Help insulating unvented roof?

[digdug18]

My garage roof was recently converted(6 months ago), when we bought our house from a flat roof to a peaked roof, I have a ridge vent, but no soffit vents. I'd like to insulate the roof, but am unsure what to do about the venting, as there is no place to add venting to it.

 

[Rosco]

Use spray foam on the underside of the rafters/decking. Leave the roof vent there and do not add soffit vents. If it were not a garage I would say to block the ridge vent off, but a ridge vent will allow some vapours and gases to vent.

 

[digdug18]

All that sounds good, but I plan on heating and cooling the garage in the coming year, won't leaving the roof vent funnel the hot air up through it in the winter time?

 

[Joey-D]

I am having the same problem. I am insulated to the rafter (Enough room between the insulation and sheathing for the air to circulate) and am reroofing it here in the next couple weeks. Should I add a ridge vent or leave it unvented since I plan on heating and air conditioning the garage?

 

[Rosco]

All that sounds good, but I plan on heating and cooling the garage in the coming year, won't leaving the roof vent funnel the hot air up through it in the winter time?

So is your cieling open to the pitch? If so I would block the ridge vent. If you have a cieling between the shop and the rafters leave it open and blow loose fill in the cieling joist.

 

[Joey-D]

No need to add a "ceiling" and blow in insulation. After doing some reading, I do need a ridge vent in the garage. My rafters are 2x6 and my insulation is R-13. This means the rafters are 5 1/2" thick and the insulation is 3 1/2". That leaves a 2" space between the sheathing and the insulation. That gives me a "cold roof". To keep condensation from being created (and future mold and rot), I need the a soffit / fascia vents to draw air in and ridge vent to draw it out. The insulation will be stapled to the ridge beam to keep the heat/cool from escaping out the ridge vent.

 

[Joey-D]

Digdug18 You need to add a vent to your soffit or fascia so air can run between the insulation and sheathing and escape out the ridge. The reason you need this air valley is to "wick" away the condensation. If you do not have eaves, you do have a couple options. You can build eaves, so you can have soffit vents or they do make fascia vents. Here is a link to their instructions...

http://www.gaf.com/Roofing/Resident...iaVent-ApplicationInstructions-249-65-248.pdf

 

[Joey-D]

I am going to make my own fascia vent, I gonna cut 2" off the existing fascia top, add a breathable membrane like reusable furnace filter, block it ever 16" and then add a new fascia board and flashing to cover the 1-1.5" void and bada bing bada boom. This will work for me as I am reroofing that area anyway.

 

[Striker]

If there is no space for a soffit vent then you need to look at intakes vents located at the bottom of the roof. Something like this:

http://www.airvent.com/homeowner/products/productImages/staticVents-slMetal.jpg

I just had a few installed on my garage to provide intake as my garage does not have soffit vents.

 

[digdug18]

Striker, that's exactly what I need to do then, yes, there is really no room, and the actual roof goes farther(lower) below the ceiling, by a couple of feet, but still is unvented.

 

[Rosco]

The spray foam insulation will seal the entire underside of the roof deck, therefore eliminating the need for vents. This issue is debated a lot, but there are many threads on here about this and I have seen plenty of houses built this way.

If you do not use the spray foam technique then you will need soffit vents to keep air moving.

 

[Striker]

The spray foam insulation will seal the entire underside of the roof deck, therefore eliminating the need for vents.

That is what they call a "conditioned attic". You need to double check to make sure if you need vented space or not depending upon your climate and local codes. Even with a conditioned attic you may still need vents.

 

[Joey-D]

Do the cost comparison, the breathable fascia / gutterboard I am doing is costing me $27.30 for new 1x8s, already have the paint, $19.64 the reusable furnace filter membrane, and $13.24 for my drip edge flashing. I am re-doing my roof, so shingles are not included, but depending on how much your existing shingles hang over, you may not need to add a row. Grand total, $60.18. Now I think spray foam is great stuff and Mike Holmes swears by it, but considering what it would cost, my fascia vent is a hell of a lot cheaper. I quoted this based on my 32' run, but have enough material for a 36-40 foot run.