Retrofit insulation
Hello to all,
Well here is my conundrum. I live in a house that was built in 1983, and it was built using the minimum materials in every aspect. The house is a modern/contemporary with vaulted ceiling up to 28′ high. Saying that the roof was framed using 2×8 rafters, and yup r-19 insulation faced bats. The walls are 2×4 with what seems to be at best 4 mil vapor barrier, r-11 unfaced bats, and 1/2″ Celotex w/5/8″ t-111 exterior siding.
I need to bring the r-value up to as (close) to minimum code. Our local code call for r-38 ceiling, r-19 walls.
My idea at first was to pull the shingles/tar paper and install 3 inches of polystyrene foam, sheet with 1/2″ osb, and then install necessary tar paper, ice and water on eves, and standing seam roof system.
Idea for the walls: Install 2″ polystyrene directly on t-111, house wrap, strapping, and then corrugated steel on top half, and either Hardi or cedar lap siding rain screen.
I am also interested in any comment about radiant barriers, and if one could be incorperated.
Go ahead and tear me a new one and set me straight. I’m pretty up to speed on new construction, but this is a area that I don’t have much experience in. Any suggestions would be greatly appreciated.
Thanks in advance
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Replies
On the roof, you probably need more insulation between the rafters, and more on top of the roof deck., You also need to eliminate the venting if you have insulation in both places. You could dense-pack the rafter bays and put 3" or more of polyiso on top of the deck. Of course this mean raising your fascia and rake boards. As an alternative, you could foam the rafter bays entirely and leave the roof deck where it is.
Plan for the walls sounds good.
Just finished insulation retrofit on a nearly identical house in southern NH. Homeowner had energy audit performed and the decision was made to yank the cathedral ceilings and R-19 batts and replace with 6" of closed cell spray foam in the rafter bays (roof isn't vented). In areas where the ceilings are flat, we are air sealing where necessary with frothpaks and blowing an additional ~16" of cellulose on top of the existing batts. Also adding 6" of SPF to the band joist since we can get to it easily. Although the walls are 2x4 with r-13 batts, we are leaving them alone as the audit indicated that the majority of air/heat loss was through the ceiling/roof. Recommend you seek the services of a good energy auditor, to identify the most bang for your buck, preferably an auditor who does not also sell insulation services.
Jason,
You have the right idea. You might consider using thicker foam; use the search feature on this website for "deep energy retrofit" to read of other projects.
You need to pay attention to thermal barrier continuity where the walls meet the roof. You also need to pay attention to air leaks. Airtight construction methods are essential.
Here's more information on ceilings: How to Build an Insulated Cathedral Ceiling.
Thanks for the responses guys. Ok I should have mentioned, is there a way to retrofit without tearing out the drywall /sheeting? One other idea I had was to tear off the sheething and have spray foam guys fill the bays with closed cell insulation, (sounds very expensive to get insulation guys on roof with no sheething).
I am not looking to have the house win any awards for being a passive house. I would just like to add more insulation to make the house a little more comfortable and bills a little lower. I would also like to not have problems with condensation and mold, which I'm sure is probably happening to some extent already.
Martin, I will check "deep energy retrofit" out and see what I can learn...
Jason,
There are many ways to insulate a cathedral ceiling. It is certainly possible to remove the roofing and roof sheathing, and to fill the rafter bays with spray foam from above. I have seen that work done. (Your contractor needs to pay attention to weather reports before opening up the roof.)
You can also work from below, or leave the existing bays untouched, and simply add more rigid foam above.
How much foam would be needed? 4"=approx. r-24? is that correct. Also would I need to close off sorrit vents?
Jason, you are doing $30-60,000 dollars of insulation work to save $2-500 per year? Am all for going green and low E just noting why you said you are doing this......
Aj,
The roof needs to be replaced already. I figured that while I was replacing the roof I would go ahead and install some type of inuslation, which is why I thought of using the rigid foam insulation, to keep costs down. I know the foam is pricey, but I think the cost would definitely be recouped over time, and what price can you put on comfort?
Martin, would 4" be about right. Do you have any experience with radiant barriers, or a product called P-2000?
Jason,
Q. "Would 4 inches be about right?"
A. In general, the more insulation, the better. It's a good idea to meet minimum building code requirements if you can afford to do so; exceeding minimum requirements is even better. Four inches of EPS has an R-value of R-16, while 4 inches of XPS has an R-value of R-20.
Q. "Do you have any experience with radiant barriers, or a product called P-2000?"
A. Yes. Here is an article on radiant barriers: Radiant Barriers: A Solution in Search of a Problem.
Marketers of P2000 have gotten into legal trouble for their exaggerated R-value claims in at least two countries (Canada and the U.S.), so you should be skeptical of any claims you read about this product. Here is an article on P2000 claims: Beware of R-Value Crooks.