do shingles breathe?

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maxwell_smart007

maxwell_smart007

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I've been applying rigid foam to the underside of my roof, due to a condition where I cannot get any insulation at all at the bottom of the roof slope using traditional methods, due to the low slope of the roof.

I had the roof checked before I started (it's about 5 years old), and began working on the insulation.

I'm now almost done, but one of the areas to which I have attached foam (but not sprayfoamed around the sides), is damp - I chiseled out the bay beside it, and it's slightly damp as well.

I have the roofer coming by this evening to check it - but I was wondering if this area can dry out to the roof side (assuming felt paper was used), or if I'm going to have to remove some of the foam to let it dry to the inside of the house (a prospect I do not relish at the moment)...

so, do shingles breathe, and allow moisture below them to escape?
 
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My opinion - if you have wood shingles, they can breathe. If you have asphalt (or similar) shingles, they probably won't because they sort of seal together.
 
We were doing asphalt a few years ago and was told that we had to (by code) install a roof ridge vent cap in addition to the vents on each end of the house because the shingles would trap moisture.
 
Andrew are you saying you applied this insulation to the underside of the shingles?? So you have shingles , tarpaper, wood, and then the insulation??????
Lin
 
Was that recommended to you or is it some kind of code there? Based on my experience fixing builder insulation mistakes on a house I owned, it may be ill-advised. Free flow of air on the underside of a roof deck is required except in very specific well-engineered situations.

From the outer surface of the shingles to the inner surface of the insulation, you have a cold to warm temperature gradient. Somewhere along that gradient you are going to be at the dewpoint temperature. Whatever moisture as water vapor has migrated into the area between the insulation and the roof deck will condense at that temperature. If the temperature gradient happens to put the dewpoint at the interface between the insulation and the roof deck, the water could be appearing at the place where you haven't sealed it.

The bigger issue, if I am understanding the situation, is that you may be creating a situation where the conditions are right for mold/rot on the underside of the deck.

Hopefully I've misunderstood the question and I'm just babbling incoherently!
 
Asphalt shingles need their underside vented or they build up too much heat and traps moisture which shortens their lifespan. The shingles will not be warranted if the installation instructions are not followed. Its logical to assume if the roof can breath it will inhale as much as it exhales so even if it dried out now you can bet it will be wet again in the future.
 
You always need to have an air space between the insulation and the roof decking, and you need to have soffit vents and some type of ridge vent or whirly birds to draw the air in the soffit and exit at near the peak. If you do not do this the decking will sweat and delaminate over time. All you would need to do is install 1" strips against the rafters and install the insulation to the bottom of the strips.
 
No, shingles absolutely do not breath.... The only way you can fully insulate a rafter bay is with icynene ( commercial spray foam) or, if allowed by your local building inspector, properly installed blown-in cellulose insulation.

Both of these methods produce a virtually vapor and moisture proof environment that does not require ventilation.

All other methods of fully insulating a roof bay ( space between the rafters) is to provide a continuous 2" air space at the top of the bay ( directly under the roof sheathing) which runs from the ridge to the soffit.

Fully insulating the bay without ventilation will create a nearly continuous supply of moisture to the underside of the roof sheathing and will cause it to rot out rather quickly. It can alos lead to rather serious infestations of mold
 
Not clear on why you are applying the insulation to the underside of the roof , rather than between and on top of the ceiling 2x4`s . Attic spaces are best held at external ambient conditions for the reasons Jeff gave , not used as another layer of insulation , particularly in our soon to be balmy , winter conditions .
 
There's an attic space at the 'high' end of the roof, and zero space at the bottom end - it's a stupid design, and it made it ridiculously cold, as there was no insulation at the bottom end, and a lot at the top...could not have room for ventillation and insulation at the bottom end. I wanted to do the traditional roof design, but the insulation contractor said it just was too narrow a space at the end.

We were told to spray foam the underside of the roof, but it was extremely cost prohibitive for the r value I wanted... so I was going with 6" of ridid, closed-cell foam adhered to the underside of the roof decking, sculpted to fit in the 'zero headroom' section to provide as much r value as possible, and held in place by copious sprayfoam around the edges to make a tight seal...

The sprayfoam contractor said that this would make the roof a conditioned space as long as the r value is high enough, like in a cathedral ceiling - without need (or want) to ventilate the structure. so essentially it's closed-cell foam adhered to the roof deck to make the attic (such as it is) conditioned space...basically a 'new' concept, as the old method of airflow through the attic was not working on this roof (low slope, poor design)

Closed cell foam should be a vapour barrier in 6" thickness, should it not?

Regardless, I think I have to try and pull down some of the foam I've adhered to the roof at the bottom, and let it dry out, while my roofing contractor fixes the shingles above.

Am I totally wrong here?
 
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I have always understood that the proper way is to establish a ventilation channel using these foam vents which are stapled on to the underside of the roof deck. Then you can jam as much insulation under them as you want. That doesn't stop condensation, but at least it keeps it away from the wooden deck.
 
The problem is that 6" of rigid insulation does not act the same as sprayfoam. You need a 2" air space with rigid insulation to provide ventilation to eliminate the condensation that forms due to the air infiltration through the gaps ( even tiny) in the seams of the rigid. This is why sprayfoam and some cellulose sprayed is the only code approved method for eliminating the ventilation space.

maxwell_smart007 said:
There's an attic space at the 'high' end of the roof, and zero space at the bottom end - it's a stupid design, and it made it ridiculously cold, as there was no insulation at the bottom end, and a lot at the top...could not have room for ventillation and insulation at the bottom end. I wanted to do the traditional roof design, but the insulation contractor said it just was too narrow a space at the end.

We were told to spray foam the underside of the roof, but it was extremely cost prohibitive for the r value I wanted... so I was going with 6" of ridid, closed-cell foam adhered to the underside of the roof decking, sculpted to fit in the 'zero headroom' section to provide as much r value as possible, and held in place by copious sprayfoam around the edges to make a tight seal...

The sprayfoam contractor said that this would make the roof a conditioned space as long as the r value is high enough, like in a cathedral ceiling - without need (or want) to ventilate the structure. so essentially it's closed-cell foam adhered to the roof deck to make the attic (such as it is) conditioned space...basically a 'new' concept, as the old method of airflow through the attic was not working on this roof (low slope, poor design)

Closed cell foam should be a vapour barrier in 6" thickness, should it not?

Regardless, I think I have to try and pull down some of the foam I've adhered to the roof at the bottom, and let it dry out, while my roofing contractor fixes the shingles above.

Am I totally wrong here?
Click to expand...
 
maxwell_smart007 said:
There's an attic space at the 'high' end of the roof, and zero space at the bottom end - it's a stupid design, and it made it ridiculously cold, as there was no insulation at the bottom end, and a lot at the top...could not have room for ventillation and insulation at the bottom end. I wanted to do the traditional roof design, but the insulation contractor said it just was too narrow a space at the end.

We were told to spray foam the underside of the roof, but it was extremely cost prohibitive for the r value I wanted... so I was going with 6" of ridid, closed-cell foam adhered to the underside of the roof decking, sculpted to fit in the 'zero headroom' section to provide as much r value as possible, and held in place by copious sprayfoam around the edges to make a tight seal...

The sprayfoam contractor said that this would make the roof a conditioned space as long as the r value is high enough, like in a cathedral ceiling - without need (or want) to ventilate the structure. so essentially it's closed-cell foam adhered to the roof deck to make the attic (such as it is) conditioned space...basically a 'new' concept, as the old method of airflow through the attic was not working on this roof (low slope, poor design)

Closed cell foam should be a vapour barrier in 6" thickness, should it not?

Regardless, I think I have to try and pull down some of the foam I've adhered to the roof at the bottom, and let it dry out, while my roofing contractor fixes the shingles above.

Am I totally wrong here?
Click to expand...

Most everyone is telling you that the moisture is coming from up through the house and condensing on the bottom of the sheeting, not from the outside through the shingles.
 
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