[aeruslady]

Existing roof, interior exposed tongue and groove inside, guessing the pitch is 4/12, its time to re shingle and would like to add some insulation. What are my options?
What is the advantage of shingle over metal or vice versa? Someone please give me some guide lines or ideas.
Naomi

 

[Grumpy]

How is the current roof insulated? Is the insulation above or beneath the roof sheathing/substrate? Is there any current ventilation?

A normal shingle roof is a cold deck design, where the bottom of the sheathing/substrate is exposed to air and the roof is then ventilated to exhaust hot air and moisture. The ceiling would then be insulated in a cold deck design.

It could also be a warm deck design which is not very popular with shingles, although is sometimes allowable. In this case a rigid insulation board would be installed ontop of the cheathing/substrate and the shingles installed to that. You would then NOT ventilate or would used a ventilated insulation board similiar to a ventilated nail base.


The types of insulation which can be used for either application are many, so we're going to need some more details to give you an accurate assessment as to your options.

 

[Grumpy]

As for metal, metal what? Metal shingles? Metal Panels? What kind of metal? Steel, Copper, Aluminum? Metal is usually going to cost more, though most types of GOOD metal roofing if properly installed will last longer than the typical asphalt shingle. Notice I said GOOD metal, because there is some cheap chit dog house material on the market as well. If you want to go with a metal roof be prepared for a true investment in your property. The only draw back I can think of to metal is this: 1) it dings easier from hail. 2) limited skilled labor, metal roofing is an art and most roofers honestly don't have that talent. So if you are considering a metal roof make sure the person you hire has done 5 or 6. You don't want them learning on your job.

 

[aeruslady]

Roof insulation

Grumpy, thanks for responding to my question. I am just doing research before I start looking for a professional roofer. I want to have some knowledge so I know what to ask when interviewing potential roofers.
I believe there is decking (exterior) on top of the tongue and groove (interior) with regular shingles. I thought it would be a good time to add some insulation since the shingle have to be pulled off. I am looking for the best way to cut down on utility use. Here in GA metal roofs are used in our national forest for fire prevention purposes. My main goal is to cool the house the best I can.

 

[Grumpy]

Oh chit. I didn't notice the first time you said exposed T&G. My mistake. Here is my suggestion: Convert it to a warm deck and install Atlast Polyisocyanurate insulation VENTILATED nail base. This combines insulation with ventilation so as not to void your manufacturer shingle warranty. There is alot of grey area about shingle warrantys when it comes to warm decks or roofs with no ventilation. I say this because with the rising popularity of spray foam beneath the sheathing, some warrantys have been altered to allow this.

A warranty won't keep the water out. In my experience a shingle roofing system installed directly to the ISO will fail in 10-15 years. I speculate this is due to zero ventilation as well as off-gas from the poly iso. I could be wrong, and really can't explain WHY it happends, just know from experience that it DOES happen.



An 1" POly Iso board will have an R value of about 6. Not much, but butter than naught.

On a side note a metal roof can be bought reflective which may help in cooling. But there are also reflective asphalt shingles too.