Calculating Ventilation Area of Attic

Does having the heating system located in the attic contribute to the heat build up and require additional ventilation. Also, my home has a mansard roof line and I don't believe the builder installed adequate ventilation. The home is located in South Carolina where it does get extremely hot!

The furnace in the attic, in my opinion, would not add to the heat load. My guess is that you are talking about summer months when the furnace is not on. You should read my columns about Turbine Vents, and install several.

Hi Tim,

I have a question about my ridge vent.
My upstairs rooms get very hot in summer.
The attic is 40x24ft and I have a ridge vent that goes along the 40ft ridge. However, the slit in the attic for the vent is only 1 inch wide and not centered, but is one side of the ridge. According to the suggested minimum ventilation area - it is OK. My question is: is this slit too small to allow the vent to work properly? I live in East Tn - it is already getting warm upstairs and it is only spring.

Thanks and great site.

Tim,

Can you have too much ridge venting compared to soffit venting area?

In your example above, 40% of 5 square ft equals only 2 square ft. and you would need only 5 of the 9 inch dia metal pots? This assumes soffit vents provide 60%.

What is the open area of one of the standard soffit vents? Sorry I don't have exact dimensions, but look like about 3 inches x 12 inches.

Thanks,

Hi Tim:

I live in East Tennessee. I have two ac units. The one upstairs is a ac?heatpump unit. My concern is the heat builup in the attic. the dimensions of the attic are as follows: 56 feet by 20. the house has a 12/12 pitch and the height at the center is approx 3 ft. i have 8 pot vents. I am thinking of replacing one pot vent with a 1500cfm exhaust fan. i also have soffit vent,BUT I have r30 insulation along knee wall and celing and this may impede flow of air to attic area. do you have any suggestion as to whether i need more intake or not. my soffit area runs the lenght of the house on both sides and is approx 18 inches wide.

thanks

vic zammit

I have a gable installed exhaust fan in the attic. The attic is about 1400 sq ft. How much vent area is needed for this attic.

Martin

We have an attic with walk up stairs, which we would like to convert to living space.

Right now the attic has poor insulation on the floors, ceiling and rafters.

The attic also houses the furnace and A/C air handler.

If we sprayed insulation as thick as possible on the attic rafters and attic walls, and conditioned the attic, would we still need ventilation in the attic?

Why is attic ventliation necessary?

Tim,

My MasterFlow power vent dosen't turn on anymore. I suspect its burnt out. Given the following, would you Not replace it: Sq ft of attic = 4700 (plus 525 above attached garage); NFA of about 150 sq in in the soffits (continuous in only 3/4 of contiguous soffit); 6 RT 65 louvers for ~ 360 NFA. The Pro 1 Power Vent by GFA calls for 760 NFA for a 3000 sq ft house and I think that means in the soffits or facia. I'm guessing the non working Power vent burnt out because of insufficient air. What's your recommendation. Thanks.

How does having an A/C unit in the attic change the amount of air I must exchange each hour?

Does it change the amount of intake vents I need?

My almost 55 years old house is in WestVancouver /BC/Canda.The house attic needs insulation(R-50).There are 4 ventilation on soffits(E&W seides)and three ventilation on the roof.Does the attic needs ridge ventilation?Attic=1400sqft.lenghtof house38ftx18=684:144=4.75sqft.Pleaselet me know,if the attic needs ridge ventilatin? or it would be enough that i install two soffit vents on N&S and a vent on roof?Thank you

On June 1st 2008 I see someone asked same question.

Is it possible to have to much ridge vent vs. your soffit vent?

Tim, I have a cabin in the mountains about 7800 feet. wanting to know about insulation and venting. The space is 30x40 with 10/ 12 pitch. It has gable vents on both sides. My problem is the insulation, as I had roof joists that also made a loft. 20 feet is high ceiling wih plenty of room for insulation and air space. The loft area is 20 feet, right on the roof if I follow the rafters. I am worried about not enough air space between insulation in the loft and the roof. The roof is metal. Thanks for any help

We have roof vents (in addition to a ridge vent) on our house in FL and when we get large rain storms, the water is coming in the roof vent just on one side and running down the wall into my living area. Do we need roof vents on both sides of the house or is one side enough if it is large enough?

Good morning,
So what is the net open area of a common soffit vent strip?
Thanks,
Greg

A friend of mine has a modular home that has mold growth on the ceiling sheet rock right near the ridge or seem of the two halves of the house on the inside. If there was a roof leak I would expect to see water staining on the sheetrock. Therefor I think this growth was feuled by humidity and condensation caused by the inside of the roof getting too hot and the inside of the house being cooled to a temperature that would cause the moisture in the air to reach the dew point. My question is would a better ventalated roof help fix this problem and can I use the same calculation as mentioned above to size the ventalation for this type of roof. The isside of the roof is promade of two foot wooden trusses and stuffed with blown in insulation.

Tim
With the above calculation guide, you mentioned that a ridge vent had 900 sq in which is good. Does that mean that a soffit vent is not necessary, what about the 40/60 rule. Also, I have vaulted ceilings, does cubic feet enter into the calculations? Do we use the outside dimensions of the house for the calculation?

witch type of attics needs to ventilating and witch type don't need to ventilation? and what about canopies?