don't do this because our structures have such a large safety factor built into them.

was asking because I inherited a pole building and we have no info on it and no idea who built it or anything!

 

[bczygan]

was asking because I inherited a pole building and we have no info on it and no idea who built it or anything!

Typically pole buildings have no ceiling and aren't designed for one. That said, since there is a safety factor in construction, I certainly wouldn't worry about hanging a metal ceiling, lights and maybe some insulation. Especially true if the insulation was secured to the top chord of the truss rather than the bottom.
DW is a little heavier, and a pole barn typically has trusses much further apart than the standard 2'oc. This requires additional framing, so it may be a problem. If you can insert, or build in place, additional trusses to support additional loads and cut the spans for the DW, then it can work.
Storage in pole barn trusses?...I might put some very light things near the walls, but not much else unless I knew it was designed for it.

One good thing about wood framing though. It will deflect more with additional loads, so you can measure what you are doing to it. Remember that all beams deflect. You want to keep the deflection to stricter tolerances for finished ceilings, lesser tolerances (More deflection per span) for spaces with no ceiling. Typical deflection amounts are 1/180, 1/240 and 1/360th of span. For instance, a space with no ceiling might have an allowable deflection of 1/180th of span. A 24 foot span could deflect 1.6". With a finished ceiling you might use 1/360th with a .8" deflection. Of course, using dimensional lumber you can put the boards with camber up to negate some of the deflection.

And loads are figured based on even loading, not point loads. Spread your loads out as much as possible.

 

[bczygan]

Thanks again. Glad to be here . I've asked for a copy of the engineering drawings. The thing is, I didn't ask him to build to a price, or to match what someone else quoted me. I just told him what I wanted. He didn't have to go the cheap-o route. All it would've taken was a two minute lesson on trusses. Maybe it's just SOP for them to do it as cheaply as possible.....

(BTW, I don't blame him for wanting to maximize his profits. I'm a capitalist through and through! If one option costs more than another, tell me why it's worth it. You may be able to convince me! In this case, he could have.)

The other factor is time. Time is worth money. If a contractor has to educate the client, he will need to charge more. To a contractor, a fast smooth job is a profitable job.

A good way to make sure he does take to time to offer you all the options is to negotiate that up front. Sound him out and get a feel for how he works. Let him know the type of client you want to be. Let him know that once you are offered different options, your decisions will be quick and sure. A lot of clients can't make up their minds when offered options and hold up the job.
Plus, some contractors just have one favorite way of doing things. The more educated you can make yourself, as the consumer, the better. You will be able to ask all the right questions and make judgments about your potential contractors because of your own knowledge. There are a million decisions in the construction of a building. There should be a million questions asked by the owner, and answered to his satisfaction. A good contractor will appreciate that attention to detail, because he knows you will be getting exactly what you want, and that will make you a satisfied customer.

That is why I am a maniac for details in construction documents (Plans, specs, selections etc.). And it is all about the relationship. Create one with your contractor, nurture it, and you will both benefit.

If you and I see eye to eye, and have the meeting of the minds, we will both be happy with the result.