Doubling Cathedral Roof Insulation Worth It?
Hi There!
I want to replace a 20 year old shingle roof with a standing seam metal roof and thought it might be the best/only opportunity to add insulation as well. While I’ll always prioritize sustainability over ROI, I don’t have an endless budget. After two years of research, energy audits and working with various architects and contractors I have selected the best quotes and options, but still struggle with making the right decision. Here are some facts and figures to put it all into perspective:
House: Built in 1965 (Zone 6) with lots of original glass windows/walls, door blower test came in at 3.5 ACH
Roof: Cathedral roof current R value around 30 (2 inch foam spray and 6 inch fiberglass blanket, leaves maybe 2 more inches of space for venting (see photo). Ventilation: Sofit vents, ridge vents and 4 hip vents (that are leaking during strong summer rains and most roofers don’t install those anymore)
Quotes: Around $20K for a new shingle roof, $55K for a standing seam metal roof (26 gauge, mechanically seamed), $65K to double insulation from R30 to R60 by adding 6 inches of polyiso on top of the roof.
After consulting with a reputable energy auditor (30 yrs in business over 20K residential homes inspected) who said that I have the best possible set up for an old house with cathedral roof and the protected energy savings would be less than $100/year. Also the roof only accounts for 1/3 of heat loss and the other 2/3 for the walls and flooring, so maybe better to invest there?
Does anyone think the $65k is justified and well worth it, or has any other better ideas/options to add insulation, maybe replacing the fiberglass blanket with rock wool, but that requirers taking the entire sheathing off of the roof, which might be even more costly?
Any advice and/or recommendations are very much appreciated.
That you in advance.
Best,
Joe
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Replies
It looks like from the picture that the spray foam was done from the roof, shooting down onto the sheetrock, prior to adding FG batt & the covering w/plywood before adding the shingles?
Hi, yes, I believe the spray foam was added onto the sheet rock, so the current layers from the inside out would be as follows: Redwood tongue and groove ceiling, sheet rock, spray foam, fiberglass blanket, roof sheathing and then shingles.
Here is the statement from the energy auditor:
"The spray foam insulation combined with blanket insulation provides an effective durable air/moisture barrier and effective R-value for the blanket insulation. The blower door diagnostics @ 3.5 ACH confirms the spray foam applied to the ceiling wood plank was successful..... A typical 1960s build with wood plank ceiling would be 7+ ACH. I would NOT recommend redesigning the roof deck insulation assembly."
Should I just take him by the word and better look for other places (windows, walls, floors etc.) to invest in more energy efficient insulation?
Thanks so much for your input!
Have you considered solar shingles?
https://www.certainteed.com/products/solar-products/solstice-shingle
Joe,
I can't think of a single good argument for spending the $65K.
Switch to a metal roof. Enjoy when it rains knowing you don't need to worry about leaks. Spend a tenth of what the insulation would have cost on something fun instead.