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rigid insulation or fiberglass???

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Forum topic by chopper6322 posted 02-13-2014 06:16 PM 924 views 0 times favorited 26 replies Add to Favorites Watch
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chopper6322

59 posts in 1104 days


02-13-2014 06:16 PM

Topic tags/keywords: question

So I am finally getting around to insulating my shop and am curious as to which route i should go with money being the biggest factor. I have a metal building with 2×4 framing in South Texas where it gets extremely hot in the summer. i plan to finish it with 7/16” OSB but am not sure if i want the R-13 Fiberglass insulation for 2×4 walls, or if the 1/4 inch rigid foam would give me good enough results. I have a small air conditioner and as of right now it doesn’t seem to drop the temprature at all in the shop. I guess my goal would be to drop it maybe from 100 degrees outside to 80ish in the shop. Any input would be great, thanks a lot.

-- "As iron sharpen iron, so one man sharpens another" Proverbs 27:17


26 replies so far

View a1Jim's profile

a1Jim

112335 posts in 2268 days


#1 posted 02-13-2014 06:32 PM

If you have the budget a spray on foam would give you the best insulation and stop a lot of air infiltration, of course this is done by a insulation contractor. If your budget won’t allow that then use high density fiberglass R15 for walls and blown in in the attic (if you have one)or R30 batts in the roof. you can buy expanding foam to fill any holes you might have.

-- http://artisticwoodstudio.com Custom furniture

View Oldtool's profile

Oldtool

1853 posts in 881 days


#2 posted 02-13-2014 06:59 PM

Chopper,

I’m no expert, but I found this web site that may help in your decisions:
http://web.ornl.gov/sci/roofs+walls/insulation/ins_02.html

-- "I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The point is to bring them the real facts." - Abraham Lincoln

View Dez's profile

Dez

1116 posts in 2768 days


#3 posted 02-13-2014 08:17 PM

I agree with a1Jim! They do have do-it-yourself kits in some areas.

-- Folly ever comes cloaked in opportunity!

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crank49

3458 posts in 1662 days


#4 posted 02-13-2014 08:37 PM

Chopper, you asked if R13 fiberglass would work or if 1/4” rigid foam would be OK.??
1/4” rigid foam would have less than an R value of 1 so are you planning to put in 12 layers of the foam?
That’s how much you would need to equal the fiberglass.

I have heard that having a skim coat of spray in foam and then putting the 3” fiberglass batts in would give a good wall for not too much more than just the standard fiberglass.

But in Texas I’d think you want at least a full fiberglass insulated wall and as much as you can afford in the roof. More the better.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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chopper6322

59 posts in 1104 days


#5 posted 02-13-2014 08:46 PM

crank- I miss typed, and meant 3/4” but yes i see your point i would still need 4 sheets to equal the R value of fiberglass. Thanks for the info guys looks like fiberglass it’ll be :) Another question i have, and there may not be a simple answer, but which side do i want the paper facing?

-- "As iron sharpen iron, so one man sharpens another" Proverbs 27:17

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DrDirt

2500 posts in 2433 days


#6 posted 02-13-2014 10:08 PM

No such thing as too much insulation…. it would be like owning too many clamps.

-- "If we did all the things we are capable of doing, we would literally astonish ourselves." Edison

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DrDirt

2500 posts in 2433 days


#7 posted 02-13-2014 10:08 PM

No such thing as too much insulation…. it would be like owning too many clamps.

-- "If we did all the things we are capable of doing, we would literally astonish ourselves." Edison

View Arminius's profile

Arminius

304 posts in 2494 days


#8 posted 02-13-2014 10:17 PM

A bit puzzled by the comparison – EPS board is R5 per inch of thickness, R14 fiberglas is around 3.5 inches thick. EPS board is a little more expensive on a per R-unit basis, but it is a lot easier to airseal. A wall with fiberglas insulation will always be a little thicker, because any sort of compression on the insulation compromises effectiveness.

View Gene Howe's profile

Gene Howe

5781 posts in 2119 days


#9 posted 02-13-2014 10:37 PM

Maybe not in your budget but foil backed fiberglass is what I’d recommend. It’s designed to reflect heat back into the room. But, just put the foil facing the exterior wall to reflect the heat out.
Foil backed insulation can be dangerous if ever an electrical wire shorts across it. Not much of a concern if The foil is tight against the exterior wall.
I went with R16 in the walls and R32 IIRC, in the ceiling. Here in AZ, the shop stays tolerably cool with no A/C.
My exterior walls are stucco over plywood and the roof is Pro Panel, a metal roofing.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Dark_Lightning's profile

Dark_Lightning

1763 posts in 1800 days


#10 posted 02-14-2014 03:28 AM

The paper faces the side with the least moisture, which you will have to figure out. How is your shed designed? You can use a radiant barrier product if you have the right ventilation scheme, and save a pile of money. I have radiant barrier insulation in the roof of my house, and it paid for itself in less than two years. The foil backed foam has a similar effect on insulation. The heat rejection from the foil may exceed the insulation value of the foam in the right application.

View Grandpa's profile

Grandpa

3190 posts in 1366 days


#11 posted 02-14-2014 04:56 AM

Fiberglass with the paper side to the inside. I live in SW Oklahoma and believe this is what you want. They make some stuff today that is better and still designed for 3-1/2 inch walls. Get that. You want about 16 to 18 inches in the attic. They call it the point of diminishing returns. You reach a point where you can add 6 inches and not see it on the utility bill so there is a possibility of too much insulation. A lot is good but too much does no more good than a lot. Ventilation is important in your attic also but you didn’t ask about that.

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chopper6322

59 posts in 1104 days


#12 posted 02-14-2014 03:56 PM

My shop has a barn style roof and so there is no attic and i haven’t thought about ventilation at all, no soffets or anything, I suppose maybe there is more to this than i thought :) maybe i need to put an attic in and install some roof vents? will that do any good without airflow from the bottom of the attic as well?

-- "As iron sharpen iron, so one man sharpens another" Proverbs 27:17

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Dark_Lightning

1763 posts in 1800 days


#13 posted 02-14-2014 05:38 PM

2X4 only gives R-11 at the roof. I bet for your area the recommended insulation is around R-30. I’m in So Cal and that’s what is recommended here (building code required for homes). In your case I’d recommend foam, since 3.5 inches is about R-21. Stuff it in the bays between rafters and nail light straps across them if they don’t have nailing strips of some sort around the perimeter.

View Gene Howe's profile

Gene Howe

5781 posts in 2119 days


#14 posted 02-14-2014 05:47 PM

A ceiling at 8-10’ might be wise. Especially if you want to insulate it. There are numerous ways to vent an attic.
Static vents at each end, electric fan vents at one or both ends, a “whole house” fan in the ceiling with static vents in the ends, or one or more of those globular like roof vents that spin as the attic heats up.
The main idea is to prevent heat build up in the attic which will transfer to the space below.
We have the “whole house” fan in our home. We open a few windows and run it a 10 or 15 minutes before going to bed so it pulls in the cooler night air and cools the house (at least those rooms with the open windows) and it cools the attic. Mine is controlled by a wall switch only. One could put it on a timer or use a thermostatically controlled switch.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Grandpa's profile

Grandpa

3190 posts in 1366 days


#15 posted 02-14-2014 07:26 PM

The best system is ridge vents on the ridge. This has no moving parts or bearings to wear out. It is at the apex of the roof. remove the ridge cap if you have composition shingles. cut an inch off the decking on each side of the ridge pole then put on the cap. Get the kind that comes in 4 ft. sections. Put on a new ridge cap. Go to the lower edge of the roof and decide where the insulation will no longer touch the decking. Install “turtles” there to all air to circulate in. The system should draft from bottom to top like a chimney. If you use gable vents with the ridge cap it will circulate up there and never exchange the air below. The insulation needs to be kept dry (and the structure too). I would consider installing some joists like a scissor truss would offer. This can be stick built. Then install a ceiling on that. That will do as much good as the insulation since you don’t have that barrier. In a home you figure 1 sq ft of open ventilation for every 150 sq ft of attic floor. You divide that in half and put half of it near the ridge and half near the bottom of the attic or in the soffit area. By installing the joists you also lower the insulation away from the roof and decking. You will like that better in 15 years. The insulation can trap moisture and ruin the decking. You want to keep the attic for storage if you can build it strong enough. by putting in the scissors you have moved the insulation away from the wall and still kept most of the space open for storage. By using a whole house or attic fan, you only cool the building when the fan is on. If that is at bed time or the end of the day then the heat is built up for all the afternoon sun shining on the roof all afternoon. The turbine system works but they have only 113 sq inches of opening for a 12 diameter opening. Takes a lot of them if you need 2 or 3 feet. BTW the wind turns them and not the heat. The air would have to flow out at about 5 mph per hour to spin them from heat. In my area the wind wears the bearings out in a couple of years. If you choose to use those be sure the base is vertical. Those that lean out of in have a short bearing life since the bearings are not designed for a side load. Sorry this is so long but I inspect homes and I see a lot of ways to do thing wrong or poorly. I also see a lot of ruined homes. Our thinking has changed drastically since we build better homes today than those from the 1920’s. That is an old house in my part of the country.

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