Attic venting with porch detail

[yhuynh]

I'm in the middle of reviewing my truss shop drawings and can't figure out how to properly vent my attic with the way the porch roof meets the building.

In theory, I only need 1/300 = approx 4sqft of venting which would be covered by the soffits on the back of the building and above the garage door, but I worry that the air flow will be uneven.

The main roof on the building is 6/12 pitch, which dies into a 5/12 porch roof. The problem is that the ledger for the porch rafters is going to be where the soffit normally would be for approx 17' of the building. I explored dropping the porch roof so I can add the soffit into the truss roof, but the height of the porch opening gets too low for my liking even if I raise it to 4/12.


Using blow in cellulose in the attic and planning to use LP soffit on the other side of the building.

I've been mulling this over for the last 4 hours and am coming up empty. Looking for a savior, thanks for your help!

 

[jack stand]

Mid America makes a nice vinly rectangular louver in many sizes.
Pop one in that little porch gable as high up as your happy with visually.
There's also a long vent that's like half of a vented ridge cap. It's formed to flash the roof/wall connection.

 

[firebirdparts]

The easy answer is don't have a ledger board. I admit though that's a strong way to do it. If I removed it I would probably add some blocking to keep all my porch rafters vertical. You would want to nail your rafters to the side of the trusses, but it's still inherently less stable.

 

[firebirdparts]

More labor-intensive alternative is drill big holes in the ledger board.

 

[larry4406]

Change the porch truss to a bearing style that sits on the double top plate thereby eliminating the ledger board.

Sister the main roof and porch roof trusses side by side then the insulation baffle can pass thru.

 

[yhuynh]

Thanks everyone for the replies! Interesting to see the different products out there.

I wanted to avoid too major of a change like removing the ledger board, as I don't want to have to go back to my engineer. Someone else I spoke with recommended that I hold the rafters high on the ledger; that seems like a fairly simple change so that's what I'm planning to go with!

Then going to install a long vent on the porch ceiling like this one, though I have to find one that is for thicker material: https://plasticomponents.com/produc...offit-applications-1-34-2-58-3-4-and-6-vents/

Here's a drawing in case anyone is curious!

 

[rsparks64]

Perhaps add a fan in that space to help circulate the air. We did that in one of our houses and controlled it with a thermostat. It worked well once it heated up and lowered our A/C bill some.

 

[firebirdparts]

That seems good to me. Easier than drilling holes.