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Old 01-26-2010, 12:13 AM   #1
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Flat Roof and Blown Insulation...

Hi, this is my second post.

I am living in one of those recession hit cities where the city is compensating itself for it's lack of funding by more traffic enforcement and OTHER THINGS that sort of put people at an economical disadvantage... I would explain more, but the politics of things just makes feel like sleeping in late... Anyway, I am a DIY'er by choice and by circumstances beyond my control. I have been planning on winning the lottery for the past few years, but I am still waiting. So while I am waiting I have decided to take on a new project that will involve insulating a flat roof...

Anyway, SUPPOSE you had a place that you referred to as your HOUSE (Could be a code word for something else, but I cannot confirm or deny this info.) And this house is constructed of cinderblock and concrete slab with a FLAT WOOD ROOF. The HOUSE does not have insulation because it may have originally been intended as a place for foundry equipment to operate in. Most of the HOUSE has ten foot ceilings and there are bare rafters spaced about 16" that hold up wood decking (as if there could be a hardwood floor above... but it's only a roof.) The rafters are about 2"x8" (eye estimation) in most places and the electrical is all exposed but contained in metal conduit. The electrical has couple places for welder outlets, but most are just outlets for light bulbs and standard grounded power outlets.

Since I have low ceilings, as opposed to 16'+, I have decided to used forced air, bend me over and take it in the shorts suspended from the ceiling gas heater. Since the place does not have insulation, I thought that it might be a great addition to the place and that it would help the go green aesthetic of my wallet. It may also keep the place cooler in the summer other than my velvet Elvis painting.

Now, I have been researching a few products and I know that there are some fanatical types out there who prefer the foam. I am going to be real honest and tell you that my experience with foam has not been the greatest. I once dated a girl who used foam and the foam just did not work. FOAM is NOT really an option. It is expensive, it expands, it looks kind of like tapioca pudding... OH Yeah, did I mention that it was expensive? If you feel like foam is an option for me, I am sure I will read your reply, but you had better not be a 3-M manufacturer's representative... Just saying.

Anyway, I have about 2000 square feet of roof to insulate. My first thought was a Tube IR heater that I found on Craigslist and to just leave the roof/ceiling as is... However, I thought that it might be less expensive to just insulate the ceiling and use the forced air heater... So I thought I would use unfaced fiberglass batts (r-30 9-1/2" x 15" x 25') Because Home De Po has it on sale. However, this is about $800.00 just for the batts, sooooo.... I ended up looking at the eco friendly cellulose blow the thing in the hole option and my wheels began to turn... and the next thing you know I am pricing up 1/2"& 5/8"sheetrock, and 40+ bags of blow... And now my plan is to put up the drywall, cover over the metal elecrical conduit (steel) and then blow the insulation in. No vapor barrier. Just sheetrock and cellulose.

... but then it occurred to me that I may not be able to blow this stuff in from the bottom and was wondering if anybody has done this before and what they experienced. Can you blow this stuff in flat spaces with enough blow to insulate the ceiling or am I not being practical. Should I hand pack the stuff up there or get a tamper? (I thought of the pink boards and cutting them to each space, but the cellulose is the least expensive by volume.)

I have it clocked like this;
1. Cellulose sandwiched behind drywall.
2. Fiberglass Batts behind drywall.
3. No insulation and a used Schmenke tube IR heater that is about 40 feet long.
4. No insulation and one hella expensive gas bill for a couple of months.
5. Clothing from the Salvation Army drop off bins from around the city. (Poly cotton fiber blend with some rayon and wool mixed in.)
6. Sawdust and human hair and used newspapers behind paper mache.
7 .Used pallets and peanut packing.
8. Leaves and cardboard. (I will have to wait until next fall...)
9. Straw at $3.00 to $4.00 a bale...

I am open to opinions, options, and suggestions...
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Old 01-26-2010, 06:56 AM   #2
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The problem you have is this. The way it is now, the heat from your building is keeping the roof deck warm. It is also costing you to heat that deck, but being warm, no moisture can condense. When you add insulation, the heat will stay inside where you want it, but the roof deck will become cold. Most likely it will become cold enough for moisture to condense on the underside. You need to insulate, but you also need to create a ventilation path for moisture to get out from the bottom of the roof deck. That moisture will be many times worse without a vapor retarder on the warm side of your insulation layer. It doesn't matter whether you use fiberglass, straw, leaves or cellulose. The same principals apply.
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Old 01-26-2010, 11:50 AM   #3
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Thanks for the response...
Okay, suppose I add a vapor retarder... will the blowing cellulose into the flat roof are still work?

What if I just use sheetrock and no insulation... that has to have some r-value.
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Old 01-26-2010, 12:27 PM   #4
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What he said ^^^^ regarding ventilation. UNLESS you do a spray foam of some type. I head the 3M is especially good

The foam has a vapor barrior build in, so to speak, and does not need an 'attic' air space above.

If you want to do cellulose you would install a ceiling and create an attic. probably build the ceiling at 8' and give yourself 2' of attic (less after accounting for joist thickness). Then you would need to make sure the attic is vented. Possibly block vents at opposite ends.

After all of that spray foam might be cheaper. Hire it out maybe.
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Old 01-26-2010, 12:42 PM   #5
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2000 sqft of foam... Tin foil would probably be my cheapest solution.

Sounds to me like my biggest problem is sheetrock... maybe I should just put in batts and some sort of open lath/wood strips... to hold the insulation in.
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blown insulation , cellulose , flat roof , sheetrock

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