Radiant Barrier OSB Over Skip Sheathing--PLEASE HELP


#1

We live in San Diego County (inland where it gets very hot in summer) and have a historical home from 1910 (not well insulated) and yesterday sheathed half of our roof in radiant barrier OSB right over the skip sheathing (we had removed two layers of asphalt shingles and one layer of old cedar shingles from 1910). My dad is my contractor (retired) and didn’t think I needed to do that but went along with me to make me happy. He has never used radiant barrier OSB. I am now realizing as I’m researching more that the skip sheathing touching underneath the foil will decrease the effectiveness of the product, which is fine, not a big deal, but even worse could make it even MORE hot in our attic by conducting heat through the wood??? Not what we want! We have to sheath the other half today, should we just switch to regular OSB? Is it worth it to remove the radiant barrier OSB and replace with regular OSB on the half we did yesterday? This was all a last minute decision on my part as I was trying to ensure our hot little house stays as cool as possible in summer. Now I’m worried it will be worse off (even hotter). We are planning to do lots of ventilation on the side of the roof we are sheathing today. Please help!


#2

Put the OSB with the radiant barrier on. Use “H” clips between the pieces. Don’t worry about the radiant barrier touching the skip sheathing even though it reduces the effectiveness at ONLY those contact points.

Your attic will be cooler than if it had no radiant barrier. It will NOT be hotter with radiant barrier.

Make sure you retrofit (if needed) your roof with proper ridge vents and add soffit vents. Soffit vents are the intake and ridge vents are the exhaust. If you have gable end vents then seal them from the inside with pieces of the OSB radiant barrier decking. You don’t want soffit vents, gable end vents and ridge vents. The gable end vents will short circuit the air flow from bottom to top.

The primary function of soffit vents and ridge vents is to relieve moisture in the attic. Relieving moisture in the attic makes your attic insulation work in the correct manner. Moist insulation does you no good. The secondary function of soffit vents and ridge vents is to relieve heat from the attic.

I did the same thing on my own house in Houston. It gets very hot and very humid here. Remove wood shingles, remove some of the skip sheathing to allow for maximum unimpeded radiant barrier exposure, install CDX or OSB with radiant barrier facing down, use “H” clips, install shingles, yada yada yada. I added ridge vents (only wind turbines previously) and then added 16" x 8" louvered soffit vents in the approximate ratio suggested. It is not perfect (it never is) but it works as it should.

Don’t worry too much about what you have read on the internet regarding radiant barrier making your attic hotter. That opinion was most likely proffered by someone writing for a group selling another product.

Your are doing the right thing.


#3

Thank you so much for your feedback! So, our house is old (built in 1910) and only has the original wooden gable vent with a solar powered fan right behind it. From everything I’ve read, the original cedar roof was self-ventilating and no venting (besides that fan) has been added since. Now that we’ve finished sheathing over the skip sheathing we need to figure out the best ventilation possible for our scenario. Our scenario: hot and pretty dry climate in summer (not dealing with much humidity here in Escondido–inland in San Diego county also not a lot of rain), small home (very steep pitched roof with lots of open attic space which covers 864 sq ft of the house’s interior). My dad (also my contractor) did some blocking in the attic to make the house more structurally sound, so he says a ridge vent isn’t an option at this point (I think he also thinks they’re a pain in the ass). Also, because our house is a registered historical home and we are going to be applying for the Mills Act this month, I don’t think we should be doing a bunch of holes (soffit vents) on the top piece of wood siding of the house right under the eaves because it would be changing the look of the home. What would the next best scenario be? Do you think putting 2 low profile Ohangen vents on the top and bottom of each side of the roof is sufficient (for a total of 8 altogether, if that makes sense)? I think the code here is 1 sq ft of venting for each 150 as ft? I want to ventilated the best we can because A. It gets HOT here in summer and B. we are doing a dark charcoal GAF Timberline reflector series roof which is considered a cool roof, but I’m still worried about how hot it will get since it’s much darker than the lighter gray roof we had on our house (granted that was laid over another layer of asphalt shingles and over the original cedar shingles. My husband is way less concerned about all this and is deferring to my dad, but I am deferring to you! Thanks in advance!


GAF Timberline HD Reflector Series "Charcoal" color: Good choice in So Cal or too hot? PLEASE HELP!
#4

Thank you so much for your feedback! So, our house is old (built in 1910) and only has the original wooden gable vent with a solar powered fan right behind it. From everything I’ve read, the original cedar roof was self-ventilating and no venting (besides that fan) has been added since. Now that we’ve finished sheathing over the skip sheathing we need to figure out the best ventilation possible for our scenario. Our scenario: hot and pretty dry climate in summer (not dealing with much humidity here in Escondido–inland in San Diego county also not a lot of rain), small home (very steep pitched roof with lots of open attic space which covers 864 sq ft of the house’s interior). My dad (also my contractor) did some blocking in the attic to make the house more structurally sound, so he says a ridge vent isn’t an option at this point (I think he also thinks they’re a pain in the ass). Also, because our house is a registered historical home and we are going to be applying for the Mills Act this month, I don’t think we should be doing a bunch of holes (soffit vents) on the top piece of wood siding of the house right under the eaves because it would be changing the look of the home. What would the next best scenario be? Do you think putting 2 low profile Ohangen vents on the top and bottom of each side of the roof is sufficient (for a total of 8 altogether, if that makes sense)? I think the code here is 1 sq ft of venting for each 150 as ft? I want to ventilated the best we can because A. It gets HOT here in summer and B. we are doing a dark charcoal GAF Timberline reflector series roof which is considered a cool roof, but I’m still worried about how hot it will get since it’s much darker than the lighter gray roof we had on our house (granted that was laid over another layer of asphalt shingles and over the original cedar shingles. My husband is way less concerned about all this and is deferring to my dad, but I am deferring to you! Thanks in advance!

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#5

I think you are overthinking it. Does the house have gable vents as many older homes often do?


#6

There is 1 gable vent. Someone put a solar powered fan right behind it.