Hello Robert in Ontario Canada.

I remember you mentioning something about doing spray foam insulation in your attic, is that right?

I was just reading on a few things about it from other people. They were saying that insurance companies will not insure homes if they are spray foamed in the attic. The thought is that it creates moisture problems and rots the wood, plus it can deteriorate any shingles much faster.

Is that true where you are?

Have you heard anything about this?

I will skip over the positives and concentrate on the negatives of spray foam. If the contractor doing the install is the tradesman, not a new member on his crew, and he can trace back to chemicals from the manufacturer and mixes them himself: Then you stand a 85% things will turn out okay.

If you are planning to encapsulate the entire attic you need to remove any venting to the outside. You also need to add a vent from your HVAC unit as well as a return register.

In essence you are making the attic area climate controlled like the rest of the house.

There should be no moisture problems unless there is a leak from the outside. Because there is no heat build up there will not be damage to the shingles that happens when the attic is not vented and builds up massive heat.

Most attics that I have seen (online) with spray foam have just sprayed the attic floor, leaving good ventilation from the eave to the top of the roof.

Back in the 90's we hired a company to spray vaulted ceilings. Once the electric was all in place there were no problems or concerns.

It wasn't cost effective to do the entire house back then. I doubt it would be now either, even though spray foam does work better than fiberglass overall.

We had the exterior floors of our studios spray-foamed with closed-cell foam. Where we had previously multiple hunks of insulation and plywood now one relatively thin layer was there, and it also helped stabilize the entire unit.

Tenants saw an effect in that lowered draftiness.

Simply explaining the science around encapsulating an attic.

With a completely sealed attic you are not using much more from your HVAC as the insulation keeps the outside temperatures at bay. Mostly you just want air movement.

High ceilings helped the heat to get above the people. Another win for transoms. But then in the winter it takes more to keep the heat down where the people live. Trade off because they had mechanical ways to heat, but not cool.

I believe that large windows were more for light than temperature controls. Maybe a little one upmanship as glass was harder to get and maintain. Doing better than the Jones's and all that.

Also I do not think that old houses were built to breathe. I believe it just happened to be a bonus. A completely sealed house now can cause issues with air quality. A little make up air is for the best.