Do I need to follow the insulation code in any circumstance?
I am converting the sun room to bedroom.
The room is isolated from main building and faced with garage. Only 200sqft room.. no bathroom will be installed in the room.
The room have nothing but the roof above.
I want to insulate the ceiling ( roof sheathing ). This is in Chicago so.. requirement is R-48. However, in this case, I need to lower the ceiling and the cost is about $1000.(including material and labor) because my rafter is only 3.3 inch depth. Therefore, I called Insulation company. the service guy told me that I dont need R48 for this particular room. R19 fiberglass is enough.. I was surprised because my all problem can be solved. Is it true???
If so,, I can save lots of money and time.
Please give me an advice…
If I have to follow the code, then I need to install the drop ceiling. In that case what is the proper insulation technique for the ceiling?
Thank you for your advice in advance.
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In general, if the space is going to be actively heated & cooled, it has to be built to code. If it is not actively heated and cooled and is doored-off from the fully conditioned space with an exterior-grade door, it doesn't usually need to meed code for R-values.
If engineering calculations can demonstrate that even though it's less than code it still meets the overall energy use performance requirement the prescribed R-values can usually be ignored, but would usually require sign-off by a registered qualified engineer.
Your local building department should be able to spell out the requirements for your project, but if it's going to be a bedroom you may have to apply for a variance based on how practical it is to make it meet code for R-value. If the thermal performance of the newly upgraded room isn't terrible at R19 it's likely to be granted. You may be asked to replace some of the window area with insulated wall, or increase the wall-R to make up for the lower performance ceiling.
R19 fiberglass is about the worst insulation product out there (except for radiant barriers), and has to be installed with air-barriers on both sides. When compressed to 5.5" (as in a 2x6 framing cavity) it only performs at R19, since the R value is tested when it is ~6", and not compressed. In a Chicago climate any fiber-insulated roof would also need to have 1" of space between the roof deck and the fiberglass. This may be one of the rare instances where it's worth going with 3-4" of closed cell spray polyurethane (at $3-4 per square foot). If you do that it can be applied directly to the underside of the roof, and would provide structural strength as well.
If you can find an installer, it's much greener use a water-blown product such as Icynene MD-R-200 or MD-R-210, which run about R5/inch, but don't use the climate-damaging HFC245fa blowing agent.
http://www.icynene.com/sites/default/files/downloads/ProSeal%20Eco%20MD-R-210%20Technical%20Data%20Sheet_August%202013.pdf
http://www.icynene.com/fbdocs/MD-R-200-USAProductInformationApril2013.pdf
(Do not confuse this with the higher-performance MD-C-200, which is blown with HFC245fa.)
With 3-3.5" of MD-R-200 fully filling your rafter bay cavity you have sufficeint R value to add up to R30 in fiber below that. But since you don't have the space, installing 2x4s perpendicular to your rafter beams and adding R15 rock wool or fiberglass would also do, bringing the center-cavity R to about R32-R36, and would have less thermal bridging than R38 between 2x12 rafters. With the low thermal bridging it would come close to meeting code performance, while only lowering the ceiling by 3.5". But that much spray foam is expensive, and it would have to be installed in two 2" lifts with a cooling time between lifts. for a 200 square foot ceiling it could easily be $800 or even $1000 just for the foam, depending on how competitive the local market is. But with ~3" of foam and 2x4s spaced 24" on center perpendicular to the original rafters with R15 batts you will have roughly double the performance of R19s.
If I recall from your other thread the rafters are not on a standard spacing, which would make any batt-insulation solution between those rafters difficult (impossible?) to do well. But if batts are the only affordable solution, rather than R19s you would be much better off using R23 rock wool, which is manufactured at 5.5" thickness, (not 6"), and is higher density, making it far more air-retardent than the low-density R19 batts.
Whichever approach you take it will be more complicated and expensive than the typical vented-attic. Sugo haseyo!
Mansig Yoon,
This is a green building site. We assume that if you are posting questions here, you care about energy conservation. For energy conservation, it's best to install at least the minimum amount of insulation required by the building code. You can probably get away with less insulation, however, as long as your local code authority either agrees or looks the other way.
I would be worried about any contractor who urges you to insulate this ceiling with R-19 fiberglass. If the fiberglass insulation is installed wrong (without a proper air barrier and ventilation channels), this approach can lead to moisture accumulation and rot.
Good luck.
Mr. Dana,
Thank you for your great advice.
It is always great help for me. My original rafter's are 4 by 4 so.. the depth is only 3.5inch.. I can't install R23. However I can install 3 inch form (is this EPS or XPS? ) In the previous discussion, you recommend me to use EPS. I wonder why you recommended it? is there any practical reason?
By the way, If I lower the ceiling with 2 by 4 24 inch spacing or with drop ceiling.. I can use R15.
Practically.. I have lots of 2 inch PolyISO) and I bought lots of R19 batt for the insulation too.. so I wonder if there is anyway to use it with EPS for the insulation. Is there any alternate way to seal air instead of spray foam(this stuff is not cheap.)?
Mr. Martin,
Thank you for your advice. I will not go with R-19. My dream is gone with your advice. I consider him as a professional.. Therefore, I asked him if it works or not several times... ..
Mansig Yoon,
Here's my advice:
1. You need framing members that allow you to install ceiling drywall. Ideally, these framing members should be 16 inches on center. One way to accomplish that is to strap your ceiling with 1x4s. These 1x4s are installed at 90 degrees to the existing rafters. (You could use 2x4s instead if you wanted more depth.)
2. You should insulate your roof with closed-cell spray foam. If you can't afford closed-cell spray foam, you should probably use the cut-and-cobble method (rigid foam with air sealing at the perimeter of each piece of foam). I don't like to advise the use of cut-and-cobble insulation for unvented roof assemblies, because there is a risk of moisture accumulation if the air sealing is imperfect, but you have a unique situation. Moreover, you keep coming back with reasons why it is impossible to insulate this roof by conventional means -- so you'll probably end up compromising, one way or another.
The R23 recommendation was only because you were talking about installing R19s, which would also need a a 5.5" deep cavity. The difference in performance is more than the R4-R5 difference in labeled R-value implies.
If you are going to use rigid foam anywhere under the roof deck without venting the roof, it has to be sufficiently vapor permeable to make it a drying path for the roof deck, but sufficiently vapor-tight that it doesn't raise the moisture content of the roof too high over the course of a winter. Polyiso of any thickness with foil facers is WAY too vapor tight for drying. But 2-4" of unfaced EPS (no thin plastic or foil laminated to either side) would have a reasonable water vapor permeance range. At long as it is perfectly air tight it can work well, but it has to be perfect.
Even after you seal the rigid foam in place well with can-foam, it is worth installing a flexible vapor permeable or semi-permeable sheet-membrane type material on the room side of the insulation to create a near-perfect air barrier. Relying on the can-foamed seams to stay air-tight forever may be too optimistic. While polyethylene sheeting would be flexible enough, it is far too vapor-tight. But a "smart" vapor retarder such as Intello Plus or Certainteed MemBrain would work. These materials become more vapor-open if they need to let moisture out, but are otherwise fairly vapor tight. In your case your primary interest in them would be as an air barrier with very few seams to seal. (Menards sells 8' x 100' sheets of MemBrain on their retail web-site, but don't always stock it in stores. It comes in wider sheets than that, but you'd have to find a distributor who handles it. 475 Building Supply sells Intello on their web-store- it's more rugged than MemBrain, also more vapor tight. Either will work.)