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bacchus258
Cellulose insulation questions

I am going to bring my attic insulation up to the current recommendation for my area which is R-48. I now only have about an R-9 or so of old fiberglass insulation and will blow in the appropriate amount of cellulose insulation on top. The house has the original gable vents and a newer ridge vent but very few soffit vents as you can see in the picture below. I plan to install plastic rafter vents but notice that there is a large gap from where the wall's top plate is and the rafter vent and the cellulose insulation will fill this void. It seems that this will clog the few soffit vents that exist. My questions are:

Is it okay to fill this gap with the insulation?
If not, do I just cover the gap with something like 1/4" luan?
Should I cover the gable vents to allow better airflow from the soffits to the ridge vent?
Do I have to add more soffit vents?

Any sound advise is greatly appreciated.

Thank you,
Bruce

summbear48
Re: Cellulose insulation questions

It seems like you are talking about loose filling in the attic above the existing insulation right? You have the vents in place (the blue plastic it looks like) so that should be exactly what you need to keep the air-flow of the soffits intact. If there is a gap between the plastic and the vents and you know the cellulose would cover it up, you could install a 1x4 or 1x6 at the end, cut to fit in between the joists (I assume 16") to keep the cellulose from covering your air holes. The airflow will help move that hot air away from the roof and effectively keeping the shingles cooler. make sure you have a dormer or vent at the top of your roof for the soffitt holes to vent to. Most buildings are not up to code so adding another dormer or turbine or forced air fan (try solar!) could also help a lot.

you might even want to think about buying some radiant barrier and installing on your rafters with shiny side down. this will help keep the convection heat down in the summer and keep the heat in in the winter, I have installed in my attic and even when installing it you can feel the difference of the heat penetration. hope this helps.

Re: Cellulose insulation questions

Thank you for your response although I don't think that I can blow insulation into the soffit cavity without blocking the few soffit vents that I have. Although the DuroVent is installed there is still a gap between it and the top plate that the cellulose insulation will fill. If anyone knows if this must be filled or not please let me know. I have seen some products online that fill this gap but I can't seem to find anyone online or locally that will sell less than a case of 200. Far more than I would need. I just want to be sure to do it right the first time since I do not want to have to fix a mistake later.

canuk
Re: Cellulose insulation questions

As a suggestion ... move the baffle further down into the soffit cavity.

Then place some batt insulation between the top plate and the underside of the baffle. This will provide insulation for the top plate as well provide a damn blocking the cellulose from blowing into the soffit cavty. Insulation should be covering all the areas over the top plates of the below walls.

You might use some spray foam to seal all the pentrations into the attic before applying the final insulation.
For example .... where the electrical wiring is coming into the living space from the attic as well as the vent stack , etc..

As for having both gable vents and a ridge vent .... if the gable vents are high up near the peak this can actually cause a short circuit in the ventilation.
In other words you may end up having more air circulation between the gable and ridge vents and diminishing the convection flow from the soffit vents.

Just a thought. :)

Re: Cellulose insulation questions

Thank you very much.

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