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1953 ranch with two roofs and no insulation

Hello everyone! I recently purchased my 1st home. It's a 1953 ranch in need of some major updates. First on the list is adding insulation.. because there is ZERO! The home actually has two roofs, the original being a flat roof that clearly had some leaking issues and a new (~5 year old) steeper pitched roof that sits on top. I'd like to insulate as much as I can but I'm not sure what to add or where to add it. My biggest concern is creating a moisture trap that will do more harm than good.

Because I'm a visual person, here is what I'm dealing with:

The wall studs are 2x4s and the ceiling joists are 2x12's, both 24" on center. The original flat roof has about 1" total of sheathing and roofing membrane.

I did some research about insulating flat roofed homes and found that there are a few options. Here's what I'm considering:

Option 1: Block off the ends of the rafters/joists and blow in insulation in both the walls and between the ceiling joists filling the space completely. One concern I have with this is the densely packed insulation causing the drywall to bow over the 24" span. Also, would a vapor barrier be necessary in this application?

Option 2: Leaving an air gap in between the original roof sheathing and insulation. I was thinking that regular batt insulation would work in this instance. The downside is the amount of insulation I can put inside this space will be reduced. I believe I'd only be looking at about an R30?

Option 3: Insulate above the old flat roof and treat the membrane as the vapor barrier. For this I'm not sure if unfaced batts or blow in would be better. I would utilize baffling along the sides to vent the space and block off the ends of the ceiling joists essentially extending the wall insulation up farther. The though of insulating both above and below the original flat roof seems enticing but I'd be worried about sandwiching moisture in between.

Do any/any combination of these options seem like a reasonable solution to my dilemma? In an ideal world I'd like to gut the whole house and encapsulate it with a spray foam type insulation. Unfortunately that's not in the budget.

Any and all advice would be appreciated!


Re: 1953 ranch with two roofs and no insulation

Personally I would go with option 3.


Re: 1953 ranch with two roofs and no insulation

I would go with #3 too for the reason that it would be easier to install and to be sure the insulation has full coverage.
There could be blocking or bracing in the original flat roof that could impede the blown in insulation in #1.
Plus there would be no holes in the ceiling to patch as there would be in #1.
#2 looks like it would require removing and reinstalling the ceiling and may not have enough insulation. Too much work.
As a plus recessed lights could easily be installed within the heated envelope.
Nice diagrams by the way. They explained it all.

Re: 1953 ranch with two roofs and no insulation

Hi, You are in good shape because you can turn the flat roof into an attic platform. The platform needs to be sealed with 2 layers of insolation with a dead air space between them. Hot air is lighter than cold air so you have to overcome gravity and pressure to keep the heated air inside. A house needs to breath so don't worry about the walls yet. I would use a paper vapor barrier because plastic doesn't only stop water vapor, it traps all vapors in the house. Thanks

Re: 1953 ranch with two roofs and no insulation

Option 3 would be the easiest and least expensive and actually work the best, but you give up attic storage. Either option 1 or 2 will work only if you either remove the old roof sheathing or drill lots of holes in it for ventilation. If you do that, you will have about a 10% reduction in R-value due to rafters, especially if the tops of the rafters are exposed.

You can avoid the baffles in option 3 if you use batts and cut a taper in the ends where they approach the roof. If you blow in, then you will need the baffles.

Edit: How did you do those drawings and get them into the post?

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