Roof Ventilation & Foam Insulation?

[Derek Smith]

I've been following the inspection boards for some time and have seen conflicting answers on my following question. I certainly have picked up a lot of good tips!

I have a 1930's vintage house located in the country (Osage Co, OK). The house is outside city limits and as far as the County is concerned, they don't do inspections...nor do they offer advice.

Here's my issue. The attic above the 1st floor is very poorly insulated and I plan to remove the old cellulose and re-insulate the entire space. The hope is to turn the area into a semi-conditioned (there will be supply and return vents, but no thermostat, when the downstairs needs air the attic area will receive it) storage area. The thought is, remove the old cellulose, foam insulate the 1st floor ceiling, replace the plywood floor, add knee walls, foam insulate then drywall the knee walls and ceiling (underside of roof).

As is, the venting for the roof/attic space is minimal consisting only of a ridge vent with a ~1.5" "soffit" vent running the perimeter of the roof. There is not a true soffit built to extend the roof away from the perimeter walls, it's just a vent the former owner had the roofers install when the roof was replaced ?? years ago. My thought is that I would add baffles to the underside of the roof from the small "soffit" vent all the way up to the ridge vent so that when I foam the underside the baffles will preserve what little venting exists.

I was also thinking of adding the foil radiant heat barrier I have seen between the baffles and the foam. Or should it go between the underside of the roof and the baffles?

What are the downsides that I am sure I am missing with my above plan. Any ways to improve it? If pic's of the "soffit" vent and attic space would be helpful I can certainly add them.
Thanks
Derek

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[Jim Luttrall]

Sounds like you are mixing technologies without a good understanding of the principles.
Semi-conditioned is not what you describe. Any room with heating vents and returns is "conditioned".
My advice is to totally scrap your plans and go back to the drawing board. For instance insulating the ceiling/floor between conditioned spaces is a waste of money and accomplishes nothing toward energy conservation.
Typical air sealing and insulation methods may be a better fit for an older home. Numerous things need to be addressed before insulating such as removing any old knob and tube electrical wiring.
In general foam insulation is a good product BUT be sure to understand the physics of what you are doing BEFORE doing something that is virtually impossible to reverse, especially in a 1930's home.
Check out the Building Science Corporation website.

[James Bohac]

Dereck,
Jim has made some excellent points! There is no need to insulate the floor/ceiling space as you are creating conditioned space above this area. The ventilation of the attic space will no longer be needed as the spray foam should be installed at the roof against the sheathing. Other concerns to consider are providing proper combustion air for any gas fired systems located in the attic. I recommend consulting with a licensed contractor before performing any work.

[Derek Smith]

My mistake for calling the planned area "semi-conditioned".

As for the knob and tube wiring, it's all already been replaced by my father who is a licensed Electrical Contractor here in OK. Had him bury my service from the pole as well and replacing my main panel. Local Co-Op Electric company inspected it (their inspector) prior to reconnecting my service.

The gas fired furnace was installed by a friend of his who does HVAC (licensed as well) for a living. The furnace has been correctly installed with a direct vent (properly screened) to the outside for make up air (including proper slope and does not have too many turns). The furnace vent is located properly away from the make up vent. The furnace room is in the attic but it will be behind the knee wall, the area it is in has plenty of space on all sides for access. I also had him replace all the ducts (someone had put in flex before) with rigid ducts. Just to be thorough, I should note the furnace is also in a drain pan which is tied to the overflow condensate drain line.

Other than a small amount of electric there are no other utilities in the attic, everything is in the crawl space. The supply/return ducts for the house go from the furnace down a chase to the crawl space.

I guess I should have added these details at the beginning. Basically I'm providing the materials and grunt labor for the whole renovation and utilizing friends (like the above) to supply the knowledge and technical know how...several cases of beer are a lot cheaper than paying the going rate.

There seems to be two schools of thought out there (from my research) as to whether or not to maintain venting for the roof sheathing; that's why I asked for your opinions. Several roofing companies I have talked to maintain that for my warranty to remain valid, there must be an air space between the sheathing. Most of the foam companies I have talked to say I (warranty aside) don't need a space.

Thanks...

[James Bohac]

I have to side with Insulation folks on this one! There have been many documented issues with damage due to moisture, specifically at gaps in poorly insulated cathedral ceilings.
I do not see any reasons why shingles manufacturers would void warranties. I would understand if due to excess heat build-up at the underside of a roof, but this should not occur.

JMHO

[Bob Spermo]

Have you thought about re-sizing the HVAC system? There is a good chance that after all of your insulation is added a new load calculation would produce the need for a smaller unit.

[Peter Russell]

I would go with the un-vented roof assembly but there are a few steps that should be taken to ensure success.

Here's a good article on un-vented roofs in hot, humid climates.

http://www.buildingscience.com/docum...ofing-shingles

Also, many shingle MFG. now warranty their shingles on un-vented roof but it's limited. IKO for one will cover them for 10 years.

"REDUCED WARRANTY COVERAGE FOR INSTALLATION OF SHINGLES ON INSULATED ROOF DECKS
The coverage under this Limited Warranty is reduced for any Shingles, which are applied to any of the following:
a) roof deck assemblies (of slopes greater than 2 in 12) where foam insulation is prefabricated into the roof deck system (commonly known as “nail board insulation”), or
b) where insulation is installed immediately beneath an acceptable roof deck system.
In the event that such Shingles are installed on insulated or unventilated decks the Warranty Period available to the Owner is reduced to 10 (ten) years with no Iron Clad Protection coverage. The annual reduction figure in this case shall be 10% per year"

I would not insulate the floor but you will need to make sure all penetrations are sealed. Also make sure the venting for bathrooms and kitchen are properly done.

Here is a good link with all the info you need to understand un-vented roof assemblies.
Building Science Information

I have seen many of these systems in place, albeit in a cold climate and have given expert testimony in a construction litigation case, partly involving a HVAC system that was installed in the attic. In this case the heat generated for the heating unit cause the temperature in the attic to rise over 50 degrees, on days when it was below freezing, and resulted in ice damming and water intrusion. I think keeping the HVAC system within the homes thermal boundary makes sense but has to be done with a well thought out plan.

[Ken Amelin]

Derek,

Many good answers to your question.
Also, don't forget there is closed cell and open cell type foam insulation. Closed cell type is a better option for the roof deck.

[Jerry Peck]

Closed cell type is a better option for the roof deck.

Depends on who you talk to.

"Closed-cell foam would be used for roofing applications." Closed Cell and Open Cell Spray Foam Insulation - Spray Foam Information Directory - SprayFoam.com

"Closed cell foam should never be used on wooden roof decks." Open Cell vs Closed Cell Spray Foam Insulation | Comparison

[Raymond Wand]

Open cell is vapour permeable and permits two way drying of assemblies
and when applied to the underside of a roof deck, will allow for bulk water to pass through and visibly expose the location of an exterior roof leak.
Mason Knowles: Articles

[Jerry Peck]

Open cell is vapour permeable and permits two way drying of assemblies ...

That is the theory behind it, yes.

... and when applied to the underside of a roof deck, will allow for bulk water to pass through and visibly expose the location of an exterior roof leak.

In real life, having seen that *not happen*, that is a real good theory when applied as the theory goes - that it is VAPOUR (VAPOR to us down here) PERMEABLE ... and vapor eventually works its way through, provided the surface was not allowed to skin over and become burned from UV, creating a solid surface which does not let anything through it.

Water, on the other hand, does not go through open cell foam, I have tried it. You can use open cell foam as a sponge, fill it with water, wring the water out of it, and then let the sponge dry out ... er ... let the open cell foam dry out, and it will, unless there is something blocking the exposed surfaces of it, something such as being skinned over and burned by UV or having wood placed against it - then the moisture must dry out through the wood, which only happens if the wood is not being continually wetted (such as from a roof leak).

[Garry Sorrells]

Derek
A little more somethin-something on the subject :

Florida Researchers Take a Closer Look at Spray-Foam Roof Retrofits - Insulation - JLC Online

[Ted Menelly]

I would add baffles in all bays to the ridge or if you have a flat ceiling overhead where you actually have a small attic space. I would add a flat ceiling instead of running the drywall all the way up to the peak. Before the baffles I would spray a radient barrier on the underside of the plywood of the roof. Once the baffles are in place spray the foam in and then add drywall. The foaming of the knee walls is a good idea.

You get a radiant barrier, ventilation and insulation. I would never spray foam in or any insulation tight to the underside of the roof deck. Always ventilate.

Insulating between floors. I think it is a good idea for nothing more than sound deadening any noise. A good pad and quality carpet should take care of the rest of the noise. Obviously any electric in that floor or ceilings below should rake place.

I guess the biggy is? Is the floor joist or should I say ceiling joists below large enough to carry a load on them from above.