How to insulate exposed joist ceiling


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Old 05-25-14, 11:46 PM
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How to insulate exposed joist ceiling

Hello , my first post so be gentle I am renovating my spare bedroom and want to do something cool , so I decided to leave ceiling joists exposed and put wood panels on top of them , there is only attic above no floor. Now I am not sure how to insulate this all , where to put vapor barrier etc. Thank you for help - Rob
 
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Old 05-26-14, 03:56 AM
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Your wood panel will be your inside ceiling and everything else will have to go above, except for some insulation at the exposed ends of each joist cavity. Vapor barrier on top of the wood panel with all seams taped. Also tape any staple holes so it becomes your air barrier. Then lots of rigid insulation on top of that. I don't know your area in CA, but probably 18" of Roxul cross stacked.

Baffles in the eaves to allow ventilation from the soffits yet get as much as possible insulation over the outside walls.

Since this is probably not the entire attic floor, install small vertical retaining walls to contain the insulation allowing the added insulation to overlap other insulated areas.

Watch for air paths that allow flow into adjacent cavity spaces or into the attic, air tight is a must.

Bud
 
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Old 06-04-14, 12:46 AM
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Thank you for reply. I gutted ceiling this weekend and must say this will be a bit "headscratcher" for me. In corner between wall and joists (please see photo) is only little room to insulate so I will have to do small soffit, vapor barrier will be very hard to seal in that spot. Also note that attic in this old house is not vented thru soffit. Next worry is how flammable this whole setup will be... wood panel and rigid insulation seems to be very flammable combo, should I somehow stick with 5/8" drywall between joists instead? Sorry for all these questions, I would really love to keep joists exposed for that special look. House is located in Victoria BC so cold is not as much of issue here. Oh and room is only 10x11 ft. Thanks again for help.
 
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Old 06-04-14, 07:41 AM
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I'm scratching my head as well. I don't see an immediate option for soffit (low) venting. Is there an overhang outside that could provide a protected vent area if you opened a path through the top plate area?

Do you or will you have high venting somewhere. Maybe some wider area photos would help. Outside as well.

Bud
 
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Old 06-04-14, 10:12 PM
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OK , here are two pics. Since there is no soffit vent somebody installed vents low and high... when I gutted room there was no evidence of moisture or mold anywhere - no vapor barrier and insulation missing on top of the wall = old school but it worked over 70 years! I am still not sure if I should put drywall in between joists or wood on top, I like more wood on top since I will be able to walk on it with no worries and it should make whole thing much stronger , I just have to use silicone to seal tongue and groove so there is no air leak. I will have to make soffit inside because as you can see on previous pictures in corner where ceiling and wall meet there would be only 3 1/2" for insulation. I know in my case it is hard to help, but any thoughts are very welcome Thank you for help - Rob
 
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Old 06-05-14, 12:23 AM
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I have visited many very leaky old homes that have had no moisture problems for all of their existence. The challenge is converting them to be more energy efficient, which includes air sealing. At today's energy costs people can't afford to be heating the great outdoors through those leaks.

Insulating the attic floor AND using that space for storage doesn't work together. 16+ inches of insulation with a walking deck several inches above that is rarely what people envision. But that is what our northern climates need. Below the insulation there needs to be a good rigid air barrier and a vapor barrier in close contact. Decking over that space above the insulation provides a potential condensation layer.

Let's see if others jump in with any additional advice.

Bud
 
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Old 06-05-14, 12:53 PM
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So here is my plan on picture. I do understand to your concern about heating great outdoors now , also I don't plan any storage or floor above - space in attic is too small for it anyway, I just wanted to say that if I use wood on top of joists and somebody/me will be walking for some reason in attic I don't have to worry about "going thru ceiling in that area. I will update here with pics , just need to pick some wood in lumber store and insulation. Does that picture make sense to you? Also looks like that extruded polystyrene is not flammable? Thank you for help - Rob
 
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