I’m inspecting 24 new Townhouses, they all have a flat roof system with no ventilation at all, and excepted by the AHJ.
The building plans do not call for any ventilation of the rafter system…
I’ve never seen a manufactured soffit vent, gable vent, or ridge vent. I’ve always constructed them myself as a necessary part of the structure.
If you make it yourself, do the math.
Free is exactly that, Unencumbered by nothing, not so much a 1 single louver. Louvers and coverings reduce the free flow of air. I use a 50% reduction of free flow for louvers vents, 75% reduction for turbines and I follow the MFG instruction for other systems. Wood louvers are very inefficient at a 75% reduction to free flow… Hope that helps
I did a new house on Monday. 1600 sq ft floor plan. No turbine, ohagen(sp) or soffit wents. Only one 2ft gable vent on one end of the attic area. I recommended more ventilation and insulation. The insulation was only about R-20 and was supposed to be R-32. My client brought this up to the super who asked the builder and they all ended up with the prints at the county building.
I guess here in AZ., for ventilation,they do not use the IRC. In 2001 or 2 due to thermal imaging, they came up with thier own formula and can almost have zero ventilation to create a dead air space. They said the lack of moisture here does not create problems that are found elsewhere.
Today (Wed.) I got a call from our client saying that although the builder stated that the current vent is ok according to the code, he is going to install 8 Ohagen(sp) vents. My client also said that today they went and blew in more insulation.
Sometimes things work out the way they should…
Mark, I have been finding less ventilation, more insulation on the ceilings, and a thermal barrier on the OSB lately (new construction).
More information, please.
Pretty please.
Oh please oh please.
Darn margaritas.
Sorry R2, so far I can’t find a pic. They are called O’hagen roof vents or invisivents. They look just like the tiles when you are looking at a tile roof. Same colors, same profile, they just stick up about 1/2 inch or inch higher then the tiles. So from the road you can not even tell they are on the house.
Ah-ha.
I know exactly what you’re talking about. Thanks.
not to hijack another thread, but i’ve been looking for some info on metal roofs installed over shingles. it seems to be common practice up here, my question is, does this effect the venting at all, they do have ridge vents, kind of, and there’s about 1’’ of air space between metal and shingle. the ridge and drip edges aren’t “air tight” but they do deflect water well.
If any one has pics of O’hagen vent could you please post them?
How do you know the s/f amount for, say a turbine, as opposed to a passive vent opening.?
Linda
If I read the code correctly, *“the total area is permitted to be reduced to 1 to 300” *provided mechanical ventilation is provided. You don’t measure the space provided by the mechanical ventilators–you measure the attic area and other ventilation openings and that ratio should be 1 to 300.
The best thing to do is not to do any calculations. Leave that to the contractor you refer the situation to.
O’ hagen vents
We have found In Canada that turbines might not be the best way to remove air from the attic for many reason .
(I) They do leak snow under some conditions .
(2) They work no better the normally asperated vents in no breese.
(3) They some times work too well in a strong breese and pull air from the home even lifting the attic door some times .
(4) They always get noisy after a while
at 7:00 pm they sound like loud clock
At 10:00 pm they sound like a car idling ,
at 2:00 am they sound like a train sitting next door .
In many cases people remove them never to have a turbine again . That is my vote NO TURBINE.
Roy sr
Another problem that can occur with it is that a turbine vent can create a vortex in the attic space. If there is blown in or loose fill insulation, you should always check to make sure that it hasn’t been blown around, or even sucked out.
Chris
messed up
disregard
I’ve always been told the general rule rule of thumb is 1/300 with a vapor barrier and 1/150 without.
i give
disregard again
Linda,
What I do (right or wrong) is look at the size of the opening in the roof sheathing from inside the attic, measure it and calculate mow many SF it is. They’re usually about 1 SF.
ft