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bduncan118 01-21-2013 06:31 AM

Insulation Question
I've got a question for you good people. I am building a room in my attic. I live in hot south alabama. It gets scorching hot upstairs. I am wanting to use r19 as insulation. The walls in the room will be 2x4's. All walls with the exception of 1 will be unfinished on the outside. My thought process is to put the insulation in the 2x4 cavity and the outside of the wall will have the overflow. The one wall will be sistered up to another wall that is a 2x4 wall so the r19 will have no problem in there. Is this OK to do? I want the best insulation in the room possible. Thanks for your time!

md2lgyk 01-21-2013 06:36 AM

What insulation is in the ceiling?

bduncan118 01-21-2013 06:40 AM

Anything I want to put in it. Any recommendation?

Taylor Rae 01-21-2013 08:55 AM


Originally Posted by bduncan118 (Post 1098454)
Anything I want to put in it. Any recommendation?

As much as possible.

Gary in WA 01-21-2013 07:58 PM

R-30 is recommended for your location;


Now that the attic is a "habitable space" --- egress door or window is required, as are smoke alarms, permanent stairs, correctly sized floor joists, etc.;

You want to separate the knee wall from attic air wind-washing it, degrading the R-value. Air seal all attic penetrations (wiring/plumbing holes) from below with canned foam/tin; Caulk the knee wall/floor joint, per code, establish the air/thermal barrier to get maximum gain from your insulation.


bduncan118 01-21-2013 08:16 PM

Gary, thanks so much for the input. I am putting an egress window in. There are already full size steps going to the second floor. There is already 1 bedroom up there and the attic is a walk in large room. The flooring is already down. This happened during construction. My builder is writing me a statement expalining the framing is 2x10 16" on center for the floors. He said that may or may not satisfy the building inspector.
There are no knee walls. The ceilings will be 8 ft high with straight walls. I could go 18ft ceilings if I wanted too.
So I think my original question is still unanswered. Can I use a higher r rating if it doesn't bother anything sticking out the back of the framed walls?

carpdad 01-21-2013 08:43 PM

2x10 is good for the floor, but what does it mean that it may/may not pass the inspection? Span is important here, not how big the lumber is. I think you want your builder to make this clear.

For you, you want the hot air to move out. I would put roof or gable fan with big enough supply intake on opposite end. Put baffles where roof rafters meet wall studs so that supply air can travel to the vent fan. If you have at least 6" of soffit, consider using full vent vinyl soffits. These are vinyl soffits that have holes on entire surface.
With good ventilation, r13 for walls and r30 for ceiling is good. Without the vents, no amount of insulation will keep it cool enough. Fiber glass insulation works best in a dead space. Any air flow over it will diminish its function. You might consider foam panel (dont go up to roof deck) on outside of the knee wall then r13. Then r30 or 40 dense pack cellulose on ceiling.

bduncan118 01-21-2013 08:54 PM

Sorry I should have been more specific. I meant that the inspector might not make me have an engineer come sign off on the floor. These are some pics of the area

Here are some links to some pics of the area I'm building.

Gary in WA 01-21-2013 09:25 PM

From the pics, it appears the 2x4 vertical temporary braces/supports can be removed from under the ridge board, as you probably knew already.

You need to air block the small attic (at soffit vents behind full wall) from outside air going under the flooring with solid blocking or foamboard.

Best is f.b. on the attic side of the wall (mastic/taped against air infiltration) with/without an ignition barrier, depends on your inspector and local code for your state. Foamboard links;

Any fibrous insulation sticking out the back of the wall is subject to air infiltration, which goes right through it easily (think furnace filters). You want it covered-air tight. Using f.b. as a cover on the attic side stops moisture/air from readily passing in bulk- trying to get to the cool room/drywall/cavity- to condense summertime moisture in the air.

How deep are the soffits and what type of vents exist now?


bduncan118 01-21-2013 10:06 PM

Im unsure of the soffit size. There is already one bedroom on the same floor. So Im thinking the venting is done already. The builder built the attic ready to be framed on top of.

I am all about moving the post but was unsure if it was safe to do that. I could get a 21x14 room out of it if i did. Instead of 10x21. There are similar posts running across the house. 3 or 4 of them.

Gary in WA 01-21-2013 10:16 PM

Better pictures would help....


bduncan118 01-21-2013 10:18 PM
A video of the attic
3:30 on goes upstairs

Gary in WA 01-21-2013 10:56 PM

Thanks! It appears to me those 2x4's are just temporary supports the framers used to hold up the sections of ridge boards. They are probably placed close to the same end on each section of ridge. Then the framers could add opposite rafters to the board and just left the 2x's there afterward. The furnace ducting is supported on one, leave that alone as I doubt it is your plans over that area anyway. The two in middle of the room and one from gable end wall can remove. Leave the built-up beam (purlin) alone- it is supporting the rafters, shortening their total span. I saw on big section of louvered/screened soffit venting, are they placed throughout the perimeter? I ask because if vinyl with the punched holes- are only 4.65 per foot, to match the ridge would require at least two foot deep soffits for a balanced system. Pics of the soffits exterior would help--- if interested in attic ventilation system other than builder said "meets code"... Nice attic dormer (w. window)...


bduncan118 01-22-2013 06:29 AM

1 Attachment(s)
Here is a pic of the outside soffit. It runs the entire front and back of the house.

md2lgyk 01-22-2013 07:32 AM


Originally Posted by bduncan118 (Post 1098454)
Anything I want to put in it. Any recommendation?

What size are your rafters? To put in air baffles and R30 insulation you really need them to be 2x12s.

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