Attic ventilation brick house

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Old 04-12-13, 09:24 PM
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Attic ventilation brick house

Hi- I have an approximately 60 year old brick house with no soffit vents nor space for them. On the side of the house at the peak of the roof there are openings in the brick 4x2 bricks wide on each side of the house as vents. I'm wondering what is the best way to ventilate the attic to obtain better second floor temperature. Do I knock out the bricks, install gable vents and put in fans or do I simply install the fans over the brick holes? Or do I install a roof fan?
 
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Old 04-13-13, 03:47 AM
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What do you mean by better second floor temperature? Is it too cold or too hot?
 
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Old 04-13-13, 05:40 AM
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Too hot in the summer.....
 
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Old 04-13-13, 09:18 AM
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Do the missing bricks make a hole all the way into the attic? I'm not a brick man, but bricks use a drainage plane (a gap) behind them to allow them to dry. I'm wondering if those missing bricks are part of that function?

I assume your attic is getting very hot. Is this a wide open (unfinished) attic? How well is the attic floor insulated?

Using attic fans can be a problem if you are air conditioning the house and it is not air sealed between house and attic. A fan exhausting hot air needs a larger open area to allow cooler air to come in and preferably, that cooler air needs to be directed to the soffit area.

One sq ft of net free vent area for every 150 sq ft of attic floor. Half high and half low is the typical old house vent recommendation.

Bud
 
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Old 05-22-13, 12:18 PM
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Here's what the brick openings look like on both sides of the house. So if you can picture the whole roof... there's no ridge vent and no soffit vent (or space for them-no overhang).

I'm wondering if I put a 1200 CFM fan attached with a plenum and mount it on top of the holes it'll work..

Otherwise, do I try and knock some of the bricks out of there to add additional area for in/out air flow with the fan?
 
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Old 05-22-13, 02:03 PM
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If your attic has 1,000 ft² of floor space and is an average of 4' high you have a volume of 4,000 ft³. With a 1,200 cfm fan blowing at those opening let's assume you achieve 400 cfm of exhaust. That would mean you will replace all of the air in that attic every 10 minutes. If the opening were large enough for the fan to operate at full capacity you would replace all of the air in 3.5 minutes. In either case, I doubt you need that large of a fan.

However, there is a down side to using a fan. If you have not addressed all of the leakage between the house and attic, and there is always a lot, you will be pulling conditioned air (assuming you run an air conditioner) from the house into the attic. Research has shown this to result in more loss than gain.

If you go with a fan, increase the openings and reduce the size of the fan and provide a larger opening for fresh air to enter. Keeping the path as open as possible reduces the negative pressure created inside.

Bud
 
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Old 05-22-13, 02:12 PM
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Bud
Thanks for the response.

The floor space up there is somewhere in the 600-800 ft^2 range.

I'd rather not get a big fan, but it seem as though the only ones listed at HD, Lowes or on Amazon are in the 14"+ range. Any other ideas on something reasonably priced?

To address the sealing issue, all I need to do is the ceiling penetrations, right?

Finally, knocking out the brick won't cause an issue? Thoughts on that?
 
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Old 05-22-13, 04:14 PM
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Here's some more reading for you. The first half deals with whole house fans. The rest talks about powered fans.
Fans in the Attic: Do They Help or Do They Hurt? | GreenBuildingAdvisor.com

As the article will suggest, insulation on that attic floor is far more important than ventilation. Plus it is easier to install and doesn't use electricity. I see your attic is serving as a storage shed. Could you add a couple of inches of rigid foam board. Actually, what is there for insulation should be the first question? Then, can you add more?

Bud
 
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Old 05-22-13, 07:59 PM
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Thanks for the link...

There's almost no insulation under those boards so my plan was to take them up and spray in cellulose to the height of the rafters then put them back down. I realize that isn't ideal in terms of recommended height, but we really need the space for storage.

I was hoping that coupled with a gable fan would improve the second floor temp, which is completely unbearable.

Any thoughts on removing some of those bricks to make for a larger space to move air when/if I add two gable fans (one per row of bricks).
 
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Old 05-23-13, 12:28 AM
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I would install some insulation first and see how it performs. Do you run air conditioning? If so, once you insulate you will see a huge difference. If you spray in foam, be sure to protect electrical boxes from being buried. Spray foam can be expensive as well. An insulation product that is a bit less expensive but works well is mineral wool (ROXUL). very dense and can be detailed into place for a good installation.

But adding insulation will make a difference, more so than the fans.

Bud
 
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