Insulation Savings

[bankeny]

After hours of research we have finally decided to have closed cell spray foam installed in the attic right on the roof deck. It's a walk up attic and we want to use the space. Insulating the roof with foam seemed to be the best way to turn the attic into conditioned space while maximizing head room and air sealing at the same time.

We will go with 3" which should be an R-value of around 21... Much better than the little bit of vermiculite that's currently underneath the attic floorboards!

Can anyone here who has done a similar project chime in on how much it decreased their heating bills?

I know there's lots of variables, but just looking for a ballpark. We are in southern Minnesota where the heater can run probably 7-8 months of the year. Last year was our first year in the house and we spent just over $1,200 in natural gas. I was expecting much worse!

[phil]

You can do that but your roofing won't last as long because it wont be able to cool by transfering the heat from the roofing down. You can get wavy foam stuff that you put up there first and install ridge vents so that some air can come in the eves and circulate to the ridge and come out, that will cool your roofing material, then you can unsulate below the wavy stuff. it kind of looks like the old wavy clear or green tinted fiberglass stuff people often use for awnings but it is a closed cell pink foam material.
I have been using foam sheets, they come 3.5 or 4 inches thick and 4' x 8' it is the same stuff as the spray foam cyanacrilic or cyanacrilite ( spelling? ) I think it is foamy crazy glue basically. it is closed cell . i cut it to fit the studs then strap it to keep it in place then use the canned spray foam stuff to fill any gaps against the studs. You can get it with a foil coating if you want.

another option you may consider depending on your costs and how your roof is , is to put strapping then the foam sheets on top of your roof then a new roof on top of that , in other words to put the insulation on top of the roof, then plywood then your roofing and leave your old roof where it is. and that will work really well, but you will have the cost of a new roof now as well. Id consult with some roofers as well as the foam spray guys. get some estimates then even if you do it yourself you can compare the costs of the estimates.

I'd weigh up the options , just realize that what you are about to do will shorten the life of your roofing materials. its a trade off. if you guestimated and said your roof costs will last half as long and weigh half the cost of the new roof into your equation of not how much heat you use but how much you are saving in heat by doing this I think you'd find it isn't economical, but it depends which way you sharpen your pencil. you could also put good quality insulation where the vermiculite is , in mine I used roxul and then sheeted with plywood and painted , in the non living space which is storage for me. I am not sure what the R value of insulation is but mine had pink fiberglass and lots of dust so it was nice to just clean it all out and start over with that insulation. Vermiculite might not be such a bad think to leave alone if it isn't as disgusting as my insulation was.

I'd be tempted to see if you can put the rigid foam in 2 inch sheets flush with the bottom of the 2x4's and leave an air gap between that and your plywood sheeting or whatever it is. Yea it is a little less R value statistically but maybe not because all that heat your roof absorbs has to go somewhere so the gap might actually improve efficiency, in the summer anyway.

depending how your house is confugured, If you put an open stairway to the attic it pretty much defeats the insulation at floor level because the heat can rush up the stairwell.

the double roof works well. It does mean you'd also have work to do to refit your fascia boards and gutters, but I think it is the best option in terms of heat savings and in keeping the house comfortable because you can have one insulated roof above another with the air gap and ridge vent but it probably isn't the cheapest option.
Phil

[bankeny]

Thanks Phil!

The shingles were replaced by the previous owner 5-6 years ago. There is no ridge vent or soffit vents. The wood soffits were covered in aluminum and I believe a piece a trim was removed leaving a very small gap (just large enough for birds and bats to enter the attic!) but not large enough to be a proper vent IMO. There is a small gable vent on two (the larger) of the four gable ends.

The hot roof debate is an interesting one to read/study! I looked at the CertainTeed warranty information and a non-vented roof is covered if the insulation is installed directly to an approved roof deck. They mention plywood or OSB as acceptable. Our roof deck is the original boards installed over 100 years ago.

[phil]

I guess those old boards might even be 2 inches and could have an R value in themselves. Doesn't seem like a great option ot put another roof over your relatively new one. I think I'd be tempted to look at the different types of closed cell foam sheets. Its more expensive than pink or Roxul but has a better R value for the number of inches and you wouldn't need the corrugated foam stuff.

Here we have some grants you can get through the power company if you get them in they can do an assessment of your insulation and recommend changes and if you do all they say they can give you some money to make your home more efficient. they can do things like use colored gasses to see whare the heat is going or measure airflow through doorways and such and perhaps help make more educated decisions. i could probably have. I just didn't want anyone in my hair telling me what to use or how to go about it or to make timelines, but there may be private companies that can help. Roofers often equate to rednecks but they may have some good ideas too. something like one of those onion shaped vents that spins might be efficient but might look pretty dorky on top of a heritage house. some old houses had,, i don't know what to call it but a square thing about say 2 or three feet square with its own little roof, surrounded in lattice, used for venting? sometimes they sort of imitate a bell tower. something like that might look nicer ? Just thinking you don't want to mess with your good roof in order to have ridge venting. opening holes and mosquito screen might improve flow through the eves?

[Mick_VT]

I wonder if you could use styrofoam baffles under the spray on foam. Like these: https://www.youtube.com/watch?v=5DX25Vz2jDc

[phil]

I think the spray foam might actually dissolve that stuff, It would just take a simple experiment to find out though

[Mick_VT]

well of course the other option is to use that then use bats over the top and not go the spray route at all.

[shazapple]

Most shingle manufacturers limit or void the warranty if there isn't proper ventilation. I think Certainteed is the only one that doesn't (and only if you use fiberglass shingles). Regardless, I think ventilation is a best practice that should be observed.

Spray foam contractors shouldn't spray over top of the foam baffles as they wouldn't hold the weight of the spray foam and even if they did the expansion would probably crush them. The biggest advantage spray foam has is its ability to air seal, however a decent contractor can accomplish the same with fiberglass for much less cost.

What I've done in my house is make baffles out of rigid insulation by cutting a board to fit in between the rafters but using a thin strip of insulation as a standoff from the roof deck. Then I fill the rest of the cavity with batt insulation and strap another insulation board overtop of the rafters. With true 2x6 rafters you can get almost R18 between the rafters, then another 5 or 10 on top of the rafters.

[phil]

I am assuming the original poster just has 2x4's and because that roof insulation is so important, if it was me I would only use a rigid foam product in there, the white, blue pink or the cyanacrlic board are all good and some are more pricey. The guy i got the foam board stuff from said it was the best insulation you can get in a 2x4 wall. I don't know everything but after using it a bit I do think it is way better than bats of pink or roxul

I put fiberglass pink in but Im even tempted to open it up to change it i don't think pink insulation was the right product for my space but I didn't know better at that time. Attics get so hot, I think its one space that investment pays off. in walls , well they don't transfer as much heat as the roof does so anything is better than nothing. with the roof I'd spring for the good stuff.
I guess spray foam is good too, maybe even thin paneling could be used for the space for airflow, or maybe there are products they can spray against, the spray guys would know what works best they must run into this and I am sure there is a solution.

[kelt65]

Thanks Phil!

The shingles were replaced by the previous owner 5-6 years ago. There is no ridge vent or soffit vents. The wood soffits were covered in aluminum and I believe a piece a trim was removed leaving a very small gap (just large enough for birds and bats to enter the attic!) but not large enough to be a proper vent IMO. There is a small gable vent on two (the larger) of the four gable ends.

The hot roof debate is an interesting one to read/study! I looked at the CertainTeed warranty information and a non-vented roof is covered if the insulation is installed directly to an approved roof deck. They mention plywood or OSB as acceptable. Our roof deck is the original boards installed over 100 years ago.

Phil's right ... and even if you think your house has no soffit vents, isn't it balloon framed? If so, that provides I think more than enough venting for your attic as all the wall cavities are open channels from the open crawlspace under the house to the attic. Assuming your house is raised and does not have an enclosed basement, that is.