Ventilate flat roof??

[Gitche Gumee Kid]

Back in 1980, I purchased a 40 acre rural parcel. Built an earth sheltered home there. It had small broken down dwelling on it with a full concrete foundation.(circa--> depression era).Dirt (sand) floor.Thought it would make a great root cellar.

I have finally razed the old building and decked over the foundation(12'x20'). I used OSB and rubber roofing. Will insulate with fg batts.

My question: Would each space between the each floor joist need a vent ? ( maybe a small vent at each end of the rim joist?

Also what's the best method of getting air circulation thru the whole cellar?


Thanks in advance to all you HVAC (real or amateur)

GGK

 

[joeyd]

Some pictures always makes it easier to answer your question.

 

[Gitche Gumee Kid]

Some pictures always makes it easier to answer your question.

You're right. Just went out and snapped a few.

Hope these embed.

GGK

ETA nope I'll keep trying
Obviously , I haven't trimmed the rubber yet.

 

[quicksandfarmer]

Back in 1980, I purchased a 40 acre rural parcel. Built an earth sheltered home there. It had small broken down dwelling on it with a full concrete foundation.(circa--> depression era).Dirt (sand) floor.Thought it would make a great root cellar.

I have finally razed the old building and decked over the foundation(12'x20'). I used OSB and rubber roofing. Will insulate with fg batts.

My question: Would each space between the each floor joist need a vent ? ( maybe a small vent at each end of the rim joist?

Also what's the best method of getting air circulation thru the whole cellar?


Thanks in advance to all you HVAC (real or amateur)

GGK

What has me confused is your reference to "floor joists." I assume by this you mean the roof? Generally it's a good idea to have an air space between the insulation and the roof sheathing, and for that space to be vented. Unless there is some way for air to circulate each bay needs to be separately vented.

 

[joeyd]

I would think that venting the space like it was a raised foundation home would work. You are going to use the space for storage and are not going to occupy it.

http://images.lowes.com/product/converted/736223/736223132050lg.jpg

409.1 Ventilation. The space between the bottom of the floor joists and the earth under any building
(except such space as is occupied by a basement or cellar) shall be provided with ventilation openings
through foundation walls or exterior walls. Ventilation openings shall be provided with corrosion-resistant
wire mesh, with the least dimension being 1/8 inch (3.2 mm). The minimum net area of ventilation openings
shall not be less than 1 square foot for each 150 square feet (0.67 m2 for each 100 m2) of crawl space
area. One such ventilating opening shall be within 3 feet (914 mm) of each corner of said building.

 

[MacLawn]

Eddie, Eddie, calling old Eddie here...

Me? I ain't got ary a clue.

 

[dusty3030]

Since you already built your roof I'd foam board it between the joists and leave them as is. Add a whirly bird to the back furthest from the door to vent it.

 

[BuilderML]

First i would not use fiberglass to insulate the roof. To me you have only 1 choice. Closed cell spray foam sprayed directly to your osb decking. This will stop the heat transfer into your root cellar. If fiberglass with airspace above is not done perfectly you will be trapping the cool moist air in the void and when the sun beats down on your black roof and heats if up you will have condensation issues. Again if i haven't said it already avoid firberglass in this structure. Hope this helps.

 

[/pine]

FWIW...dead air space in horizontal spaces is actually OK insulation...

If outside air can get into the space via vents so will the moisture within the air...a problem occurs when said moisture permeates the wood, sheetrock (ceiling etc.)...the issue can be that the moisture in the air allowed into the space does not exit...
Again...FWIW...

 

[noller9]

If they are going to be a floor joice someday, which from my lifes experience may be ten years, I would use fiberglass insulation knowing you could take it down someday and use it somewhere else. If you predrill for wiring you will get air flow above the insulation. if you ran aluminum venting (2" wide} down the upper side of the rim board tying in the joice on both sides you would have venting.

Personally I would not vent it to the outside.

 

[ErikVann]

What's the intended purpose of the venting? Flat roofs don't typically have vents. I agree with Builderml, spray foam is the way to go. Allowing air flow under your flat roof will be inviting several moisture related issues. Roof venting works as a chimney effect air moves up from the soffit vents and exits the ridge vent. This keeping the roof surface cool in the winter time so that there is no melting from heat loss for the structures, in The summer it vents hot air generated from the roof surface thus keeping the attic cooler.
In a flat roof situation you are unable to rely on a chimney effect to move air through the vented space. You will develop mold and sooner than you think the osb will deteriorate. Osb is particularly susceptible to rot caused by atmospheric moisture condensation. If you can't swing spray foam use rigid foam board and make absolute certain that you do an excellent job of sealing all joints and terminations.