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Raising the roof to fit insulation

jar546

jar546

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The ceiling joists are cantilevered out on both sided of the structure and held in place with hurricane clips. There is a double top plate placed on top of the joists and the rafter's birdsmouth sits on that to give the required bearing. The rafter tail is then secured to the end of the ceiling joists.

I cannot see any reason why this would not be a compliant installation. I actually like it but we never see this in our area until recently.

f7c7feeb.jpg


be748205.jpg
 
I'm always surprised to see hand framed roofs on this board. Almost everything done here (Minnesota) use trusses. That being said, our State energy code requires raised heel trusses for proper insulation above the exterior top plate. This application would meet our minimum standard.

Joe
 
i'm not liking the fact that the rafter tie is happening beyond the bearing point and the birdsmouth notch. am i being paranoid? Where is George Roberts anyway?
 
this application should have a barrier at the outside edge of the insulation (windwash barrier).

Pwood, what is your concern with the rafter tie beyond the bearing point? If it is nailed at the bird'smouth and the sheating above and then has a solid sub-fascia that it is secured to at the outer edge I don't see how it can rotate laterally and uplift should not be a problem.

Joe
 
mn joe said:
this application should have a barrier at the outside edge of the insulation (windwash barrier).Pwood, what is your concern with the rafter tie beyond the bearing point? If it is nailed at the bird'smouth and the sheating above and then has a solid sub-fascia that it is secured to at the outer edge I don't see how it can rotate laterally and uplift should not be a problem.

Joe
Click to expand...
code requires blocking at bearing for rafters and for joists. i see neither. looks like perhaps an engineer should approve the alternative.
 
code requires blocking at bearing for rafters and for joists.
Click to expand...
IRC 2006 R802.8 Says:

"Rafters and ceiling joists having a depth-to-thickness ratio exceeding 5 to 1 based on nominal dimensions shall be provided with lateral support at points of bearing to prevent rotation."

This scenario doesn't seem to fall into that category. It would seem that the main concern is uplift because of the presence of the hurricane clips (they will have some overturning resistance as well). I would think that if this is the case then the rafters should be attached to the new plates in the same manner. It does appear though that the rafters may be attached to the end of cantilevered portion of the ceiling ties(can't actually see it so not sure). If this is the case then maybe that connection is enough to satisfy requirements....Again hard to tell without seeing it up close and personal.

My bad. Missed the rafters secured to ceiling joists.
 
I know this is a shed but...

From memory here... There is a requirement in the IRC that requires the insulation to extend all the way out to the outside of the wall. I'll have to dig it out of course.... but the clearance above the top plate is required which nobody is enforcing from what I can tell......

I'll research and get back with a code section if nobody else come up with it first...
 
This situation is a continual issue for me. The codes require a "rafter tie", the continuous member tying rafters together to counteract rafter thrust. The IRC and the commentary are clear and direct with no apparent leeway. Unfortunately, few structures are built in a manner that would make it possible or practical to install a rafter tie in the manner the code requires. Installing the "code approved" rafter tie entails setting the rafter and the ceiling joist side by side on the supporting member, which leaves little room for the insulation required by the energy code. (most houses around here are still stick-framed, hips and built with raised heel heights which makes the traditional rafter tie impossible) The WFCM does allow the rafter tie to be moved up in the roof, as long as it remains in the bottom 1/3 of the attic space but again often times this is not possible or practical. I just don't think the code had the size and scope of the houses today in mind a lot of the time. Bonus rooms are a real problem for the builders around here. I am a firm believer in the validity of the rafter tie, especially after seeing many of the houses around here being built without them and seeing first hand what happens. I do wish the code could update itself with some alternate methods of compliance such as the one pictured. I have seen this very detail in a JLC engineering article and have allowed it a few times. In my humble opinion it does comply with the code. As for the insulation......I would rather see good structure with a little compromised insulation than good insulation with a little compromised structure! All in all, trusses would be easier to inspect and given the methods I see better.
 
Aren't the "hurricane clips" required to be attached to the roof rafters and the top plates?

Just looking in the Simpson-Strongtie catalog, it appears that all of their "hurricane

ties" actually attach to the rafters and then to the top plates.

Just askin'...

Mule,

Is Jeff actually insulating his shed? If so, then Section N1102.2.1 ( 2006 IRC ) might

be the section you are searching for.

.
 
Yep! That's what I was thinking about. I was talking about structures other than accessory buildings though. I don't know of anyone (AHJ) that requires the uncompressed inulation all of the way past the top plate.

N1102.2.1 Ceilings with attic spaces. When Section N1102.1

would require R-38 in the ceiling, R-30 shall be deemed to satisfy

the requirement for R-38 wherever the full height of

uncompressed R-30 insulation extends over the wall top plate

at the eaves. Similarly R-38 shall be deemed to satisfy the

requirement for R-49 wherever the full height of uncompressed

R-38 insulation extends over the wall top plate at the

eaves. This reduction shall not apply to the U-factor alternative

approach in Section N1102.1.2 and the Total UA alternative in

Section N1102.1.3.
 
globe trekker said:
Aren't the "hurricane clips" required to be attached to the roof rafters and the top plates? Just looking in the Simpson-Strongtie catalog, it appears that all of their "hurricane ties" actually attach to the rafters and then to the top plates.
Click to expand...
If the clip is to the joist, and the rafter connects to the joist, then a load path exists. Whether than load path is sufficient is of course another matter, and in Jeff's shed, the uplift on the rafter acts upon a lever arm relative to the clip to some degree. Nailing the rafter to the double 2x, the double 2x's together, and then to the joist would offer a direct load path...as would a strap. That's not to say that nails at the ends of the rafter and joist won't work, but there is a lever arm there.
 
brudgers,

Would you say that there exists a weak point in Jeff's framing ( as shown ),

..because of the bird's mouth notch? The degree of weakness is not in

debate, just that it does exist?

.
 
Huricane clips are designed to resisting uplift, not rafter thrust.
 
Robert S said:
Huricane clips are designed to resisting uplift, not rafter thrust.
Click to expand...
Some are, some aren't. However, most have some lateral capacity parallel to the wall plane, and many have capacity perpendicular to it. Refer to the manufacturer's catalog and be aware that USP and Simpson deal with load combinations differently when it comes to clip capacity.
 
globe trekker said:
brudgers, Would you say that there exists a weak point in Jeff's framing ( as shown ), ..because of the bird's mouth notch? The degree of weakness is not in debate, just that it does exist?.
Click to expand...
If there is no load path at that point, yes. If it is nailed together there, no.
 
There is no weak point in that design and the birds mouth creates the load path through the double upper plate on top of the joists. The hurricane clips make this design work well for uplift, the rafters are tied directly to the extended ceiling joists which keeps the walls from spreading when the roof is loaded.

I may be partial but I don't see where it is not code compliant. :)
 
jar546 said:
There is no weak point in that design and the birds mouth creates the load path through the double upper plate on top of the joists. The hurricane clips make this design work well for uplift, the rafters are tied directly to the extended ceiling joists which keeps the walls from spreading when the roof is loaded.I may be partial but I don't see where it is not code compliant. :)
Click to expand...
Well it's a shed. Were it a structure that required a permit in my area there would be frieze blocks with boundary nailing and if the wall OSB is there for much more than decoration, the edges would be blocked. But hey, it's a shed so the unorthodox framing is good enough and plenty strong.

This thread is all the way up to three stars. The critics can't be trusted.

Years ago one of the office suits asked me to build him a bird house. How could I say no? I didn't like the egocentric, jerk so I built an elaborate bird house. It had patios and chimneys, multiple roof styles and was solid. There was six or more compartments. What it didn't have was any openings for birds. Six months later I asked him how the bird house was working out. He said he hadn't noticed any birds hanging out. I told him why. He became angry enough that I know he hadn't noticed before I told him.

So what's the point?

Does there always have to be a point?
 
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Just more grist for the mill,

This is an old method known as a raising plate. The ceiling joists project over the wall to form the soffit. The raising plate is nailed flat to it and the rafters with just a level cut are spiked to the plate. A nice raised heel cantilevered roof but not real well connected.

oldrafter.jpg


A cantilevered truss does the same thing but is better connected;

attictruss.jpg
 
A neighbor who is a civil engineer built her house this way, but left out the raised plate. Added a plywood gusset to tie rafter to joist. She also made an exterior cladding to a wainscot height by setting fieldstone in little slip forms sized 8X8X16. Three faces were flat except for an inset, the fourth has stone projecting. The blocks were made over several years a few at a time with mortar mixed a wheelbarrow at a time.
 
ICE said:
So what's the point? Does there always have to be a point?
Click to expand...
LOL. Here we have a common bird that loves to build on ledges a nest of mud and moss. If the birdhouse has enough overhang and weather protection it would do sans openings. Eastern phoebe, a flycatcher species, catches bugs on the wing all day long.
 
Comer sounds like a great place! few beers and sit around watching birds snag bugs in flight all day. good stuff, sign me up :mrgreen:
 
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