I have a crawl space on the second floor of my home. The ceiling (top) of the crawl space is the roof of my home, hence is very cold. I have heard that putting insulation directly under a roof may damage the roof / shingles. Is this true? If so, what is the best way to handle this? Would just placing some boards on the ceiling of the crawl space be fine to at least minimize the cold coming through the roof? Thanks.

The place for insulation in a situation such as you describe is in the CEILING of the room below (or the floor of the crawl space; same thing), NOT in the roof above the crawl space.

If the crawl space has a floor, the floor should be removed, and insulation placed between the ceiling joists. The thickness will depend on the requirements of the region where you live, and the depth of the ceiling joists.

The floor is indeed already insulated. Is that sufficient then? Would doing the ceiling indeed damage the roof? What about, as I mentioned, just putting a piece of plywood over the ceiling joists to minimize air flow?

The insulation and crawl space floor already block cold air from the roof from entering your living space. If you put boards under the rafters, you will be creating unventilated enclosed spaces which could accumulate moisture, leading to possible mold issues and rotting of structural members.

The idea is to keep the roof cold, and most roofing shingle manufacturers advise against insulating directly under the roof. Again, if you did, there would be no ventilation between the underside of the roof and the insulation, and the same problems could arise.

If you have a problem with the ceiling, then you need to add more insulation IN the ceiling, by removing the floor and possibly "furring" the joists (adding wood to their tops) to create more depth and thus more space for insulation.

quote:

"The ceiling (top) of the crawl space is the roof of my home, hence is very cold. I have heard that putting insulation directly under a roof may damage the roof / shingles. Is this true? "

No, this is NOT true.

Insulation is routinely placed in roof rafters with absolutely no harm to shingles.

Every cathedral ceiling...
Every Cape Code style home...
Every roof frame with structural insulated panels....has insulation placed directly in the roof rafters or part of the roff assembly and shingle longevity is not reduced.

In fact, 'sealed' attic designs, just as sealed crawlspace designs, are the most energy efficient means by which an attic or crawlspace can be constructed.

Sealed attic designs utilize insulation in the rafters as well as knee and exterior walls and eliminate all air communication to the outside.

This not only saves energy, it reduces moisture problems when adequately designed and implemented.

Placing attic insulation in the floor of the attic can work, and has worked for decades, but it is not the only, nor necessarily, the best means to insulate.

The key to placing cavity insulation in rafters is to make sure the space between the insulation and roof deck is properly ventilated when using fiberglass or blown insulations.

What is the proper way to vent fiberglass placed in the ceiling rafters then? My confusion now is that I am getting conflicting answers. Ice ****s were one of the major concern I had, as well as problems of a similar nature that may occur in the summer.

What will mitigate against ice dams is keeping the roof cold. That helps prevent snow from melting, creating water flowing down the roof to the overhangs, where the roof is again cold, so the water re-freezes there and voila, an ice dam occurs. If the roof is kept at nearly the same temperature as the outside, then melting is minimized, and ice dams are much less frequent.

What will keep the roof cold would be proper attic (or, what you have called a crawl space) ventilation. Insulation in a ceiling doesn't need to be vented, because presumably the attic is vented. People sometimes mistakenly close the attic vents in winter, thinking that they are saving heat, not realizing that the ventilation is even more important in winter than in summer.

Doesn't insulating the ceiling though create potential damage to the roof in the summer due to the extreme temperatures? No one has addressed the summer time at all since it is winter right now.

My issue now then is to make sure the space is adequately vented. Any easy suggestions on how to check this (without of course being able to see the space)? Wouldn't vetining the space make it cold though (sorry if these quaestions are completely ignorant)? I know a while back we bought some long flat styrofoam type sheets (sorry I don't know what they are called) ti ventilate our top attic and have some left. Do you know what these are and if they are adequate in doing the job and how to properly install them?

Ventilation moderates the temperature in the summer, and keeps the roof cold in the winter. That's why vents MUST remain open all year round.

Yes, the ventilated crawl space will be cold...almost as cold as the outdoors; that's the point. Keep the roof cold.

I don't know what those sheets are that you describe, but they probably have little to do with ventilation, unless they are the foam sections that are placed above insulation at the lower part of a ceiling/roof, to ensure that soffit ventilation has a path through to the ridge vent. If that's what they are, they would have no use in your attic/crawl space...it should be vented by louvers in the end walls, or by a combination of soffit vents and ridge vents.

quote:

Doesn't insulating the ceiling though create potential damage to the roof in the summer due to the extreme temperatures? No one has addressed the summer time at all since it is winter right now.

I addressed it and the answer is:

No, it does NOT.

Shingles placed over insulated rafters spaces do NOT fail at greater rates.

If they did, then it would be evident in all shingles above cathedral ceilings, and above cape cod style roofs and above Structural Insulated Panles...where the rafters or roof system itself is insulated. yet this is never observed in reality.

The reality is that shingles last just as long over insulated rafters as they do over ventilated attics.

Those are presumably shingles over VENTILATED insulated rafters. If there has been no provision for adequate ventilation above the insulation, it's a very different story, and some shingle manufacturers will not honor warranties if insulation is placed directly under and in contact with the roof sheathing.

Adequate ventilation must have an inlet, usually soffit vents, and an outlet, usually ridge vents, with a clear and unobstructed path between the two.

The ventilation serves to moderate temperatures in warm weather, and to keep the roof cold in cold weather, as well as to allow moisture, which can reduce the value of insulation greatly, to escape from the assembly.

So my final understanding is this:

Insulation directly under the roof is fine, but there needs to be some space between the insulation and the roof deck, correct? Would placing a plywood board over the insulation on the ceiling help? The crawl space is all that truly needs to be ventilated, not the space between the insulation and the ceiling, correct?

The part that seems a bit counter-intuitive to me is this. I am trying to reduce the cold in the crawl space by inuslating the ceiling, but at the same time it sounds like the crawl space needs to be as cold / warm as outside. Why waste time then insulating the roof if the room will remain cold anyway from the vents. I should then just focus on making sure the insulation between the crawl space and the living area is adequate. Am I looking at this incorrectly?

Well, your conclusion is OK but some details along the way are not.

It is not sufficient to have space between insulation and roof sheathing if that space is not properly ventilated by having a low air inlet such as soffit vents and a high air outlet such as a ridge vent.

A plywood board over the ceiling insulation might help minimally, but don't expect to be able to measure the difference.

I'm not sure exactly what your original problem was, but if your room ceiling is properly insulated, the temperature in the crawl space should not matter. The insulation in your room ceiling will depend on the region where you live. In colder regions, it should be R-30 or R-38, which is equivalent to 9 inches of typical fiberglass insulation. In warmer regions, perhaps R-19 would suffice, which is equivalent to 5 1/2 inches of fiberglass.

If you have less insulation than that, and your ceiling joists will not accomodate more insulation between them, you can do either of two things: (1) add wood to the tops of the ceiling joists and replace the insulation with new insulation of the proper thickness, or add sufficient UNFACED insulation above the existing insulation; or, (2) add sufficient unfaced insulation running perpendicular to the ceiling joists, over your existing insulation.

The only time you would need to add wood to the tops of the ceiling joists is if you need a floor in the crawl space.

But your conclusion, that you should concentrate on the ceiling, is correct.

I'm not sure I got you. You said that my conclusion about concentrating on the ceiling is correct? I think I had asked whether I could just focus on the wall between the living area and the crawl space and make sure that area is sufficiently insulated, then forget about the ceiling. The way I look at it is it would not matter how cold the crawl space is, as long as there is enough protection (insulation) between the crawl space and the living area. Basically, I would be creating a small space that is very cold, but surrounding it with insulation to keep the cold trapped in there.

Again, if I have to vent the crawl space and it should be as cold inside the space as it is on the outside (which it probably is right now), why should I bother insulating the ceiling?

Sorry, my mistake. I assumed you were talking about a crawl space ABOVE a room, not alongside a room, but you have now corrected my misconception.

In that case, yes, concentrate on the wall which separates the crawl space from the living space. Normally, walls will now have an insulation rating of R-19. Depending on the age of your house and its location, your wall may be R-11 or less, if very old.

If you have access to the studs, you can replace older insulation. The most you can fit in a 2x4 stud wall is R-13, and that insulation is hard to find, so you may be limited to R-11. If your studs are 2x6, you can fit R-19 or the harder-to-find R-21. If you'd like to have R-19 but only have 2x4 walls, you can add 2x2 strips to the studs and use R-19.

And yes, the insulated WALL should isolate the cold (or in summer, the heat, in the crawl space.

Sorry for the misconception.

Now I think we're on the same page. That was my original plan, which was to just handle the wall and not worry about the ceiling. Now that I think about it, I believe there is a vent in the ceiling of the crawl space, so I don't really want to cover that since it seems important.

I will probably just add additional insulation along the wall and cover that insulation with a thin plywood board as I have heard that reducing insulation's direct contact with air is better (that true?). There is existing insulation already on the wall though I don't know if it's any good. Should I remove it or add some on top if possible? That's all probably easier than messing with the ceiling.

Whether or not you remove the insulation depends on how old it is, how thick it is, and what condition it's in. What color is it? If it's pink, and not sagging, and completely filling the spaces between the studs, it's probably fine. If it's yellowish, kind of sagging, and sort of irregular, then I would replace it.

If your studs are 2x4 and you want more insulation, you can put deeper insulation in, such as R-19, which will stick out 2 inches, but then you can't put playwood over it.

I really don't think the plywood will do very much for you, but it won't hurt anything either, so if it makes you feel better, do ahead and install it. If you want thicker insulation AND plywood, you can add 2x2's to the 2X4's, using long screws to hold them in place, then install R-19 insulation and your plywood.

Be sure you place the vapor retarder side of the insulation IN toward the inner wall surface, which is probably wallboard. The vapor retarder always goes on the winter warm side of the wall, which is toward the living space, unless you live in the deep south.

Oh, and make sure there is only ONE vapor retarder. If by chance you choose to add insulation over the existing insulation, use UNFACED insulation, or if the new layer has a vapor retarder, slash the living daylights out of it before you install it.

The insullation I say may be bad is actually a grayish color. Parts of the wall have the insulation flaking off even, and that is what makes me think it all may be starting to go bad.

Insulation is cheap enough. I would replace it with as much fiberglass roll insulation as you can fit in the depth of the studs.
2x4 studs: R-11 or R-13 if you can find it.
2x6 studs: R-19 or R-21 if you can find it.
R-13 and R-21 are sometimes difficult to find, but whatever you install will likely be an improvement.