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Old 06-15-2010, 12:16 PM   #1
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1971 Mansard Attic Ventilation Nonexistent


HI,

I am trying to improve my attic ventilation on my 1971 mansard. Currently I have 4 exhaust vents, but the inlets at the bottom of the mansard roofline (under gutters), do not actually vent into the attic space under the roof line.

I am looking at removing the fascia board where my roofline flatness out from the side of the house, but I am trying to determine the best way to do this. I have found an option made by GAF, called a Cobra Fascia Flow intake vent system. But they recommend 43' of venting, and at $125 dollars a piece this is an expensive option, about $527 after tax. Plus it only comes in white.

My attic is about 130-140 degrees during the summer and my house will not cool under 80 degrees during the day. I have a baby on the way, and her room is about 85 during the summer. I can't put her in their if I cannot figure this out.

Please help!

Thanks,
Brian
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Last edited by 1971Mansard; 06-15-2010 at 12:20 PM.
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Old 06-15-2010, 12:51 PM   #2
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1971 Mansard Attic Ventilation Nonexistent


How well is the attic insulated?

I'm guessing that the area between the steep slope of the roof and the interior wall is probably not connected to the lower pitch attic area.

Some at this forum are advocates of edge venting. I've never used it, but it might be an option for the upper roof edge.

Another option would be to add some type of dormer vents.

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Old 06-15-2010, 01:46 PM   #3
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1971 Mansard Attic Ventilation Nonexistent


Yes th events at the bottom of the roofline, which were meant to vent into the attic were blocked at some point at the slope change on the roofline.

I have about 6" of insulation in floor of the attic.
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Old 06-15-2010, 01:58 PM   #4
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1971 Mansard Attic Ventilation Nonexistent


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Originally Posted by 1971Mansard View Post
Yes th events at the bottom of the roofline, which were meant to vent into the attic were blocked at some point at the slope change on the roofline.

I have about 6" of insulation in floor of the attic.
I'd pursue adding more insulation, ie, blow in cellulose (at least 6") over the existing. You don't say where you're located, but you must be at least kind of south with that cooling problem.

Are the exhaust vents on the rear plane(s)? Maybe add some more down lower for inlet. By adding insulation, you reduce the need to get the heat out of the attic. You also reap the benefit of less heat loss in winter. It does need some venting to remove any moisture that escapes from the living space.

Got pull down attic stairs? How well are they sealed?
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Old 06-15-2010, 02:00 PM   #5
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1971 Mansard Attic Ventilation Nonexistent


I just got off the phone with a roofing subcontracting. He did not believe that adding inlets would provide any improvement to the temperature inside of my house, that the only option would be to add a dedicated AC unit outside for the 1st floor.

This is contrary to what I have heard on these forums. I have had an AC crew look at by HVAC system and they said my AC output should be enough to cool my first floor.

thoughts?
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Old 06-15-2010, 02:24 PM   #6
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1971 Mansard Attic Ventilation Nonexistent


Quote:
Originally Posted by 1971Mansard View Post
I just got off the phone with a roofing subcontracting. He did not believe that adding inlets would provide any improvement to the temperature inside of my house,that the only option would be to add a dedicated AC unit outside for the 1st floor.

This is contrary to what I have heard on these forums. I have had an AC crew look at by HVAC system and they said my AC output should be enough to cool my first floor.

thoughts?
I would tend to agree to a point. But the reason it's so hot upstairs is that the heat from the attic is coming through the inadequate insulation. Before I bought more AC equipment, I'd try the cheap, relatively easy fix that will benefit you year round and also benefit you even if you have to get more A/C equipment. Add some insulation.

I had a similar problem. 6" of chopped fiberglass and a 25 year old A/C unit that could barely keep the house tolerable running full blast all day long. Blew in 8-12 inches of cellulose on top of the fiberglass on a 95 degree day. It was 79-80 degrees in the house when we started. 4 hours later when we finished (about 2PM on a sunny day), it was down to 76 degrees and the A/C was cutting off occasionally.

If there ever was a DIY project, blowing cellulose in an attic like yours is it. I'd remove a few shingles in several places and cut some holes in the sheathing and blow from outside. Patch the hole back in, replace the shingles and move to the next spot. Or hire it out.

If the added insulation doesn't get it cool enough, pursue the second A/C unit. I bet you don't have to.

Have the HVAC guys looked at the air returns? The system may be unbalanced.
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Old 06-15-2010, 02:24 PM   #7
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1971 Mansard Attic Ventilation Nonexistent


No, I dont have any pull down stairs, unfortunately.

I will definitely be blowing more insulation, any idea on how much that costs (1400 sq. ft.)?

I do still want to add inlet vents at the eaves though.
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Old 06-15-2010, 02:24 PM   #8
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I cant help too much with the question but your house is beautiful.

Shane
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Old 06-15-2010, 02:46 PM   #9
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1971 Mansard Attic Ventilation Nonexistent


Quote:
Originally Posted by 1971Mansard View Post
No, I dont have any pull down stairs, unfortunately.

I will definitely be blowing more insulation, any idea on how much that costs (1400 sq. ft.)?

I do still want to add inlet vents at the eaves though.
A bale (16 cu ft) runs about $9 locally. 40 bales would give you 6"-8"+ of additional insulation (10" of cellulose is R38, IIRC). The big boxes will "lend" a blower if you buy the bales from them. So, it looks like about $360. Probably a little over twice that to hire it out.

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I cant help too much with the question but your house is beautiful.

Shane
That is a nice looking house.
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Old 06-15-2010, 03:11 PM   #10
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1971 Mansard Attic Ventilation Nonexistent


There are many reports on the Web about attic ventilation and it depends on several variables. Some reports may disagree with others for reasons known or unknown.

You could also ask each contractor what he bases his choice on.

I'd probably rent a fan, make a temporary exhaust and intake vent and determine how many air changes per hour you need to do a reasonable job of lowering your room temps, on a typical sunlit, windless day in your area. If there is no noticeable room temp. difference at high CFMs at mid afternoon you'll need some other method.

I see that you live in a place with seasonal change. To some extent your latitude will affect your results.

Last edited by Yoyizit; 06-15-2010 at 03:15 PM.
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Old 06-15-2010, 07:59 PM   #11
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1971 Mansard Attic Ventilation Nonexistent


You would need to inastall a continuous exhaust vent at the top of the mansard wall and also a continuous intake vent system at the bottom of the mansard.

Before they had such a product available for the mansard wall exhaust application, I re-configured an existing piece of Shingle Vent II for that type of application by cutting it in half length-wise and then covering it with a new fascia board and the upper low slope roof sheet metal counter-flashing.

Now, Smart Vent from DCI Products Inc. makes a product that would work, so i would purchase that instead of doing it my old way.

Ed
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Old 06-15-2010, 08:02 PM   #12
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Here are some photos.
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1971 Mansard Attic Ventilation Nonexistent-muhr-004-resized-wall-vent-svii-forums.jpg   1971 Mansard Attic Ventilation Nonexistent-muhr-005-resized-wall-vent-svii-forums.jpg   1971 Mansard Attic Ventilation Nonexistent-muhr-008-resized-wall-vent-svii-forums.jpg   1971 Mansard Attic Ventilation Nonexistent-muhr-010-resized-wall-vent-svii-forums.jpg   1971 Mansard Attic Ventilation Nonexistent-muhr-013-resized-wall-vent-svii-forums.jpg  

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Old 06-16-2010, 10:32 AM   #13
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1971 Mansard Attic Ventilation Nonexistent


Thanks Ed the Roofer. Great Pictures.

What are your thoughts on the Roofing Contracter I talked to saying that attic ventilation will not help lower the temperature in my house? He says I need a dedicated AC unit. I live in Kentucky... I have already shut off all of the vents in my basement and it was still 82 F in my house when I got home last night.

Thanks,
Brian
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Old 06-16-2010, 07:40 PM   #14
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1971 Mansard Attic Ventilation Nonexistent


The 2 elderly women who live in that home could not even go upstairs due to the extreme heat issues they experienced.

But, if you noticed, the top roof was a flat roof versus a sloped shingle roof. We installed a white thermoplastic single ply Duro-Last membrane roof on that instead of the previous black hot asphalt roof material they had, which had to decrease the heat absorbtion significantly.

But, all in all, the comfort factor that the two women enjoyed after we did their roofs completely enhanced their living comfort conditions tremendously.

Ventilation and color of the roof surface, as long as it is not black will do you plenty of good.

I am glad you like the photos!!!

Ed
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Old 06-17-2010, 11:30 AM   #15
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1971 Mansard Attic Ventilation Nonexistent


Brian, I'd add this type of radiant barrier: http://www.atticfoil.com
If you have access into attic, all you need is a staple gun to put this up along the rafters. I did our house last year in the fall and it's made a world of difference. Also add more insulation in your attic...6" just isn't enough. The great thing about the foil is that the attic stays cooler, so your ductwork is cooler. Another thing I'd consider, for summer anyway, is getting solar screens installed. Easy DIY since all your windows look the same size. Your main goal should be keeping heat out because this will ease load on your a/c. My attic never gets over 115*

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