I have an older roof that is starting to look unattractive (a little wavy in areas, shingles are starting to show ware) and will need replaced before long. I Currently have about an 800 square feet house. I really like the look and durability of a metal slate roof. A neighbor down the street just recently put on a new metal shingle roof and everyone comments how absolutely fantastic it looks.  But the ROI would be a LONG time and I don't know how long I will live here, whether it's going to be five more years or longer. I haven't started getting bids yet, but my impression is that a metal roof is probably going to cost 2-3x as much, is that about right?

Also, another consideration is ventilation. I currently have an older design with 2 end gable vents supplying intake air for a solar powered attic fan. I could probably just leave this ventilation system in place which seems to be adequate or I could change to a passive ventilation with a ridge and soffit vent. It will drive up the cost of course.

And is radiant barrier something to consider when doing a new roof?

Thanks!

In some situations re-roofing can be considered an opportunity for putting rigid insulation above the roof deck and going with a sealed semi-conditioned unventilated attic approach. By putting the rafters, decking and ridge beam partially inside the thermal envelope it runs drier and has less thermal & moisture cycling. It's not an insignificant expense though, and has to be considered carefully. (It's a lot more than the cost of soffit & ridge venting.)

The economic & comfort benefits of radiant barrier depends on whether A: the attic has HVAC ducts and B: the attic R value is at current code-min or more. With code+ R values and no ducts above the attic insulation there is very little benefit to radiant barrier. In a cooling dominated climate going for a CRRC rated "cool roof" finish to the shingle or metal is more effective than radiant barrier and has very low (if any) net uptick in cost. In heating dominated climates cool-roof finishes add a very modest amount to the net energy use. About the only time radiant barrier is a clear financial winner in most locations is situations with uninsulated ductwork & air handler in a sub-code R value attic, but applying the cost of RB to bringing the R-value up to code is often a better value since it reduces both the heating and cooling loads. Study the chart on P5 of this document, and compare it to your R-values, location & duct conditions:

http://www.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/RBFactSheet2010.pdf


Metal shingles may look nice, but be aware that they can be noisy under hail & rain. Depending on the acoustics of the attic & attic insulation it can be more than a small background noise in the rooms below the attic floor.

There are almost no home improvements of the roofing or insulation variety that "pay off" in under 5 years. If the plan is to flip it in 6 years repairing any roof deck/rafter issues that caused the sags and spending the cash on updating a kitchen or bath room is probably a better "investment" than a 50-year roof, super-insulated unvented attic, etc.

That makes sense. I never really considered the possibility of bringing the attic into the conditioned space. Mainly because the access to the attic is very tight and building some kind of stairs to it would be difficult. It could only be used as a storage space, which I really don't need.

The radiant barrier was just something I was thinking about because I thought if I were ever to do it the ideal time would be when a new roof is being put on. I have more heating days than cooling (Iowa) but it can get pretty hot. Would a lighter color roof be a good thing to explore?

My attic is already insulated heavily. I just had several more inches of fiberglass blown bringing the total r-value to 60. I had all of the leaks and penetrations from the conditioned space into the attic sealed off about one year ago so my air leakage into the attic is under control.

Regarding some of the roof sagging, I'm not sure if it's the sheathing or decking (I don't know the difference between the two actually) that's the problem but I talked to a roofer last winter (I think I want to work with him) and he told me it's an easy fix.

Thanks for the info! I appreciate it.

With a blower-door verified low-leakage ceiling and R60 fiberglass in the attic the additional benefits of EITHER RB or a conditioned attic approach are not cost-effective, and would not make an appreciable difference in creature comfort.

Bringing the attic into conditioned space has little to do with using it as living space- it's usually done to be able to achieve better air tightness to the house as a whole, and to avoid gains/losses from attic routed ducts. If you have no ducts in the attic, at your air tightness & R values there is no rationale for going that route.

A light colored roof would bring down the average cooling load by a miniscule amount, but increase the average heating load by an even larger (but still miniscule) amount. The only exception to this would be if you had an unusually (for IA), low pitch to the roof, say 2:12 or less, in which case a cool-roof finish CRRC rated for low angle roofs would be worth seeking out.

To bring down the cooling load, bring down the solar gain. On south facing windows awnings or overhangs work pretty well. On east or west facing windows, consider installing low-E storm windows over the existing windows, or exterior operable sun-filtering shades. Low-E storms would also lower the heating load.

Thanks for the detailed information.

So would it be better to use this opportunity to go from 2 gable vents (intake) and a roof-mounted solar attic fan (exhaust) to a ridge and soffit vent system?

I have a wireless temp and humidity monitor for my attic. The temp and humidity are both under pretty good control.

Attic fans powered off the grid consume more power than the cooling power they offset, and drive infiltration by depressurizing the attic. If you're concerned about protecting your stored goods from extremely high temps radiant barrier stapled to the rafters will knock quite bit off the temperature peaks (but again, has very minimal effect on the energy use of the building at your R-values.)  It'll raise both peak & average temps of our shingles though.

Soffit to ridge venting does a better job of drying the roof deck than gable vents, and will lower the shingle & attic temps somewhat.  Making the cross section of the soffit venting greater than that of the ridge venting lowers the stack forces on the conditioned space by keeping the attic from becoming depressurized.

See:

http://www.finehomebuilding.com/how...g.aspx


http://www.greenbuildingadvisor.com...ting-roofs