Expert: Dan Merrill - 10/15/2009

Question
QUESTION: I recently bought a 100 year old house with a slate roof.  I have a slate roof question and a couple insulation questions (there is currently no insulation in the attic).  The angle of the roof is about 45 degrees.  There is an attic space above the middle of the second floor rooms and crawl/storage spaces around the outside of the second floor rooms.  Half of the ceilings in the second floor rooms is angled because the rafters and the roof are right above the ceiling.  

A couple of the slates on the roof have fallen off and there is signs of old water damage but we have had several heavy rains since we moved in and it doesn't appear to be leaking currently.  How important is it to get those slates replaced and what sort of price range am I looking at (if you can estimate sight unseen)?

As far as the insulation... I was planning on laying insulation flat in the attic above the second floor rooms and blow in insulation between the rafters where the ceiling is angled.  I was also thinking about putting insulation between the rafters above the side crawl spaces.  Should I install baffles first to keep the insulation off of the bottom side of the roof?  Originally there was no ventilation in the attic.  I have added a couple gable vents and a thermal switch fan.  Is that enough or should I go around and install soffet vents also?

Thanks for your help.
Eric

ANSWER: Since you have a Slate roof it is important to find a Slate roof expert to do occasional maintenance for you, they need to be very experienced. An amateur repair person can do a LOT of damage to a good Slate roof, sometimes they totally destroy them (not uncommon).
We recommend that a Slate roof be inspected every spring. Slates do occasionally break from ice, snow and other hazards. You should get an immediate service to replace the broken Slates. Water can do a lot of damage even if you can't see leaks.

The only insulation I would recommend for your situation is spray foam.
It is important to find an experienced foam contractor who commonly installs both open-cell and closed-cell foams. You don't want to be talked into one kind of foam because that is the only one the contractor sells.
A hybrid system of open-cell and closed-cell foam insulation is usually the best way to go. The foam is most often sprayed on the underside of the roof. This prevents covering up old wiring and other problems in old homes.
With a good foam system you will not want a vented attic, when done correctly the attic is considered "conditioned space" by code.
There are also pour-in types of foam that can be used in the walls of old homes, this stuff in combination with a foamed attic/roof will make a dramatic difference in your heating and cooling bills. Foam is not cheap, but it will be the best investment you ever made. It will save you money on energy every month of every year for the rest of the life of the building.

Good luck, let me know how it goes.

Dan

---------- FOLLOW-UP ----------

QUESTION: Ok, assuming I cannot afford spray in foam, what would be my next best solution?  I currently have nothing so I figure even regular insulation would be an improvement.  I have heard that if you install regular insulation in the rafters right below the roof you could have a moisture problem that could ruin the insulation and/or damage the underside of the roof.

Thanks,

Eric

Answer
The closed-cell spray foam is the only material I know of that will do everything you need to do without causing other problems like absorbing moisture, etc. as you noted.

Make sure you get several quotes on the spray foam, there is a huge difference in pricing.
For example: We quoted out a job this summer. The highest quote was $25,000 the lowest was under $10,000. This was a rather large job. But this wide range of quotes are common.

As a variance of this, you could install sheet foam on the underside of the rafters. You would want to use ISO foam or extruded EPS, sheets with a radiant barrier have additional benefits, like the super tuff-r by Dow. You would have to be very careful to caulk %26 tape all seams for it to be effective. One benefit of doing the insulation this way is that it is an easy DIY project if you are careful and you can install what you can afford. Install 1" now if that is all you can afford, then install another inch next year. If you do this make sure you stagger all seams and seal them well so you don't trap moisture anywhere.

If your home still has wiring on the attic floor (very common) do not apply insulation over it. These wires can run hot and if there is insulation over them the heat can build up and cause fires.

Good luck,

Dan