Our new house in NW Connecticut is underway. We are hoping to insulate with icynene foam everywhere except the garage. One of the on -line sites for this product stated that if you use icynene you do not need to use house wrap- is this true?
We were planning on using Dow’s housewrap material. Siding will be cedar shingles. Has anyone used Houseslicker under shingles- I am told it helps them breath and they last longer.
For the uninitiated all the discussions and opinions concerning insulation, housewrap, air barriers, vapor barriers etc. can be baffling to say the least. We will be heating the house with a Tarm wood/oil furnace. While having good insulation is important to us I question whether the trouble and expense of building SUPER TIGHT is justified if I am burning free wood and don’t want to get involved with installing heat exchangers to compensate for an impervious shell.
Thanks for any help or opinions.
RM
Replies
A housewrap material serves two purposes. In order of importance:
1. It is the secondary drainage plane for any wetness (wind-driven, leaks, etc.) that can and will get behind the exterior siding. You don't want water on the sheathing, period. Sheathing by itself won't keep water out of the wall cavity.
2. If properly integrated with other aspects of an exterior air barrier system (seams taped, flexible sealant between framing members, sill seal, etc.), then it can keep air from leaking through the cavity.
In your case, if the foam is applied properly, that will be your air barrier, provided other places air gets in and can't be addressed by foam are properly sealed during construction.
You still need a drainage plane behind the shingles.
Edit: Then there is the matter of compatibility of Tyvek with cedar siding. Somewhere I read of a redesign of the product in 2000 (?) that reduces the problem. Others say Typar is better in this respect. Still others will argue that regular #15 tarpaper, tried and proven over the years, is best.
By "Houseslicker," do you mean Benjamin Obdyke's Homeslicker, that 7 or 10 mm mesh material? That would be one way to keep cedar off Tyvek, and having a vapor space behind the shingles helps them dry and hold paint longer, but applying individual shingles over it may be problematic, especially narrower widths cut to fit around windows, etc. I think there was an article in FH within the last year on doing shingles over a rainscreen.
Yeah, there is a lot out there to read and digest. All the above commentary comes from pouring through all that and seeing what makes sense in what situation. Just my thoughts. Others with more input will be along.
Edited 6/28/2008 10:27 am ET by DickRussell
Another edit: As to ventilation needs vs. "supertight," why are you planning to foam the house if you want it to leak enough to provide fresh air? Maybe the house can be heated by free wood now, but how about later, years from now?
The problem with making a house "tight, but not too tight - it has to breathe" is that by depending on leakage to provide fresh air for the occupants, first you have no idea of how much air is leaking in. All you know is that in cold, windy weather it leaks most, and in mild, windless weather it won't leak much at all. In between, not only don't you know how much air you are getting in, but you have no control over it.
I think it is Minnesota (someone check me on this) that now requires a certain degree of tightness in new construction AND mechanical ventilation for positive control of fresh air for the house. If you want tight, you want ventilation.
Edited 6/28/2008 10:35 am ET by DickRussell
wrap anyway, and get it as tight as you can.
you do not want the house to self ventilate, you want to control the ventilation. thats what windows are for, but there are better ways to introduce air as ventilation to the house.
the house can not automatically with leaks properly monitor itself and get ventilation right, if it does at some times come out ok it is dumb luck thanks to the amount of leaks and weather/climate conditions, even a broken clock is right twice a day.
if you have a fire in a house you need combustion air, a heat exchanger will warm up fresh air as it comes into the house so you don't freeze while you are trying not to asphyxiate yourself, of course cracking a window will work.
So ... instead of expensive "tyvek" you should be able to switch to the age old 15# felt under your siding and be good to go.
Tightness must be accompanied by 'mechanical breathing' ... ventilation or you could be asking for trouble. Remember controlled mechanical ventilation is more energy efficient than leaving ventilation up to mother nature (wind and thermal forces).
THAT WAS ONE OPTION- WE ENDED UP USING THE DOW WRAP AND WILL PROBABLY USE THE HOMESLICKER.
THANKS FOR THE INPUT
Before I cpould contribute intelligently, I need to know, how are you planning to supply makeup air for the solid fuel combustion?
And why have you chosen icynene foam instead of polyurethene?
Do you mean Homeslicker? not house slicker?
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Hi piffin- thanks for the reply. Yes there will be make up air in the cellar for the furnace. We will be using HomeSlicker, not house slicker- my mistake.
Based on all the input we are going with Dow wrap material.
Icynene vs urethane- I was under the impression that icynene is better product but I would appreciate any info on alternatives. I was in the urethane foam business for thirty years molding insulation products for OEM applications and was lucky to get a k factor of .19 once freon was eliminated as a blowing agent. Is there a commercial urethane foam that competes with icynene?
Thanks
The primary national brand is Corbond.Google it up.They are responsible for most of the testing for various apps. I hear Icynen installers selling their product based on quotes form the Corbond test data and sales literature, but icy in no where near as good as poly.Icy if rated about R-3.7 or so per inch.
The ureathene foams are closer to R-7 per inch.The icy is not a VB because it is open celled. Urethene is closed cells and a darn good VB seal
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I have some concerns on the foam First if there is a fire does it become toxic like pvc? and second if the house becomes so tight are we asking mold to grow? Mech vent is ok but I am wondering is it worth it ?
Thanks Piffin,
I believe you should be fine with 15lb felt. I actually replaced siding on a 6 year old house recently. It was cedar and had tyvek behind it. The house was sweating, the house wrap appeared to be wicking the water down the wall; however, the moisture was being soaked up by the cedar and rotting from the backside.