20x30 with loft - ROOF: Ridge board or Truss?...

[ajbremer]

Tuesday - October 25th, 2011

My 20x30 with loft countryplans shows me how to make my own trusses. It seems easy enough but then again I see many people here use the ridge beam at the top. Which one would be easier?

Also, should the 2x6x16' rafters be 16" o/c or 24" o/c or does that depend on how thick my 4 x 8 sheets are?

Thanks for all of your help. I understand 'mostly' what to do when it comes to laying down my Advantech 3/4" subfloor and I 'think' I understand mostly about how to do the walls and rough openings BUT the roof is another thing. I am not afraid of heights and don't mind doing whatever it takes to get up there. I also would like a cathedral ceiling - does the cathedral ceiling make the roof a lot harder?

[MountainDon]

I understand 'mostly' what to do when it comes to laying down my Advantech 3/4" subfloor and

What does "mostly" not cover. Let's look at that before using any nails.

Cathedral ceiling Q?   How much insulation do you want in that roof and have you given thought as to how to achieve it?

[MountainDon]

There's insulation info for OK at the bottom of the document in this link. Includes a map

http://www.energycodes.gov/publications/techassist/residential/Residential_Oklahoma.pdf

[MountainDon]

So I'm back. The insulation info recommends R30 ceiling/attic/roof for most of OK with R38 in the panhandle. R30 fiberglass batts are 9 1/2 inches thick unless you have the R30C which are 8 1/4 inch thick.  In a cathedral ceiling there should be a minimum 1 inch air space for ventilation above the insulation and just below the roof sheathing. Building Science recommends 2 inches for best ventilation. That means some hefty rafters; 2x12 for the R30. Here's a compression chart that helps explain.



So with that in mind I'd suggest a couple of things. 1. Check on a special truss to achieve the appearance you want and permit R30 minimum insulation.  2. Consider sheathing the roof per usual and then installing layers of rigid foam over that. Then a second sheathing and the final roofing, shingles, etc.  3. Check spray in place foam against the underside of the roof sheathing. If #2 or #3 are done right the vent spacing can be eliminated. Both #2 and #3 can also be used to get away from requiring 2x12 rafters.

Real factory made trusses are maybe the best bet.They also remove any doubts about building loft kneewalls and the forces that rafters would be applying outwards on those wall tops.


And if there's anything in the "mostly understood" about the walls lket's also discuss them before cutting wood or driving nails.

[davidj]

The cathedral ceiling with beam was a bunch of work.  We spent weeks framing our roof - setting posts, craning in beam, cutting and setting 2x12 rafters, messing around with eave details. Definitely the most difficult part of the framing by far, and a fair bit of money too. A couple of people who know what they are doing can put up the trusses on a 20x30 in a few hours, especially as most truss companies will drop them on the roof for you.

If I was doing it again I'd definitely look into scissor trusses, especially for a 1 1/2 story (mine's only a one story).  That being said, the full cathedral ceiling is nice and lots of friends and family now have their own story of passing up 2x12s for me to nail in!

[Squirl]

Sometimes it comes down to how many people you have or if you have access to a crane.

I assume you meant ridge beam as in the description, not the subject of a ridge board.  Ridge beams are very heavy, and usually require a few people or a crane to put in place.  They also can require posts  to cut down on span and carry the load directly down to the foundation.

Engineered trusses are usually lighter.  If premade they can be lifted by a few people, or put in place with a crane.  Difficult to move single handed.  If made on site, they may be able to be built and placed single handed. 

So it depends on how many people you have or what you have access to, to base ease on.

[suburbancowboy]

When I did my 20 X36 After pricing them out and accounting for 120 pound snow load I went with the scissor trusses.  They where 20% cheaper and like what has been said much easier to set up.  12 12 pitch on the outside and 9 12 on the inside.  There is still plenty of vault in the ceiling.

[CjAl]

9/12 on the inside.wont get you the needed headroom in the loft with ten foot walls. You will be looking at roughly 9' at the peak. Sound high but it will only leave you about 8 feet of width at 6' or more height. If thats enough then go for it.

Thats off the top of my head numbers and assuming an 18" knee wall. So dont murder me if its not exact.

Personally if i can get away with 9/12 pitch im framing it so i can have 9/12 on the outside so.i can actually walk on it. You cant walk on a 12/12.

Ridge beams.can be made from built up 2x12's so that you can do one at a time if you have no way to crane up a huge beam. Then you can wrap them in whatever wood you like. Its cheaper to build.it up and wrap it in cedar 1x the it is to get a 8x14" cedar beam thats for sure.


The site built truss in the plans gives you like 11" on the portion of doubled up 2x6. You could fit the R38c (c for cathederal) in there. R30 may fit better though. You can finish the cieling where the flat collar tie portion is and use any blown in or matt insulation you want on top of it. That wouldnt give you a true cathederal

[CjAl]

But close to it.








Sorry, i hit submit and on my tablet i cant modify it so i.made this second post

[John Raabe]

Yep, a true cathedral ceiling is a single rafter ceiling with a structural ridge beam at the top. To get decent insulation values (R30 +) you need 2x12 for batts and perhaps foam insulation if you want something better.