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Rainscreen wall venting

thecoopers's picture
We are coming to the point of venting our rainscreen exterior walls. I would like to get the input from experienced individuals on how I am considering handling the upper venting. It seems that upper venting is most commonly handled by allowing for a small space in upper trim that is screened from the backside to allow air to escape. The current issue of FH had and article that used 3 inch vent plugs. Here is my specific thought. Vent air in the wall space through 3 inch holes drilled and screened in the exterior wall as high up as possible back into the unconditioned attic and then out through the continuous ridge vent. I would appreciate responses that are meant to be helpful. Joe

joe (post #206788, reply #1 of 8)

whether helpful or not is for you to decide.

 

Would it be wise to introduce what could be moist air coming from the bottom of your siding (near grade) up into your attic space?

Are there plans for soffit venting (if a soffit is figured)?

What would the detail be up each gable wall (if a gable)?

Knowing inspections and firestops inside, how do they treat open beyond 8-10 ft up the side of the house and/or into an attic space?

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Thanks for the helpful reply (post #206788, reply #2 of 8)

Calvin,

 

The concept that your first question addressed is the one I have had the most concern about. The moisture level of air entering the airspace behind the clading at the bottom and exhausting into the attic would seem to be similar to or less than the continous soffit vent air (vented soffit on eave ends and solid soffit on gable ends) which we have installed.

 

The detail of the gable ends for air movement would be:

Through screening at bottom cavity spaces between vertical 1x3 nailers 24 inches on center (house built with Advanced Framing concepts

Rising up the side of the wall in the spaces between vertical nailers

Reaching two 3 inch holes bored through exterior exterior sheating and exiting into the attic at the highest point possible

Rising to the continuous ridge vent with a 4 inch cut out

 

I an not quite sure what you meant by: "knowing inspections and firestops inside, how do they treat open beyond 8-10 ft up the side of the house and/or into an attic space" so I will ask for clarification. In case this has anything to do with it, we are building in a rural county in the Smokie Mountains where there are no building inspections.

 

I appreciate you exploring this concept with me.

 

Joe

joe (post #206788, reply #3 of 8)

I don't know that we agree on the moisture content of entry at grade v. up higher at a soffit vent.

As far as the inspector and firestopping channels that are open up to and into the attic space..............beats me, never had the occasion to look it up or ask.  I'm familiar with their concerns and demands within the dwelling.  If required, they would certainly defeat your idea of venting

To me (and I did not take a look at our sister online forum-Green Bldg Advisor-the purpose of rainscreen is to drain water, not necessarily to allow air to move up and into an attic and out the roof.

Sorry I can't be of more help.  Thanks for bringing this up, I like to learn as often as I can.

 

Heck, just learned about the building of a straw bale house last night.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Reply to comment (post #206788, reply #4 of 8)

Thank you Calvin talking with me about this thought.

 

Joe

From a practical standpoint (post #206788, reply #5 of 8)

From a practical standpoint (ignoring codes), if you were in a wildfire danger region then having the rainscreen vent into the attic would seem to be a bad idea, since any fire reaching the wall would naturally be drawn into the attic.  There would also be a danger, in other locations, of drawing in a fire from an out-of-control outdoor grill, or from an electrical fire at the service entrance.  But fires starting inside would likely reach the attic before they breached the wall.

So consider the odds.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Rainscreen venting (post #206788, reply #7 of 8)

Thank you Dan for your thoughts, they surely are worth considering. Its beginning to look like exterior venting will be the plan.

 

Joe

I resided my house in 2010-11 (post #206788, reply #6 of 8)

I resided my house in 2010-11 using a ventilated rainscreen wall. While researching the techniques involved, I ran into your question (where to vent the rain screen at top) in quite a few forums, etc. Almost universally the answer given was that it probably isn't wise to introduce any more moisture into the soffit/attic/roof, and the safest way was to vent to the outside of the wall via a fascia board held away from the siding by about 1/2 inch. The specific discussions and designs can be found at numerous sites (including info on how to detail the insect screen involved), but here are a few:

FHB, August-September, 2010, pp.32ff

FHB, February-March, 2001, pp.86ff

JLC, March, 2006, pp.1ff

 

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". . . and only the stump, or fishy part of him remained."

Rainscreen venting (post #206788, reply #8 of 8)

Hokuto your post tipped the scale. I am going to abandon tnterior venting and utilize an exterior technique. Thank you very much for the resources you shared.

 

Joe