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Do I have to go 1 1/2" roof insulation?

Posted:
Tue Jul 05, 2005 8:43 am
by IraRat
For all you hot weather guys, with AC, do I have to go 1 and 1/2 inches on the roof insulation?
I'm a little concerned about not kerfing the two pieces just right, whereas I would have uneven bulges that will rise above the spar heights. I'll be kerfing with a blade.
Will the earth stop rotating on its axis and will mountains fly into space if I can find a sheet of 1" and just use that? Or will that 1/2" of void hurt the whole insulation formula that I'm sure a lot of you guys can recite?
Finally, am I just being paranoid about the difficulty of inserting these 2 panels to curve to the interior roof line and come flush with the top of the spars?

Posted:
Tue Jul 05, 2005 8:54 am
by Chris C
Irarat,
I think the thickness is entirely up to you. However, insulation works on a "dead air" theory, I think. In other words, if you plan to kerf your insulation with a knife, I'm assuming the kerfs would end up on the outside of the curve and that leaves the resultant "v" theoretically uninsulated!

Personally I'd suggest kerfing with a table saw, the way we do in woodworking, and cut the inside of the curve so the space is closed up after you make your bend, That way the insulating factor remains intact.

Just my opinion, of course.

Posted:
Tue Jul 05, 2005 9:11 am
by IraRat
Good point--but alas, no table saw.
I'm assuming you say table saw because of the thickness of the blade. With a hand blade, you won't get a thick enough cut to do it on the inside.
But now that I think about it, the Cubby plans don't even call for kerfing. That the 3/4 insulation, even doubled, will bend to the curve.
How many of you guys kerfed those panels? I know Tom did, and I assumed I would so too. So maybe I WILL have to do it the way I originally planned anyway:
Kerfing on the outside with a blade, and using two layers. This will reduce some of the loss from those exposed cuts.

Posted:
Tue Jul 05, 2005 9:50 am
by s4son
Ira,
Could you use three 1/2 inch pieces? Just a thought.
Scott

Posted:
Tue Jul 05, 2005 10:01 am
by IraRat
I have to see what's available with this. Another one of my concerns was that I was using this very bendable 1/8 ply--if they were ever going to send me the damn stuff from Boston.
I've been on the phone with them this morning and I was about to go ballistic. Which is totally out of character for me.
Anyway, the 1/8 stuff I originally ordered is EXTREMELY bendy, and I'm afraid that too much pressure will bulge it into the cabin. So I just got off the phone with them AGAIN, they have the bendy birch in 1/4, and they're gonna send me that instead.
The adventure continues...

Posted:
Tue Jul 05, 2005 12:36 pm
by Ross Wade
Hey Ira,
Once you glue the 1/8" ply to the ribs and along the sides, there won't be a problem with bulging. I glued two layers of 1/8" ply for the roof. The first layer I glued and nailed it in place. The second layer was glued, clamped in the middle and nailed along the edges.
You can use a hand held circular saw and kerf the insulation. Just make sure that you clamp down a straight edge (fence), this way all the kerfs will be straight. I would kerf the roof insulation about every 1/2" and 3/4's of the thickness, of the insulation, in depth. Saw kerfing is a messy process but well worth it.
Hope this helps,
Ross

Posted:
Tue Jul 05, 2005 1:24 pm
by IraRat
Ross Wade wrote:Hey Ira,
Once you glue the 1/8" ply to the ribs and along the sides, there won't be a problem with bulging. I glued two layers of 1/8" ply for the roof. The first layer I glued and nailed it in place. The second layer was glued, clamped in the middle and nailed along the edges.
You can use a hand held circular saw and kerf the insulation. Just make sure that you clamp down a straight edge (fence), this way all the kerfs will be straight. I would kerf the roof insulation about every 1/2" and 3/4's of the thickness, of the insulation, in depth. Saw kerfing is a messy process but well worth it.
Hope this helps,
Ross
Hey, Ross! How you doing!? Haven't seen you here for awhile!
Two major questions about your post which have me confused:
Glue along the sides? I had no intention of gluing the interior ceiling skin edges to the interior side walls. Cosmetically, isn't that going to be a nightmare, and structurally, is that going to accomplish anything?
Second, how can I regulate the depth of a kerf cut using a circular saw? If it's a matter of me trusting my visual judgment, believe me:
I can't TRUST my visual judgment.

Posted:
Tue Jul 05, 2005 1:28 pm
by Chris C
IraRat,
There is a fixed depth adjustment on most skill saws. Just adjust for the depth you want, set up a straight edge, and take your time cutting all the slots. Easier still, just go with your own suggestion of using thinner insulation and don't bother with kerfing.

Posted:
Tue Jul 05, 2005 1:34 pm
by IraRat
Chris C wrote:There is a fixed depth adjustment on most skill saws. Just adjust for the depth you want, set up a straight edge, and take your time cutting all the slots.
There is?
Can you believe I'm actually building this thing and I didn't know that?
No comments, Woody--I know that YOU can believe that!

Posted:
Tue Jul 05, 2005 1:50 pm
by Woody

Posted:
Tue Jul 05, 2005 2:05 pm
by IraRat
What happened to you??? Did you drop your 10 amp microwave on it!?
Lucky it wasn't a 13 amp convection/microwave--they're a lot HEAVIER!!!
This is sick--everything leads back to TD talk. And my wife just called me, not too thrilled, telling me that 3 of my 6 expected deliveries arrived today.
And I had to borrow $20 from her this morning for gas and beer.

Posted:
Tue Jul 05, 2005 5:54 pm
by Woody
IraRat,
Well long story short. I hadn't planned on doing it. I was docking a 65' Sport fish and it was very stormy, windy and raining hard when we came back in. I jumped to the dock to secure a spring line. When I landed on the dock, being wet and very slippery, I slid and caught a raised deck board with my left foot. Since I was still sliding across the dock and my left foot had stopped, while the rest of me was still sliding. I rolled and twisted my ankle up under me and went down. torn ligaments and cracked ( hairline fracture)my tibia parrallel to the bone by the ankle. So that's it
Moral to the story, Let the other guy make the "Leap of faith" and I stand on board, at the helm, and laugh thinking it a was funny

Posted:
Tue Jul 05, 2005 8:18 pm
by TomS
Ira,
The main thing abour kerfing that insulation is keeping the kerf lines straight and parallel. I kerfed my insulation on the table saw. I'd run a kerf, move the fence and kerf again.
You can use the circular saw. Just make sure to use a cutting guide to keep your kerfs straight and parallel.
I didn't encounter any problems with the insulation bulging my interior or exterior roof skins. Besides maintaining striaght and parallel kerf lines, you also want to make sure insulation fits the spaces between the spars. If you cut it too wide, it will bulge out. I had to go back and cut some pieces a second time or even third time to obtain the proper fit.
Go ahead and install the full 1 1/2 inch thickness using two layers of 3/4 inch thick layers. Just take your time and make sure the pieces fit properly and you'll be fine.
I did get a small bulge in in my interior roof skin the lower at the bottom-front on the steet side. But, that was caused by a mistake I made when I skinned the interior. I didn't spot it until after the glue dried. The insulation had nothing to do with it.
In hind sight, the 1/8 bending birch was perhaps a little too bendy. The 1/4 should be a bit stiffer and still be able to bend to the Cubby profile.

Posted:
Tue Jul 05, 2005 8:48 pm
by madjack
...Woody,
DAYUMMMMM son I bet that hurt...OW OW OW OW...GET WELL SOON
madjack
p.s. doesn't Ira just make your day

Posted:
Tue Jul 05, 2005 8:54 pm
by Woody
Madjack.
This time I broke the connection, get it, .......BROKE the connection. ow ouch darn that hurts
And yes it does make my day