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Attic Floor Joist Insulation & Vents?: Best method?


CaliforniaSteve's Avatar
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09-19-03, 03:52 PM   #1  
CaliforniaSteve
Attic Floor Joist Insulation & Vents?: Best method?

I have a 3 unit apartment bldg which hasn't any insulation in the walls or the ceiling. Since I'm in California where the temperatures are usually around 70 degrees most of the year and don't very more than 20 degrees it hasn't been too much of a problem. Still, I'm about to reroof the bldg and want to add attic crawl space floor joist insulation during the reroofing job in order to make it cooler in the summer for the tenants. I also want to add roof turbines and drill eave vents for proper attic ventilation in order to release the heat above the insulation so that it will not radiate into the top floor bedrooms.
1)Any suggestions out there on which type of insulation (batts or blown in fiberglass or cellulose--someone suggested Cocoon cellulose insulation?)
2)Any suggestions on what type of non-electric attic ventilation should be used and the quantity for the 2400sq.ft. attic crawl space? Should I drill eave vents or use dormer/eyebrow vents for the intake on the lower part of the roof and turbines on the top? How many of each should I use? Or do you suggest other vents?
Thanks!
CaliforniaSteve

 
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09-19-03, 04:36 PM   #2  
I'm a big believer in RADIANT BARRIER, with RIDGE AND SOFFIT vents. Radiant barrier will keep lots of the heat out, ridge and soffit vents are the best way to keep the air moving THROUGHOUT the attic space, turbines and gable vents don't do either.
All three are relatively inexpensive (I realize nothing in California is inexpensive) to do when re-roofing. 3 years ago we re-roofed a house in the Bay Area, we removed enough decking to get into the (relatively low sloped) attic. We spray painted the paint type of radiant barrier as all of the deck was in good shape and it was made of 1 X 6 so easy to remove small areas for access. IIRC our total (extra) cost of materials for the paint, ridge vents and soffit vents was about $300, (the paint was about $35-40/gallon). Since the roofing material was about $1500 and the dumpster was another $150-$200 I thought that was pretty good.

BTW, this house is in the East Bay, where summer temperatures are routinely in the 90s and 100s.
This is a house that I've had as a rental since 1978 and since then it's noticeable cooler in the summer and tenants no longer suggest that I add central air. It has a window unit in the den and another in the master bedroom. I consider it money well spent. It's also something I do to every house I've re-done in Texas.
Frank

 
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09-19-03, 06:06 PM   #3  
CaliforniaSteve
Roofing and attic/crawlspace insulation

Thank you SlumlordFrank for the info, but I need clarification. You mentioned using radiant barriers and then you write that you sprayed it on? I thought the only radiant barrier was a mylar-like vinyl sheeting that was stapled underneath the studs holding up the roof? How then can it be sprayed on?
Also, some roofers are telling me that the eave vents let way too little of the air seep through the top and that the turning turbines at the top create a vacuum sucking the air out at a heavy rate as the air gets hotter in the attic space. Is this true?

 
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09-22-03, 06:29 AM   #4  
Sherwin Williams distributes a radiant barrier paint although IIRC it's also available elsewhere, I think the name is "Radiance", try a web search. I think it was about $35-$40/gallonI had a relatively low pitch so attic access was a problem. Also, radiant barriers are only effective if there is direct sunlight, if you have lots of shade they're not real effective.

From all the study I've done ridge and soffit vents done correctly are not only more effective they look better too. I think the State of Florida web site may have been where I found some of this. Too many roofers just continue to do what they've always done without ever researching new methods. I've even heard lots of roofers say that ridge vents leak in rainstorms and can't withstand snow!! If that were the case they wouldn't be as popular in Alaska and Colorado as they are.

Turbines would need to be place about every 12 to 18 inches to provide enough area to vent the typical attic, and they would still need to have soffit vents to let air in at the BOTTOM. Think of the airtightness of the old VW Beetle. Gable vents can only provide cross-ventilation, nothing from the bottom to move air through in a continuous stream, in fact if you have gable vents and install ridge and soffit vents you need to close off (I just use saturded felt board on the inside) the gable vents or they can reduce the effectiveness of the ridge vents.

I've lived in Texas for 25 years and most of that time was in Houston, our A/C season ran from late March until October, so reducing our A/C bills was a real concern. In addition to the above items we also used SOLAR SCREENS (not the film crap) on all of our West and South facing windows. The important thing with heat is keeping it out to begin with. When I moved here in 1978 most new houses were being built with 6" fiberglass batts in the attic, the last house I had in Houston was built in 1990 and it had about 16" batts. The house we moved into this spring was built in 1982 and the first thing we did was beef up our insulation. The radiant barrier has to wait due to some other things I am doing to the house right now. But I'll probably do it over the winter. My electric bills are about 1/3 lower than the previous 2 years averaged.

BTW, the radiance paint is also available for interior applications and can be "tinted" for ceilings and walls if attic access is impossible as in cathedral ceilings.

Good luck

Frank

 
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