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-   -   Superinsulation retrofits? (http://www.diychatroom.com/f103/superinsulation-retrofits-111794/)

Badfish740 07-24-2011 09:41 AM

Superinsulation retrofits?
 
Building a superinsulated home has always been of interest to me, but given the status of the housing market these days my wife and I have abandoned our plans of building a new home and instead are planning to stay long term in our existing home. We are in NJ and have a 2 bedroom, 1 bath ranch on a full basement that was built in the late '60s. There is fiberglass in the walls and attic, but I'm sure that even for the time it was the bare minimum. The fiberglass in the ceiling is barely 6" thick. I plan to address this with blown in cellulose after taking care of air leakage into the attic. It should cost me about $1000 doing it myself (free 24 HR blower rental from Lowes with purchase of cellulose) to get to R-60. The walls however, are another story. We have vinyl siding that is faded and dated, so we could definitely go for an updated exterior. There is just tar paper vapor barrier underneath and I believe there is a fiberboard product like Homasote underneath of that. I would want to do a complete tear off, foam all windows, doors, and any other openings from the outside, and then cover with Tyvek Housewrap. Beyond that I'm lost. I've looked at the various rigid foam boards on the market but never seen them used-can someone point me to a good forum/blog about adding rigid foam to the exterior of an existing home? I'm assuming that whatever I end up going with, the siding nails will have to be long enough to penetrate through the foam into the sheathing, correct? It is even possible to install siding this way? We are thinking of going with Hardi-plank.

TrapperL 07-24-2011 05:28 PM

You'd be surprised just how much you can bring to an older home energy efficiency wise. I'd suggest doing the research at this website:
http://www.buildingscience.com/index_html
I've been to several of their seminars and what they say sometimes sounds so off the wall that it couldn't work....but it does. Down here we fight the incredible heat. It sounds like it's pretty dumb to completely seal the attic off- zero ventilation. But I've witnessed it myself and their methods work extremely good. They have different methods for different parts of the country. If nothing else, it's extremely interesting reading.

Unless you've worked with any cementious siding products, they aren't for the average home owner. You have to remember you're working with a piece of cement. It doesn't cut, work, or nail like wood products and frankly, if you don't have a siding nail gun, you either need to find an installer or find another type of siding.

GB Greg 07-25-2011 01:44 PM

Without offering brand names or manufacturers....

There are several solutions to your exterior walls. Probably the lowest impact would be to foam fill the walls. I can't speak for rock-wool, cellulose or blown fiberglass, but there are foams out there designed specifically for cavity fill that will compact any existing cellulose, rock-wool or fiberglass.

The best foam for a retro fit has an R-Value of 5.1 per inch of thickness. In a hollow 2x4 wall, this means a +18 R-value. Since you have what could be R-13 but is more likely an R-6 or so based on age. The foam could compress that to maybe 1" thick giving you 2.5" of foam at 5.1 R per inch. You'd be gaining almost 13 R with existing fiberglass. The net result isn't going to be R-13 plus R-6 since you reduce the R-value of the fiberglass by compressing it. At the very least, the added R-value could be 13. Generally this work is conducted from the outside of the house. The vinyl siding would be removed where the foam will be installed then replaced once complete.

You could still use rigid foam boards or even insulated siding too. By building out the frames surface of your wall, you could be creating other issues too. If you add 1" foam board how does that affect your windows and doors? Are you going to have to retrim the exterior sides of your windows and doors since the outside wall became 1" thicker? You'll have to study what you have, determine if one renovation could force a second renovation and consider the cost/benefit of the renovation.

Badfish740 07-25-2011 02:55 PM

Quote:

Originally Posted by GB Greg (Post 693311)
Without offering brand names or manufacturers....

There are several solutions to your exterior walls. Probably the lowest impact would be to foam fill the walls. I can't speak for rock-wool, cellulose or blown fiberglass, but there are foams out there designed specifically for cavity fill that will compact any existing cellulose, rock-wool or fiberglass.

The best foam for a retro fit has an R-Value of 5.1 per inch of thickness. In a hollow 2x4 wall, this means a +18 R-value. Since you have what could be R-13 but is more likely an R-6 or so based on age. The foam could compress that to maybe 1" thick giving you 2.5" of foam at 5.1 R per inch. You'd be gaining almost 13 R with existing fiberglass. The net result isn't going to be R-13 plus R-6 since you reduce the R-value of the fiberglass by compressing it. At the very least, the added R-value could be 13. Generally this work is conducted from the outside of the house. The vinyl siding would be removed where the foam will be installed then replaced once complete.

You could still use rigid foam boards or even insulated siding too. By building out the frames surface of your wall, you could be creating other issues too. If you add 1" foam board how does that affect your windows and doors? Are you going to have to retrim the exterior sides of your windows and doors since the outside wall became 1" thicker? You'll have to study what you have, determine if one renovation could force a second renovation and consider the cost/benefit of the renovation.

All good points, thanks. I did some research on building science and found their case study on homes that used rigid foam to achieve total wall R-values of 35-40. This option looks the most attractive to me for a few reasons-first, its truly a DIY project since it requires no special spraying equipment or expertise, second, we're not all that happy with the way the house looks anyway. The vinyl is cracked and faded in spots and trimming the windows would give the house a fresh look. Finally, we could use a new front and back door as both are old and a source of wasted energy/leaks. We heat our home with wood that I source for free so in terms of savings on heat, it's really a savings of labor and money spent on chainsaw/log splitter maintenance. Last winter I burned 5 cords to get us through the winter-it would be nice to only have to burn 3.

However, the summer is where I'm looking to not only increase savings, but overall comfort. Our house never really gets that cool because the central air simply cannot keep up with the heat gain from the sun during the day. The rear of the house faces directly south and we have no trees for shade. The air conditioner will run continuously to keep the house at 77-78 degrees when the temperature is in the low 90s. Once the sun goes down however the house will cool in a reasonable amount of time even when it remains in the 80s through the night. Of course a large part of this is heat coming from the attic, but I would think that a large amount of heat is radiating through the south facing wall of the house as well. Interestingly, the Building Science study does not address air conditioning so I'm trying to find others who have done this type of retrofit and what they've found during the summer months.

AGWhitehouse 07-25-2011 04:21 PM

Sheath your entire house with a nail-base rigid foam panel. The current project I'm on is using Hunter H-Shield NB panels (hpanels.com). There are other manufacturers that make similar products, but that's a start point.

I wouldn't spray foam the interior wall cavity. If you air seal the exterior right, then you won't have a benefit to spray foam at the interior. if you ever need to retrofit you'll be cursing the day you chose to install it.

The attic insulation you installed is great, but an air barrier at the attic side will greatly help the efficiency. If it is exposed then air is allowed to travel through the fibers and greatly reduce the effectiveness.

Gary in WA 07-27-2011 11:05 PM

Check the chart for ceiling sag: http://www.energyguide.com/library/E...SubjectID=8375

Exterior foam, and why foam outside:http://www.greenbuildingadvisor.com/...foam-sheathing
http://www.greenbuildingadvisor.com/...s-and-ceilings
http://www.coastalcontractor.net/cgi...icle.pl?id=123
http://gbt.buildcentral.com/Forums/t...c/Default.aspx

Gary


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