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cp31817 04-29-2012 09:27 PM

Attic ventilation and Whole House fan
Hello everyone,
I have some questions regarding proper attic ventilation and do I have enough ventilation for a whole house fan. I live in Temecula in Southern California. The house is 5 years old. I will apologize in advance for the length of this post.

My attic is 2068 sq ft. for easier calculations I will use 2100 sq ft using the 1/150th rule = 14 sq feet of ventilation needed x 144 =2016 sq inch = 1008 sq inch of intake and 1008 sq inch of exhaust. (This is Net Free Area)
Intake:I have 2 gables at each end approx 12x18 (in the picture it looks to me like two side by side gables not just 1 large one) So using calculations from airvent 12x18 x 4 vents = 864 x .5 = 432 sq inches of nfa intake. I also have one small gable on the front of the home approx 10x10=100 x .5 = 50 sq inches of nfa, So total intake is 482 sq inches of nfa.
Exhaust-I have 5 under-eave vents only located on the back side of the house. 12 x 4 x 5 vents = 240 x .5 = 120 sq inches of nfa.
Now IF my calculations are correct this is way under what we need for proper attice ventilation. I have intake of 482 sq in nfa and exhaust of 120 sq in of nfa. even If I was not to calculate net free area I would still be short.
Are my calculations correct? Am I missing something? Are maybe one of those pipes sticking out of the roof ventilation? Thank you very much for any help. I am driving my husband crazy doing calculations and researching. I have posted the pictures in my photo album. Thank you for your help

cleveman 04-29-2012 10:49 PM

I don't see anything wrong with your calculations.

However, you refer to the gable vents as intakes and eave vents as exhaust.

I would think the eave vents are intakes as well as the gable vents.

Do you not have any vents on the roof, or a continuous vent on the ridge of the roof?

Funny, I always seem to have a hip roof with a continuous ridge vent. Then I special order a fully vented metal soffit panel. People have told me that the fully vented is not necessary, and that is why they stock the half vented. One guy told me that if I get that much air in the attic, it will never be exhausted. I just smiled and told him the wind blows where I live.

And that is a fact. Often when I'm installing the soffit, I'll be on the leeward side of the roof and I can feel the heat rolling out at me, through the attic.

And that cross-ventilation brings me back to your gable vents. These may be intake and exhaust vents.

Ideally, you should have soffit intakes and ridge exhaust. This will ventilate the entire roof through the rafter chutes. You won't just have air entering in the gable and going out the other gable, leaving the bottom side of the roof very hot. You will have air entering the rafter bays at the soffit, and racing up the rafter bay through the chutes, exiting at the ridge.

Your gable vents are like a guy shooting a stream of water right through your roof, and not getting anything wet.

cp31817 04-30-2012 09:12 AM

attic ventilation
yes you are correct the gables are exhaust and the under eave vents are intake :icon_confused:. I do get a very nice breeze here however it comes from the front of the house to the back, not from side to side. I do not have any type of continuous ridge vents of soffit vents. I don't think that I have any roof tile vents. When I poke my head in the attic I only see light from the 3 gables (see pics). I haven't even checked to see if the under eave vents are blocked! I am afraid of heights and just getting on that tall ladder is enough, and my husband feels I am over thinking the issue :laughing:. Do you know what some of those vents on my roof are? Could they be exhaust vents? If they are would you know how much they vent?
However I am worried if i install a WHF that if my attic is under ventilated that I will have more problems (blow back...pressure). We purchased this home new and my warranty states it is a 10 yr warranty.....but I wasn't sure if the 10 year warranty covered not enough vents. I just didn't want to call and stir up things to find out that my attic was properly vented. This certainly is not my area of expertise.

cleveman 05-01-2012 07:55 PM

I don't see any photos of your home.

Your "under eave" vents are soffit vents.

Are you sure you don't have a continuous ridge vent?

If you just have soffit and gable vents, I would pitch a ***** to the homebuilder.

One should probably have pictures before going further, but I think you want to get rid of your gable vents and go with a continuous ridge vent and enough soffit venting to make things work.

Do you see rafter chutes in the attic?

cp31817 05-01-2012 08:54 PM

poor attic ventilation

Cleveman can you see my photo album? Yes they are soffit vents.....didn't know that the two names were not interchangable 8|. No I do not have continous ridge vents!! I only have the 2 end gables and 1 10x10 front gable and a total of 5 12 x 4 soffit vents.....that is what started me down this yellow brick road seemed not enough ventilation after researching WHF and ventilation.
I called the roofing company who did the work hired by the builder...I have a 10 yr warranty on the roof through peaderson and dean. The representative stated that they had used O'Hagin's tile vents on my roof and most likely I did not know what to look for. I explained that my husband has been on the roof multiple occasions and although he was not looking for the these roof tiles I was fairly sure he would of noticed them.
She stated that there was no way they could have passed inspection with the city if they did not use them. I am trying to keep it civil and did not bring up arguments to the contrary.

SOOOO to appease me they sent out a person this a.m. The worker went into the attice took photos....saw NO baffles for the 5 soffit vents...and no o'hagin tile vents from the inside of the attic. He also went up on the roof and saw no evidence either!
It is doubtful that I will get ridge vents since it appears that the builder specified to use o'hagin's roof vents. So most likely that is what will be used. Many of my neighbors have these type/style vents and also eyebrow vents.

I went up on the o'hagin site and inputted my roof size and it stated that the tiles are to be placed near the ridge and near the soffitt. How close from the ridge and how close to the soffitt?? Also I have solar on one side of my roof......I am assuming they will need to uninstall the solar panels for proper placement...don't you feel that they are responsible to pay for this removal and replacement of the panels since it was their error in ventilation? Can you use o'hagin tile vents and gable vent along with soffit vents. I would prefer ridge vents and continuous soffit vents BUT I may not have that option but I will ask.

Thank you so very much for all of your help and input I am out of my area of expertise and I have spend soooo many hours on the internet trying to become informed. I am now attempting to locate the California bldg codes so I know what the laws are for minimal ventilation for the year my home was built. The house is approx 5 yrs old (I have lived here 4 yrs). I will keep you updated and thank you again for all of your help!

What is a rafter chutes????

If you cannot view my album please let me know!!

cleveman 05-02-2012 07:18 AM

I found your photo album and looked.

Your type of construction is more mediterranean than midwestern.

A rafter chute is some plastic or even cardboard insert which is stapled between the rafters (often 2x4 trusses) to keep the 3 1/2" x 14 1/2" space open for air flow. They are installed on top of the wall and are generally 4' long, so they run up the underside of the roof for 4'.

Here, we blow in about 17" of cellulose to get an r-50 value, and the rafter chutes keep the cellulose from plugging the rafter spaces or "bays".

If I remember your photos correctly, you have an open soffit. These would be full of wasp nests and bird nests here, so we don't use them. We put on a metal fascia cover, and a perforated or slotted metal soffit cover.

You will want to make sure that your soffit vents are open on the inside, and that air can flow through them up the rafter spaces and into the attic. You should be able to see some light coming from them when you are in the attic.

Your rafters are possibly much beefier in order to carry those roofing tiles. Are they concrete tiles or some composite material?

Anyway, you must have a very sturdy truss or thick rafters to carry that load, although you should never have any snow on the roof.

What type of insulation do you have in the attic?

That "chimney" looking stack is not for a fireplace? Is it just ornamental?

It makes sense that the roof tile manufacturer would offer some tiles with a vent. These probably cost more than the standard tiles. Your roof would require lots of them, and it would require no gable vents. In fact, if you use ridge venting, many would argue that the gable vents would only serve to "short circuit" your airflow. The air would come in the gable vents and go out the ridge, or come in the soffit and go out the gable. You want the air to go in at the bottom of the roof and travel naturally towards the top, constantly adding cool outdoor air and exhausting heated air.

You're doing a great job with your research and your husband should be very appreciative.

I can see how the cost of the ridge vent tiles would lead one to use the bare minimum amount of them.

Do you have sheathing on the roof, or does it have a 1x2 strap every foot or so nailed into the rafters/trusses? If you are ever in an old barn or agricultural building in europe, you'll notice that the strapping was the original way to set those tiles. Obviously, they didn't have much lumber to work with and plywood wasn't around.

cp31817 05-02-2012 12:41 PM

Hello Cleveman,

Have a question for you. Spoke to the rep from peaderson and dean. She stated that I have roof vents-o'hagins on my roof over my garage 5 of them. This is where the builder specified the vents to go! I asked how does vents on my roof garage vent my attic. Her response was it doesn't but it is not her problem. They were a sub contract to the builder!?! I asked if the building codes specify. she stated they come to a job after the plywood and felt have been laid and all the vents, t-tops etc are marked and they install what they are told. So in my opinion ignorance is bliss???? They can just install a roof that is dramatically under ventilated and they are not held responsible???

I asked her that if "X" amount of ventilation for the attic is needed and the attic does not have it who is responsible? She stated the builder, the city for allowing the house to pass inspection, and of course her company.

Are the vents on the lower roof (over the garage) allowed to count as ventilation for my attic???

I will post pics of my roof she is sending them to me...also hubby promised to go up on the roof and take pics etc....and look for rafter shots etc.....
I am off to talk to my builder now. Any advice you can provide would be great!

cleveman 05-02-2012 07:22 PM

It is somewhat of a good thing that the porch and garage attic are vented. This shows that someone knew the attics needed to be vented.

I would want those vents as high as possible. Any inlets in the soffits for the porch and garage attics?

Your attic shots look pretty standard, but we don't usually run the forced air in the attic here. Do you have an hvac system on both floors?

You won't be able to hold the city responsible for anything, but you can certainly chew them out a new one. Maybe they can pay closer attention to what is going on from present forward.

Those roof vents don't look too complicated. I would hope that your builder would go ahead and install a bunch of them for you.

I don't know what to tell you. There are a lot of people everywhere in the world in every business doing substandard work. You're doing a good job of rectifying the situation you have been given.

cp31817 05-02-2012 07:55 PM


No, no inlets for the garage or covered porch!! I just want to talk to the city inspectors to see why they thought this home was properly vented. I came across some info regarding my builder. He has dissolved the company and the roofing co is denies and responsibility. UGHH it seems that the more I find out the more complicated it all becomes. Cleveland, I started a new post entitled "home Builder dissolved" I decided to start a new post so that maybe I could get suggestions on this new development. Thank you for all of your help I appreciate it very much.......I will keep you informed on what happens next.

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