Redoing my roof: how should I redo my insulation?

Question

I live in Denver. My 60 year old house is 1.5 stories. The upstairs has a highly sloped roof and definitely has insulation in the relatively narrow attic and I believe has insulation at the angled portions of the second story and in the hip walls. However, that insulation is not updated since 60 years ago and was found by a home energy audit to be insufficient.

I have to have my roof redone this year due to hail damage. The roof is asphalt shingles. Most of the attic space is tiny, like 4 feet tall. There are currently vents on the sides of the house, but no vents in the top nor any vents in the soffit. There is an attic-fan which draws are in through the vents on the side of the house - the fan runs on on a thermostat.

• Should I have the roofers take off all the shingles and plywood in the roof, redo the insulation in the attic/walls, and then reinstall the roof?
• If not, what strategy is the best in terms of cost, improved comfort, energy savings?

A picture may be worth a thousand words? Here's a cross-section focused on where we have insulation, of what quality, and where we have access.

Answer 1

Unless you need to, don't rip off the sheathing. At 60 years old, it may need it anyways. If you look at the roof can you see dips between the rafters? If the sheathing is still flat, keep it in place.

Your best bet is probably blown-in cellulose. You can hire a company to handle it, or rent the machine from your home center. You should only need a small access point to get the nozzle in, large enough for a rake to smooth out any irregularities.

Answer 2

If you're getting your roofing materials replaced and the roof decking exposed, you have a golden opportunity! What you could do is add several inches (4+", preferably 6+") of roofing polyiso over the exposed roof decking (no need to remove it unless it's rotten or moldy) before installing new underlayment and roofing. Use foil-faced polyiso for the top layer, then install vented ridge-to-eave purlins and cover that with foil-faced roof decking with the foil facing down. Then install the new underlayment and roof over that. Many roofers--including nearly all who do commercial jobs--will be familiar with this approach.

This will transform your roof into a "hot roof" with a radiant barrier and ventilation over the insulation, and the attic will be transformed into "interior" space, if that's something that would be desirable. A part of this work would be to remove/block off the old soffit vents, ridge vents, turtle vents, gable vents, or any other vents. The only ventilation you need is the new channel between the polyiso and the new roof decking.

A major advantage of this configuration is that compared to a "cold roof"/vented attic, it can all but eliminate heat gain from the roof, especially if you take the opportunity to insulate between the rafters (with anything vapor-permeable, like fiberglass, mineral wool, denim batts, or cellulose). It's also the best and cheapest way to make the attic into habitable space if that's something you'd like to do at some point (e.g. turning it into a bonus room or another bedroom or something). If you decide to do that later, your only option is spray foam which is much more expensive. There are also benefits if there are any ducts in the attic.

If this isn't something you're interested in doing, or these advantages don't seem compelling when weighed against the substantial cost of such an operation, then the impending roofing job presents no other special opportunities for improving your attic's insulation. You can add more insulation to a vented attic at any time, irrespective of whether or not the roofing materials are being replaces.

Answer 3

If your Insurance is involved & especially can approve of & pick up the decking replacement expense. Then, absolutely go that route! However, have the Roofer Sub-Contract it out to an actual Insulation Company, so it has a better chance of being done right...if you can't inspect the work.

You'll want a Vapor Barrier, as much Insulation that will fit or the highest R-value affordable (Batts, Blown-In or Sprayed-In), Venting Baffles on top of the insulation, maybe even a Radiant Barrier on top of the Baffles & Eave or Soffit Vents that flow to a newly installed Ridge Vent. Also, preferably new gutters & downspouts with Gutter Guards. If any or all of that's needed or desired.