To Ridge Vent Roof? or Keep it Capped?

[pgtr]

I've got a 2 car detached GA with an open attic (gable roof). When I built it years ago I stapled fiberglass in the roof rafters. Then I put up that aluminum clad 4x8 1/2" foam sheeting. It was easy to lift up into the attic area and of course to cut/size and it helped brighten up the GA with a reflective surface.

Before putting the insulation up in the rafters I put boards across the openings into the soffit area but I also drilled large holes in the boards and stapled screen material across each hole. When installing the soffit boards I also put in soffit vents. They are not continuous soffit vents - I just put in 3 foot strip and left about 2 feet or so between...

The point is there is an open area in the soffit cavity and there are vent holes from there to each roof rafter 'channel'. Now that channel is largely 'filled in' with fiberglass batting though I suspect some degree of air could pass thru the fiberglass and/or any small space between the fiberglass and the roof decking. The attic space itself - while open to the GA space below - is sealed from the soffits/raffters.

But the ridge of the the roof is *NOT* vented. I'm facing a new shingling job soon. When I painted last year I noticed a little mold here and there around the ridge vents. It's somewhat humid, hot summers, rarely freezes.

Vent? Or keep the ridge capped?

Thanks!

 

[Mustang1167]

I would vent it. Since you took the time to make the soffit vents functional it would make sense to install a ridge vent. One piece of the puzzle does not work well without the other.

 

[Kaizen]

I suspect you will find moisture in that insulation and probably mold. there is no air movement. so if you do a ridge you need to put the baffles in the whole way. this will keep the deck cooler and extend the asphalt roof.

 

[pgtr]

Thanks for the fast comments! I worried about the mold too - I should have added... I've peaked inside the soffits and a couple of rafters - no mold whatsoever. The very modest amount of mold was at the vents here and there was all I think.

Now that I think about it - I probably saw a hint of mold here and there in a nook or cranny if I took too many years between power washing. And I never really power wash the vents much at all. And I'd see the occasional hit of mold on the house ridge vents - those are continuous and that roof is vented and has traditional blown in insulation - again no mold inside.

My original idea was to do it like 'weep holes' like what they do on the lower sides of exterior walls of houses rather than fully vent it... Really didn't know what I was doing at the time - just seemed like a good idea at the time and it kept my options open.

I'm seeing some newer homes completely fill these rafters in with spray in foam - interesting - if I had to do it again I might consider it.

Thanks again

 

[DougWil]

I'm seeing some newer homes completely fill these rafters in with spray in foam - interesting - if I had to do it again I might consider it.

In a few years you will see some of those homes with the entire roof ripped off chasing black mold and rotted OSB caused by water leaks that are undetectable from being encased in foam.

 

[Kaizen]

My original idea was to do it like 'weep holes' like what they do on the lower sides of exterior walls of houses rather than fully vent it... Really didn't know what I was doing at the time - just seemed like a good idea at the time and it kept my options open.


Thanks again

those are for brick or stone. different material different method.

 

[LS6 Tommy]

Sounds like you're most of the way to having functioning soffit & ridge vents. I'd complete the job.
Ridge vents are required by Code around here now. I'm in a Cape and I only have gable vents and the original stapled in fiberglass in between the joists, right up against the bottom of the decking. There is no place to add soffit vents. A ridge vent will do nothing for me, but it will be required when I reroof and there is no practical way to make the ridge vent work properly. Stupid...

Tommy

 

[pgtr]

Sounds good - I'll pursue it.

Insurance is picking up the tab (hail storm) on the shingle job - I'll have to pay the upgrade cost difference for the ridge vents. Some roofers charge a lot by the foot for adding this. By contrast, I put 12 feet on a shed project myself and it seemed pretty quick, easy and low cost to install.

Speaking of which - I've sometimes seen that after the plastic vents are nailed down - with time they can sometimes pop up a little. Is it worth specing screws rather than the standard nails most vents come with?

Thanks again for the comments - I'll be adding vents.

 

[Kaizen]

I would spec longer nails then normal roofing nails. Screws would work but I'd be worried it would deform the cap and look like **** from the ground.


Sent from my iPhone using Tapatalk

 

[DC73]

You don't want air flowing through your fiberglass insulation. It de-rates the r-value.

Closed cell spray foam under the roof deck with no vent is definitely the best option but is also the highest cost option.

The correct way to install a ridge vent in your situation is to remove the existing insulation and create a 1" vent channel just below the roof deck. You can put 1" spacers along side each rafter, then use rigid foam insulation panels, drywall, plywood etc, to create the vent channel. You can then reinstall your fiberglass insulation.

Here's another option that building scientists have come up with (assumes you are in climate zones 1, 2 or 3 - they have not yet signed off on this approach for climate zones 4 or higher): Install a ridge vent but first cover the hole in the roof completely with a vapor permeable membrane that is an air barrier. This allows water vapor to escape but keeps your conditioned air inside. There are smart membranes that serve this purpose.

See BuildingScience.com and GreenBuildingAdvisor.com for info on insulating cathedral ceilings or creating unvented attics.

DC

 

[csp]

x2 what DC73 said. Insulation works best with no air flow through it.