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Old 12-16-2004, 08:21 PM
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Location: Connecticut, USA
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Roof truss spacing in new home construction

I'm having a new house built here in Connecticut.

The builder plans to use 2" x 4" roof trusses spaced 24" on-center. I understand this is pretty typical.

Should I have the builder decrease the spacing to 19.2", or even 16"?

As an engineer (not structural, though), I understand that trusses are incredibly strong. Nevertheless, they look so flimsy, and I tend to want to have a large margin of safety. I also want to be able to safely add more blown-in insulation, which rests on the drywall.

In addition, the builder uses 1/2" ceiling drywall, and 24" seems like a huge span for this. As the builder is a production builder building out a whole subdivision, he doesn't want to increase the drywall thickness.

He will, however, increase the number of trusses. He wants $2,500 more for 16" spacing, and $1,750 more for 19.2" spacing.

If I upgrade, am I wasting my money? Thanks!

More details:
Type of trusses: Fink "W" trusses
Span: 28 feet (with interior walls down the centerline of the house)
Length of house: 52 feet
Slope: 7/12
Old 12-16-2004, 08:54 PM
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It's difficult to say you're "wasting money" in that you'll end up with a stiffer roof and reduce the likelihood of drywall developing sag over time. I don't know what your local or state building code would be up there-the numbers gave me a somewhat uneasy feeling as you have a fairly shallow roof pitch, and I'm contemplating snow loading in addition to the dead load of the finished assembly itself. I've never used trusses, personally-still doing things the old-fashioned way with solid sawn members. The bottom line is that if it passes code, some PE somewhere put his or her seal on it.
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Old 12-16-2004, 09:15 PM
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Location: Saskaboom
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Quote:
Originally Posted by danceswithcats
as you have a fairly shallow roof pitch
Eh? 7/12 is shallow? Your standard ranch-style bungalow typically has a 4/12 pitch roof. From my time in a truss plant, 7/12 is on the steep side of average these days, at least in these parts. I can't speak for Conneticut. I wouldn't think that New England has substantially greater snow loading concerns than Saskatchewan, though.

24" truss spacing is very standard as well. As to whether it's worth it to add a few extra trusses, I just don't know. I'm not an engineer either, and don't have the long-term experience to tell stories about stuff built 20 years ago. Remember, though, that the roof only has to bear its own weight, unlike walls, and if there's a bearing wall down the centre of the house, I would think that the only issue to merit any concern here would be drywall sag, about which I am even less qualified to speak.
Old 12-16-2004, 10:18 PM
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many years ago, i was a framing carpenter. sixteen inches on center was the standard then (at least where i live)

my house is a little older than some in the neighborhood. my roof rafters are on sixteen inch centers, and my roof sheathing is three quarter inch tongue and groove. no sags or dips after 40 years

the house next door was built after the codes were changed and has a roof on twenty four inch centers. the sheathing plywood is probably half inch thick and there are noticeable dips between the rafters.

were i to build today, i would go with the sixteen centers and thicker sheathing. it makes for a more solid roof.

ymmv

lh
Old 12-17-2004, 09:40 AM
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Roof trusses at 24" centres with 1/2" plywood sheathing is pretty much standard in my area where we get similar snow loading as you do down in Conn. If you were just using roof rafters, 16" would be more appropriate, ditto for floor joists. Of course, there's no reason why you can't decrease the spacing if it will give you more peace of mind.
Old 12-17-2004, 10:30 AM
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well, the lumber house (most likely) had those trusses designed to support your particular house. i'd just go with what they specified.

and trusses may look flimsy, but they're amazingly strong. if you're used to seeing stick built rafter roofs, i can understand the leeriness, becuase rafters are so closely spaced.

now, if the carpenters start hacking up those trusses, then you might want to have a little talk with them. once those things are comprimised, it's anyone's guess what will happen with them.
Old 12-17-2004, 03:52 PM
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OK, I talked to the builder again, and he is willing to increase the ceiling drywall thickness from 1/2" to 5/8" for $750.

Also, the builder normally uses 1/2" OSB roof sheathing. He's going to get me a price for 5/8" OSB roof sheathing. It will probably add $1,000. (He said "more than $750.")

I'll probably go with this, though I'm acutely aware that I'm getting screwed on the upgrade pricing.
Old 12-17-2004, 05:08 PM
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I'm building an additon on my house in the Colorado mountains. Lot's and lot's of snow load. I got trusses engineered for 24" and put them on 16. Just cause I over do stuff.

It was great untill my brother and I sheathed it. The only way to access it was from below. Quite a pain in the ass working up through 16" with a tool belt on. It was pretty tight quarters.
Old 12-17-2004, 06:11 PM
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Quote:
Originally Posted by robby
OK, I talked to the builder again, and he is willing to increase the ceiling drywall thickness from 1/2" to 5/8" for $750.

Also, the builder normally uses 1/2" OSB roof sheathing. He's going to get me a price for 5/8" OSB roof sheathing. It will probably add $1,000. (He said "more than $750.")

I'll probably go with this, though I'm acutely aware that I'm getting screwed on the upgrade pricing.
The extra stiffness in the thicker rock is a plus, but have to ask-how are the rockers hanging the board? If they are glue and screw guys, then fine. Nailed overhead board without construction cement on 2/0 centers is Nail Pop City waiting to happen, IMHO.

You may not be getting hosed as badly as you think. The softwood industry has been volatile, and tariff arguments are happening between the US and Canada. Some of the smaller producers have been eaten up leaving only the big few behind.
Old 12-17-2004, 11:05 PM
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Join Date: Jul 2003
Location: City of the Red Chicken
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Quote:
Originally Posted by robby
OK, I talked to the builder again, and he is willing to increase the ceiling drywall thickness from 1/2" to 5/8" for $750.

Also, the builder normally uses 1/2" OSB roof sheathing. He's going to get me a price for 5/8" OSB roof sheathing. It will probably add $1,000. (He said "more than $750.")

I'll probably go with this, though I'm acutely aware that I'm getting screwed on the upgrade pricing.
Just a vote of support for upgrading. Mass built houses are built to minimum possible specs, not to best recommended practices. You may not be happy every day for spending this money, but you will save yourself a chance to be unhappy. I vote for the upgraded sheathing, drywall, AND 16" trusses.
Old 12-29-2015, 07:06 AM
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16" spacing

I purchased a home with 24" spaced trusses 25 years ago. My roof was wavy and it leaked. Learned that lesson! The next new home has 16" 2"x 6" spaced studs and rafters. It may be overbuilt to these engineers that like to flirt with limits, but the roof is flat after 16 years and no leaks. Jump on the roof and you don't feel like you're going through. In my opinion I'd go with a different builder.
Old 12-29-2015, 07:33 AM
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Quote:
Originally Posted by Steve24 View Post
I purchased a home with 24" spaced trusses 25 years ago. My roof was wavy and it leaked. Learned that lesson! The next new home has 16" 2"x 6" spaced studs and rafters. It may be overbuilt to these engineers that like to flirt with limits, but the roof is flat after 16 years and no leaks. Jump on the roof and you don't feel like you're going through. In my opinion I'd go with a different builder.
Just thought I'd mention to you that you just brought up an eleven-year-old thread. Nevertheless, welcome to the SDMB.
Old 12-29-2015, 07:34 AM
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...

Last edited by Oddball_92; 12-29-2015 at 07:34 AM.
Old 12-29-2015, 07:39 AM
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Incidentally, robby, do you have an update for us on the house in question?
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