Venting a hip roof

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Old 05-28-13, 09:25 AM
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Venting a hip roof

I have a combo hip/gable roof, w/ continuous soffit vents, soffit baffles on the gable sides, ridge vents with baffle. When I go into the attic, it's clear the ventilation is not moving properly. Is there a way to either increase pressure on the soffit side, or decrease it at the ridge vent to increase air movement?
I do not want to add an attic fan, because it will just suck the cold air out of the living space. I have tried to completely seal it, but this is impossible.
I am thinking of increasing the height of the ridgevent baffle to block the windflow and create more negative pressure.

thank you.
 
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Old 05-28-13, 09:44 AM
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There are different ridge vents that claim to take better advantage of the wind. From your description I was not able to follow exactly what you have. ??soffit baffles on the gable side?? What I would expect would be soffit baffles for low vents, ridge vents for high and a gable vent for high as well. Some hip roofs will have ridge vents on the slopes as well. I'm really good at the terminology.

But, from the start. Guidelines recommend 1 ft˛ of net free vent area for every 150 ft˛ of attic floor. Half high and half low. Increasing the low is preferable, but do not decrease the high. If you do not know what your vents have for net free area, search for something similar and check their specifications. My opinion on ridge vents differs from some mfgs who list 100% NFA when we know all of the screen or filters will reduce the air flow.

Once you determine you have all of the vent area you should have, make sure there is a clear path for that air to flow. All too often the roofers have covered the ridge vents so do a smoke test to confirm the hot air is being pushed out.

The down side to natural venting is it only works with a hot attic. As the temperature drops so do the natural forces (gravity) power your venting.

Let us know what you have for vent area and that you have a clear path.

Bud
 
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Old 05-28-13, 06:14 PM
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it's clear the ventilation is not moving properly
How exactly is it "clear" that your existing ventilation is not acting as it should? Soffit and ridge ventilation don't create a noticable breeze through your roof. And when they are working properly, your roof and attic will still be very hot. After all, you're in Florida. Not sure what you are expecting, or what you are saying is "clear" -ly not working properly.

I have never seen a soffit-ventilated gable end. There may be vented soffit panels covering the gable end eves, (to match the soffit panel pattern on the rest of the house) but I have never seen them be functional.

A smoking incense stick is a good way to visually see the airflow in an attic. Air will move from bottom (intake) to top (exhaust) on a warm, calm day when the warm air in the roof is rising. But depending on a lot of factors, (like a very windy day or too much soffit / intake ventilation) air can also blow right in the soffit on one side of the house (windward side) and exit the soffit on the other side of the house (leeward side), which really isn't bottom to top ventilation. But that doesn't mean there is necessarily anything wrong either. It just means it's really windy outside.
 
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Old 06-03-13, 12:57 PM
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Thanks for the reply Bud.
Sorry, I am just learning. My total sq. ft. of attic space is 2,850. Yes, I have soffit baffles(durovents)in all clear pathways to the ridgevent. I have 150 Lf of 12" lanced aluminum soffit vent(tag said 9 sq. in nfa per sq/ft). This is the only area of soffit vent that has clear run to the ridge vent(meaning to run between the rafters, next to the roof sheathing, without any 2x6's or 2x8's in the way). I have another 238 lin. ft. of the same aluminum soffit vent on the other areas where the path to the ridge vents is blocked by like a 2x8 in between each rafter. These are mainly on the
I have approx. 55 linear feet of ridge vents. I think it is shingle vent. I have no ridge vents on the slopes or a gable vent.
Thanks for your help.
 
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Old 06-03-13, 01:01 PM
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Hi XSleeper. Thanks for the input. I guess I was not expecting a roof deck around 140 to 150 F. Since the previous owner put all the duct work in the attic, I am trying to cool it off, but don't know if it's possible. I will try the incense. Today is warm, and calm. Thanks
 
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Old 06-03-13, 03:53 PM
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Natural attic ventilation is typically poor at best. The main reason is that it takes heat to power the process so at best you get partial cooling. Then, when you add in the amount of energy the sun can impact onto those shingles you are lucky to see any improvement.

if at some point you choose to replace your shingles, a lighter color with reflective properties to send the radiant energy back into the air before it heats your attic, can be very effective.

The time frame when attic venting can help is the thermal carry over after the sun goes down. Then you have cooler air pushing in and forcing the warm air out, without the sun constantly replenishing that energy.

One possibility for those blocked gable bays would be a ridge vent on the slopes. They make them specifically for that purpose and then the soffits have a place to work with.

Bud
 

Last edited by Bud9051; 06-03-13 at 03:54 PM. Reason: spelling
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Old 06-03-13, 05:32 PM
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Hopefully that ductwork is insulated.
 
 

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