Attic insulation and plastic baffles for ventilation

[Cheyenne Dave]

That sounds reasonable and make sense, if the rafter bay is also insulated as in the drawing.
I insulated all of my roofs as well as the attics, a cool roof lowers the attic temperature by at least 20 degrees in Summer and keeps it about 10 degrees warmer in Winter, the baffles work well to inhibit ice dams.

The rafter bay would only be insulated in a living space, but not an unheated space. The roof system should be thought of as more of an umbrella, shedding water but allowing the unheated attic space to remain as close to outside temperature as possible.

C.D.

[MoparNorm]

Sorry Dave,
I must disagree.
And it doesn't depend entirely upon the climate zone. In Summer climes in the southwest, I've insulated my attics and roofs in un-conditioned spaces, since 1975. It keeps the structure at least 20 degrees cooler in summer and saves thousands per year in cooling costs. When it's 85 degrees outside, with an uninsulated roof, the attic temps can reach over 130 degrees.
My customers are very happy with that savings.
The reverse is also true, in winter. Keeping the heat in the house from reaching the roof and melting the snow prevents ice dams and water damage. And the heating costs are less.

[Gordon Maney]

Sorry Dave,
I must disagree.
And it doesn't depend entirely upon the climate zone. In Summer climes in the southwest, I've insulated my attics and roofs in un-conditioned spaces, since 1975. It keeps the structure at least 20 degrees cooler in summer and saves thousands per year in cooling costs. When it's 85 degrees outside, with an uninsulated roof, the attic temps can reach over 130 degrees.
My customers are very happy with that savings.
The reverse is also true, in winter. Keeping the heat in the house from reaching the roof and melting the snow prevents ice dams and water damage. And the heating costs are less.

But....doesn't that simply mean that your ceiling is not adequately insulated? ...if your room temperature is higher if you don't insulate between the rafters, we really need more insulation between the ceiling joists? Then you would not need to insulate between rafters.

[MoparNorm]

What we have here is a failure to communicate..ha!ha!
I'll try to do a better job explaining it:

The ceiling of a room is insulated, as much as R-30 depending upon the construction (joist size) and the Climate Zone requirements (this is one case where more is better).
A normal attic space above the insulated room in summer can be as much as 130 degrees, it's a solar heat box. The room below is properly insulated but by late afternoon that room's insulation would have been passively fighting back that 130 degrees for many hours and eventually loses the battle. Insulation buys time, it is not a magic barrier that prevents heating and cooling, it is a barrier that slows the movement of heat and cold.
In a room cooled to 72 degrees in summer, that attic is nearly 60 degrees hotter than the room below. Thermometers placed at the floor of the room and at the ceiling of the room will show nearly a 15 degree difference. When you insulate and ventilate the attic you can cut the attic temperature by as much as 30 degrees. That's 30 degrees that your air conditioning system is not fighting to overcome. Your A/C temperature is still set at 72, but the ceiling temperature may only be near 80 now, making the room "feel" much more comfortable and allowing your air conditioner to run less and save on cooling costs.
In winter the effect is the same except reversed, the ventilation is closed to allow the attic to heat up. Since heat rises, approx. 80% of heating loss is out of the roof. The attic insulation helps retain the attic heat, but prevents the heat from reaching the underside of the roof which melts snow and causes ice dams.

There are many other facets to properly insulating a home, such as draft stops, thermal/moisture barriers, properly sealed. Door and windows, eave construction, home orientation to the sun, etc.
I've been building passive solar homes since the 70's. At some point in the mid 80's the humidity levels of our lovely planet had risen to a point where passive solar does not work in every climate, you need a very dry climate. However I have found that, by applying the techniques I learned over the years, to conventional construction, heating and cooling costs could be dramatically lowered.
Production and tract homes are not built this way because it costs a few dollars more and slows down production times.
I've always tried to push the envelope...or in this case, seal the envelope better!

[Gordon Maney]

So, then, what are you using in the spaces between the rafters, foam board?

I think I would worry about using paper faced glass bats, due to the humidity in the air in that space.

Really what it boils down to is, more is better.

[MoparNorm]

So, then, what are you using in the spaces between the rafters, foam board?

I think I would worry about using paper faced glass bats, due to the humidity in the air in that space.

Really what it boils down to is, more is better.

I use R22 glass batts with a moisture barrier on BOTH sides of the batt. I haven't used paper in many years. Even in areas where moisture is not a problem, the heat makes the paper (and in some cases the foil) very brittle in a matter of a few years.

[Gordon Maney]

What do you mean by moisture barrier, in this case?

[Cheyenne Dave]

Yo Normy...

Sorry Dave,
I must disagree.
And it doesn't depend entirely upon the climate zone. In Summer climes in the southwest, I've insulated my attics and roofs in un-conditioned spaces, since 1975. It keeps the structure at least 20 degrees cooler in summer and saves thousands per year in cooling costs. When it's 85 degrees outside, with an uninsulated roof, the attic temps can reach over 130 degrees.
My customers are very happy with that savings.
The reverse is also true, in winter. Keeping the heat in the house from reaching the roof and melting the snow prevents ice dams and water damage. And the heating costs are less.

We seem destined to disagree, at least on this subject. I'm sure your customers are happy with your new construction techniques and energy saving results, in structures that were designed with that in mind . By SAVING thousands of dollars on the heating/cooling costs, they must be monsters in size...or they are just bungalows in Cali...heheh!!

I too have decades of experience in this field. The major thrust of my work has been in the restoration/rehabilitation of many different types of construction. What we started talking about here is ventilation. Why? Because we are not only concerned with energy savings, but the removal of moisture from the structure, for the mutual well being for the building and it's occupants.

Why?

Because moisture causes premature paint, roof deck, and structural damage. Because living in too closed a space is reported to be not good for us. I've been dealing with it for years. I fail to see how insulating the roof over an unheated space, that is over a well insulated space, does anything more than slow the exit of harmful moisture vapor. I'm very interested in hearing how to properly ventilate such a space, without negating all that extra insulation. With proper ventlation techniques, I can keep an attic space temperatures surprsingly low.

There is quite a strong arguement that buildings such as Gordon's are still around due, in large part, to how "loose" they were built. I feel there is a happy medium between living in a stuffy super envelope and the wide open spaces. A house with a well insulated ceiling covered by a very well ventilated attic space (along with as many of the other options you mention in your other posts as one can afford) goes a long way towards that goal.

Am I living in the past, letting the world pass me by? That's just crazy talk! I drive a Power Wagon, I am totally up on what's new! And my customers are just fine with that too... HAHA!

C.D.

[Clint Dixon]

Interesting subject

.....Because moisture causes premature paint, roof deck, and structural damage. Because living in too closed a space is reported to be not good for us. I've been dealing with it for years. I fail to see how insulating the roof over an unheated space, that is over a well insulated space, does anything more than slow the exit of harmful moisture vapor.... C.D.

Dave, you have seen my house. Our's is a modified A-frame with a cathedral ceiling. I did not know it until I started tearing apart the structure to build my upstairs dormer, but whoever built the house placed the bats of paper backed insulation right against the underside of the roof sheeting. We have about a 24-inch tall "attic" at the very peak of the roof with a gable vent and continuous soffit vents at both eaves None of these vents were doing any good with the insulation against the roof sheeting. Our asphalt shingles were curling as you mentioned from the lack of ventilation. When I discovered the problem, I tore out as much insulation as I could, in the side attics behind the knee walls at both sides of the bedroom, and all between the rafters forming the slanted ceiling above the bedroom. The insulation was wet from condensation and the roof sheeting was discolored. I installed spacers like those talked about here, only mine are made of a thin polystyrene type of plastic. Now our soffit vents and gable end vents are actually working and ventilating the underside of the roof sheeting. You can actually see the airflow by placing a piece of paper at the soffit vents. The new shingles that I laid appear to be fairing much better. I only wish I could do the same above the cathedral ceiling, but this would require removing 500 sq ft of rough sawn white oak and drywall.

We have also had an ongoing problem with window condensation since we moved into the house in 1986. Replacing the old Crestline windows with top-of-the-line Marvin double hung units did not help. Our window rep found out that our whole house is coated inside with vapor barrier between the sheets of drywall and the insulation, locking winter moisture in the house and forcing it to try to escape through the windows. All of my new construction has been completed without the plastic vapor barrier. In the rooms without the vapor barrier, the windows show less condensation during the winter.

[Gordon Maney]

Dave, you have seen my house. Our's is a modified A-frame with a cathedral ceiling. I did not know it until I started tearing apart the structure to build my upstairs dormer, but whoever built the house placed the bats of paper backed insulation right against the underside of the roof sheeting. We have about a 24-inch tall "attic" at the very peak of the roof with a gable vent and continuous soffit vents at both eaves None of these vents were doing any good with the insulation against the roof sheeting. Our asphalt shingles were curling as you mentioned from the lack of ventilation. When I discovered the problem, I tore out as much insulation as I could, in the side attics behind the knee walls at both sides of the bedroom, and all between the rafters forming the slanted ceiling above the bedroom. The insulation was wet from condensation and the roof sheeting was discolored. I installed spacers like those talked about here, only mine are made of a thin polystyrene type of plastic. Now our soffit vents and gable end vents are actually working and ventilating the underside of the roof sheeting. You can actually see the airflow by placing a piece of paper at the soffit vents. The new shingles that I laid appear to be fairing much better. I only wish I could do the same above the cathedral ceiling, but this would require removing 500 sq ft of rough sawn white oak and drywall.

We have also had an ongoing problem with window condensation since we moved into the house in 1986. Replacing the old Crestline windows with top-of-the-line Marvin double hung units did not help. Our window rep found out that our whole house is coated inside with vapor barrier between the sheets of drywall and the insulation, locking winter moisture in the house and forcing it to try to escape through the windows. All of my new construction has been completed without the plastic vapor barrier. In the rooms without the vapor barrier, the windows show less condensation during the winter.

Isn't that fascinating with regard to what it tells us about moisture migrating through the insulation?

Do you run a humidifier?

I cannot recall where I read or heard this, but supposedly, carpenters are now learning that houses that were wrapped in Tyvek for quite some time now have a lot of decay in their framing, supposedly because of it being a vapor barrier, even though it was not supposed to be.

As Dave said, my house was quite loose, and still is, I suppose. But, prior to siding it, I tore off all of the lap siding. The people putting the siding on then covered the entire house with 3/4 inch, foil covered foam, and the seams were taped. That certainly is stopping moisture.

Occasionally when it rains, afterwards, I see water has run down from the lower edge of the laps, so.... where did that come from? Between the siding and the foam, I guess, but how did it get in there?

I think a lot of evil lurks where we cannot see.

[MoparNorm]

We seem destined to disagree, at least on this subject. I'm sure your customers are happy with your new construction techniques and energy saving results, in structures that were designed with that in mind . By SAVING thousands of dollars on the heating/cooling costs, they must be monsters in size...or they are just bungalows in Cali...heheh!!

I too have decades of experience in this field. The major thrust of my work has been in the restoration/rehabilitation of many different types of construction. What we started talking about here is ventilation. Why? Because we are not only concerned with energy savings, but the removal of moisture from the structure, for the mutual well being for the building and it's occupants.

Why?

Because moisture causes premature paint, roof deck, and structural damage. Because living in too closed a space is reported to be not good for us. I've been dealing with it for years. I fail to see how insulating the roof over an unheated space, that is over a well insulated space, does anything more than slow the exit of harmful moisture vapor. I'm very interested in hearing how to properly ventilate such a space, without negating all that extra insulation. With proper ventilation techniques, I can keep an attic space temperatures surprsingly low.

There is quite a strong arguement that buildings such as Gordon's are still around due, in large part, to how "loose" they were built. I feel there is a happy medium between living in a stuffy super envelope and the wide open spaces. A house with a well insulated ceiling covered by a very well ventilated attic space (along with as many of the other options you mention in your other posts as one can afford) goes a long way towards that goal.

Am I living in the past, letting the world pass me by? That's just crazy talk! I drive a Power Wagon, I am totally up on what's new! And my customers are just fine with that too... HAHA!

C.D.

Should I have put this in bold?

When you insulate and ventilate the attic you can cut the attic temperature by as much as 30 degrees.

I don't think we disagree on the concept at all Dave, I do think that we have more cooling concerns here than you may have there, however we have also found that there are winter benefits as well.
Short of completely gutting the gable, there is a limit to how much ventilation can be achieved, so any roof is still going to have a solar heat gain that transmits to the living space below. Insulating the underside of the roof deck has worked very well for us. I started using mylar covered batts, in R 4, the same that you see under the roof of metal buildings, it worked so well that we doubled the layers in the next house. You certainly do need enough passive and active attic ventilation to move the required cfm of superheated air out of the attic space, roof turbines, gable and ridge vents, both powered and unpowered are a important key to the system.
Remember, we have many areas here above 8,000 feet in addition to our desert and beaches, I build in 4 climate zones...in a 100 mile radius!
Yes, Gordon's home probably did survive because it was poorly sealed, but I've found that there are ways to make a home air tight and still move the air to prevent, rot and mold and other undesirable effects of moisture.
Good techniques and craftsmanship are always effective.
And yes, there are tiny bungalows out here! = ) As well as 6,000 to 14,000 sq. ft. monsters. A 1600 sq ft. house can have a $300+ a month summer cooling costs when it's over 110 everyday for 6 weeks.
A large portion of my work is restoration and remodel, it's great fun and a challenge to take a older, poorly insulated home and make it work correctly.

[Cheyenne Dave]

Isn't that fascinating with regard to what it tells us about moisture migrating through the insulation?

Do you run a humidifier?

I cannot recall where I read or heard this, but supposedly, carpenters are now learning that houses that were wrapped in Tyvek for quite some time now have a lot of decay in their framing, supposedly because of it being a vapor barrier, even though it was not supposed to be.

As Dave said, my house was quite loose, and still is, I suppose. But, prior to siding it, I tore off all of the lap siding. The people putting the siding on then covered the entire house with 3/4 inch, foil covered foam, and the seams were taped. That certainly is stopping moisture.

Occasionally when it rains, afterwards, I see water has run down from the lower edge of the laps, so.... where did that come from? Between the siding and the foam, I guess, but how did it get in there?

I think a lot of evil lurks where we cannot see.

The ideal moisture vapor barrier would allow vapor from the inside to migrate outside, while preventing any intruding water from entering from the outside. Tyvek and other wraps are supposed to be up to this challenge, when properly installed.

We create moisture within our homes from bathing, cooking and breathing. A big help with this moisture can be the religious use of exaust fans; in the bathrooms during showers and in the kitchen while cooking. I suppose not breathing isn't much of an option, hehhe...The tendancey is for water vapor to migrate up, along with hot air. But the sun, like on a southern exposure, can also draw moisture out through the walls. Clint, you likely found more damage on the south-facing roof exposure for this reason. This is one source of exterior paint failure. I have removed celulose insulation from a south-facing wall and found it to be loaded with moisture. I am not keen on celulose insulation.

If the moisture can't escape, you will have mold and decay. As far as the craft-faced type of batt insulation, the vapor barrier (paper) side should always face the living space. That means in floors, the paper needs to be against the deck, or use unfaced batts. In the walls and ceiling it should face the room.

Clint, your type of roof can be a challenge to vent properly, as a retrofit project. It may be possible to ventilate the remaining roof area by attacking it from the outside. Instead of removing all that nice interior ceiling, you could strip the roof from the outside and deal with from that side. Just a thought, I wouldn't advocate such a radical approach without knowing that you will thoroughly investigating all your options. Perhaps a house call is in order!

Gordon, I am having a problem visualizing where you are seeing water. Is your new siding steel or what?
C.D.

[MoparNorm]

Isn't that fascinating with regard to what it tells us about moisture migrating through the insulation?.....

Gordon, I'm not sure that is Clint's problem. He stated that the moisture barrier is on the INSIDE of the insulation.
As Dave stated, most moisture comes from the inside, from the humidity caused by our bodies, breathing and activities with-in the home. A well sealed barrier would prevent moisture from reaching Clint's insulation. So one can assume that either the barrier is not well sealed, or the source of the moisture is from the exterior.
Dave is also correct that in the zeal to superinsulate houses and install moisture barriers a lot of untested, untried and downright lame concepts were attempted.
Supposedly the new Tyvek is similar to gore-tex in that it allows moisture to wick out while stopping outside air infiltration. I do know it is hardy stuff. I've seen houses wrapped with it that for whatever reason did not get siding installed for several years, the Tyvek was still as good as new years later when the siding was installed.
Anyone looking up at an old wood shingle roof will see daylight pouring through, but not a drop of water, it's the same with so-called air tight houses that are built correctly, the intent is to stop air infiltration in winter, but allow moisture to escape to the outside. I'm not sure that common plastic wrap is the way to go.

[Clint Dixon]

....Do you run a humidifier?....

We do not run a humidifier, but we do have a LOT of house plants.

....Clint, you likely found more damage on the south-facing roof exposure for this reason....Clint, your type of roof can be a challenge to vent properly, as a retrofit project....you could strip the roof from the outside and deal with from that side....Perhaps a house call is in order!...C.D.

Yes, the south was much worse than the north. In about 25 years I should need new shingles and can attack the problem then!?! We are always available to schedule house calls! ;^)

Gordon, I'm not sure that is Clint's problem....A well sealed barrier would prevent moisture from reaching Clint's insulation. So one can assume that either the barrier is not well sealed, or the source of the moisture is from the exterior....

It appears that the problem developed because of the lack of ventilation between the insulation and the roof sheeting. Even though the roof had vapor barrier between the rafters and drywall, SOME moisture was still getting through. It was just that most of it was migrating to the windows and what got through the vapor barrier was being held there by the insulation against the underside of the sheeting.

[Gordon Maney]

In about 25 years I should need new shingles and can attack the problem then!?!

Is the way clear so that I will be able to get through with my walker, so that I can watch?