Attic insulation

[helmet-rough6734]

Helping out my sister in building their attic. I plan to insulate the rafters with fiberglass and a layer of rigid foam. But it looks like it will block the soffit-to-ridge airflow we're always told is key to avoid moisture issues. How do I go about this? By the way, we are in Vancouver and you know climate here can be damp. Thanks everyone!

 

[DamienHushTM]

Helping out my sister in building their attic. I plan to insulate the rafters with fiberglass and a layer of rigid foam. But it looks like it will block the soffit-to-ridge airflow we're always told is key to avoid moisture issues. How do I go about this? By the way, we are in Vancouver and you know climate here can be damp. Thanks everyone!

That airflow is a make or break detail for a damp climate. You need to install insulation baffles or 'rafter vents' up against the roof sheathing 1st which creates an air channel from the soffits to the ridge. What R-value are you aiming for with your foam and fiberglass combo?

 

[New_Pie_1991]

Agree with the response above. Those baffles keep a clear path for air to flow up to the ridge. They're easy to find at hardware stores and make a big difference in preventing moisture buildup.

 

[juggern0t]

Also air seal any gaps below the insulation to keep warm, moist air from sneaking in, good ventilation plus proper air sealing is the combo you want

 

[LemongrassLime]

The Ventilated rafter system is probably your best bet, but let's say that for some reason this might not be an option, in which case you'll probably need to consider and unvented foam roof which should work in theory, but you'll need to make sure you do it right. Inspect every corner and make sure everything is sealed tight and make sure you're using at least R-20, but more would be better.