another venting question

[dug]

I am installing ceiling insulation now and have run into a problem. On the gable ends of my house, and both sides of my dormer there are fly rafters that support the overhangs. They are laid flat and so are 1 and 1/2 inches deep, 24 inches on center.

I am using the foam duravent baffles to create air space for venting in the rafter bays and am unsure how to vent the bays with the fly rafters. The duravent baffles create a 1 and 1/2 inch space, the same depth as the fly rafters. I am already compressing the r30 insulation 1 & 1/2 inches (10 in. rafters) so I'd really like not to compress it any more.

The two solutions I have dreamed up are to-

(1) Cut notches on all the fly rafters with a circular saw, which would be a real PITA, or-

(2) drill holes on the inside rafter (next to fly rafter) to allow those bays to vent into the one adjacent to it.

I like option 2 better because it would be much easier but I'm not sure if that would be adequate. would this work?

Alternate solutions appreciated!

[Redoverfarm]

I am installing ceiling insulation now and have run into a problem. On the gable ends of my house, and both sides of my dormer there are fly rafters that support the overhangs. They are laid flat and so are 1 and 1/2 inches deep, 24 inches on center.

I am using the foam duravent baffles to create air space for venting in the rafter bays and am unsure how to vent the bays with the fly rafters. The duravent baffles create a 1 and 1/2 inch space, the same depth as the fly rafters. I am already compressing the r30 insulation 1 & 1/2 inches (10 in. rafters) so I'd really like not to compress it any more.

The two solutions I have dreamed up are to-

(1) Cut notches on all the fly rafters with a circular saw, which would be a real PITA, or-

(2) drill holes on the inside rafter (next to fly rafter) to allow those bays to vent into the one adjacent to it.

I like option 2 better because it would be much easier but I'm not sure if that would be adequate. would this work?

Alternate solutions appreciated!

http://countryplans.com/smf/index.php?topic=9877.msg126454#msg126454.

Normally the fly rafters are not insulated or vented.  At least they were not in mine.  If you drill holes then they will have to be close to the sheeting to make it into the vents that you have (insulated space) in the adjoining rafter bays which are primarily over the living space. You will not want to dump air from the fly rafters into the insulation of those adjoining spaces. 

[dug]

Normally the fly rafters are not insulated or vented.  At least they were not in mine.  If you drill holes then they will have to be close to the sheeting to make it into the vents that you have (insulated space) in the adjoining rafter bays which are primarily over the living space. You will not want to dump air from the fly rafters into the insulation of those adjoining spaces.
Posted on: Today at 06:57:46 AM

A picture is worth 1000 words but I couldn't find one, sorry.

The part I'm referring to is inside the home in the end rafter bays where the fly rafter extends into the the home and attaches to the first rafter in. Basically the end bays have a "ladder" all the way up.

I was thinking on my way into town this morning and drilling the holes in the rafters wouldn't work unless I modified the baffles somehow. Still thinking- will try to take a pic. later.

[dug]

Here is a pic of the rafter bay I am trying to figure out how best to vent it. -



I was thinking about cutting notches like this about 3/8 in. deep and nail a thin scrap of plywood over it and fit the baffles in between the fly rafters. It wouldn't provide a lot of airflow but I think it would work, but take a fair amount of labor.

I was hoping someone might have an easier, and better solution for this problem.

One thing I thought of was that I could just use R-19 in those bays and be done with it. Would this be a viable solution?  It would be by far the easiest way but I would rather not lose valuable insulation if I can help it, though I'm already losing some by squashing the R-30 a little.

[Redoverfarm]

Dug why not just set your circular saw to the depth (1/2") and make enough passes to get you 1-1&1/2"  wide , cover with 1/4" luan and call it good.  Although it is not the same width as the duravent opening it should be good enough to let the air vent through the one bay.

[Don_P]

Don't notch the ladder, that is already a minimal way of building an overhang. I've done it that way plenty of times and have probably posted pictures of it. Duravent over it and take the energy hit or use foam in that bay.

[dug]

Thanks Redoverfarm & Don P.

Both points were something I was wondering about, that the notching method would even give enough venting area and would those notches weaken that structure much.

I think I 'll just take the energy hit even though I'm not so happy about it.

Thanks!