Design question about attic ventilation baffles

970 Views 6 Replies 3 Participants Last post by DanInVA, Jun 25, 2020

DanInVA

Discussion Starter · Jun 25, 2020

I've been trying to educate myself on insulation and while I understand the purpose of ventilation baffles but I'm not understanding the purpose about the common design.

I see that all ventilation baffles provide 1"-2" air channel and the baffles are any where from 2'-5' long.

Why are baffles not going more than 5' and not just all the way up and really close to the roof ridge?

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mark sr

· #2 · Jun 25, 2020

The baffle only needs to provide air flow to above the insulation. Extending them all the way to the top wouldn't help move the air above the insulation.

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DanInVA

Discussion Starter · #3 · Jun 25, 2020

mark sr said:
The baffle only needs to provide air flow to above the insulation. Extending them all the way to the top wouldn't help move the air above the insulation.

Would extending the baffle to near the ridge also allow the baffle to act as a radiant heat barrier?

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3onthetree

· #4 · Jun 25, 2020

They are in short lengths, 1) because they are frail 2) most situations are unfinished attics so they extend just far enough to keep the area clear of insulation where the rafter meets the top plate of wall 3) if you have an insulated roof and need to extend up to ridge then you connect multiple ones

Only if they are reflective would they be a radiant barrier, and even then the fastening lips and lack of going over the rafters would negate the effectiveness.

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DanInVA

Discussion Starter · #5 · Jun 25, 2020 (Edited)

3onthetree said:
They are in short lengths, 1) because they are frail 2) most situations are unfinished attics so they extend just far enough to keep the area clear of insulation where the rafter meets the top plate of wall 3) if you have an insulated roof and need to extend up to ridge then you connect multiple ones

Only if they are reflective would they be a radiant barrier, and even then the fastening lips and lack of going over the rafters would negate the effectiveness.

Thanks. So my thought is to remove my existing flimsy baffles which are also not sealed at all at the top plate. I would make new baffles out of foam board, along with a vertical piece for the top plate and all sealed with canned spray foam. That should be rigid enough.

A 60's home 1000sq/ft with blown insulation about 20 years go. I'm thinking of removing all insulation, building the baffles, filling ceiling air gaps, and putting rockwool between joists and then another rockwool layer perpendicular.

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3onthetree

· #6 · Jun 25, 2020

All they are doing is keeping the insulation from blocking air flow from the soffit vent to the upper venting. No sealing is needed, and strength shouldn't be a concern. The vertical dam would be for blow-in insulation to prevent it from entering the soffit overhang. Do you have a pic of what you have and describe what your end game is?

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DanInVA

Discussion Starter · #7 · Jun 25, 2020

3onthetree said:
All they are doing is keeping the insulation from blocking air flow from the soffit vent to the upper venting. No sealing is needed, and strength shouldn't be a concern. The vertical dam would be for blow-in insulation to prevent it from entering the soffit overhang. Do you have a pic of what you have and describe what your end game is?

This house is in South NJ near the coast. Pretty humid at times.

The vertical part of the baffle would be to also reduce wind/air over the insulation.

Something like this:

The current state of things:

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