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Worth the extra R value???

Started by shinnlinger, April 07, 2009, 08:23:36 PM

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shinnlinger

Hi,

For my roof, I am planning to stack 3 2inch foam panels on top of each other to give me a 6 inch foam panel.  This will give me an R-in the mid 3O's
The panels I bought used and don't have foil.  I could put down a layer of 1inch foil faced first that gives me both the foil and an extra 5 R or so which will put me over 40-r for the roof.  This extra layer will cost me $1200 I really don't have, but could swing.

I am planning on heating with wood.  Is it worth $1200 for the extra 5 R and the foil face?

Thanks.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

Ironwood

Anything you can gain in R-value, you will not regret. PERIOD. We heat our 1920's home VERY cheaply w/ NG. When folks around us tell us of their 300-600 monthly heating bills, I don't even want to tell them about my $120 MAX bill, usually 90-100 in prime winter months. We redid the house 10 years ago and went all out in insulating (I suppose we could have done more, but we like windows :) ) and it is smallish and vertical (Gambrel roofed) additonally the sound dampening nature is great as well. Spend the money now, it wil only be more difficult to try to retro fit later.


      Ironwood
There is no scarcity of opportunity to make a living at what you love to do, there is only scarcity of resolve to make it happen.- Wayne Dyer

moonhill

Will the foil face have an air space?  Even then I would put the $1200 into something else.  I believe the continuous foam layer will perform better due to it's ability to prevent air leaks.

Tim
This is a test, please stand by...

shinnlinger

Moonie,

No air space, and that is why I am asking if it is worth it.

The plan is to build a stop/cleat along the eave tied into the rafter tails and then stack the panels 3 deep alternating seams and then screwing with panel screws thru 2x4s vertically running them over the top, and then horizontally string along the 2x and screw on ribbed roofing.

Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

moonhill

It sounds good to me but the foil will need an air space to work properly, so skip the foil. 

Tim
This is a test, please stand by...

Don_Papenburg

$1200.00 is cheap heat for a one time charge.  For the most part it will payback in the first year or two.  If you seal the joints on the foam I think you could get by without foil .  Stager the joints on each layer of foam and seal them so that you have no free air movement. Free air movement  is the worst energy waster that you can have. 
Frick saw mill  '58   820 John Deere power. Diamond T trucks

moonhill

shinnlinger, is the cost of the foil layer $1200?  Or is the total cost of the foam included in that also, if that is the case the foam is a deal?  $1200 for a layer of foil, and no air space, will not return that much cash in any amount of time.

Tim
This is a test, please stand by...

mad dog

                                                                                                                                 When I built My log home I used 2'' Koppers 2 layers all the joints were staggered Make sure You vent it well
mad dog 78 acres,pasqualli tractor,L-15 woodmiser

witterbound

Don't the 2x's create air space above the foam panels?

shinnlinger

Thanks guys,

I will stager the seams on the 3 layers so they don't line up and it sounds like not worth the foil due to no air. BUT is it worth the R?  I can save some $ just putting more foam in there. What is an r-35 roof like vs an r-40 roof?

I would hope a vertical 2x4 on top of the foam then strapped horizontally and ribbed roof would be sufficiently vented.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

okie

Don't know about the foil thing but I was wondering where you purchased your used foam?
Thanks.
Morgan
Striving to create a self sustaining homestead and lifestyle for my family and myself.

shinnlinger

Hi,

I have decided to stick with 3 layer plan A for now, but I may put another inch of foam on the inside between the purlins before I rock it.  Would foil work there? or would the rock negate the foil?

Okie,  I had a thread on here a year ago about built up foam panels and some one on here tipped me off to a seller on E-bay who sold the used polyiso by the tractor trailer load, something like 600 R-12 2 inch 4x8 sheets for 5 large.  I had a buddy who had a project where he needed some foam also so we went in on it together.  I will be able to insulate my 2500 sqft timber frame roof to a r-36(3 layers) and the walls(2 layers) to an R-24 for about $3500.  You can get different thicknesses and sizes.  We are pleased with the quality and condition of the sheets.  Some crushed corners and such, but not bad.  If you don't need 600 sheets, have a place to store it and are up for it, I will suggest that you could probably sell what you don't want quickly and easily based on the people that keep asking me if I have any extra.  You might just break even or even make $ if you don't need that much.

What was a little odd was we ordered it with only $1000 down, but it kept getting delayed and delayed and to be fair, we didn't mind as we didn't need it right away and the seller did offer to ship something else, but 6 months later a semi shows up completely unannounced.  Lucky I happened to be around with time on my hands and have a tractor with forks to unload, or there would have been one unhappy truck driver.  Fortunately the driver didn't want a check and in the end we were pleased.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

okie

Thank you, I found them. Unfortunately I don't need half that much and wouldn't have room to store it.
Striving to create a self sustaining homestead and lifestyle for my family and myself.

Jim_Rogers

Quote from: shinnlinger on April 08, 2009, 05:46:24 PM
BUT is it worth the R?  I can save some $ just putting more foam in there. What is an r-35 roof like vs an r-40 roof?

I think there is a percentage that the roof is suppose to be vs the walls. For example we all know that heat rises, so the roof has to be a higher percentage of insulation then the walls.
You wouldn't do R-30 walls and a R-30 roof. But you would do a R-30 wall and a R-45 roof.

I'll have to do some research and find out what the exact percentage over the walls the roof should be.

And that should be your goal to make these R values right, so that you don't loose heat out your roof or out your walls.....

I'll email a friend who is has taken a lot of courses in building sciences and get the correct values or percentages and when I have an answer I'll post it.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

shinnlinger

Thanks Jim, that would be good to know.

I can add another inch or two on the inside and still have decent purlin 6x7 to look at so I can add to my R-36 some if needed.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

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