[snic]

I need to replace my roof. While I'm at it I'd like to install adequate attic ventilation. At the moment, the attic outlined in the picture below has just two small gable vents. I'd like a more modern system in which the air flows from the bottom of the attic to the ridge.

On the long edge (45 ft on the right side), there are no soffits. My roofing contractor says he can install a vented fascia at minimal cost. (Something like this, but not identical - basically it replaces the fascia board.) He can also install a ridge vent. (By the way, the roof pitch is 4:12.)

Note that to the left of the attic, the house has vaulted ceilings, so there is no attic. Will it be a problem if the only intake ventilation in the attic is from one side (i.e., the fascia vents)?

Another question is how to balance the intake and exhaust ventilation. According to the rule of 300, I need 374 square inches NFA, split evenly between intake and exhaust. A standard ridge vent (18 sq in NFA per linear foot) would provide 810 and the fascia vent would provide half that (405). Apparently one wants to avoid having more exhaust than intake because that can cause weather to be sucked in through the exhaust vent. So, what's the best way to make sure the system is balanced?

Obviously 810 square inches of exhaust is overkill. Is it possible to install a ridge vent on only half the length of the ridge? That would balance it exactly. If so - which half? Just in the middle, so there is an equivalent length of unvented ridge on either side?

 

[Windows on Wash]

Soffits?

Easiest is a ridge and soffit vents.

 

[snic]

There are no soffits anywhere under this roof.

 

[Nealtw]

There are no soffits anywhere under this roof.

Is there an air gap above the insulation in that space that would allow air flow?

 

[snic]

Is there an air gap above the insulation in that space that would allow air flow?

Good question. I'm not sure, because that attic is such a pain to get into. There is one tiny hatch, and it's only about 4 feet high at the tallest point.

I'm having an energy audit done hopefully at the end of this week (assuming we won't be under lockdown around here by then). They should assess the insulation situation (I already know it's inadequate and they'll tell me to install more) and I'll ask about the air gap. I'm sure there is some way of introducing one if there isn't already. The company that makes th FasciaVent product I linked to above has some sort of baffle that can be used, I think.

 

[Nealtw]

Good question. I'm not sure, because that attic is such a pain to get into. There is one tiny hatch, and it's only about 4 feet high at the tallest point.

I'm having an energy audit done hopefully at the end of this week (assuming we won't be under lockdown around here by then). They should assess the insulation situation (I already know it's inadequate and they'll tell me to install more) and I'll ask about the air gap. I'm sure there is some way of introducing one if there isn't already. The company that makes th FasciaVent product I linked to above has some sort of baffle that can be used, I think.

You might consider flat strapping with 2x4 and sheet it again.

 

[snic]

You might consider flat strapping with 2x4 and sheet it again.

Please explain? I don't understand your diagram, or what "flat strapping" is. Do you have a link to a site that explains it?

 

[Nealtw]

Please explain? I don't understand your diagram, or what "flat strapping" is. Do you have a link to a site that explains it?

Something like this with or with out the foam board that they have here.

 

[snic]

Something like this with or with out the foam board that they have here.

That might make sense for the vaulted ceilings where there is no attic. But where there is an attic where sufficient insulation is (or can be) installed between the living space and attic, why would you insulate the roof?

 

[Nealtw]

That might make sense for the vaulted ceilings where there is no attic. But where there is an attic where sufficient insulation is (or can be) installed between the living space and attic, why would you insulate the roof?

No, this was suggested just for the vaulted part where you don't have and likely can't get venting above insulation that is there now.

Venting the rest of the roof would be different discussion. :wink2:

 

[snic]

No, this was suggested just for the vaulted part where you don't have and likely can't get venting above insulation that is there now.

Venting the rest of the roof would be different discussion. :wink2:

It's an interesting idea, although likely to be quite expensive. I'll ask the energy auditor about it.

In the meantime I remain perplexed about how exactly the ventilate that attic...

 

[Nealtw]

It's an interesting idea, although likely to be quite expensive. I'll ask the energy auditor about it.

In the meantime I remain perplexed about how exactly the ventilate that attic...

Expensive is depending on what it is compared to.

It is actually cheaper than re and re the vaulted ceiling to add ventilation or more insulation. Just an option to keep in mind.


So does the rest of the house have overhangs, soffet or nothing at all?

 

[snic]

Expensive is depending on what it is compared to.

It is actually cheaper than re and re the vaulted ceiling to add ventilation or more insulation. Just an option to keep in mind.

It IS an interesting idea for the vaulted ceilings. Part of those areas don't have soffits, so actually adding the foam+framing on top as described in the video you linked to would allow us to add an overhang. That might have the beneficial effect of protecting the windows a bit more from the weather, prolonging their life. But we're talking about at least 1,000 square feet of roof here, probably more, just over the vaulted ceilings. Let's say 1200. That's 38 4x8 ft foam boards for just a single layer. For 2 layers of 2" thick R13 (for a total of R26), that would be $3000 (at $40 per foam board, according to Home Depot). Then there's the 2x4s and new plywood decking - now we're up to what, $6, 7 thousand? And then labor. Easily $10,000. Now, that might not be so outrageous if it really saves us money - our heating bills are probably around $5000 per year, so if this saves us $1000, the payback time isn't too crazy. But I don't know how much the savings would actually be.

Now, is there any reason why the existing roof decking can't be removed and reused? Why not put the foam board right on the rafters? Or would the labor cost of removing the decking exceed the cost of buying new plywood?

So does the rest of the house have overhangs, soffet or nothing at all?

The part of the house I'm concerned about (the attic outlined in the picture) doesn't have soffits/overhangs. There's another attic that does have soffits (but not soffit vents), so it's clear what to do with that attic - add soffit and ridge vents.

The two attics are not connected, so I need to figure out a solution for this one.

 

[Nealtw]

It IS an interesting idea for the vaulted ceilings. Part of those areas don't have soffits, so actually adding the foam+framing on top as described in the video you linked to would allow us to add an overhang. That might have the beneficial effect of protecting the windows a bit more from the weather, prolonging their life. But we're talking about at least 1,000 square feet of roof here, probably more, just over the vaulted ceilings. Let's say 1200. That's 38 4x8 ft foam boards for just a single layer. For 2 layers of 2" thick R13 (for a total of R26), that would be $3000 (at $40 per foam board, according to Home Depot). Then there's the 2x4s and new plywood decking - now we're up to what, $6, 7 thousand? And then labor. Easily $10,000. Now, that might not be so outrageous if it really saves us money - our heating bills are probably around $5000 per year, so if this saves us $1000, the payback time isn't too crazy. But I don't know how much the savings would actually be.

Now, is there any reason why the existing roof decking can't be removed and reused? Why not put the foam board right on the rafters? Or would the labor cost of removing the decking exceed the cost of buying new plywood?




The part of the house I'm concerned about (the attic outlined in the picture) doesn't have soffits/overhangs. There's another attic that does have soffits (but not soffit vents), so it's clear what to do with that attic - add soffit and ridge vents.

The two attics are not connected, so I need to figure out a solution for this one.

Removing the sheeting would be more labour intensive and may not be usable the second time and then you might still want venting above the foam so you would be back to 2x4s and sheeting. Anything with out venting is never the best solution.

 

[Nealtw]

The part of the house I'm concerned about (the attic outlined in the picture) doesn't have soffits/overhangs. There's another attic that does have soffits (but not soffit vents), so it's clear what to do with that attic - add soffit and ridge vents.

The two attics are not connected, so I need to figure out a solution for this one.

There are things that the roofer can do with vented drip edge and eyebrow vents.



The pictures are what we have helped roofers do and I am just guessing what you might have now.
1. is just adding 2x4 or 2x3 rafter tails to extend out far enough.

2. is adding a curve to the bottom of the rafters