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JOHNBUSHE
ventilation

my roof rafters are 18.5 to 19 on center ,6 inch boards,rafter vents are made for 16 on center and 22 on center any alternatives to vent properly just fixed mold problem so now i want to vent and insulate,and also should i buy 22 inch insulation and cut down and then cut edge to expose facing to staple to rafters,please help

RJordan
Re: ventilation

As a spray foam contractor, perhaps I'm not impartial. But when I work in attic after attic with fiberglass and see nothing but problems, I become suspicious. Fiberglass lets air through it and the air carries heat and moisture. The real solution to your problem is to seal the attic and spray the underside of the roof deck with foam. Doing what you plan will have little benefit.

JOHNBUSHE
Re: ventilation
RJordan wrote:

As a spray foam contractor, perhaps I'm not impartial. But when I work in attic after attic with fiberglass and see nothing but problems, I become suspicious. Fiberglass lets air through it and the air carries heat and moisture. The real solution to your problem is to seal the attic and spray the underside of the roof deck with foam. Doing what you plan will have little benefit.

if it gets spray foam insulation how will it breathe ? dont you need air flow up rafters?please explain?

JOHNBUSHE
Re: ventilation

if it gets spray foam insulation how will it breathe

canuk
Re: ventilation
JOHNBUSHE wrote:

if it gets spray foam insulation how will it breathe ? dont you need air flow up rafters?please explain?

Just doing the underside of the roof isn't the complete way of doing this.
All exterior surfaces of the attic --- underside of the roof ---- gable walls ---- etc. --- need to be covered.
This creates a semi-conditioned space by raising the inside temperature during the winter and lowering the inside temps. during the summer.
When this happens there isn't a necessity to require the attic to breath per Se.
By raising the temperature and closing off the venting you are maintaining a pressurized space with a more constant temperature lessening vapour drive from the interior into the attic and condensing ---- though it still is important to seal any penetrations from the interior into the attic.

RJordan
Re: ventilation

I m always confused when people say buildings need to
"breathe". Buildings are not living. What do you mean?

RJordan
Re: ventilation

OK OK. I am playing devil's advocate and you more or less fell into my trap.

People are speaking very imprecisely when they say buildings need to breathe. Buildings are not living. So buildings don't need to breathe.

What is meant is that people in buildings need healthy air. This is the point of the Fine Homebuilding article. It is about providing healthy air to people and I agree totally. A leaky building is no guarantee the building has proper ventilation. That only happens with a properly designed ventilation system. People breathe because we have a respiratory system, not because we are full of holes. When builders say this, I wonder how they went about making it not too leaky or not too tight. Doesn't their building leak more on a cold windy day than on a warm, still April day? Where do these leaks occur? How did they keep moist air from the building and causing rot?

Secondly, buildings need to be protected from moisture. This is a longer, important, discussion. Attic "ventilation", however, isn't the answer.

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