Author Topic: 20 x 20 w bedroom in Ohio  (Read 18993 times)

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Offline Mike 870

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Re: 20 x 20 w bedroom in Ohio
« Reply #75 on: December 03, 2017, 10:13:16 AM »
How many inches of insulation did you go with?  My thinking is, Iím much more likely to get an R40 ceiling performing at R40 with foam.  Whereas someone with bats or blown in cellulose might get R60 performing at R 40 or so fourth.  Didnít know some forms of metal needed sheathing, thanks for the heads up.  I used structural GRK screws as a first method of attaching my rafters to my top plate.  They are pricey indeed!

Offline Don_P

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Re: 20 x 20 w bedroom in Ohio
« Reply #76 on: December 03, 2017, 01:00:00 PM »
Wrap and strap performs better than sprayed in between framing, I've run 5-6 inches mostly in the last decades. When Dad first started foil faced polyiso over solid roof decking in the early 70's we were putting 2" foam down over 2.25" thick wood roof T&G.
 When it is dried in one of the deck cleaners with oxalic acid in it would wake that ash back up.
 Half dovetail on the tie, nice  :)

Offline NathanS

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Re: 20 x 20 w bedroom in Ohio
« Reply #77 on: December 03, 2017, 02:39:30 PM »
We are in a regular 2 story with flat attic. We did R-23 in the walls, 2.75" on the outside - about R-15 to R-18 and R-60 in the attic. I had kept an eye on craigslist for a few months when a commercial roofer started listing the polyiso for $10 a sheet. If you keep an eye out you might find a really good deal, there are also some online retailers that sell used material that may be worth looking at.

I think if you put 5-6 inches on top you could get by with a pretty small wood stove.

The wood framing really does kill batt insulation. From memory, a 2x6 wall with R-19 batts performs at around R-10 to 13 depending on 16" vs 24", headers and all that.

The negative of thick foam - probably not as much so on the roof, but still needs careful planning, is that you have to hide it with a lot of smart flashing and trim work. It was a ton of extra work for siding, I'll tell you that...

Offline Mike 870

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Re: 20 x 20 w bedroom in Ohio
« Reply #78 on: December 03, 2017, 03:13:55 PM »
Don are you needing venting over that amount of foam on the roof?  I am in zone 4 for heading/cooling.  Iíve been led to believe itís not needed with that thickness but I donít want to make a mistake.  Iíll look into oxalic acid.  Thanks for the compliment on the ties.

Nathan Iím not looking forward to all the extra work the foam will cause.  I am going to put 1.5 inches outside my walls as well.

Offline Don_P

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Re: 20 x 20 w bedroom in Ohio
« Reply #79 on: December 03, 2017, 04:47:18 PM »
I've used unvented 6" SIPS on a roof here with no problems but when we do the wrap and strap roof it gets flatways 2x4's up and down the roof over the foam/over the rafters and then 5/8 osb and roofing, so that is vented. When we were doing the 2" foam back in the day we were using 3" roofing nails and applying shingle right over the foil faced foam. The foil cooked the shingles, that was when we started the sleepers and vented channel over the foam.

Offline dablack

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Re: 20 x 20 w bedroom in Ohio
« Reply #80 on: December 04, 2017, 07:22:42 AM »
We went a different way here in Texas but here it is:
On top of the OSB decking, we put horizontal 2x4s spaced 4' apart so we could lay the 3/4" sheets of 4' wide rigid foam in-between.  Two layers of foam got it up even with the 2x4 and then we put the metal on.  Have 4" of spray foam under the roof deck.  With a silver metal roof, it stays nice and cool.  This is obviously a non-vented roof. 

We got the foam used on craigslist.  4'x24' sheets 3/4" thick for REALLY cheap.  Came off the roof of old chicken houses that were being torn down.  If I was doing it now, I would have put vertical 2x4s with two layers of foam in-between, then horizontal 2x4s and two layers of foam, then metal.  That would have gotten me 3" of rigid foam and almost zero thermal bridging.  No long screws needed and the metal attaches to the horizontal 2x4s. 

Austin

Offline Mike 870

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Re: 20 x 20 w bedroom in Ohio
« Reply #81 on: December 04, 2017, 04:45:27 PM »
Thanks for all the pointers guys.  Once I realized what I wanted to do was called wrap and strap It was easier for me to research it.  I had never heard that term before.  Did another work trip today so hereís a few more photos.  Got the other half of the ceiling in the main room and built the supports for the covered back porch.  Eventually I hope to use the rest of my Ash on cover for the Front porch.









Offline NathanS

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Re: 20 x 20 w bedroom in Ohio
« Reply #82 on: December 05, 2017, 04:29:50 AM »
Looks awesome. You are moving fast.

For doing my walls in foam I mainly used the "REMOTE" manual and the deep mass energy retrofit guides. The buildingscience.com website also has a lot of good info in general but you can definitely tell those guys 'think' about building more than actually building...

http://www.cchrc.org/sites/default/files/docs/REMOTE_Manual.pdf

https://buildingscience.com/documents/guides-and-manuals/gm-mass-save-der-builder-guide/view

Offline Mike 870

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Re: 20 x 20 w bedroom in Ohio
« Reply #83 on: December 05, 2017, 06:38:24 AM »
Ha, I hear you on that.  Lately I've been considering just doing exterior foam on the walls where it would be easy to do.  Mostly the North and East side of the cabin.  There are minimal windows and fewer tricky details to deal with.  Of course my biggest concern is cooling in the summer, so that wouldn't help there much.  So who knows what I'll do.  I do change my mind a lot during the process.