Do I Still Need To Calculate Ventilation?

nolo

I have continuos 100 percent intake ventilation through soffits that overhang at least a foot around the whole house. I am planning on buying 3 20ft rolls of ventsure rolled ridge vent. The roof is 4 in 12 with approximately 2300 square feet of surface area. If I do need to calculate ventilation, can someone point me in the right direction? A large portion of the house has cathedral ceilings. I would think a ridge vent would need to go all the way accross all of the trusses since there is no attic space. Is this correct?

roofwiz74

http://www.owenscorning.com/around/v...etermining.asp

__________________
You have ONE advantage over me.....you can kiss my butt and I can't!!

Grumpy

www.airvent.com www.rollvent.com they have calculators online.

Ed the Roofer

Yes, you are correct with that assumption. You also have to ensure that all of the rafter bays provide at least a 1 1/2 " to 2 " free air passageway for the air to flow freely from the soffits up through to the ridge line of the roof.

If the insulation is packed in too tight, there will more than likely be internal moisture problems.

The solution to that is to install "Baffle Vents" in each of the rafter bays all the way from the eaves to the ridges, which lay on top of the insulation to allow the free flowage of ventilated air flow.

Ed

theroofinggod

yes , Ijust finished one,the old insulation was overstuffed and soaked w/condensation,all the plywood buckled,the soffit bays were closed between the rafters ,we opened them up and installed so raftermate went into the soffit 3",installed new wood fascia,vinylsoffit(boxed)w/vented panels every 3rd piece and new aluminum fascia cover-full ridge vent of course ,WHAT A DIFFERENCE!

Ed the Roofer

TRG,

If you did all that work to solve the ventilation intake problem, why did you only use 1 out of 3 vented panels for the soffits?

If this is a vaulted/cathedral ceiling, then every single rafter bay needs to have properly calculated fresh air intake flowage installed.

Ed

nolo

The insulation will not block air flow. I still haven't had a chance to calculate air flow. I installed 100 percent soffits. Can I go wrong with just installing 100 percent ridge vent and doing no calculations? I mean more is better right.

Ed the Roofer

If the cathedral/vaulted ceiling spans the entire width of the roof where the 100 % ventilated soffit panels were installed and you ensured that you had the 1 1/2" to 2" air flowage space above the ceiling insulation and under the roof sheathing with either insulation baffle vents or the unobstructed air flow space was already present and you ensured that all of the soffit intake vents were not blocked or clogged from allowing the new fresh air to enter and travel upwards, then yes you absolutely need to install the proper equal amount or at least the maximum amount of exhaust ventilation allowable for your situation to create complete unimpeded air flowage from all of the soffit vents upwards to exhaust out of the entire corresponding ridge length.

Caveat:
Although I do not agree with some opposing theories due to hands on experiences, there is a well founded and valid oppositional point of view which recommends against the merits of ventilation in a cathedral/vaulted ceiling structure. My own personal experiences shoot this theory right out the window though.

Ed

nolo

Can you tell me what the reasons are for not ventilating a cathedral ceiling. It was vented before with outtake vents. It only had intake vents (soffits). I didn't notice any moisture or mold problems when I removed the plywood.

nolo

I just read something that states attic ventilation can do more harm in warm humid climates. Since outside air is more humid, the ventilation brings the humid air into the attic space. This can cause condensation on ducts and other issues. I also read an article that at tightly insulated cathedral cavity is better. It doesn't allow this hot humid air in. The latter does make sense to me. If the humid moist air is blocked off, then there shouldn't be any moisture issues. The study also concluded that shingle temps only rose a couple of degrees between vented and unvented cathedral cavities. I live in a really humid/hot climate. I'm hoping I didn't make a mistake. There wasn't any adverse effects from no ventilation. I hope I don't replace the roof in 20 years only to find out I did more harm than good.

Ed the Roofer

Good job of research.

You obviously found a few of the studies or links regarding the opposing view-point regarding the need for ventilation, but the shingle manufacturers warranty exclusions take precedence and so do the current governing codes.

As I stated, I have seen the significant devestation of the interior rafter bay cavities and decking due to no ventilation on a cathedral/vaulted style ceiling.

Ed